xref: /openbmc/linux/fs/namei.c (revision 6aa7de05)
1 /*
2  *  linux/fs/namei.c
3  *
4  *  Copyright (C) 1991, 1992  Linus Torvalds
5  */
6 
7 /*
8  * Some corrections by tytso.
9  */
10 
11 /* [Feb 1997 T. Schoebel-Theuer] Complete rewrite of the pathname
12  * lookup logic.
13  */
14 /* [Feb-Apr 2000, AV] Rewrite to the new namespace architecture.
15  */
16 
17 #include <linux/init.h>
18 #include <linux/export.h>
19 #include <linux/kernel.h>
20 #include <linux/slab.h>
21 #include <linux/fs.h>
22 #include <linux/namei.h>
23 #include <linux/pagemap.h>
24 #include <linux/fsnotify.h>
25 #include <linux/personality.h>
26 #include <linux/security.h>
27 #include <linux/ima.h>
28 #include <linux/syscalls.h>
29 #include <linux/mount.h>
30 #include <linux/audit.h>
31 #include <linux/capability.h>
32 #include <linux/file.h>
33 #include <linux/fcntl.h>
34 #include <linux/device_cgroup.h>
35 #include <linux/fs_struct.h>
36 #include <linux/posix_acl.h>
37 #include <linux/hash.h>
38 #include <linux/bitops.h>
39 #include <linux/init_task.h>
40 #include <linux/uaccess.h>
41 
42 #include "internal.h"
43 #include "mount.h"
44 
45 /* [Feb-1997 T. Schoebel-Theuer]
46  * Fundamental changes in the pathname lookup mechanisms (namei)
47  * were necessary because of omirr.  The reason is that omirr needs
48  * to know the _real_ pathname, not the user-supplied one, in case
49  * of symlinks (and also when transname replacements occur).
50  *
51  * The new code replaces the old recursive symlink resolution with
52  * an iterative one (in case of non-nested symlink chains).  It does
53  * this with calls to <fs>_follow_link().
54  * As a side effect, dir_namei(), _namei() and follow_link() are now
55  * replaced with a single function lookup_dentry() that can handle all
56  * the special cases of the former code.
57  *
58  * With the new dcache, the pathname is stored at each inode, at least as
59  * long as the refcount of the inode is positive.  As a side effect, the
60  * size of the dcache depends on the inode cache and thus is dynamic.
61  *
62  * [29-Apr-1998 C. Scott Ananian] Updated above description of symlink
63  * resolution to correspond with current state of the code.
64  *
65  * Note that the symlink resolution is not *completely* iterative.
66  * There is still a significant amount of tail- and mid- recursion in
67  * the algorithm.  Also, note that <fs>_readlink() is not used in
68  * lookup_dentry(): lookup_dentry() on the result of <fs>_readlink()
69  * may return different results than <fs>_follow_link().  Many virtual
70  * filesystems (including /proc) exhibit this behavior.
71  */
72 
73 /* [24-Feb-97 T. Schoebel-Theuer] Side effects caused by new implementation:
74  * New symlink semantics: when open() is called with flags O_CREAT | O_EXCL
75  * and the name already exists in form of a symlink, try to create the new
76  * name indicated by the symlink. The old code always complained that the
77  * name already exists, due to not following the symlink even if its target
78  * is nonexistent.  The new semantics affects also mknod() and link() when
79  * the name is a symlink pointing to a non-existent name.
80  *
81  * I don't know which semantics is the right one, since I have no access
82  * to standards. But I found by trial that HP-UX 9.0 has the full "new"
83  * semantics implemented, while SunOS 4.1.1 and Solaris (SunOS 5.4) have the
84  * "old" one. Personally, I think the new semantics is much more logical.
85  * Note that "ln old new" where "new" is a symlink pointing to a non-existing
86  * file does succeed in both HP-UX and SunOs, but not in Solaris
87  * and in the old Linux semantics.
88  */
89 
90 /* [16-Dec-97 Kevin Buhr] For security reasons, we change some symlink
91  * semantics.  See the comments in "open_namei" and "do_link" below.
92  *
93  * [10-Sep-98 Alan Modra] Another symlink change.
94  */
95 
96 /* [Feb-Apr 2000 AV] Complete rewrite. Rules for symlinks:
97  *	inside the path - always follow.
98  *	in the last component in creation/removal/renaming - never follow.
99  *	if LOOKUP_FOLLOW passed - follow.
100  *	if the pathname has trailing slashes - follow.
101  *	otherwise - don't follow.
102  * (applied in that order).
103  *
104  * [Jun 2000 AV] Inconsistent behaviour of open() in case if flags==O_CREAT
105  * restored for 2.4. This is the last surviving part of old 4.2BSD bug.
106  * During the 2.4 we need to fix the userland stuff depending on it -
107  * hopefully we will be able to get rid of that wart in 2.5. So far only
108  * XEmacs seems to be relying on it...
109  */
110 /*
111  * [Sep 2001 AV] Single-semaphore locking scheme (kudos to David Holland)
112  * implemented.  Let's see if raised priority of ->s_vfs_rename_mutex gives
113  * any extra contention...
114  */
115 
116 /* In order to reduce some races, while at the same time doing additional
117  * checking and hopefully speeding things up, we copy filenames to the
118  * kernel data space before using them..
119  *
120  * POSIX.1 2.4: an empty pathname is invalid (ENOENT).
121  * PATH_MAX includes the nul terminator --RR.
122  */
123 
124 #define EMBEDDED_NAME_MAX	(PATH_MAX - offsetof(struct filename, iname))
125 
126 struct filename *
127 getname_flags(const char __user *filename, int flags, int *empty)
128 {
129 	struct filename *result;
130 	char *kname;
131 	int len;
132 
133 	result = audit_reusename(filename);
134 	if (result)
135 		return result;
136 
137 	result = __getname();
138 	if (unlikely(!result))
139 		return ERR_PTR(-ENOMEM);
140 
141 	/*
142 	 * First, try to embed the struct filename inside the names_cache
143 	 * allocation
144 	 */
145 	kname = (char *)result->iname;
146 	result->name = kname;
147 
148 	len = strncpy_from_user(kname, filename, EMBEDDED_NAME_MAX);
149 	if (unlikely(len < 0)) {
150 		__putname(result);
151 		return ERR_PTR(len);
152 	}
153 
154 	/*
155 	 * Uh-oh. We have a name that's approaching PATH_MAX. Allocate a
156 	 * separate struct filename so we can dedicate the entire
157 	 * names_cache allocation for the pathname, and re-do the copy from
158 	 * userland.
159 	 */
160 	if (unlikely(len == EMBEDDED_NAME_MAX)) {
161 		const size_t size = offsetof(struct filename, iname[1]);
162 		kname = (char *)result;
163 
164 		/*
165 		 * size is chosen that way we to guarantee that
166 		 * result->iname[0] is within the same object and that
167 		 * kname can't be equal to result->iname, no matter what.
168 		 */
169 		result = kzalloc(size, GFP_KERNEL);
170 		if (unlikely(!result)) {
171 			__putname(kname);
172 			return ERR_PTR(-ENOMEM);
173 		}
174 		result->name = kname;
175 		len = strncpy_from_user(kname, filename, PATH_MAX);
176 		if (unlikely(len < 0)) {
177 			__putname(kname);
178 			kfree(result);
179 			return ERR_PTR(len);
180 		}
181 		if (unlikely(len == PATH_MAX)) {
182 			__putname(kname);
183 			kfree(result);
184 			return ERR_PTR(-ENAMETOOLONG);
185 		}
186 	}
187 
188 	result->refcnt = 1;
189 	/* The empty path is special. */
190 	if (unlikely(!len)) {
191 		if (empty)
192 			*empty = 1;
193 		if (!(flags & LOOKUP_EMPTY)) {
194 			putname(result);
195 			return ERR_PTR(-ENOENT);
196 		}
197 	}
198 
199 	result->uptr = filename;
200 	result->aname = NULL;
201 	audit_getname(result);
202 	return result;
203 }
204 
205 struct filename *
206 getname(const char __user * filename)
207 {
208 	return getname_flags(filename, 0, NULL);
209 }
210 
211 struct filename *
212 getname_kernel(const char * filename)
213 {
214 	struct filename *result;
215 	int len = strlen(filename) + 1;
216 
217 	result = __getname();
218 	if (unlikely(!result))
219 		return ERR_PTR(-ENOMEM);
220 
221 	if (len <= EMBEDDED_NAME_MAX) {
222 		result->name = (char *)result->iname;
223 	} else if (len <= PATH_MAX) {
224 		struct filename *tmp;
225 
226 		tmp = kmalloc(sizeof(*tmp), GFP_KERNEL);
227 		if (unlikely(!tmp)) {
228 			__putname(result);
229 			return ERR_PTR(-ENOMEM);
230 		}
231 		tmp->name = (char *)result;
232 		result = tmp;
233 	} else {
234 		__putname(result);
235 		return ERR_PTR(-ENAMETOOLONG);
236 	}
237 	memcpy((char *)result->name, filename, len);
238 	result->uptr = NULL;
239 	result->aname = NULL;
240 	result->refcnt = 1;
241 	audit_getname(result);
242 
243 	return result;
244 }
245 
246 void putname(struct filename *name)
247 {
248 	BUG_ON(name->refcnt <= 0);
249 
250 	if (--name->refcnt > 0)
251 		return;
252 
253 	if (name->name != name->iname) {
254 		__putname(name->name);
255 		kfree(name);
256 	} else
257 		__putname(name);
258 }
259 
260 static int check_acl(struct inode *inode, int mask)
261 {
262 #ifdef CONFIG_FS_POSIX_ACL
263 	struct posix_acl *acl;
264 
265 	if (mask & MAY_NOT_BLOCK) {
266 		acl = get_cached_acl_rcu(inode, ACL_TYPE_ACCESS);
267 	        if (!acl)
268 	                return -EAGAIN;
269 		/* no ->get_acl() calls in RCU mode... */
270 		if (is_uncached_acl(acl))
271 			return -ECHILD;
272 	        return posix_acl_permission(inode, acl, mask & ~MAY_NOT_BLOCK);
273 	}
274 
275 	acl = get_acl(inode, ACL_TYPE_ACCESS);
276 	if (IS_ERR(acl))
277 		return PTR_ERR(acl);
278 	if (acl) {
279 	        int error = posix_acl_permission(inode, acl, mask);
280 	        posix_acl_release(acl);
281 	        return error;
282 	}
283 #endif
284 
285 	return -EAGAIN;
286 }
287 
288 /*
289  * This does the basic permission checking
290  */
291 static int acl_permission_check(struct inode *inode, int mask)
292 {
293 	unsigned int mode = inode->i_mode;
294 
295 	if (likely(uid_eq(current_fsuid(), inode->i_uid)))
296 		mode >>= 6;
297 	else {
298 		if (IS_POSIXACL(inode) && (mode & S_IRWXG)) {
299 			int error = check_acl(inode, mask);
300 			if (error != -EAGAIN)
301 				return error;
302 		}
303 
304 		if (in_group_p(inode->i_gid))
305 			mode >>= 3;
306 	}
307 
308 	/*
309 	 * If the DACs are ok we don't need any capability check.
310 	 */
311 	if ((mask & ~mode & (MAY_READ | MAY_WRITE | MAY_EXEC)) == 0)
312 		return 0;
313 	return -EACCES;
314 }
315 
316 /**
317  * generic_permission -  check for access rights on a Posix-like filesystem
318  * @inode:	inode to check access rights for
319  * @mask:	right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC, ...)
320  *
321  * Used to check for read/write/execute permissions on a file.
322  * We use "fsuid" for this, letting us set arbitrary permissions
323  * for filesystem access without changing the "normal" uids which
324  * are used for other things.
325  *
326  * generic_permission is rcu-walk aware. It returns -ECHILD in case an rcu-walk
327  * request cannot be satisfied (eg. requires blocking or too much complexity).
328  * It would then be called again in ref-walk mode.
329  */
330 int generic_permission(struct inode *inode, int mask)
331 {
332 	int ret;
333 
334 	/*
335 	 * Do the basic permission checks.
336 	 */
337 	ret = acl_permission_check(inode, mask);
338 	if (ret != -EACCES)
339 		return ret;
340 
341 	if (S_ISDIR(inode->i_mode)) {
342 		/* DACs are overridable for directories */
343 		if (!(mask & MAY_WRITE))
344 			if (capable_wrt_inode_uidgid(inode,
345 						     CAP_DAC_READ_SEARCH))
346 				return 0;
347 		if (capable_wrt_inode_uidgid(inode, CAP_DAC_OVERRIDE))
348 			return 0;
349 		return -EACCES;
350 	}
351 
352 	/*
353 	 * Searching includes executable on directories, else just read.
354 	 */
355 	mask &= MAY_READ | MAY_WRITE | MAY_EXEC;
356 	if (mask == MAY_READ)
357 		if (capable_wrt_inode_uidgid(inode, CAP_DAC_READ_SEARCH))
358 			return 0;
359 	/*
360 	 * Read/write DACs are always overridable.
361 	 * Executable DACs are overridable when there is
362 	 * at least one exec bit set.
363 	 */
364 	if (!(mask & MAY_EXEC) || (inode->i_mode & S_IXUGO))
365 		if (capable_wrt_inode_uidgid(inode, CAP_DAC_OVERRIDE))
366 			return 0;
367 
368 	return -EACCES;
369 }
370 EXPORT_SYMBOL(generic_permission);
371 
372 /*
373  * We _really_ want to just do "generic_permission()" without
374  * even looking at the inode->i_op values. So we keep a cache
375  * flag in inode->i_opflags, that says "this has not special
376  * permission function, use the fast case".
377  */
378 static inline int do_inode_permission(struct inode *inode, int mask)
379 {
380 	if (unlikely(!(inode->i_opflags & IOP_FASTPERM))) {
381 		if (likely(inode->i_op->permission))
382 			return inode->i_op->permission(inode, mask);
383 
384 		/* This gets set once for the inode lifetime */
385 		spin_lock(&inode->i_lock);
386 		inode->i_opflags |= IOP_FASTPERM;
387 		spin_unlock(&inode->i_lock);
388 	}
389 	return generic_permission(inode, mask);
390 }
391 
392 /**
393  * __inode_permission - Check for access rights to a given inode
394  * @inode: Inode to check permission on
395  * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
396  *
397  * Check for read/write/execute permissions on an inode.
398  *
399  * When checking for MAY_APPEND, MAY_WRITE must also be set in @mask.
400  *
401  * This does not check for a read-only file system.  You probably want
402  * inode_permission().
403  */
404 int __inode_permission(struct inode *inode, int mask)
405 {
406 	int retval;
407 
408 	if (unlikely(mask & MAY_WRITE)) {
409 		/*
410 		 * Nobody gets write access to an immutable file.
411 		 */
412 		if (IS_IMMUTABLE(inode))
413 			return -EPERM;
414 
415 		/*
416 		 * Updating mtime will likely cause i_uid and i_gid to be
417 		 * written back improperly if their true value is unknown
418 		 * to the vfs.
419 		 */
420 		if (HAS_UNMAPPED_ID(inode))
421 			return -EACCES;
422 	}
423 
424 	retval = do_inode_permission(inode, mask);
425 	if (retval)
426 		return retval;
427 
428 	retval = devcgroup_inode_permission(inode, mask);
429 	if (retval)
430 		return retval;
431 
432 	return security_inode_permission(inode, mask);
433 }
434 EXPORT_SYMBOL(__inode_permission);
435 
436 /**
437  * sb_permission - Check superblock-level permissions
438  * @sb: Superblock of inode to check permission on
439  * @inode: Inode to check permission on
440  * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
441  *
442  * Separate out file-system wide checks from inode-specific permission checks.
443  */
444 static int sb_permission(struct super_block *sb, struct inode *inode, int mask)
445 {
446 	if (unlikely(mask & MAY_WRITE)) {
447 		umode_t mode = inode->i_mode;
448 
449 		/* Nobody gets write access to a read-only fs. */
450 		if (sb_rdonly(sb) && (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
451 			return -EROFS;
452 	}
453 	return 0;
454 }
455 
456 /**
457  * inode_permission - Check for access rights to a given inode
458  * @inode: Inode to check permission on
459  * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
460  *
461  * Check for read/write/execute permissions on an inode.  We use fs[ug]id for
462  * this, letting us set arbitrary permissions for filesystem access without
463  * changing the "normal" UIDs which are used for other things.
464  *
465  * When checking for MAY_APPEND, MAY_WRITE must also be set in @mask.
466  */
467 int inode_permission(struct inode *inode, int mask)
468 {
469 	int retval;
470 
471 	retval = sb_permission(inode->i_sb, inode, mask);
472 	if (retval)
473 		return retval;
474 	return __inode_permission(inode, mask);
475 }
476 EXPORT_SYMBOL(inode_permission);
477 
478 /**
479  * path_get - get a reference to a path
480  * @path: path to get the reference to
481  *
482  * Given a path increment the reference count to the dentry and the vfsmount.
483  */
484 void path_get(const struct path *path)
485 {
486 	mntget(path->mnt);
487 	dget(path->dentry);
488 }
489 EXPORT_SYMBOL(path_get);
490 
491 /**
492  * path_put - put a reference to a path
493  * @path: path to put the reference to
494  *
495  * Given a path decrement the reference count to the dentry and the vfsmount.
496  */
497 void path_put(const struct path *path)
498 {
499 	dput(path->dentry);
500 	mntput(path->mnt);
501 }
502 EXPORT_SYMBOL(path_put);
503 
504 #define EMBEDDED_LEVELS 2
505 struct nameidata {
506 	struct path	path;
507 	struct qstr	last;
508 	struct path	root;
509 	struct inode	*inode; /* path.dentry.d_inode */
510 	unsigned int	flags;
511 	unsigned	seq, m_seq;
512 	int		last_type;
513 	unsigned	depth;
514 	int		total_link_count;
515 	struct saved {
516 		struct path link;
517 		struct delayed_call done;
518 		const char *name;
519 		unsigned seq;
520 	} *stack, internal[EMBEDDED_LEVELS];
521 	struct filename	*name;
522 	struct nameidata *saved;
523 	struct inode	*link_inode;
524 	unsigned	root_seq;
525 	int		dfd;
526 } __randomize_layout;
527 
528 static void set_nameidata(struct nameidata *p, int dfd, struct filename *name)
529 {
530 	struct nameidata *old = current->nameidata;
531 	p->stack = p->internal;
532 	p->dfd = dfd;
533 	p->name = name;
534 	p->total_link_count = old ? old->total_link_count : 0;
535 	p->saved = old;
536 	current->nameidata = p;
537 }
538 
539 static void restore_nameidata(void)
540 {
541 	struct nameidata *now = current->nameidata, *old = now->saved;
542 
543 	current->nameidata = old;
544 	if (old)
545 		old->total_link_count = now->total_link_count;
546 	if (now->stack != now->internal)
547 		kfree(now->stack);
548 }
549 
550 static int __nd_alloc_stack(struct nameidata *nd)
551 {
552 	struct saved *p;
553 
554 	if (nd->flags & LOOKUP_RCU) {
555 		p= kmalloc(MAXSYMLINKS * sizeof(struct saved),
556 				  GFP_ATOMIC);
557 		if (unlikely(!p))
558 			return -ECHILD;
559 	} else {
560 		p= kmalloc(MAXSYMLINKS * sizeof(struct saved),
561 				  GFP_KERNEL);
562 		if (unlikely(!p))
563 			return -ENOMEM;
564 	}
565 	memcpy(p, nd->internal, sizeof(nd->internal));
566 	nd->stack = p;
567 	return 0;
568 }
569 
570 /**
571  * path_connected - Verify that a path->dentry is below path->mnt.mnt_root
572  * @path: nameidate to verify
573  *
574  * Rename can sometimes move a file or directory outside of a bind
575  * mount, path_connected allows those cases to be detected.
576  */
577 static bool path_connected(const struct path *path)
578 {
579 	struct vfsmount *mnt = path->mnt;
580 
581 	/* Only bind mounts can have disconnected paths */
582 	if (mnt->mnt_root == mnt->mnt_sb->s_root)
583 		return true;
584 
585 	return is_subdir(path->dentry, mnt->mnt_root);
586 }
587 
588 static inline int nd_alloc_stack(struct nameidata *nd)
589 {
590 	if (likely(nd->depth != EMBEDDED_LEVELS))
591 		return 0;
592 	if (likely(nd->stack != nd->internal))
593 		return 0;
594 	return __nd_alloc_stack(nd);
595 }
596 
597 static void drop_links(struct nameidata *nd)
598 {
599 	int i = nd->depth;
600 	while (i--) {
601 		struct saved *last = nd->stack + i;
602 		do_delayed_call(&last->done);
603 		clear_delayed_call(&last->done);
604 	}
605 }
606 
607 static void terminate_walk(struct nameidata *nd)
608 {
609 	drop_links(nd);
610 	if (!(nd->flags & LOOKUP_RCU)) {
611 		int i;
612 		path_put(&nd->path);
613 		for (i = 0; i < nd->depth; i++)
614 			path_put(&nd->stack[i].link);
615 		if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
616 			path_put(&nd->root);
617 			nd->root.mnt = NULL;
618 		}
619 	} else {
620 		nd->flags &= ~LOOKUP_RCU;
621 		if (!(nd->flags & LOOKUP_ROOT))
622 			nd->root.mnt = NULL;
623 		rcu_read_unlock();
624 	}
625 	nd->depth = 0;
626 }
627 
628 /* path_put is needed afterwards regardless of success or failure */
629 static bool legitimize_path(struct nameidata *nd,
630 			    struct path *path, unsigned seq)
631 {
632 	int res = __legitimize_mnt(path->mnt, nd->m_seq);
633 	if (unlikely(res)) {
634 		if (res > 0)
635 			path->mnt = NULL;
636 		path->dentry = NULL;
637 		return false;
638 	}
639 	if (unlikely(!lockref_get_not_dead(&path->dentry->d_lockref))) {
640 		path->dentry = NULL;
641 		return false;
642 	}
643 	return !read_seqcount_retry(&path->dentry->d_seq, seq);
644 }
645 
646 static bool legitimize_links(struct nameidata *nd)
647 {
648 	int i;
649 	for (i = 0; i < nd->depth; i++) {
650 		struct saved *last = nd->stack + i;
651 		if (unlikely(!legitimize_path(nd, &last->link, last->seq))) {
652 			drop_links(nd);
653 			nd->depth = i + 1;
654 			return false;
655 		}
656 	}
657 	return true;
658 }
659 
660 /*
661  * Path walking has 2 modes, rcu-walk and ref-walk (see
662  * Documentation/filesystems/path-lookup.txt).  In situations when we can't
663  * continue in RCU mode, we attempt to drop out of rcu-walk mode and grab
664  * normal reference counts on dentries and vfsmounts to transition to ref-walk
665  * mode.  Refcounts are grabbed at the last known good point before rcu-walk
666  * got stuck, so ref-walk may continue from there. If this is not successful
667  * (eg. a seqcount has changed), then failure is returned and it's up to caller
668  * to restart the path walk from the beginning in ref-walk mode.
669  */
670 
671 /**
672  * unlazy_walk - try to switch to ref-walk mode.
673  * @nd: nameidata pathwalk data
674  * Returns: 0 on success, -ECHILD on failure
675  *
676  * unlazy_walk attempts to legitimize the current nd->path and nd->root
677  * for ref-walk mode.
678  * Must be called from rcu-walk context.
679  * Nothing should touch nameidata between unlazy_walk() failure and
680  * terminate_walk().
681  */
682 static int unlazy_walk(struct nameidata *nd)
683 {
684 	struct dentry *parent = nd->path.dentry;
685 
686 	BUG_ON(!(nd->flags & LOOKUP_RCU));
687 
688 	nd->flags &= ~LOOKUP_RCU;
689 	if (unlikely(!legitimize_links(nd)))
690 		goto out2;
691 	if (unlikely(!legitimize_path(nd, &nd->path, nd->seq)))
692 		goto out1;
693 	if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
694 		if (unlikely(!legitimize_path(nd, &nd->root, nd->root_seq)))
695 			goto out;
696 	}
697 	rcu_read_unlock();
698 	BUG_ON(nd->inode != parent->d_inode);
699 	return 0;
700 
701 out2:
702 	nd->path.mnt = NULL;
703 	nd->path.dentry = NULL;
704 out1:
705 	if (!(nd->flags & LOOKUP_ROOT))
706 		nd->root.mnt = NULL;
707 out:
708 	rcu_read_unlock();
709 	return -ECHILD;
710 }
711 
712 /**
713  * unlazy_child - try to switch to ref-walk mode.
714  * @nd: nameidata pathwalk data
715  * @dentry: child of nd->path.dentry
716  * @seq: seq number to check dentry against
717  * Returns: 0 on success, -ECHILD on failure
718  *
719  * unlazy_child attempts to legitimize the current nd->path, nd->root and dentry
720  * for ref-walk mode.  @dentry must be a path found by a do_lookup call on
721  * @nd.  Must be called from rcu-walk context.
722  * Nothing should touch nameidata between unlazy_child() failure and
723  * terminate_walk().
724  */
725 static int unlazy_child(struct nameidata *nd, struct dentry *dentry, unsigned seq)
726 {
727 	BUG_ON(!(nd->flags & LOOKUP_RCU));
728 
729 	nd->flags &= ~LOOKUP_RCU;
730 	if (unlikely(!legitimize_links(nd)))
731 		goto out2;
732 	if (unlikely(!legitimize_mnt(nd->path.mnt, nd->m_seq)))
733 		goto out2;
734 	if (unlikely(!lockref_get_not_dead(&nd->path.dentry->d_lockref)))
735 		goto out1;
736 
737 	/*
738 	 * We need to move both the parent and the dentry from the RCU domain
739 	 * to be properly refcounted. And the sequence number in the dentry
740 	 * validates *both* dentry counters, since we checked the sequence
741 	 * number of the parent after we got the child sequence number. So we
742 	 * know the parent must still be valid if the child sequence number is
743 	 */
744 	if (unlikely(!lockref_get_not_dead(&dentry->d_lockref)))
745 		goto out;
746 	if (unlikely(read_seqcount_retry(&dentry->d_seq, seq))) {
747 		rcu_read_unlock();
748 		dput(dentry);
749 		goto drop_root_mnt;
750 	}
751 	/*
752 	 * Sequence counts matched. Now make sure that the root is
753 	 * still valid and get it if required.
754 	 */
755 	if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
756 		if (unlikely(!legitimize_path(nd, &nd->root, nd->root_seq))) {
757 			rcu_read_unlock();
758 			dput(dentry);
759 			return -ECHILD;
760 		}
761 	}
762 
763 	rcu_read_unlock();
764 	return 0;
765 
766 out2:
767 	nd->path.mnt = NULL;
768 out1:
769 	nd->path.dentry = NULL;
770 out:
771 	rcu_read_unlock();
772 drop_root_mnt:
773 	if (!(nd->flags & LOOKUP_ROOT))
774 		nd->root.mnt = NULL;
775 	return -ECHILD;
776 }
777 
778 static inline int d_revalidate(struct dentry *dentry, unsigned int flags)
779 {
780 	if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE))
781 		return dentry->d_op->d_revalidate(dentry, flags);
782 	else
783 		return 1;
784 }
785 
786 /**
787  * complete_walk - successful completion of path walk
788  * @nd:  pointer nameidata
789  *
790  * If we had been in RCU mode, drop out of it and legitimize nd->path.
791  * Revalidate the final result, unless we'd already done that during
792  * the path walk or the filesystem doesn't ask for it.  Return 0 on
793  * success, -error on failure.  In case of failure caller does not
794  * need to drop nd->path.
795  */
796 static int complete_walk(struct nameidata *nd)
797 {
798 	struct dentry *dentry = nd->path.dentry;
799 	int status;
800 
801 	if (nd->flags & LOOKUP_RCU) {
802 		if (!(nd->flags & LOOKUP_ROOT))
803 			nd->root.mnt = NULL;
804 		if (unlikely(unlazy_walk(nd)))
805 			return -ECHILD;
806 	}
807 
808 	if (likely(!(nd->flags & LOOKUP_JUMPED)))
809 		return 0;
810 
811 	if (likely(!(dentry->d_flags & DCACHE_OP_WEAK_REVALIDATE)))
812 		return 0;
813 
814 	status = dentry->d_op->d_weak_revalidate(dentry, nd->flags);
815 	if (status > 0)
816 		return 0;
817 
818 	if (!status)
819 		status = -ESTALE;
820 
821 	return status;
822 }
823 
824 static void set_root(struct nameidata *nd)
825 {
826 	struct fs_struct *fs = current->fs;
827 
828 	if (nd->flags & LOOKUP_RCU) {
829 		unsigned seq;
830 
831 		do {
832 			seq = read_seqcount_begin(&fs->seq);
833 			nd->root = fs->root;
834 			nd->root_seq = __read_seqcount_begin(&nd->root.dentry->d_seq);
835 		} while (read_seqcount_retry(&fs->seq, seq));
836 	} else {
837 		get_fs_root(fs, &nd->root);
838 	}
839 }
840 
841 static void path_put_conditional(struct path *path, struct nameidata *nd)
842 {
843 	dput(path->dentry);
844 	if (path->mnt != nd->path.mnt)
845 		mntput(path->mnt);
846 }
847 
848 static inline void path_to_nameidata(const struct path *path,
849 					struct nameidata *nd)
850 {
851 	if (!(nd->flags & LOOKUP_RCU)) {
852 		dput(nd->path.dentry);
853 		if (nd->path.mnt != path->mnt)
854 			mntput(nd->path.mnt);
855 	}
856 	nd->path.mnt = path->mnt;
857 	nd->path.dentry = path->dentry;
858 }
859 
860 static int nd_jump_root(struct nameidata *nd)
861 {
862 	if (nd->flags & LOOKUP_RCU) {
863 		struct dentry *d;
864 		nd->path = nd->root;
865 		d = nd->path.dentry;
866 		nd->inode = d->d_inode;
867 		nd->seq = nd->root_seq;
868 		if (unlikely(read_seqcount_retry(&d->d_seq, nd->seq)))
869 			return -ECHILD;
870 	} else {
871 		path_put(&nd->path);
872 		nd->path = nd->root;
873 		path_get(&nd->path);
874 		nd->inode = nd->path.dentry->d_inode;
875 	}
876 	nd->flags |= LOOKUP_JUMPED;
877 	return 0;
878 }
879 
880 /*
881  * Helper to directly jump to a known parsed path from ->get_link,
882  * caller must have taken a reference to path beforehand.
883  */
884 void nd_jump_link(struct path *path)
885 {
886 	struct nameidata *nd = current->nameidata;
887 	path_put(&nd->path);
888 
889 	nd->path = *path;
890 	nd->inode = nd->path.dentry->d_inode;
891 	nd->flags |= LOOKUP_JUMPED;
892 }
893 
894 static inline void put_link(struct nameidata *nd)
895 {
896 	struct saved *last = nd->stack + --nd->depth;
897 	do_delayed_call(&last->done);
898 	if (!(nd->flags & LOOKUP_RCU))
899 		path_put(&last->link);
900 }
901 
902 int sysctl_protected_symlinks __read_mostly = 0;
903 int sysctl_protected_hardlinks __read_mostly = 0;
904 
905 /**
906  * may_follow_link - Check symlink following for unsafe situations
907  * @nd: nameidata pathwalk data
908  *
909  * In the case of the sysctl_protected_symlinks sysctl being enabled,
910  * CAP_DAC_OVERRIDE needs to be specifically ignored if the symlink is
911  * in a sticky world-writable directory. This is to protect privileged
912  * processes from failing races against path names that may change out
913  * from under them by way of other users creating malicious symlinks.
914  * It will permit symlinks to be followed only when outside a sticky
915  * world-writable directory, or when the uid of the symlink and follower
916  * match, or when the directory owner matches the symlink's owner.
917  *
918  * Returns 0 if following the symlink is allowed, -ve on error.
919  */
920 static inline int may_follow_link(struct nameidata *nd)
921 {
922 	const struct inode *inode;
923 	const struct inode *parent;
924 	kuid_t puid;
925 
926 	if (!sysctl_protected_symlinks)
927 		return 0;
928 
929 	/* Allowed if owner and follower match. */
930 	inode = nd->link_inode;
931 	if (uid_eq(current_cred()->fsuid, inode->i_uid))
932 		return 0;
933 
934 	/* Allowed if parent directory not sticky and world-writable. */
935 	parent = nd->inode;
936 	if ((parent->i_mode & (S_ISVTX|S_IWOTH)) != (S_ISVTX|S_IWOTH))
937 		return 0;
938 
939 	/* Allowed if parent directory and link owner match. */
940 	puid = parent->i_uid;
941 	if (uid_valid(puid) && uid_eq(puid, inode->i_uid))
942 		return 0;
943 
944 	if (nd->flags & LOOKUP_RCU)
945 		return -ECHILD;
946 
947 	audit_log_link_denied("follow_link", &nd->stack[0].link);
948 	return -EACCES;
949 }
950 
951 /**
952  * safe_hardlink_source - Check for safe hardlink conditions
953  * @inode: the source inode to hardlink from
954  *
955  * Return false if at least one of the following conditions:
956  *    - inode is not a regular file
957  *    - inode is setuid
958  *    - inode is setgid and group-exec
959  *    - access failure for read and write
960  *
961  * Otherwise returns true.
962  */
963 static bool safe_hardlink_source(struct inode *inode)
964 {
965 	umode_t mode = inode->i_mode;
966 
967 	/* Special files should not get pinned to the filesystem. */
968 	if (!S_ISREG(mode))
969 		return false;
970 
971 	/* Setuid files should not get pinned to the filesystem. */
972 	if (mode & S_ISUID)
973 		return false;
974 
975 	/* Executable setgid files should not get pinned to the filesystem. */
976 	if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP))
977 		return false;
978 
979 	/* Hardlinking to unreadable or unwritable sources is dangerous. */
980 	if (inode_permission(inode, MAY_READ | MAY_WRITE))
981 		return false;
982 
983 	return true;
984 }
985 
986 /**
987  * may_linkat - Check permissions for creating a hardlink
988  * @link: the source to hardlink from
989  *
990  * Block hardlink when all of:
991  *  - sysctl_protected_hardlinks enabled
992  *  - fsuid does not match inode
993  *  - hardlink source is unsafe (see safe_hardlink_source() above)
994  *  - not CAP_FOWNER in a namespace with the inode owner uid mapped
995  *
996  * Returns 0 if successful, -ve on error.
997  */
998 static int may_linkat(struct path *link)
999 {
1000 	struct inode *inode;
1001 
1002 	if (!sysctl_protected_hardlinks)
1003 		return 0;
1004 
1005 	inode = link->dentry->d_inode;
1006 
1007 	/* Source inode owner (or CAP_FOWNER) can hardlink all they like,
1008 	 * otherwise, it must be a safe source.
1009 	 */
1010 	if (safe_hardlink_source(inode) || inode_owner_or_capable(inode))
1011 		return 0;
1012 
1013 	audit_log_link_denied("linkat", link);
1014 	return -EPERM;
1015 }
1016 
1017 static __always_inline
1018 const char *get_link(struct nameidata *nd)
1019 {
1020 	struct saved *last = nd->stack + nd->depth - 1;
1021 	struct dentry *dentry = last->link.dentry;
1022 	struct inode *inode = nd->link_inode;
1023 	int error;
1024 	const char *res;
1025 
1026 	if (!(nd->flags & LOOKUP_RCU)) {
1027 		touch_atime(&last->link);
1028 		cond_resched();
1029 	} else if (atime_needs_update_rcu(&last->link, inode)) {
1030 		if (unlikely(unlazy_walk(nd)))
1031 			return ERR_PTR(-ECHILD);
1032 		touch_atime(&last->link);
1033 	}
1034 
1035 	error = security_inode_follow_link(dentry, inode,
1036 					   nd->flags & LOOKUP_RCU);
1037 	if (unlikely(error))
1038 		return ERR_PTR(error);
1039 
1040 	nd->last_type = LAST_BIND;
1041 	res = inode->i_link;
1042 	if (!res) {
1043 		const char * (*get)(struct dentry *, struct inode *,
1044 				struct delayed_call *);
1045 		get = inode->i_op->get_link;
1046 		if (nd->flags & LOOKUP_RCU) {
1047 			res = get(NULL, inode, &last->done);
1048 			if (res == ERR_PTR(-ECHILD)) {
1049 				if (unlikely(unlazy_walk(nd)))
1050 					return ERR_PTR(-ECHILD);
1051 				res = get(dentry, inode, &last->done);
1052 			}
1053 		} else {
1054 			res = get(dentry, inode, &last->done);
1055 		}
1056 		if (IS_ERR_OR_NULL(res))
1057 			return res;
1058 	}
1059 	if (*res == '/') {
1060 		if (!nd->root.mnt)
1061 			set_root(nd);
1062 		if (unlikely(nd_jump_root(nd)))
1063 			return ERR_PTR(-ECHILD);
1064 		while (unlikely(*++res == '/'))
1065 			;
1066 	}
1067 	if (!*res)
1068 		res = NULL;
1069 	return res;
1070 }
1071 
1072 /*
1073  * follow_up - Find the mountpoint of path's vfsmount
1074  *
1075  * Given a path, find the mountpoint of its source file system.
1076  * Replace @path with the path of the mountpoint in the parent mount.
1077  * Up is towards /.
1078  *
1079  * Return 1 if we went up a level and 0 if we were already at the
1080  * root.
1081  */
1082 int follow_up(struct path *path)
1083 {
1084 	struct mount *mnt = real_mount(path->mnt);
1085 	struct mount *parent;
1086 	struct dentry *mountpoint;
1087 
1088 	read_seqlock_excl(&mount_lock);
1089 	parent = mnt->mnt_parent;
1090 	if (parent == mnt) {
1091 		read_sequnlock_excl(&mount_lock);
1092 		return 0;
1093 	}
1094 	mntget(&parent->mnt);
1095 	mountpoint = dget(mnt->mnt_mountpoint);
1096 	read_sequnlock_excl(&mount_lock);
1097 	dput(path->dentry);
1098 	path->dentry = mountpoint;
1099 	mntput(path->mnt);
1100 	path->mnt = &parent->mnt;
1101 	return 1;
1102 }
1103 EXPORT_SYMBOL(follow_up);
1104 
1105 /*
1106  * Perform an automount
1107  * - return -EISDIR to tell follow_managed() to stop and return the path we
1108  *   were called with.
1109  */
1110 static int follow_automount(struct path *path, struct nameidata *nd,
1111 			    bool *need_mntput)
1112 {
1113 	struct vfsmount *mnt;
1114 	int err;
1115 
1116 	if (!path->dentry->d_op || !path->dentry->d_op->d_automount)
1117 		return -EREMOTE;
1118 
1119 	/* We don't want to mount if someone's just doing a stat -
1120 	 * unless they're stat'ing a directory and appended a '/' to
1121 	 * the name.
1122 	 *
1123 	 * We do, however, want to mount if someone wants to open or
1124 	 * create a file of any type under the mountpoint, wants to
1125 	 * traverse through the mountpoint or wants to open the
1126 	 * mounted directory.  Also, autofs may mark negative dentries
1127 	 * as being automount points.  These will need the attentions
1128 	 * of the daemon to instantiate them before they can be used.
1129 	 */
1130 	if (!(nd->flags & (LOOKUP_PARENT | LOOKUP_DIRECTORY |
1131 			   LOOKUP_OPEN | LOOKUP_CREATE |
1132 			   LOOKUP_AUTOMOUNT))) {
1133 		/* Positive dentry that isn't meant to trigger an
1134 		 * automount, EISDIR will allow it to be used,
1135 		 * otherwise there's no mount here "now" so return
1136 		 * ENOENT.
1137 		 */
1138 		if (path->dentry->d_inode)
1139 			return -EISDIR;
1140 		else
1141 			return -ENOENT;
1142 	}
1143 
1144 	if (path->dentry->d_sb->s_user_ns != &init_user_ns)
1145 		return -EACCES;
1146 
1147 	nd->total_link_count++;
1148 	if (nd->total_link_count >= 40)
1149 		return -ELOOP;
1150 
1151 	mnt = path->dentry->d_op->d_automount(path);
1152 	if (IS_ERR(mnt)) {
1153 		/*
1154 		 * The filesystem is allowed to return -EISDIR here to indicate
1155 		 * it doesn't want to automount.  For instance, autofs would do
1156 		 * this so that its userspace daemon can mount on this dentry.
1157 		 *
1158 		 * However, we can only permit this if it's a terminal point in
1159 		 * the path being looked up; if it wasn't then the remainder of
1160 		 * the path is inaccessible and we should say so.
1161 		 */
1162 		if (PTR_ERR(mnt) == -EISDIR && (nd->flags & LOOKUP_PARENT))
1163 			return -EREMOTE;
1164 		return PTR_ERR(mnt);
1165 	}
1166 
1167 	if (!mnt) /* mount collision */
1168 		return 0;
1169 
1170 	if (!*need_mntput) {
1171 		/* lock_mount() may release path->mnt on error */
1172 		mntget(path->mnt);
1173 		*need_mntput = true;
1174 	}
1175 	err = finish_automount(mnt, path);
1176 
1177 	switch (err) {
1178 	case -EBUSY:
1179 		/* Someone else made a mount here whilst we were busy */
1180 		return 0;
1181 	case 0:
1182 		path_put(path);
1183 		path->mnt = mnt;
1184 		path->dentry = dget(mnt->mnt_root);
1185 		return 0;
1186 	default:
1187 		return err;
1188 	}
1189 
1190 }
1191 
1192 /*
1193  * Handle a dentry that is managed in some way.
1194  * - Flagged for transit management (autofs)
1195  * - Flagged as mountpoint
1196  * - Flagged as automount point
1197  *
1198  * This may only be called in refwalk mode.
1199  *
1200  * Serialization is taken care of in namespace.c
1201  */
1202 static int follow_managed(struct path *path, struct nameidata *nd)
1203 {
1204 	struct vfsmount *mnt = path->mnt; /* held by caller, must be left alone */
1205 	unsigned managed;
1206 	bool need_mntput = false;
1207 	int ret = 0;
1208 
1209 	/* Given that we're not holding a lock here, we retain the value in a
1210 	 * local variable for each dentry as we look at it so that we don't see
1211 	 * the components of that value change under us */
1212 	while (managed = READ_ONCE(path->dentry->d_flags),
1213 	       managed &= DCACHE_MANAGED_DENTRY,
1214 	       unlikely(managed != 0)) {
1215 		/* Allow the filesystem to manage the transit without i_mutex
1216 		 * being held. */
1217 		if (managed & DCACHE_MANAGE_TRANSIT) {
1218 			BUG_ON(!path->dentry->d_op);
1219 			BUG_ON(!path->dentry->d_op->d_manage);
1220 			ret = path->dentry->d_op->d_manage(path, false);
1221 			if (ret < 0)
1222 				break;
1223 		}
1224 
1225 		/* Transit to a mounted filesystem. */
1226 		if (managed & DCACHE_MOUNTED) {
1227 			struct vfsmount *mounted = lookup_mnt(path);
1228 			if (mounted) {
1229 				dput(path->dentry);
1230 				if (need_mntput)
1231 					mntput(path->mnt);
1232 				path->mnt = mounted;
1233 				path->dentry = dget(mounted->mnt_root);
1234 				need_mntput = true;
1235 				continue;
1236 			}
1237 
1238 			/* Something is mounted on this dentry in another
1239 			 * namespace and/or whatever was mounted there in this
1240 			 * namespace got unmounted before lookup_mnt() could
1241 			 * get it */
1242 		}
1243 
1244 		/* Handle an automount point */
1245 		if (managed & DCACHE_NEED_AUTOMOUNT) {
1246 			ret = follow_automount(path, nd, &need_mntput);
1247 			if (ret < 0)
1248 				break;
1249 			continue;
1250 		}
1251 
1252 		/* We didn't change the current path point */
1253 		break;
1254 	}
1255 
1256 	if (need_mntput && path->mnt == mnt)
1257 		mntput(path->mnt);
1258 	if (ret == -EISDIR || !ret)
1259 		ret = 1;
1260 	if (need_mntput)
1261 		nd->flags |= LOOKUP_JUMPED;
1262 	if (unlikely(ret < 0))
1263 		path_put_conditional(path, nd);
1264 	return ret;
1265 }
1266 
1267 int follow_down_one(struct path *path)
1268 {
1269 	struct vfsmount *mounted;
1270 
1271 	mounted = lookup_mnt(path);
1272 	if (mounted) {
1273 		dput(path->dentry);
1274 		mntput(path->mnt);
1275 		path->mnt = mounted;
1276 		path->dentry = dget(mounted->mnt_root);
1277 		return 1;
1278 	}
1279 	return 0;
1280 }
1281 EXPORT_SYMBOL(follow_down_one);
1282 
1283 static inline int managed_dentry_rcu(const struct path *path)
1284 {
1285 	return (path->dentry->d_flags & DCACHE_MANAGE_TRANSIT) ?
1286 		path->dentry->d_op->d_manage(path, true) : 0;
1287 }
1288 
1289 /*
1290  * Try to skip to top of mountpoint pile in rcuwalk mode.  Fail if
1291  * we meet a managed dentry that would need blocking.
1292  */
1293 static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
1294 			       struct inode **inode, unsigned *seqp)
1295 {
1296 	for (;;) {
1297 		struct mount *mounted;
1298 		/*
1299 		 * Don't forget we might have a non-mountpoint managed dentry
1300 		 * that wants to block transit.
1301 		 */
1302 		switch (managed_dentry_rcu(path)) {
1303 		case -ECHILD:
1304 		default:
1305 			return false;
1306 		case -EISDIR:
1307 			return true;
1308 		case 0:
1309 			break;
1310 		}
1311 
1312 		if (!d_mountpoint(path->dentry))
1313 			return !(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT);
1314 
1315 		mounted = __lookup_mnt(path->mnt, path->dentry);
1316 		if (!mounted)
1317 			break;
1318 		path->mnt = &mounted->mnt;
1319 		path->dentry = mounted->mnt.mnt_root;
1320 		nd->flags |= LOOKUP_JUMPED;
1321 		*seqp = read_seqcount_begin(&path->dentry->d_seq);
1322 		/*
1323 		 * Update the inode too. We don't need to re-check the
1324 		 * dentry sequence number here after this d_inode read,
1325 		 * because a mount-point is always pinned.
1326 		 */
1327 		*inode = path->dentry->d_inode;
1328 	}
1329 	return !read_seqretry(&mount_lock, nd->m_seq) &&
1330 		!(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT);
1331 }
1332 
1333 static int follow_dotdot_rcu(struct nameidata *nd)
1334 {
1335 	struct inode *inode = nd->inode;
1336 
1337 	while (1) {
1338 		if (path_equal(&nd->path, &nd->root))
1339 			break;
1340 		if (nd->path.dentry != nd->path.mnt->mnt_root) {
1341 			struct dentry *old = nd->path.dentry;
1342 			struct dentry *parent = old->d_parent;
1343 			unsigned seq;
1344 
1345 			inode = parent->d_inode;
1346 			seq = read_seqcount_begin(&parent->d_seq);
1347 			if (unlikely(read_seqcount_retry(&old->d_seq, nd->seq)))
1348 				return -ECHILD;
1349 			nd->path.dentry = parent;
1350 			nd->seq = seq;
1351 			if (unlikely(!path_connected(&nd->path)))
1352 				return -ENOENT;
1353 			break;
1354 		} else {
1355 			struct mount *mnt = real_mount(nd->path.mnt);
1356 			struct mount *mparent = mnt->mnt_parent;
1357 			struct dentry *mountpoint = mnt->mnt_mountpoint;
1358 			struct inode *inode2 = mountpoint->d_inode;
1359 			unsigned seq = read_seqcount_begin(&mountpoint->d_seq);
1360 			if (unlikely(read_seqretry(&mount_lock, nd->m_seq)))
1361 				return -ECHILD;
1362 			if (&mparent->mnt == nd->path.mnt)
1363 				break;
1364 			/* we know that mountpoint was pinned */
1365 			nd->path.dentry = mountpoint;
1366 			nd->path.mnt = &mparent->mnt;
1367 			inode = inode2;
1368 			nd->seq = seq;
1369 		}
1370 	}
1371 	while (unlikely(d_mountpoint(nd->path.dentry))) {
1372 		struct mount *mounted;
1373 		mounted = __lookup_mnt(nd->path.mnt, nd->path.dentry);
1374 		if (unlikely(read_seqretry(&mount_lock, nd->m_seq)))
1375 			return -ECHILD;
1376 		if (!mounted)
1377 			break;
1378 		nd->path.mnt = &mounted->mnt;
1379 		nd->path.dentry = mounted->mnt.mnt_root;
1380 		inode = nd->path.dentry->d_inode;
1381 		nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);
1382 	}
1383 	nd->inode = inode;
1384 	return 0;
1385 }
1386 
1387 /*
1388  * Follow down to the covering mount currently visible to userspace.  At each
1389  * point, the filesystem owning that dentry may be queried as to whether the
1390  * caller is permitted to proceed or not.
1391  */
1392 int follow_down(struct path *path)
1393 {
1394 	unsigned managed;
1395 	int ret;
1396 
1397 	while (managed = READ_ONCE(path->dentry->d_flags),
1398 	       unlikely(managed & DCACHE_MANAGED_DENTRY)) {
1399 		/* Allow the filesystem to manage the transit without i_mutex
1400 		 * being held.
1401 		 *
1402 		 * We indicate to the filesystem if someone is trying to mount
1403 		 * something here.  This gives autofs the chance to deny anyone
1404 		 * other than its daemon the right to mount on its
1405 		 * superstructure.
1406 		 *
1407 		 * The filesystem may sleep at this point.
1408 		 */
1409 		if (managed & DCACHE_MANAGE_TRANSIT) {
1410 			BUG_ON(!path->dentry->d_op);
1411 			BUG_ON(!path->dentry->d_op->d_manage);
1412 			ret = path->dentry->d_op->d_manage(path, false);
1413 			if (ret < 0)
1414 				return ret == -EISDIR ? 0 : ret;
1415 		}
1416 
1417 		/* Transit to a mounted filesystem. */
1418 		if (managed & DCACHE_MOUNTED) {
1419 			struct vfsmount *mounted = lookup_mnt(path);
1420 			if (!mounted)
1421 				break;
1422 			dput(path->dentry);
1423 			mntput(path->mnt);
1424 			path->mnt = mounted;
1425 			path->dentry = dget(mounted->mnt_root);
1426 			continue;
1427 		}
1428 
1429 		/* Don't handle automount points here */
1430 		break;
1431 	}
1432 	return 0;
1433 }
1434 EXPORT_SYMBOL(follow_down);
1435 
1436 /*
1437  * Skip to top of mountpoint pile in refwalk mode for follow_dotdot()
1438  */
1439 static void follow_mount(struct path *path)
1440 {
1441 	while (d_mountpoint(path->dentry)) {
1442 		struct vfsmount *mounted = lookup_mnt(path);
1443 		if (!mounted)
1444 			break;
1445 		dput(path->dentry);
1446 		mntput(path->mnt);
1447 		path->mnt = mounted;
1448 		path->dentry = dget(mounted->mnt_root);
1449 	}
1450 }
1451 
1452 static int path_parent_directory(struct path *path)
1453 {
1454 	struct dentry *old = path->dentry;
1455 	/* rare case of legitimate dget_parent()... */
1456 	path->dentry = dget_parent(path->dentry);
1457 	dput(old);
1458 	if (unlikely(!path_connected(path)))
1459 		return -ENOENT;
1460 	return 0;
1461 }
1462 
1463 static int follow_dotdot(struct nameidata *nd)
1464 {
1465 	while(1) {
1466 		if (nd->path.dentry == nd->root.dentry &&
1467 		    nd->path.mnt == nd->root.mnt) {
1468 			break;
1469 		}
1470 		if (nd->path.dentry != nd->path.mnt->mnt_root) {
1471 			int ret = path_parent_directory(&nd->path);
1472 			if (ret)
1473 				return ret;
1474 			break;
1475 		}
1476 		if (!follow_up(&nd->path))
1477 			break;
1478 	}
1479 	follow_mount(&nd->path);
1480 	nd->inode = nd->path.dentry->d_inode;
1481 	return 0;
1482 }
1483 
1484 /*
1485  * This looks up the name in dcache and possibly revalidates the found dentry.
1486  * NULL is returned if the dentry does not exist in the cache.
1487  */
1488 static struct dentry *lookup_dcache(const struct qstr *name,
1489 				    struct dentry *dir,
1490 				    unsigned int flags)
1491 {
1492 	struct dentry *dentry = d_lookup(dir, name);
1493 	if (dentry) {
1494 		int error = d_revalidate(dentry, flags);
1495 		if (unlikely(error <= 0)) {
1496 			if (!error)
1497 				d_invalidate(dentry);
1498 			dput(dentry);
1499 			return ERR_PTR(error);
1500 		}
1501 	}
1502 	return dentry;
1503 }
1504 
1505 /*
1506  * Call i_op->lookup on the dentry.  The dentry must be negative and
1507  * unhashed.
1508  *
1509  * dir->d_inode->i_mutex must be held
1510  */
1511 static struct dentry *lookup_real(struct inode *dir, struct dentry *dentry,
1512 				  unsigned int flags)
1513 {
1514 	struct dentry *old;
1515 
1516 	/* Don't create child dentry for a dead directory. */
1517 	if (unlikely(IS_DEADDIR(dir))) {
1518 		dput(dentry);
1519 		return ERR_PTR(-ENOENT);
1520 	}
1521 
1522 	old = dir->i_op->lookup(dir, dentry, flags);
1523 	if (unlikely(old)) {
1524 		dput(dentry);
1525 		dentry = old;
1526 	}
1527 	return dentry;
1528 }
1529 
1530 static struct dentry *__lookup_hash(const struct qstr *name,
1531 		struct dentry *base, unsigned int flags)
1532 {
1533 	struct dentry *dentry = lookup_dcache(name, base, flags);
1534 
1535 	if (dentry)
1536 		return dentry;
1537 
1538 	dentry = d_alloc(base, name);
1539 	if (unlikely(!dentry))
1540 		return ERR_PTR(-ENOMEM);
1541 
1542 	return lookup_real(base->d_inode, dentry, flags);
1543 }
1544 
1545 static int lookup_fast(struct nameidata *nd,
1546 		       struct path *path, struct inode **inode,
1547 		       unsigned *seqp)
1548 {
1549 	struct vfsmount *mnt = nd->path.mnt;
1550 	struct dentry *dentry, *parent = nd->path.dentry;
1551 	int status = 1;
1552 	int err;
1553 
1554 	/*
1555 	 * Rename seqlock is not required here because in the off chance
1556 	 * of a false negative due to a concurrent rename, the caller is
1557 	 * going to fall back to non-racy lookup.
1558 	 */
1559 	if (nd->flags & LOOKUP_RCU) {
1560 		unsigned seq;
1561 		bool negative;
1562 		dentry = __d_lookup_rcu(parent, &nd->last, &seq);
1563 		if (unlikely(!dentry)) {
1564 			if (unlazy_walk(nd))
1565 				return -ECHILD;
1566 			return 0;
1567 		}
1568 
1569 		/*
1570 		 * This sequence count validates that the inode matches
1571 		 * the dentry name information from lookup.
1572 		 */
1573 		*inode = d_backing_inode(dentry);
1574 		negative = d_is_negative(dentry);
1575 		if (unlikely(read_seqcount_retry(&dentry->d_seq, seq)))
1576 			return -ECHILD;
1577 
1578 		/*
1579 		 * This sequence count validates that the parent had no
1580 		 * changes while we did the lookup of the dentry above.
1581 		 *
1582 		 * The memory barrier in read_seqcount_begin of child is
1583 		 *  enough, we can use __read_seqcount_retry here.
1584 		 */
1585 		if (unlikely(__read_seqcount_retry(&parent->d_seq, nd->seq)))
1586 			return -ECHILD;
1587 
1588 		*seqp = seq;
1589 		status = d_revalidate(dentry, nd->flags);
1590 		if (likely(status > 0)) {
1591 			/*
1592 			 * Note: do negative dentry check after revalidation in
1593 			 * case that drops it.
1594 			 */
1595 			if (unlikely(negative))
1596 				return -ENOENT;
1597 			path->mnt = mnt;
1598 			path->dentry = dentry;
1599 			if (likely(__follow_mount_rcu(nd, path, inode, seqp)))
1600 				return 1;
1601 		}
1602 		if (unlazy_child(nd, dentry, seq))
1603 			return -ECHILD;
1604 		if (unlikely(status == -ECHILD))
1605 			/* we'd been told to redo it in non-rcu mode */
1606 			status = d_revalidate(dentry, nd->flags);
1607 	} else {
1608 		dentry = __d_lookup(parent, &nd->last);
1609 		if (unlikely(!dentry))
1610 			return 0;
1611 		status = d_revalidate(dentry, nd->flags);
1612 	}
1613 	if (unlikely(status <= 0)) {
1614 		if (!status)
1615 			d_invalidate(dentry);
1616 		dput(dentry);
1617 		return status;
1618 	}
1619 	if (unlikely(d_is_negative(dentry))) {
1620 		dput(dentry);
1621 		return -ENOENT;
1622 	}
1623 
1624 	path->mnt = mnt;
1625 	path->dentry = dentry;
1626 	err = follow_managed(path, nd);
1627 	if (likely(err > 0))
1628 		*inode = d_backing_inode(path->dentry);
1629 	return err;
1630 }
1631 
1632 /* Fast lookup failed, do it the slow way */
1633 static struct dentry *lookup_slow(const struct qstr *name,
1634 				  struct dentry *dir,
1635 				  unsigned int flags)
1636 {
1637 	struct dentry *dentry = ERR_PTR(-ENOENT), *old;
1638 	struct inode *inode = dir->d_inode;
1639 	DECLARE_WAIT_QUEUE_HEAD_ONSTACK(wq);
1640 
1641 	inode_lock_shared(inode);
1642 	/* Don't go there if it's already dead */
1643 	if (unlikely(IS_DEADDIR(inode)))
1644 		goto out;
1645 again:
1646 	dentry = d_alloc_parallel(dir, name, &wq);
1647 	if (IS_ERR(dentry))
1648 		goto out;
1649 	if (unlikely(!d_in_lookup(dentry))) {
1650 		if (!(flags & LOOKUP_NO_REVAL)) {
1651 			int error = d_revalidate(dentry, flags);
1652 			if (unlikely(error <= 0)) {
1653 				if (!error) {
1654 					d_invalidate(dentry);
1655 					dput(dentry);
1656 					goto again;
1657 				}
1658 				dput(dentry);
1659 				dentry = ERR_PTR(error);
1660 			}
1661 		}
1662 	} else {
1663 		old = inode->i_op->lookup(inode, dentry, flags);
1664 		d_lookup_done(dentry);
1665 		if (unlikely(old)) {
1666 			dput(dentry);
1667 			dentry = old;
1668 		}
1669 	}
1670 out:
1671 	inode_unlock_shared(inode);
1672 	return dentry;
1673 }
1674 
1675 static inline int may_lookup(struct nameidata *nd)
1676 {
1677 	if (nd->flags & LOOKUP_RCU) {
1678 		int err = inode_permission(nd->inode, MAY_EXEC|MAY_NOT_BLOCK);
1679 		if (err != -ECHILD)
1680 			return err;
1681 		if (unlazy_walk(nd))
1682 			return -ECHILD;
1683 	}
1684 	return inode_permission(nd->inode, MAY_EXEC);
1685 }
1686 
1687 static inline int handle_dots(struct nameidata *nd, int type)
1688 {
1689 	if (type == LAST_DOTDOT) {
1690 		if (!nd->root.mnt)
1691 			set_root(nd);
1692 		if (nd->flags & LOOKUP_RCU) {
1693 			return follow_dotdot_rcu(nd);
1694 		} else
1695 			return follow_dotdot(nd);
1696 	}
1697 	return 0;
1698 }
1699 
1700 static int pick_link(struct nameidata *nd, struct path *link,
1701 		     struct inode *inode, unsigned seq)
1702 {
1703 	int error;
1704 	struct saved *last;
1705 	if (unlikely(nd->total_link_count++ >= MAXSYMLINKS)) {
1706 		path_to_nameidata(link, nd);
1707 		return -ELOOP;
1708 	}
1709 	if (!(nd->flags & LOOKUP_RCU)) {
1710 		if (link->mnt == nd->path.mnt)
1711 			mntget(link->mnt);
1712 	}
1713 	error = nd_alloc_stack(nd);
1714 	if (unlikely(error)) {
1715 		if (error == -ECHILD) {
1716 			if (unlikely(!legitimize_path(nd, link, seq))) {
1717 				drop_links(nd);
1718 				nd->depth = 0;
1719 				nd->flags &= ~LOOKUP_RCU;
1720 				nd->path.mnt = NULL;
1721 				nd->path.dentry = NULL;
1722 				if (!(nd->flags & LOOKUP_ROOT))
1723 					nd->root.mnt = NULL;
1724 				rcu_read_unlock();
1725 			} else if (likely(unlazy_walk(nd)) == 0)
1726 				error = nd_alloc_stack(nd);
1727 		}
1728 		if (error) {
1729 			path_put(link);
1730 			return error;
1731 		}
1732 	}
1733 
1734 	last = nd->stack + nd->depth++;
1735 	last->link = *link;
1736 	clear_delayed_call(&last->done);
1737 	nd->link_inode = inode;
1738 	last->seq = seq;
1739 	return 1;
1740 }
1741 
1742 enum {WALK_FOLLOW = 1, WALK_MORE = 2};
1743 
1744 /*
1745  * Do we need to follow links? We _really_ want to be able
1746  * to do this check without having to look at inode->i_op,
1747  * so we keep a cache of "no, this doesn't need follow_link"
1748  * for the common case.
1749  */
1750 static inline int step_into(struct nameidata *nd, struct path *path,
1751 			    int flags, struct inode *inode, unsigned seq)
1752 {
1753 	if (!(flags & WALK_MORE) && nd->depth)
1754 		put_link(nd);
1755 	if (likely(!d_is_symlink(path->dentry)) ||
1756 	   !(flags & WALK_FOLLOW || nd->flags & LOOKUP_FOLLOW)) {
1757 		/* not a symlink or should not follow */
1758 		path_to_nameidata(path, nd);
1759 		nd->inode = inode;
1760 		nd->seq = seq;
1761 		return 0;
1762 	}
1763 	/* make sure that d_is_symlink above matches inode */
1764 	if (nd->flags & LOOKUP_RCU) {
1765 		if (read_seqcount_retry(&path->dentry->d_seq, seq))
1766 			return -ECHILD;
1767 	}
1768 	return pick_link(nd, path, inode, seq);
1769 }
1770 
1771 static int walk_component(struct nameidata *nd, int flags)
1772 {
1773 	struct path path;
1774 	struct inode *inode;
1775 	unsigned seq;
1776 	int err;
1777 	/*
1778 	 * "." and ".." are special - ".." especially so because it has
1779 	 * to be able to know about the current root directory and
1780 	 * parent relationships.
1781 	 */
1782 	if (unlikely(nd->last_type != LAST_NORM)) {
1783 		err = handle_dots(nd, nd->last_type);
1784 		if (!(flags & WALK_MORE) && nd->depth)
1785 			put_link(nd);
1786 		return err;
1787 	}
1788 	err = lookup_fast(nd, &path, &inode, &seq);
1789 	if (unlikely(err <= 0)) {
1790 		if (err < 0)
1791 			return err;
1792 		path.dentry = lookup_slow(&nd->last, nd->path.dentry,
1793 					  nd->flags);
1794 		if (IS_ERR(path.dentry))
1795 			return PTR_ERR(path.dentry);
1796 
1797 		path.mnt = nd->path.mnt;
1798 		err = follow_managed(&path, nd);
1799 		if (unlikely(err < 0))
1800 			return err;
1801 
1802 		if (unlikely(d_is_negative(path.dentry))) {
1803 			path_to_nameidata(&path, nd);
1804 			return -ENOENT;
1805 		}
1806 
1807 		seq = 0;	/* we are already out of RCU mode */
1808 		inode = d_backing_inode(path.dentry);
1809 	}
1810 
1811 	return step_into(nd, &path, flags, inode, seq);
1812 }
1813 
1814 /*
1815  * We can do the critical dentry name comparison and hashing
1816  * operations one word at a time, but we are limited to:
1817  *
1818  * - Architectures with fast unaligned word accesses. We could
1819  *   do a "get_unaligned()" if this helps and is sufficiently
1820  *   fast.
1821  *
1822  * - non-CONFIG_DEBUG_PAGEALLOC configurations (so that we
1823  *   do not trap on the (extremely unlikely) case of a page
1824  *   crossing operation.
1825  *
1826  * - Furthermore, we need an efficient 64-bit compile for the
1827  *   64-bit case in order to generate the "number of bytes in
1828  *   the final mask". Again, that could be replaced with a
1829  *   efficient population count instruction or similar.
1830  */
1831 #ifdef CONFIG_DCACHE_WORD_ACCESS
1832 
1833 #include <asm/word-at-a-time.h>
1834 
1835 #ifdef HASH_MIX
1836 
1837 /* Architecture provides HASH_MIX and fold_hash() in <asm/hash.h> */
1838 
1839 #elif defined(CONFIG_64BIT)
1840 /*
1841  * Register pressure in the mixing function is an issue, particularly
1842  * on 32-bit x86, but almost any function requires one state value and
1843  * one temporary.  Instead, use a function designed for two state values
1844  * and no temporaries.
1845  *
1846  * This function cannot create a collision in only two iterations, so
1847  * we have two iterations to achieve avalanche.  In those two iterations,
1848  * we have six layers of mixing, which is enough to spread one bit's
1849  * influence out to 2^6 = 64 state bits.
1850  *
1851  * Rotate constants are scored by considering either 64 one-bit input
1852  * deltas or 64*63/2 = 2016 two-bit input deltas, and finding the
1853  * probability of that delta causing a change to each of the 128 output
1854  * bits, using a sample of random initial states.
1855  *
1856  * The Shannon entropy of the computed probabilities is then summed
1857  * to produce a score.  Ideally, any input change has a 50% chance of
1858  * toggling any given output bit.
1859  *
1860  * Mixing scores (in bits) for (12,45):
1861  * Input delta: 1-bit      2-bit
1862  * 1 round:     713.3    42542.6
1863  * 2 rounds:   2753.7   140389.8
1864  * 3 rounds:   5954.1   233458.2
1865  * 4 rounds:   7862.6   256672.2
1866  * Perfect:    8192     258048
1867  *            (64*128) (64*63/2 * 128)
1868  */
1869 #define HASH_MIX(x, y, a)	\
1870 	(	x ^= (a),	\
1871 	y ^= x,	x = rol64(x,12),\
1872 	x += y,	y = rol64(y,45),\
1873 	y *= 9			)
1874 
1875 /*
1876  * Fold two longs into one 32-bit hash value.  This must be fast, but
1877  * latency isn't quite as critical, as there is a fair bit of additional
1878  * work done before the hash value is used.
1879  */
1880 static inline unsigned int fold_hash(unsigned long x, unsigned long y)
1881 {
1882 	y ^= x * GOLDEN_RATIO_64;
1883 	y *= GOLDEN_RATIO_64;
1884 	return y >> 32;
1885 }
1886 
1887 #else	/* 32-bit case */
1888 
1889 /*
1890  * Mixing scores (in bits) for (7,20):
1891  * Input delta: 1-bit      2-bit
1892  * 1 round:     330.3     9201.6
1893  * 2 rounds:   1246.4    25475.4
1894  * 3 rounds:   1907.1    31295.1
1895  * 4 rounds:   2042.3    31718.6
1896  * Perfect:    2048      31744
1897  *            (32*64)   (32*31/2 * 64)
1898  */
1899 #define HASH_MIX(x, y, a)	\
1900 	(	x ^= (a),	\
1901 	y ^= x,	x = rol32(x, 7),\
1902 	x += y,	y = rol32(y,20),\
1903 	y *= 9			)
1904 
1905 static inline unsigned int fold_hash(unsigned long x, unsigned long y)
1906 {
1907 	/* Use arch-optimized multiply if one exists */
1908 	return __hash_32(y ^ __hash_32(x));
1909 }
1910 
1911 #endif
1912 
1913 /*
1914  * Return the hash of a string of known length.  This is carfully
1915  * designed to match hash_name(), which is the more critical function.
1916  * In particular, we must end by hashing a final word containing 0..7
1917  * payload bytes, to match the way that hash_name() iterates until it
1918  * finds the delimiter after the name.
1919  */
1920 unsigned int full_name_hash(const void *salt, const char *name, unsigned int len)
1921 {
1922 	unsigned long a, x = 0, y = (unsigned long)salt;
1923 
1924 	for (;;) {
1925 		if (!len)
1926 			goto done;
1927 		a = load_unaligned_zeropad(name);
1928 		if (len < sizeof(unsigned long))
1929 			break;
1930 		HASH_MIX(x, y, a);
1931 		name += sizeof(unsigned long);
1932 		len -= sizeof(unsigned long);
1933 	}
1934 	x ^= a & bytemask_from_count(len);
1935 done:
1936 	return fold_hash(x, y);
1937 }
1938 EXPORT_SYMBOL(full_name_hash);
1939 
1940 /* Return the "hash_len" (hash and length) of a null-terminated string */
1941 u64 hashlen_string(const void *salt, const char *name)
1942 {
1943 	unsigned long a = 0, x = 0, y = (unsigned long)salt;
1944 	unsigned long adata, mask, len;
1945 	const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
1946 
1947 	len = 0;
1948 	goto inside;
1949 
1950 	do {
1951 		HASH_MIX(x, y, a);
1952 		len += sizeof(unsigned long);
1953 inside:
1954 		a = load_unaligned_zeropad(name+len);
1955 	} while (!has_zero(a, &adata, &constants));
1956 
1957 	adata = prep_zero_mask(a, adata, &constants);
1958 	mask = create_zero_mask(adata);
1959 	x ^= a & zero_bytemask(mask);
1960 
1961 	return hashlen_create(fold_hash(x, y), len + find_zero(mask));
1962 }
1963 EXPORT_SYMBOL(hashlen_string);
1964 
1965 /*
1966  * Calculate the length and hash of the path component, and
1967  * return the "hash_len" as the result.
1968  */
1969 static inline u64 hash_name(const void *salt, const char *name)
1970 {
1971 	unsigned long a = 0, b, x = 0, y = (unsigned long)salt;
1972 	unsigned long adata, bdata, mask, len;
1973 	const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
1974 
1975 	len = 0;
1976 	goto inside;
1977 
1978 	do {
1979 		HASH_MIX(x, y, a);
1980 		len += sizeof(unsigned long);
1981 inside:
1982 		a = load_unaligned_zeropad(name+len);
1983 		b = a ^ REPEAT_BYTE('/');
1984 	} while (!(has_zero(a, &adata, &constants) | has_zero(b, &bdata, &constants)));
1985 
1986 	adata = prep_zero_mask(a, adata, &constants);
1987 	bdata = prep_zero_mask(b, bdata, &constants);
1988 	mask = create_zero_mask(adata | bdata);
1989 	x ^= a & zero_bytemask(mask);
1990 
1991 	return hashlen_create(fold_hash(x, y), len + find_zero(mask));
1992 }
1993 
1994 #else	/* !CONFIG_DCACHE_WORD_ACCESS: Slow, byte-at-a-time version */
1995 
1996 /* Return the hash of a string of known length */
1997 unsigned int full_name_hash(const void *salt, const char *name, unsigned int len)
1998 {
1999 	unsigned long hash = init_name_hash(salt);
2000 	while (len--)
2001 		hash = partial_name_hash((unsigned char)*name++, hash);
2002 	return end_name_hash(hash);
2003 }
2004 EXPORT_SYMBOL(full_name_hash);
2005 
2006 /* Return the "hash_len" (hash and length) of a null-terminated string */
2007 u64 hashlen_string(const void *salt, const char *name)
2008 {
2009 	unsigned long hash = init_name_hash(salt);
2010 	unsigned long len = 0, c;
2011 
2012 	c = (unsigned char)*name;
2013 	while (c) {
2014 		len++;
2015 		hash = partial_name_hash(c, hash);
2016 		c = (unsigned char)name[len];
2017 	}
2018 	return hashlen_create(end_name_hash(hash), len);
2019 }
2020 EXPORT_SYMBOL(hashlen_string);
2021 
2022 /*
2023  * We know there's a real path component here of at least
2024  * one character.
2025  */
2026 static inline u64 hash_name(const void *salt, const char *name)
2027 {
2028 	unsigned long hash = init_name_hash(salt);
2029 	unsigned long len = 0, c;
2030 
2031 	c = (unsigned char)*name;
2032 	do {
2033 		len++;
2034 		hash = partial_name_hash(c, hash);
2035 		c = (unsigned char)name[len];
2036 	} while (c && c != '/');
2037 	return hashlen_create(end_name_hash(hash), len);
2038 }
2039 
2040 #endif
2041 
2042 /*
2043  * Name resolution.
2044  * This is the basic name resolution function, turning a pathname into
2045  * the final dentry. We expect 'base' to be positive and a directory.
2046  *
2047  * Returns 0 and nd will have valid dentry and mnt on success.
2048  * Returns error and drops reference to input namei data on failure.
2049  */
2050 static int link_path_walk(const char *name, struct nameidata *nd)
2051 {
2052 	int err;
2053 
2054 	while (*name=='/')
2055 		name++;
2056 	if (!*name)
2057 		return 0;
2058 
2059 	/* At this point we know we have a real path component. */
2060 	for(;;) {
2061 		u64 hash_len;
2062 		int type;
2063 
2064 		err = may_lookup(nd);
2065 		if (err)
2066 			return err;
2067 
2068 		hash_len = hash_name(nd->path.dentry, name);
2069 
2070 		type = LAST_NORM;
2071 		if (name[0] == '.') switch (hashlen_len(hash_len)) {
2072 			case 2:
2073 				if (name[1] == '.') {
2074 					type = LAST_DOTDOT;
2075 					nd->flags |= LOOKUP_JUMPED;
2076 				}
2077 				break;
2078 			case 1:
2079 				type = LAST_DOT;
2080 		}
2081 		if (likely(type == LAST_NORM)) {
2082 			struct dentry *parent = nd->path.dentry;
2083 			nd->flags &= ~LOOKUP_JUMPED;
2084 			if (unlikely(parent->d_flags & DCACHE_OP_HASH)) {
2085 				struct qstr this = { { .hash_len = hash_len }, .name = name };
2086 				err = parent->d_op->d_hash(parent, &this);
2087 				if (err < 0)
2088 					return err;
2089 				hash_len = this.hash_len;
2090 				name = this.name;
2091 			}
2092 		}
2093 
2094 		nd->last.hash_len = hash_len;
2095 		nd->last.name = name;
2096 		nd->last_type = type;
2097 
2098 		name += hashlen_len(hash_len);
2099 		if (!*name)
2100 			goto OK;
2101 		/*
2102 		 * If it wasn't NUL, we know it was '/'. Skip that
2103 		 * slash, and continue until no more slashes.
2104 		 */
2105 		do {
2106 			name++;
2107 		} while (unlikely(*name == '/'));
2108 		if (unlikely(!*name)) {
2109 OK:
2110 			/* pathname body, done */
2111 			if (!nd->depth)
2112 				return 0;
2113 			name = nd->stack[nd->depth - 1].name;
2114 			/* trailing symlink, done */
2115 			if (!name)
2116 				return 0;
2117 			/* last component of nested symlink */
2118 			err = walk_component(nd, WALK_FOLLOW);
2119 		} else {
2120 			/* not the last component */
2121 			err = walk_component(nd, WALK_FOLLOW | WALK_MORE);
2122 		}
2123 		if (err < 0)
2124 			return err;
2125 
2126 		if (err) {
2127 			const char *s = get_link(nd);
2128 
2129 			if (IS_ERR(s))
2130 				return PTR_ERR(s);
2131 			err = 0;
2132 			if (unlikely(!s)) {
2133 				/* jumped */
2134 				put_link(nd);
2135 			} else {
2136 				nd->stack[nd->depth - 1].name = name;
2137 				name = s;
2138 				continue;
2139 			}
2140 		}
2141 		if (unlikely(!d_can_lookup(nd->path.dentry))) {
2142 			if (nd->flags & LOOKUP_RCU) {
2143 				if (unlazy_walk(nd))
2144 					return -ECHILD;
2145 			}
2146 			return -ENOTDIR;
2147 		}
2148 	}
2149 }
2150 
2151 static const char *path_init(struct nameidata *nd, unsigned flags)
2152 {
2153 	const char *s = nd->name->name;
2154 
2155 	if (!*s)
2156 		flags &= ~LOOKUP_RCU;
2157 
2158 	nd->last_type = LAST_ROOT; /* if there are only slashes... */
2159 	nd->flags = flags | LOOKUP_JUMPED | LOOKUP_PARENT;
2160 	nd->depth = 0;
2161 	if (flags & LOOKUP_ROOT) {
2162 		struct dentry *root = nd->root.dentry;
2163 		struct inode *inode = root->d_inode;
2164 		if (*s && unlikely(!d_can_lookup(root)))
2165 			return ERR_PTR(-ENOTDIR);
2166 		nd->path = nd->root;
2167 		nd->inode = inode;
2168 		if (flags & LOOKUP_RCU) {
2169 			rcu_read_lock();
2170 			nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
2171 			nd->root_seq = nd->seq;
2172 			nd->m_seq = read_seqbegin(&mount_lock);
2173 		} else {
2174 			path_get(&nd->path);
2175 		}
2176 		return s;
2177 	}
2178 
2179 	nd->root.mnt = NULL;
2180 	nd->path.mnt = NULL;
2181 	nd->path.dentry = NULL;
2182 
2183 	nd->m_seq = read_seqbegin(&mount_lock);
2184 	if (*s == '/') {
2185 		if (flags & LOOKUP_RCU)
2186 			rcu_read_lock();
2187 		set_root(nd);
2188 		if (likely(!nd_jump_root(nd)))
2189 			return s;
2190 		nd->root.mnt = NULL;
2191 		rcu_read_unlock();
2192 		return ERR_PTR(-ECHILD);
2193 	} else if (nd->dfd == AT_FDCWD) {
2194 		if (flags & LOOKUP_RCU) {
2195 			struct fs_struct *fs = current->fs;
2196 			unsigned seq;
2197 
2198 			rcu_read_lock();
2199 
2200 			do {
2201 				seq = read_seqcount_begin(&fs->seq);
2202 				nd->path = fs->pwd;
2203 				nd->inode = nd->path.dentry->d_inode;
2204 				nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
2205 			} while (read_seqcount_retry(&fs->seq, seq));
2206 		} else {
2207 			get_fs_pwd(current->fs, &nd->path);
2208 			nd->inode = nd->path.dentry->d_inode;
2209 		}
2210 		return s;
2211 	} else {
2212 		/* Caller must check execute permissions on the starting path component */
2213 		struct fd f = fdget_raw(nd->dfd);
2214 		struct dentry *dentry;
2215 
2216 		if (!f.file)
2217 			return ERR_PTR(-EBADF);
2218 
2219 		dentry = f.file->f_path.dentry;
2220 
2221 		if (*s) {
2222 			if (!d_can_lookup(dentry)) {
2223 				fdput(f);
2224 				return ERR_PTR(-ENOTDIR);
2225 			}
2226 		}
2227 
2228 		nd->path = f.file->f_path;
2229 		if (flags & LOOKUP_RCU) {
2230 			rcu_read_lock();
2231 			nd->inode = nd->path.dentry->d_inode;
2232 			nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);
2233 		} else {
2234 			path_get(&nd->path);
2235 			nd->inode = nd->path.dentry->d_inode;
2236 		}
2237 		fdput(f);
2238 		return s;
2239 	}
2240 }
2241 
2242 static const char *trailing_symlink(struct nameidata *nd)
2243 {
2244 	const char *s;
2245 	int error = may_follow_link(nd);
2246 	if (unlikely(error))
2247 		return ERR_PTR(error);
2248 	nd->flags |= LOOKUP_PARENT;
2249 	nd->stack[0].name = NULL;
2250 	s = get_link(nd);
2251 	return s ? s : "";
2252 }
2253 
2254 static inline int lookup_last(struct nameidata *nd)
2255 {
2256 	if (nd->last_type == LAST_NORM && nd->last.name[nd->last.len])
2257 		nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
2258 
2259 	nd->flags &= ~LOOKUP_PARENT;
2260 	return walk_component(nd, 0);
2261 }
2262 
2263 static int handle_lookup_down(struct nameidata *nd)
2264 {
2265 	struct path path = nd->path;
2266 	struct inode *inode = nd->inode;
2267 	unsigned seq = nd->seq;
2268 	int err;
2269 
2270 	if (nd->flags & LOOKUP_RCU) {
2271 		/*
2272 		 * don't bother with unlazy_walk on failure - we are
2273 		 * at the very beginning of walk, so we lose nothing
2274 		 * if we simply redo everything in non-RCU mode
2275 		 */
2276 		if (unlikely(!__follow_mount_rcu(nd, &path, &inode, &seq)))
2277 			return -ECHILD;
2278 	} else {
2279 		dget(path.dentry);
2280 		err = follow_managed(&path, nd);
2281 		if (unlikely(err < 0))
2282 			return err;
2283 		inode = d_backing_inode(path.dentry);
2284 		seq = 0;
2285 	}
2286 	path_to_nameidata(&path, nd);
2287 	nd->inode = inode;
2288 	nd->seq = seq;
2289 	return 0;
2290 }
2291 
2292 /* Returns 0 and nd will be valid on success; Retuns error, otherwise. */
2293 static int path_lookupat(struct nameidata *nd, unsigned flags, struct path *path)
2294 {
2295 	const char *s = path_init(nd, flags);
2296 	int err;
2297 
2298 	if (IS_ERR(s))
2299 		return PTR_ERR(s);
2300 
2301 	if (unlikely(flags & LOOKUP_DOWN)) {
2302 		err = handle_lookup_down(nd);
2303 		if (unlikely(err < 0)) {
2304 			terminate_walk(nd);
2305 			return err;
2306 		}
2307 	}
2308 
2309 	while (!(err = link_path_walk(s, nd))
2310 		&& ((err = lookup_last(nd)) > 0)) {
2311 		s = trailing_symlink(nd);
2312 		if (IS_ERR(s)) {
2313 			err = PTR_ERR(s);
2314 			break;
2315 		}
2316 	}
2317 	if (!err)
2318 		err = complete_walk(nd);
2319 
2320 	if (!err && nd->flags & LOOKUP_DIRECTORY)
2321 		if (!d_can_lookup(nd->path.dentry))
2322 			err = -ENOTDIR;
2323 	if (!err) {
2324 		*path = nd->path;
2325 		nd->path.mnt = NULL;
2326 		nd->path.dentry = NULL;
2327 	}
2328 	terminate_walk(nd);
2329 	return err;
2330 }
2331 
2332 static int filename_lookup(int dfd, struct filename *name, unsigned flags,
2333 			   struct path *path, struct path *root)
2334 {
2335 	int retval;
2336 	struct nameidata nd;
2337 	if (IS_ERR(name))
2338 		return PTR_ERR(name);
2339 	if (unlikely(root)) {
2340 		nd.root = *root;
2341 		flags |= LOOKUP_ROOT;
2342 	}
2343 	set_nameidata(&nd, dfd, name);
2344 	retval = path_lookupat(&nd, flags | LOOKUP_RCU, path);
2345 	if (unlikely(retval == -ECHILD))
2346 		retval = path_lookupat(&nd, flags, path);
2347 	if (unlikely(retval == -ESTALE))
2348 		retval = path_lookupat(&nd, flags | LOOKUP_REVAL, path);
2349 
2350 	if (likely(!retval))
2351 		audit_inode(name, path->dentry, flags & LOOKUP_PARENT);
2352 	restore_nameidata();
2353 	putname(name);
2354 	return retval;
2355 }
2356 
2357 /* Returns 0 and nd will be valid on success; Retuns error, otherwise. */
2358 static int path_parentat(struct nameidata *nd, unsigned flags,
2359 				struct path *parent)
2360 {
2361 	const char *s = path_init(nd, flags);
2362 	int err;
2363 	if (IS_ERR(s))
2364 		return PTR_ERR(s);
2365 	err = link_path_walk(s, nd);
2366 	if (!err)
2367 		err = complete_walk(nd);
2368 	if (!err) {
2369 		*parent = nd->path;
2370 		nd->path.mnt = NULL;
2371 		nd->path.dentry = NULL;
2372 	}
2373 	terminate_walk(nd);
2374 	return err;
2375 }
2376 
2377 static struct filename *filename_parentat(int dfd, struct filename *name,
2378 				unsigned int flags, struct path *parent,
2379 				struct qstr *last, int *type)
2380 {
2381 	int retval;
2382 	struct nameidata nd;
2383 
2384 	if (IS_ERR(name))
2385 		return name;
2386 	set_nameidata(&nd, dfd, name);
2387 	retval = path_parentat(&nd, flags | LOOKUP_RCU, parent);
2388 	if (unlikely(retval == -ECHILD))
2389 		retval = path_parentat(&nd, flags, parent);
2390 	if (unlikely(retval == -ESTALE))
2391 		retval = path_parentat(&nd, flags | LOOKUP_REVAL, parent);
2392 	if (likely(!retval)) {
2393 		*last = nd.last;
2394 		*type = nd.last_type;
2395 		audit_inode(name, parent->dentry, LOOKUP_PARENT);
2396 	} else {
2397 		putname(name);
2398 		name = ERR_PTR(retval);
2399 	}
2400 	restore_nameidata();
2401 	return name;
2402 }
2403 
2404 /* does lookup, returns the object with parent locked */
2405 struct dentry *kern_path_locked(const char *name, struct path *path)
2406 {
2407 	struct filename *filename;
2408 	struct dentry *d;
2409 	struct qstr last;
2410 	int type;
2411 
2412 	filename = filename_parentat(AT_FDCWD, getname_kernel(name), 0, path,
2413 				    &last, &type);
2414 	if (IS_ERR(filename))
2415 		return ERR_CAST(filename);
2416 	if (unlikely(type != LAST_NORM)) {
2417 		path_put(path);
2418 		putname(filename);
2419 		return ERR_PTR(-EINVAL);
2420 	}
2421 	inode_lock_nested(path->dentry->d_inode, I_MUTEX_PARENT);
2422 	d = __lookup_hash(&last, path->dentry, 0);
2423 	if (IS_ERR(d)) {
2424 		inode_unlock(path->dentry->d_inode);
2425 		path_put(path);
2426 	}
2427 	putname(filename);
2428 	return d;
2429 }
2430 
2431 int kern_path(const char *name, unsigned int flags, struct path *path)
2432 {
2433 	return filename_lookup(AT_FDCWD, getname_kernel(name),
2434 			       flags, path, NULL);
2435 }
2436 EXPORT_SYMBOL(kern_path);
2437 
2438 /**
2439  * vfs_path_lookup - lookup a file path relative to a dentry-vfsmount pair
2440  * @dentry:  pointer to dentry of the base directory
2441  * @mnt: pointer to vfs mount of the base directory
2442  * @name: pointer to file name
2443  * @flags: lookup flags
2444  * @path: pointer to struct path to fill
2445  */
2446 int vfs_path_lookup(struct dentry *dentry, struct vfsmount *mnt,
2447 		    const char *name, unsigned int flags,
2448 		    struct path *path)
2449 {
2450 	struct path root = {.mnt = mnt, .dentry = dentry};
2451 	/* the first argument of filename_lookup() is ignored with root */
2452 	return filename_lookup(AT_FDCWD, getname_kernel(name),
2453 			       flags , path, &root);
2454 }
2455 EXPORT_SYMBOL(vfs_path_lookup);
2456 
2457 /**
2458  * lookup_one_len - filesystem helper to lookup single pathname component
2459  * @name:	pathname component to lookup
2460  * @base:	base directory to lookup from
2461  * @len:	maximum length @len should be interpreted to
2462  *
2463  * Note that this routine is purely a helper for filesystem usage and should
2464  * not be called by generic code.
2465  *
2466  * The caller must hold base->i_mutex.
2467  */
2468 struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
2469 {
2470 	struct qstr this;
2471 	unsigned int c;
2472 	int err;
2473 
2474 	WARN_ON_ONCE(!inode_is_locked(base->d_inode));
2475 
2476 	this.name = name;
2477 	this.len = len;
2478 	this.hash = full_name_hash(base, name, len);
2479 	if (!len)
2480 		return ERR_PTR(-EACCES);
2481 
2482 	if (unlikely(name[0] == '.')) {
2483 		if (len < 2 || (len == 2 && name[1] == '.'))
2484 			return ERR_PTR(-EACCES);
2485 	}
2486 
2487 	while (len--) {
2488 		c = *(const unsigned char *)name++;
2489 		if (c == '/' || c == '\0')
2490 			return ERR_PTR(-EACCES);
2491 	}
2492 	/*
2493 	 * See if the low-level filesystem might want
2494 	 * to use its own hash..
2495 	 */
2496 	if (base->d_flags & DCACHE_OP_HASH) {
2497 		int err = base->d_op->d_hash(base, &this);
2498 		if (err < 0)
2499 			return ERR_PTR(err);
2500 	}
2501 
2502 	err = inode_permission(base->d_inode, MAY_EXEC);
2503 	if (err)
2504 		return ERR_PTR(err);
2505 
2506 	return __lookup_hash(&this, base, 0);
2507 }
2508 EXPORT_SYMBOL(lookup_one_len);
2509 
2510 /**
2511  * lookup_one_len_unlocked - filesystem helper to lookup single pathname component
2512  * @name:	pathname component to lookup
2513  * @base:	base directory to lookup from
2514  * @len:	maximum length @len should be interpreted to
2515  *
2516  * Note that this routine is purely a helper for filesystem usage and should
2517  * not be called by generic code.
2518  *
2519  * Unlike lookup_one_len, it should be called without the parent
2520  * i_mutex held, and will take the i_mutex itself if necessary.
2521  */
2522 struct dentry *lookup_one_len_unlocked(const char *name,
2523 				       struct dentry *base, int len)
2524 {
2525 	struct qstr this;
2526 	unsigned int c;
2527 	int err;
2528 	struct dentry *ret;
2529 
2530 	this.name = name;
2531 	this.len = len;
2532 	this.hash = full_name_hash(base, name, len);
2533 	if (!len)
2534 		return ERR_PTR(-EACCES);
2535 
2536 	if (unlikely(name[0] == '.')) {
2537 		if (len < 2 || (len == 2 && name[1] == '.'))
2538 			return ERR_PTR(-EACCES);
2539 	}
2540 
2541 	while (len--) {
2542 		c = *(const unsigned char *)name++;
2543 		if (c == '/' || c == '\0')
2544 			return ERR_PTR(-EACCES);
2545 	}
2546 	/*
2547 	 * See if the low-level filesystem might want
2548 	 * to use its own hash..
2549 	 */
2550 	if (base->d_flags & DCACHE_OP_HASH) {
2551 		int err = base->d_op->d_hash(base, &this);
2552 		if (err < 0)
2553 			return ERR_PTR(err);
2554 	}
2555 
2556 	err = inode_permission(base->d_inode, MAY_EXEC);
2557 	if (err)
2558 		return ERR_PTR(err);
2559 
2560 	ret = lookup_dcache(&this, base, 0);
2561 	if (!ret)
2562 		ret = lookup_slow(&this, base, 0);
2563 	return ret;
2564 }
2565 EXPORT_SYMBOL(lookup_one_len_unlocked);
2566 
2567 #ifdef CONFIG_UNIX98_PTYS
2568 int path_pts(struct path *path)
2569 {
2570 	/* Find something mounted on "pts" in the same directory as
2571 	 * the input path.
2572 	 */
2573 	struct dentry *child, *parent;
2574 	struct qstr this;
2575 	int ret;
2576 
2577 	ret = path_parent_directory(path);
2578 	if (ret)
2579 		return ret;
2580 
2581 	parent = path->dentry;
2582 	this.name = "pts";
2583 	this.len = 3;
2584 	child = d_hash_and_lookup(parent, &this);
2585 	if (!child)
2586 		return -ENOENT;
2587 
2588 	path->dentry = child;
2589 	dput(parent);
2590 	follow_mount(path);
2591 	return 0;
2592 }
2593 #endif
2594 
2595 int user_path_at_empty(int dfd, const char __user *name, unsigned flags,
2596 		 struct path *path, int *empty)
2597 {
2598 	return filename_lookup(dfd, getname_flags(name, flags, empty),
2599 			       flags, path, NULL);
2600 }
2601 EXPORT_SYMBOL(user_path_at_empty);
2602 
2603 /**
2604  * mountpoint_last - look up last component for umount
2605  * @nd:   pathwalk nameidata - currently pointing at parent directory of "last"
2606  *
2607  * This is a special lookup_last function just for umount. In this case, we
2608  * need to resolve the path without doing any revalidation.
2609  *
2610  * The nameidata should be the result of doing a LOOKUP_PARENT pathwalk. Since
2611  * mountpoints are always pinned in the dcache, their ancestors are too. Thus,
2612  * in almost all cases, this lookup will be served out of the dcache. The only
2613  * cases where it won't are if nd->last refers to a symlink or the path is
2614  * bogus and it doesn't exist.
2615  *
2616  * Returns:
2617  * -error: if there was an error during lookup. This includes -ENOENT if the
2618  *         lookup found a negative dentry.
2619  *
2620  * 0:      if we successfully resolved nd->last and found it to not to be a
2621  *         symlink that needs to be followed.
2622  *
2623  * 1:      if we successfully resolved nd->last and found it to be a symlink
2624  *         that needs to be followed.
2625  */
2626 static int
2627 mountpoint_last(struct nameidata *nd)
2628 {
2629 	int error = 0;
2630 	struct dentry *dir = nd->path.dentry;
2631 	struct path path;
2632 
2633 	/* If we're in rcuwalk, drop out of it to handle last component */
2634 	if (nd->flags & LOOKUP_RCU) {
2635 		if (unlazy_walk(nd))
2636 			return -ECHILD;
2637 	}
2638 
2639 	nd->flags &= ~LOOKUP_PARENT;
2640 
2641 	if (unlikely(nd->last_type != LAST_NORM)) {
2642 		error = handle_dots(nd, nd->last_type);
2643 		if (error)
2644 			return error;
2645 		path.dentry = dget(nd->path.dentry);
2646 	} else {
2647 		path.dentry = d_lookup(dir, &nd->last);
2648 		if (!path.dentry) {
2649 			/*
2650 			 * No cached dentry. Mounted dentries are pinned in the
2651 			 * cache, so that means that this dentry is probably
2652 			 * a symlink or the path doesn't actually point
2653 			 * to a mounted dentry.
2654 			 */
2655 			path.dentry = lookup_slow(&nd->last, dir,
2656 					     nd->flags | LOOKUP_NO_REVAL);
2657 			if (IS_ERR(path.dentry))
2658 				return PTR_ERR(path.dentry);
2659 		}
2660 	}
2661 	if (d_is_negative(path.dentry)) {
2662 		dput(path.dentry);
2663 		return -ENOENT;
2664 	}
2665 	path.mnt = nd->path.mnt;
2666 	return step_into(nd, &path, 0, d_backing_inode(path.dentry), 0);
2667 }
2668 
2669 /**
2670  * path_mountpoint - look up a path to be umounted
2671  * @nd:		lookup context
2672  * @flags:	lookup flags
2673  * @path:	pointer to container for result
2674  *
2675  * Look up the given name, but don't attempt to revalidate the last component.
2676  * Returns 0 and "path" will be valid on success; Returns error otherwise.
2677  */
2678 static int
2679 path_mountpoint(struct nameidata *nd, unsigned flags, struct path *path)
2680 {
2681 	const char *s = path_init(nd, flags);
2682 	int err;
2683 	if (IS_ERR(s))
2684 		return PTR_ERR(s);
2685 	while (!(err = link_path_walk(s, nd)) &&
2686 		(err = mountpoint_last(nd)) > 0) {
2687 		s = trailing_symlink(nd);
2688 		if (IS_ERR(s)) {
2689 			err = PTR_ERR(s);
2690 			break;
2691 		}
2692 	}
2693 	if (!err) {
2694 		*path = nd->path;
2695 		nd->path.mnt = NULL;
2696 		nd->path.dentry = NULL;
2697 		follow_mount(path);
2698 	}
2699 	terminate_walk(nd);
2700 	return err;
2701 }
2702 
2703 static int
2704 filename_mountpoint(int dfd, struct filename *name, struct path *path,
2705 			unsigned int flags)
2706 {
2707 	struct nameidata nd;
2708 	int error;
2709 	if (IS_ERR(name))
2710 		return PTR_ERR(name);
2711 	set_nameidata(&nd, dfd, name);
2712 	error = path_mountpoint(&nd, flags | LOOKUP_RCU, path);
2713 	if (unlikely(error == -ECHILD))
2714 		error = path_mountpoint(&nd, flags, path);
2715 	if (unlikely(error == -ESTALE))
2716 		error = path_mountpoint(&nd, flags | LOOKUP_REVAL, path);
2717 	if (likely(!error))
2718 		audit_inode(name, path->dentry, 0);
2719 	restore_nameidata();
2720 	putname(name);
2721 	return error;
2722 }
2723 
2724 /**
2725  * user_path_mountpoint_at - lookup a path from userland in order to umount it
2726  * @dfd:	directory file descriptor
2727  * @name:	pathname from userland
2728  * @flags:	lookup flags
2729  * @path:	pointer to container to hold result
2730  *
2731  * A umount is a special case for path walking. We're not actually interested
2732  * in the inode in this situation, and ESTALE errors can be a problem. We
2733  * simply want track down the dentry and vfsmount attached at the mountpoint
2734  * and avoid revalidating the last component.
2735  *
2736  * Returns 0 and populates "path" on success.
2737  */
2738 int
2739 user_path_mountpoint_at(int dfd, const char __user *name, unsigned int flags,
2740 			struct path *path)
2741 {
2742 	return filename_mountpoint(dfd, getname(name), path, flags);
2743 }
2744 
2745 int
2746 kern_path_mountpoint(int dfd, const char *name, struct path *path,
2747 			unsigned int flags)
2748 {
2749 	return filename_mountpoint(dfd, getname_kernel(name), path, flags);
2750 }
2751 EXPORT_SYMBOL(kern_path_mountpoint);
2752 
2753 int __check_sticky(struct inode *dir, struct inode *inode)
2754 {
2755 	kuid_t fsuid = current_fsuid();
2756 
2757 	if (uid_eq(inode->i_uid, fsuid))
2758 		return 0;
2759 	if (uid_eq(dir->i_uid, fsuid))
2760 		return 0;
2761 	return !capable_wrt_inode_uidgid(inode, CAP_FOWNER);
2762 }
2763 EXPORT_SYMBOL(__check_sticky);
2764 
2765 /*
2766  *	Check whether we can remove a link victim from directory dir, check
2767  *  whether the type of victim is right.
2768  *  1. We can't do it if dir is read-only (done in permission())
2769  *  2. We should have write and exec permissions on dir
2770  *  3. We can't remove anything from append-only dir
2771  *  4. We can't do anything with immutable dir (done in permission())
2772  *  5. If the sticky bit on dir is set we should either
2773  *	a. be owner of dir, or
2774  *	b. be owner of victim, or
2775  *	c. have CAP_FOWNER capability
2776  *  6. If the victim is append-only or immutable we can't do antyhing with
2777  *     links pointing to it.
2778  *  7. If the victim has an unknown uid or gid we can't change the inode.
2779  *  8. If we were asked to remove a directory and victim isn't one - ENOTDIR.
2780  *  9. If we were asked to remove a non-directory and victim isn't one - EISDIR.
2781  * 10. We can't remove a root or mountpoint.
2782  * 11. We don't allow removal of NFS sillyrenamed files; it's handled by
2783  *     nfs_async_unlink().
2784  */
2785 static int may_delete(struct inode *dir, struct dentry *victim, bool isdir)
2786 {
2787 	struct inode *inode = d_backing_inode(victim);
2788 	int error;
2789 
2790 	if (d_is_negative(victim))
2791 		return -ENOENT;
2792 	BUG_ON(!inode);
2793 
2794 	BUG_ON(victim->d_parent->d_inode != dir);
2795 	audit_inode_child(dir, victim, AUDIT_TYPE_CHILD_DELETE);
2796 
2797 	error = inode_permission(dir, MAY_WRITE | MAY_EXEC);
2798 	if (error)
2799 		return error;
2800 	if (IS_APPEND(dir))
2801 		return -EPERM;
2802 
2803 	if (check_sticky(dir, inode) || IS_APPEND(inode) ||
2804 	    IS_IMMUTABLE(inode) || IS_SWAPFILE(inode) || HAS_UNMAPPED_ID(inode))
2805 		return -EPERM;
2806 	if (isdir) {
2807 		if (!d_is_dir(victim))
2808 			return -ENOTDIR;
2809 		if (IS_ROOT(victim))
2810 			return -EBUSY;
2811 	} else if (d_is_dir(victim))
2812 		return -EISDIR;
2813 	if (IS_DEADDIR(dir))
2814 		return -ENOENT;
2815 	if (victim->d_flags & DCACHE_NFSFS_RENAMED)
2816 		return -EBUSY;
2817 	return 0;
2818 }
2819 
2820 /*	Check whether we can create an object with dentry child in directory
2821  *  dir.
2822  *  1. We can't do it if child already exists (open has special treatment for
2823  *     this case, but since we are inlined it's OK)
2824  *  2. We can't do it if dir is read-only (done in permission())
2825  *  3. We can't do it if the fs can't represent the fsuid or fsgid.
2826  *  4. We should have write and exec permissions on dir
2827  *  5. We can't do it if dir is immutable (done in permission())
2828  */
2829 static inline int may_create(struct inode *dir, struct dentry *child)
2830 {
2831 	struct user_namespace *s_user_ns;
2832 	audit_inode_child(dir, child, AUDIT_TYPE_CHILD_CREATE);
2833 	if (child->d_inode)
2834 		return -EEXIST;
2835 	if (IS_DEADDIR(dir))
2836 		return -ENOENT;
2837 	s_user_ns = dir->i_sb->s_user_ns;
2838 	if (!kuid_has_mapping(s_user_ns, current_fsuid()) ||
2839 	    !kgid_has_mapping(s_user_ns, current_fsgid()))
2840 		return -EOVERFLOW;
2841 	return inode_permission(dir, MAY_WRITE | MAY_EXEC);
2842 }
2843 
2844 /*
2845  * p1 and p2 should be directories on the same fs.
2846  */
2847 struct dentry *lock_rename(struct dentry *p1, struct dentry *p2)
2848 {
2849 	struct dentry *p;
2850 
2851 	if (p1 == p2) {
2852 		inode_lock_nested(p1->d_inode, I_MUTEX_PARENT);
2853 		return NULL;
2854 	}
2855 
2856 	mutex_lock(&p1->d_sb->s_vfs_rename_mutex);
2857 
2858 	p = d_ancestor(p2, p1);
2859 	if (p) {
2860 		inode_lock_nested(p2->d_inode, I_MUTEX_PARENT);
2861 		inode_lock_nested(p1->d_inode, I_MUTEX_CHILD);
2862 		return p;
2863 	}
2864 
2865 	p = d_ancestor(p1, p2);
2866 	if (p) {
2867 		inode_lock_nested(p1->d_inode, I_MUTEX_PARENT);
2868 		inode_lock_nested(p2->d_inode, I_MUTEX_CHILD);
2869 		return p;
2870 	}
2871 
2872 	inode_lock_nested(p1->d_inode, I_MUTEX_PARENT);
2873 	inode_lock_nested(p2->d_inode, I_MUTEX_PARENT2);
2874 	return NULL;
2875 }
2876 EXPORT_SYMBOL(lock_rename);
2877 
2878 void unlock_rename(struct dentry *p1, struct dentry *p2)
2879 {
2880 	inode_unlock(p1->d_inode);
2881 	if (p1 != p2) {
2882 		inode_unlock(p2->d_inode);
2883 		mutex_unlock(&p1->d_sb->s_vfs_rename_mutex);
2884 	}
2885 }
2886 EXPORT_SYMBOL(unlock_rename);
2887 
2888 int vfs_create(struct inode *dir, struct dentry *dentry, umode_t mode,
2889 		bool want_excl)
2890 {
2891 	int error = may_create(dir, dentry);
2892 	if (error)
2893 		return error;
2894 
2895 	if (!dir->i_op->create)
2896 		return -EACCES;	/* shouldn't it be ENOSYS? */
2897 	mode &= S_IALLUGO;
2898 	mode |= S_IFREG;
2899 	error = security_inode_create(dir, dentry, mode);
2900 	if (error)
2901 		return error;
2902 	error = dir->i_op->create(dir, dentry, mode, want_excl);
2903 	if (!error)
2904 		fsnotify_create(dir, dentry);
2905 	return error;
2906 }
2907 EXPORT_SYMBOL(vfs_create);
2908 
2909 bool may_open_dev(const struct path *path)
2910 {
2911 	return !(path->mnt->mnt_flags & MNT_NODEV) &&
2912 		!(path->mnt->mnt_sb->s_iflags & SB_I_NODEV);
2913 }
2914 
2915 static int may_open(const struct path *path, int acc_mode, int flag)
2916 {
2917 	struct dentry *dentry = path->dentry;
2918 	struct inode *inode = dentry->d_inode;
2919 	int error;
2920 
2921 	if (!inode)
2922 		return -ENOENT;
2923 
2924 	switch (inode->i_mode & S_IFMT) {
2925 	case S_IFLNK:
2926 		return -ELOOP;
2927 	case S_IFDIR:
2928 		if (acc_mode & MAY_WRITE)
2929 			return -EISDIR;
2930 		break;
2931 	case S_IFBLK:
2932 	case S_IFCHR:
2933 		if (!may_open_dev(path))
2934 			return -EACCES;
2935 		/*FALLTHRU*/
2936 	case S_IFIFO:
2937 	case S_IFSOCK:
2938 		flag &= ~O_TRUNC;
2939 		break;
2940 	}
2941 
2942 	error = inode_permission(inode, MAY_OPEN | acc_mode);
2943 	if (error)
2944 		return error;
2945 
2946 	/*
2947 	 * An append-only file must be opened in append mode for writing.
2948 	 */
2949 	if (IS_APPEND(inode)) {
2950 		if  ((flag & O_ACCMODE) != O_RDONLY && !(flag & O_APPEND))
2951 			return -EPERM;
2952 		if (flag & O_TRUNC)
2953 			return -EPERM;
2954 	}
2955 
2956 	/* O_NOATIME can only be set by the owner or superuser */
2957 	if (flag & O_NOATIME && !inode_owner_or_capable(inode))
2958 		return -EPERM;
2959 
2960 	return 0;
2961 }
2962 
2963 static int handle_truncate(struct file *filp)
2964 {
2965 	const struct path *path = &filp->f_path;
2966 	struct inode *inode = path->dentry->d_inode;
2967 	int error = get_write_access(inode);
2968 	if (error)
2969 		return error;
2970 	/*
2971 	 * Refuse to truncate files with mandatory locks held on them.
2972 	 */
2973 	error = locks_verify_locked(filp);
2974 	if (!error)
2975 		error = security_path_truncate(path);
2976 	if (!error) {
2977 		error = do_truncate(path->dentry, 0,
2978 				    ATTR_MTIME|ATTR_CTIME|ATTR_OPEN,
2979 				    filp);
2980 	}
2981 	put_write_access(inode);
2982 	return error;
2983 }
2984 
2985 static inline int open_to_namei_flags(int flag)
2986 {
2987 	if ((flag & O_ACCMODE) == 3)
2988 		flag--;
2989 	return flag;
2990 }
2991 
2992 static int may_o_create(const struct path *dir, struct dentry *dentry, umode_t mode)
2993 {
2994 	struct user_namespace *s_user_ns;
2995 	int error = security_path_mknod(dir, dentry, mode, 0);
2996 	if (error)
2997 		return error;
2998 
2999 	s_user_ns = dir->dentry->d_sb->s_user_ns;
3000 	if (!kuid_has_mapping(s_user_ns, current_fsuid()) ||
3001 	    !kgid_has_mapping(s_user_ns, current_fsgid()))
3002 		return -EOVERFLOW;
3003 
3004 	error = inode_permission(dir->dentry->d_inode, MAY_WRITE | MAY_EXEC);
3005 	if (error)
3006 		return error;
3007 
3008 	return security_inode_create(dir->dentry->d_inode, dentry, mode);
3009 }
3010 
3011 /*
3012  * Attempt to atomically look up, create and open a file from a negative
3013  * dentry.
3014  *
3015  * Returns 0 if successful.  The file will have been created and attached to
3016  * @file by the filesystem calling finish_open().
3017  *
3018  * Returns 1 if the file was looked up only or didn't need creating.  The
3019  * caller will need to perform the open themselves.  @path will have been
3020  * updated to point to the new dentry.  This may be negative.
3021  *
3022  * Returns an error code otherwise.
3023  */
3024 static int atomic_open(struct nameidata *nd, struct dentry *dentry,
3025 			struct path *path, struct file *file,
3026 			const struct open_flags *op,
3027 			int open_flag, umode_t mode,
3028 			int *opened)
3029 {
3030 	struct dentry *const DENTRY_NOT_SET = (void *) -1UL;
3031 	struct inode *dir =  nd->path.dentry->d_inode;
3032 	int error;
3033 
3034 	if (!(~open_flag & (O_EXCL | O_CREAT)))	/* both O_EXCL and O_CREAT */
3035 		open_flag &= ~O_TRUNC;
3036 
3037 	if (nd->flags & LOOKUP_DIRECTORY)
3038 		open_flag |= O_DIRECTORY;
3039 
3040 	file->f_path.dentry = DENTRY_NOT_SET;
3041 	file->f_path.mnt = nd->path.mnt;
3042 	error = dir->i_op->atomic_open(dir, dentry, file,
3043 				       open_to_namei_flags(open_flag),
3044 				       mode, opened);
3045 	d_lookup_done(dentry);
3046 	if (!error) {
3047 		/*
3048 		 * We didn't have the inode before the open, so check open
3049 		 * permission here.
3050 		 */
3051 		int acc_mode = op->acc_mode;
3052 		if (*opened & FILE_CREATED) {
3053 			WARN_ON(!(open_flag & O_CREAT));
3054 			fsnotify_create(dir, dentry);
3055 			acc_mode = 0;
3056 		}
3057 		error = may_open(&file->f_path, acc_mode, open_flag);
3058 		if (WARN_ON(error > 0))
3059 			error = -EINVAL;
3060 	} else if (error > 0) {
3061 		if (WARN_ON(file->f_path.dentry == DENTRY_NOT_SET)) {
3062 			error = -EIO;
3063 		} else {
3064 			if (file->f_path.dentry) {
3065 				dput(dentry);
3066 				dentry = file->f_path.dentry;
3067 			}
3068 			if (*opened & FILE_CREATED)
3069 				fsnotify_create(dir, dentry);
3070 			if (unlikely(d_is_negative(dentry))) {
3071 				error = -ENOENT;
3072 			} else {
3073 				path->dentry = dentry;
3074 				path->mnt = nd->path.mnt;
3075 				return 1;
3076 			}
3077 		}
3078 	}
3079 	dput(dentry);
3080 	return error;
3081 }
3082 
3083 /*
3084  * Look up and maybe create and open the last component.
3085  *
3086  * Must be called with i_mutex held on parent.
3087  *
3088  * Returns 0 if the file was successfully atomically created (if necessary) and
3089  * opened.  In this case the file will be returned attached to @file.
3090  *
3091  * Returns 1 if the file was not completely opened at this time, though lookups
3092  * and creations will have been performed and the dentry returned in @path will
3093  * be positive upon return if O_CREAT was specified.  If O_CREAT wasn't
3094  * specified then a negative dentry may be returned.
3095  *
3096  * An error code is returned otherwise.
3097  *
3098  * FILE_CREATE will be set in @*opened if the dentry was created and will be
3099  * cleared otherwise prior to returning.
3100  */
3101 static int lookup_open(struct nameidata *nd, struct path *path,
3102 			struct file *file,
3103 			const struct open_flags *op,
3104 			bool got_write, int *opened)
3105 {
3106 	struct dentry *dir = nd->path.dentry;
3107 	struct inode *dir_inode = dir->d_inode;
3108 	int open_flag = op->open_flag;
3109 	struct dentry *dentry;
3110 	int error, create_error = 0;
3111 	umode_t mode = op->mode;
3112 	DECLARE_WAIT_QUEUE_HEAD_ONSTACK(wq);
3113 
3114 	if (unlikely(IS_DEADDIR(dir_inode)))
3115 		return -ENOENT;
3116 
3117 	*opened &= ~FILE_CREATED;
3118 	dentry = d_lookup(dir, &nd->last);
3119 	for (;;) {
3120 		if (!dentry) {
3121 			dentry = d_alloc_parallel(dir, &nd->last, &wq);
3122 			if (IS_ERR(dentry))
3123 				return PTR_ERR(dentry);
3124 		}
3125 		if (d_in_lookup(dentry))
3126 			break;
3127 
3128 		error = d_revalidate(dentry, nd->flags);
3129 		if (likely(error > 0))
3130 			break;
3131 		if (error)
3132 			goto out_dput;
3133 		d_invalidate(dentry);
3134 		dput(dentry);
3135 		dentry = NULL;
3136 	}
3137 	if (dentry->d_inode) {
3138 		/* Cached positive dentry: will open in f_op->open */
3139 		goto out_no_open;
3140 	}
3141 
3142 	/*
3143 	 * Checking write permission is tricky, bacuse we don't know if we are
3144 	 * going to actually need it: O_CREAT opens should work as long as the
3145 	 * file exists.  But checking existence breaks atomicity.  The trick is
3146 	 * to check access and if not granted clear O_CREAT from the flags.
3147 	 *
3148 	 * Another problem is returing the "right" error value (e.g. for an
3149 	 * O_EXCL open we want to return EEXIST not EROFS).
3150 	 */
3151 	if (open_flag & O_CREAT) {
3152 		if (!IS_POSIXACL(dir->d_inode))
3153 			mode &= ~current_umask();
3154 		if (unlikely(!got_write)) {
3155 			create_error = -EROFS;
3156 			open_flag &= ~O_CREAT;
3157 			if (open_flag & (O_EXCL | O_TRUNC))
3158 				goto no_open;
3159 			/* No side effects, safe to clear O_CREAT */
3160 		} else {
3161 			create_error = may_o_create(&nd->path, dentry, mode);
3162 			if (create_error) {
3163 				open_flag &= ~O_CREAT;
3164 				if (open_flag & O_EXCL)
3165 					goto no_open;
3166 			}
3167 		}
3168 	} else if ((open_flag & (O_TRUNC|O_WRONLY|O_RDWR)) &&
3169 		   unlikely(!got_write)) {
3170 		/*
3171 		 * No O_CREATE -> atomicity not a requirement -> fall
3172 		 * back to lookup + open
3173 		 */
3174 		goto no_open;
3175 	}
3176 
3177 	if (dir_inode->i_op->atomic_open) {
3178 		error = atomic_open(nd, dentry, path, file, op, open_flag,
3179 				    mode, opened);
3180 		if (unlikely(error == -ENOENT) && create_error)
3181 			error = create_error;
3182 		return error;
3183 	}
3184 
3185 no_open:
3186 	if (d_in_lookup(dentry)) {
3187 		struct dentry *res = dir_inode->i_op->lookup(dir_inode, dentry,
3188 							     nd->flags);
3189 		d_lookup_done(dentry);
3190 		if (unlikely(res)) {
3191 			if (IS_ERR(res)) {
3192 				error = PTR_ERR(res);
3193 				goto out_dput;
3194 			}
3195 			dput(dentry);
3196 			dentry = res;
3197 		}
3198 	}
3199 
3200 	/* Negative dentry, just create the file */
3201 	if (!dentry->d_inode && (open_flag & O_CREAT)) {
3202 		*opened |= FILE_CREATED;
3203 		audit_inode_child(dir_inode, dentry, AUDIT_TYPE_CHILD_CREATE);
3204 		if (!dir_inode->i_op->create) {
3205 			error = -EACCES;
3206 			goto out_dput;
3207 		}
3208 		error = dir_inode->i_op->create(dir_inode, dentry, mode,
3209 						open_flag & O_EXCL);
3210 		if (error)
3211 			goto out_dput;
3212 		fsnotify_create(dir_inode, dentry);
3213 	}
3214 	if (unlikely(create_error) && !dentry->d_inode) {
3215 		error = create_error;
3216 		goto out_dput;
3217 	}
3218 out_no_open:
3219 	path->dentry = dentry;
3220 	path->mnt = nd->path.mnt;
3221 	return 1;
3222 
3223 out_dput:
3224 	dput(dentry);
3225 	return error;
3226 }
3227 
3228 /*
3229  * Handle the last step of open()
3230  */
3231 static int do_last(struct nameidata *nd,
3232 		   struct file *file, const struct open_flags *op,
3233 		   int *opened)
3234 {
3235 	struct dentry *dir = nd->path.dentry;
3236 	int open_flag = op->open_flag;
3237 	bool will_truncate = (open_flag & O_TRUNC) != 0;
3238 	bool got_write = false;
3239 	int acc_mode = op->acc_mode;
3240 	unsigned seq;
3241 	struct inode *inode;
3242 	struct path path;
3243 	int error;
3244 
3245 	nd->flags &= ~LOOKUP_PARENT;
3246 	nd->flags |= op->intent;
3247 
3248 	if (nd->last_type != LAST_NORM) {
3249 		error = handle_dots(nd, nd->last_type);
3250 		if (unlikely(error))
3251 			return error;
3252 		goto finish_open;
3253 	}
3254 
3255 	if (!(open_flag & O_CREAT)) {
3256 		if (nd->last.name[nd->last.len])
3257 			nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
3258 		/* we _can_ be in RCU mode here */
3259 		error = lookup_fast(nd, &path, &inode, &seq);
3260 		if (likely(error > 0))
3261 			goto finish_lookup;
3262 
3263 		if (error < 0)
3264 			return error;
3265 
3266 		BUG_ON(nd->inode != dir->d_inode);
3267 		BUG_ON(nd->flags & LOOKUP_RCU);
3268 	} else {
3269 		/* create side of things */
3270 		/*
3271 		 * This will *only* deal with leaving RCU mode - LOOKUP_JUMPED
3272 		 * has been cleared when we got to the last component we are
3273 		 * about to look up
3274 		 */
3275 		error = complete_walk(nd);
3276 		if (error)
3277 			return error;
3278 
3279 		audit_inode(nd->name, dir, LOOKUP_PARENT);
3280 		/* trailing slashes? */
3281 		if (unlikely(nd->last.name[nd->last.len]))
3282 			return -EISDIR;
3283 	}
3284 
3285 	if (open_flag & (O_CREAT | O_TRUNC | O_WRONLY | O_RDWR)) {
3286 		error = mnt_want_write(nd->path.mnt);
3287 		if (!error)
3288 			got_write = true;
3289 		/*
3290 		 * do _not_ fail yet - we might not need that or fail with
3291 		 * a different error; let lookup_open() decide; we'll be
3292 		 * dropping this one anyway.
3293 		 */
3294 	}
3295 	if (open_flag & O_CREAT)
3296 		inode_lock(dir->d_inode);
3297 	else
3298 		inode_lock_shared(dir->d_inode);
3299 	error = lookup_open(nd, &path, file, op, got_write, opened);
3300 	if (open_flag & O_CREAT)
3301 		inode_unlock(dir->d_inode);
3302 	else
3303 		inode_unlock_shared(dir->d_inode);
3304 
3305 	if (error <= 0) {
3306 		if (error)
3307 			goto out;
3308 
3309 		if ((*opened & FILE_CREATED) ||
3310 		    !S_ISREG(file_inode(file)->i_mode))
3311 			will_truncate = false;
3312 
3313 		audit_inode(nd->name, file->f_path.dentry, 0);
3314 		goto opened;
3315 	}
3316 
3317 	if (*opened & FILE_CREATED) {
3318 		/* Don't check for write permission, don't truncate */
3319 		open_flag &= ~O_TRUNC;
3320 		will_truncate = false;
3321 		acc_mode = 0;
3322 		path_to_nameidata(&path, nd);
3323 		goto finish_open_created;
3324 	}
3325 
3326 	/*
3327 	 * If atomic_open() acquired write access it is dropped now due to
3328 	 * possible mount and symlink following (this might be optimized away if
3329 	 * necessary...)
3330 	 */
3331 	if (got_write) {
3332 		mnt_drop_write(nd->path.mnt);
3333 		got_write = false;
3334 	}
3335 
3336 	error = follow_managed(&path, nd);
3337 	if (unlikely(error < 0))
3338 		return error;
3339 
3340 	if (unlikely(d_is_negative(path.dentry))) {
3341 		path_to_nameidata(&path, nd);
3342 		return -ENOENT;
3343 	}
3344 
3345 	/*
3346 	 * create/update audit record if it already exists.
3347 	 */
3348 	audit_inode(nd->name, path.dentry, 0);
3349 
3350 	if (unlikely((open_flag & (O_EXCL | O_CREAT)) == (O_EXCL | O_CREAT))) {
3351 		path_to_nameidata(&path, nd);
3352 		return -EEXIST;
3353 	}
3354 
3355 	seq = 0;	/* out of RCU mode, so the value doesn't matter */
3356 	inode = d_backing_inode(path.dentry);
3357 finish_lookup:
3358 	error = step_into(nd, &path, 0, inode, seq);
3359 	if (unlikely(error))
3360 		return error;
3361 finish_open:
3362 	/* Why this, you ask?  _Now_ we might have grown LOOKUP_JUMPED... */
3363 	error = complete_walk(nd);
3364 	if (error)
3365 		return error;
3366 	audit_inode(nd->name, nd->path.dentry, 0);
3367 	error = -EISDIR;
3368 	if ((open_flag & O_CREAT) && d_is_dir(nd->path.dentry))
3369 		goto out;
3370 	error = -ENOTDIR;
3371 	if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry))
3372 		goto out;
3373 	if (!d_is_reg(nd->path.dentry))
3374 		will_truncate = false;
3375 
3376 	if (will_truncate) {
3377 		error = mnt_want_write(nd->path.mnt);
3378 		if (error)
3379 			goto out;
3380 		got_write = true;
3381 	}
3382 finish_open_created:
3383 	error = may_open(&nd->path, acc_mode, open_flag);
3384 	if (error)
3385 		goto out;
3386 	BUG_ON(*opened & FILE_OPENED); /* once it's opened, it's opened */
3387 	error = vfs_open(&nd->path, file, current_cred());
3388 	if (error)
3389 		goto out;
3390 	*opened |= FILE_OPENED;
3391 opened:
3392 	error = open_check_o_direct(file);
3393 	if (!error)
3394 		error = ima_file_check(file, op->acc_mode, *opened);
3395 	if (!error && will_truncate)
3396 		error = handle_truncate(file);
3397 out:
3398 	if (unlikely(error) && (*opened & FILE_OPENED))
3399 		fput(file);
3400 	if (unlikely(error > 0)) {
3401 		WARN_ON(1);
3402 		error = -EINVAL;
3403 	}
3404 	if (got_write)
3405 		mnt_drop_write(nd->path.mnt);
3406 	return error;
3407 }
3408 
3409 struct dentry *vfs_tmpfile(struct dentry *dentry, umode_t mode, int open_flag)
3410 {
3411 	struct dentry *child = NULL;
3412 	struct inode *dir = dentry->d_inode;
3413 	struct inode *inode;
3414 	int error;
3415 
3416 	/* we want directory to be writable */
3417 	error = inode_permission(dir, MAY_WRITE | MAY_EXEC);
3418 	if (error)
3419 		goto out_err;
3420 	error = -EOPNOTSUPP;
3421 	if (!dir->i_op->tmpfile)
3422 		goto out_err;
3423 	error = -ENOMEM;
3424 	child = d_alloc(dentry, &slash_name);
3425 	if (unlikely(!child))
3426 		goto out_err;
3427 	error = dir->i_op->tmpfile(dir, child, mode);
3428 	if (error)
3429 		goto out_err;
3430 	error = -ENOENT;
3431 	inode = child->d_inode;
3432 	if (unlikely(!inode))
3433 		goto out_err;
3434 	if (!(open_flag & O_EXCL)) {
3435 		spin_lock(&inode->i_lock);
3436 		inode->i_state |= I_LINKABLE;
3437 		spin_unlock(&inode->i_lock);
3438 	}
3439 	return child;
3440 
3441 out_err:
3442 	dput(child);
3443 	return ERR_PTR(error);
3444 }
3445 EXPORT_SYMBOL(vfs_tmpfile);
3446 
3447 static int do_tmpfile(struct nameidata *nd, unsigned flags,
3448 		const struct open_flags *op,
3449 		struct file *file, int *opened)
3450 {
3451 	struct dentry *child;
3452 	struct path path;
3453 	int error = path_lookupat(nd, flags | LOOKUP_DIRECTORY, &path);
3454 	if (unlikely(error))
3455 		return error;
3456 	error = mnt_want_write(path.mnt);
3457 	if (unlikely(error))
3458 		goto out;
3459 	child = vfs_tmpfile(path.dentry, op->mode, op->open_flag);
3460 	error = PTR_ERR(child);
3461 	if (unlikely(IS_ERR(child)))
3462 		goto out2;
3463 	dput(path.dentry);
3464 	path.dentry = child;
3465 	audit_inode(nd->name, child, 0);
3466 	/* Don't check for other permissions, the inode was just created */
3467 	error = may_open(&path, 0, op->open_flag);
3468 	if (error)
3469 		goto out2;
3470 	file->f_path.mnt = path.mnt;
3471 	error = finish_open(file, child, NULL, opened);
3472 	if (error)
3473 		goto out2;
3474 	error = open_check_o_direct(file);
3475 	if (error)
3476 		fput(file);
3477 out2:
3478 	mnt_drop_write(path.mnt);
3479 out:
3480 	path_put(&path);
3481 	return error;
3482 }
3483 
3484 static int do_o_path(struct nameidata *nd, unsigned flags, struct file *file)
3485 {
3486 	struct path path;
3487 	int error = path_lookupat(nd, flags, &path);
3488 	if (!error) {
3489 		audit_inode(nd->name, path.dentry, 0);
3490 		error = vfs_open(&path, file, current_cred());
3491 		path_put(&path);
3492 	}
3493 	return error;
3494 }
3495 
3496 static struct file *path_openat(struct nameidata *nd,
3497 			const struct open_flags *op, unsigned flags)
3498 {
3499 	const char *s;
3500 	struct file *file;
3501 	int opened = 0;
3502 	int error;
3503 
3504 	file = get_empty_filp();
3505 	if (IS_ERR(file))
3506 		return file;
3507 
3508 	file->f_flags = op->open_flag;
3509 
3510 	if (unlikely(file->f_flags & __O_TMPFILE)) {
3511 		error = do_tmpfile(nd, flags, op, file, &opened);
3512 		goto out2;
3513 	}
3514 
3515 	if (unlikely(file->f_flags & O_PATH)) {
3516 		error = do_o_path(nd, flags, file);
3517 		if (!error)
3518 			opened |= FILE_OPENED;
3519 		goto out2;
3520 	}
3521 
3522 	s = path_init(nd, flags);
3523 	if (IS_ERR(s)) {
3524 		put_filp(file);
3525 		return ERR_CAST(s);
3526 	}
3527 	while (!(error = link_path_walk(s, nd)) &&
3528 		(error = do_last(nd, file, op, &opened)) > 0) {
3529 		nd->flags &= ~(LOOKUP_OPEN|LOOKUP_CREATE|LOOKUP_EXCL);
3530 		s = trailing_symlink(nd);
3531 		if (IS_ERR(s)) {
3532 			error = PTR_ERR(s);
3533 			break;
3534 		}
3535 	}
3536 	terminate_walk(nd);
3537 out2:
3538 	if (!(opened & FILE_OPENED)) {
3539 		BUG_ON(!error);
3540 		put_filp(file);
3541 	}
3542 	if (unlikely(error)) {
3543 		if (error == -EOPENSTALE) {
3544 			if (flags & LOOKUP_RCU)
3545 				error = -ECHILD;
3546 			else
3547 				error = -ESTALE;
3548 		}
3549 		file = ERR_PTR(error);
3550 	}
3551 	return file;
3552 }
3553 
3554 struct file *do_filp_open(int dfd, struct filename *pathname,
3555 		const struct open_flags *op)
3556 {
3557 	struct nameidata nd;
3558 	int flags = op->lookup_flags;
3559 	struct file *filp;
3560 
3561 	set_nameidata(&nd, dfd, pathname);
3562 	filp = path_openat(&nd, op, flags | LOOKUP_RCU);
3563 	if (unlikely(filp == ERR_PTR(-ECHILD)))
3564 		filp = path_openat(&nd, op, flags);
3565 	if (unlikely(filp == ERR_PTR(-ESTALE)))
3566 		filp = path_openat(&nd, op, flags | LOOKUP_REVAL);
3567 	restore_nameidata();
3568 	return filp;
3569 }
3570 
3571 struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt,
3572 		const char *name, const struct open_flags *op)
3573 {
3574 	struct nameidata nd;
3575 	struct file *file;
3576 	struct filename *filename;
3577 	int flags = op->lookup_flags | LOOKUP_ROOT;
3578 
3579 	nd.root.mnt = mnt;
3580 	nd.root.dentry = dentry;
3581 
3582 	if (d_is_symlink(dentry) && op->intent & LOOKUP_OPEN)
3583 		return ERR_PTR(-ELOOP);
3584 
3585 	filename = getname_kernel(name);
3586 	if (IS_ERR(filename))
3587 		return ERR_CAST(filename);
3588 
3589 	set_nameidata(&nd, -1, filename);
3590 	file = path_openat(&nd, op, flags | LOOKUP_RCU);
3591 	if (unlikely(file == ERR_PTR(-ECHILD)))
3592 		file = path_openat(&nd, op, flags);
3593 	if (unlikely(file == ERR_PTR(-ESTALE)))
3594 		file = path_openat(&nd, op, flags | LOOKUP_REVAL);
3595 	restore_nameidata();
3596 	putname(filename);
3597 	return file;
3598 }
3599 
3600 static struct dentry *filename_create(int dfd, struct filename *name,
3601 				struct path *path, unsigned int lookup_flags)
3602 {
3603 	struct dentry *dentry = ERR_PTR(-EEXIST);
3604 	struct qstr last;
3605 	int type;
3606 	int err2;
3607 	int error;
3608 	bool is_dir = (lookup_flags & LOOKUP_DIRECTORY);
3609 
3610 	/*
3611 	 * Note that only LOOKUP_REVAL and LOOKUP_DIRECTORY matter here. Any
3612 	 * other flags passed in are ignored!
3613 	 */
3614 	lookup_flags &= LOOKUP_REVAL;
3615 
3616 	name = filename_parentat(dfd, name, lookup_flags, path, &last, &type);
3617 	if (IS_ERR(name))
3618 		return ERR_CAST(name);
3619 
3620 	/*
3621 	 * Yucky last component or no last component at all?
3622 	 * (foo/., foo/.., /////)
3623 	 */
3624 	if (unlikely(type != LAST_NORM))
3625 		goto out;
3626 
3627 	/* don't fail immediately if it's r/o, at least try to report other errors */
3628 	err2 = mnt_want_write(path->mnt);
3629 	/*
3630 	 * Do the final lookup.
3631 	 */
3632 	lookup_flags |= LOOKUP_CREATE | LOOKUP_EXCL;
3633 	inode_lock_nested(path->dentry->d_inode, I_MUTEX_PARENT);
3634 	dentry = __lookup_hash(&last, path->dentry, lookup_flags);
3635 	if (IS_ERR(dentry))
3636 		goto unlock;
3637 
3638 	error = -EEXIST;
3639 	if (d_is_positive(dentry))
3640 		goto fail;
3641 
3642 	/*
3643 	 * Special case - lookup gave negative, but... we had foo/bar/
3644 	 * From the vfs_mknod() POV we just have a negative dentry -
3645 	 * all is fine. Let's be bastards - you had / on the end, you've
3646 	 * been asking for (non-existent) directory. -ENOENT for you.
3647 	 */
3648 	if (unlikely(!is_dir && last.name[last.len])) {
3649 		error = -ENOENT;
3650 		goto fail;
3651 	}
3652 	if (unlikely(err2)) {
3653 		error = err2;
3654 		goto fail;
3655 	}
3656 	putname(name);
3657 	return dentry;
3658 fail:
3659 	dput(dentry);
3660 	dentry = ERR_PTR(error);
3661 unlock:
3662 	inode_unlock(path->dentry->d_inode);
3663 	if (!err2)
3664 		mnt_drop_write(path->mnt);
3665 out:
3666 	path_put(path);
3667 	putname(name);
3668 	return dentry;
3669 }
3670 
3671 struct dentry *kern_path_create(int dfd, const char *pathname,
3672 				struct path *path, unsigned int lookup_flags)
3673 {
3674 	return filename_create(dfd, getname_kernel(pathname),
3675 				path, lookup_flags);
3676 }
3677 EXPORT_SYMBOL(kern_path_create);
3678 
3679 void done_path_create(struct path *path, struct dentry *dentry)
3680 {
3681 	dput(dentry);
3682 	inode_unlock(path->dentry->d_inode);
3683 	mnt_drop_write(path->mnt);
3684 	path_put(path);
3685 }
3686 EXPORT_SYMBOL(done_path_create);
3687 
3688 inline struct dentry *user_path_create(int dfd, const char __user *pathname,
3689 				struct path *path, unsigned int lookup_flags)
3690 {
3691 	return filename_create(dfd, getname(pathname), path, lookup_flags);
3692 }
3693 EXPORT_SYMBOL(user_path_create);
3694 
3695 int vfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
3696 {
3697 	int error = may_create(dir, dentry);
3698 
3699 	if (error)
3700 		return error;
3701 
3702 	if ((S_ISCHR(mode) || S_ISBLK(mode)) && !capable(CAP_MKNOD))
3703 		return -EPERM;
3704 
3705 	if (!dir->i_op->mknod)
3706 		return -EPERM;
3707 
3708 	error = devcgroup_inode_mknod(mode, dev);
3709 	if (error)
3710 		return error;
3711 
3712 	error = security_inode_mknod(dir, dentry, mode, dev);
3713 	if (error)
3714 		return error;
3715 
3716 	error = dir->i_op->mknod(dir, dentry, mode, dev);
3717 	if (!error)
3718 		fsnotify_create(dir, dentry);
3719 	return error;
3720 }
3721 EXPORT_SYMBOL(vfs_mknod);
3722 
3723 static int may_mknod(umode_t mode)
3724 {
3725 	switch (mode & S_IFMT) {
3726 	case S_IFREG:
3727 	case S_IFCHR:
3728 	case S_IFBLK:
3729 	case S_IFIFO:
3730 	case S_IFSOCK:
3731 	case 0: /* zero mode translates to S_IFREG */
3732 		return 0;
3733 	case S_IFDIR:
3734 		return -EPERM;
3735 	default:
3736 		return -EINVAL;
3737 	}
3738 }
3739 
3740 SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode,
3741 		unsigned, dev)
3742 {
3743 	struct dentry *dentry;
3744 	struct path path;
3745 	int error;
3746 	unsigned int lookup_flags = 0;
3747 
3748 	error = may_mknod(mode);
3749 	if (error)
3750 		return error;
3751 retry:
3752 	dentry = user_path_create(dfd, filename, &path, lookup_flags);
3753 	if (IS_ERR(dentry))
3754 		return PTR_ERR(dentry);
3755 
3756 	if (!IS_POSIXACL(path.dentry->d_inode))
3757 		mode &= ~current_umask();
3758 	error = security_path_mknod(&path, dentry, mode, dev);
3759 	if (error)
3760 		goto out;
3761 	switch (mode & S_IFMT) {
3762 		case 0: case S_IFREG:
3763 			error = vfs_create(path.dentry->d_inode,dentry,mode,true);
3764 			if (!error)
3765 				ima_post_path_mknod(dentry);
3766 			break;
3767 		case S_IFCHR: case S_IFBLK:
3768 			error = vfs_mknod(path.dentry->d_inode,dentry,mode,
3769 					new_decode_dev(dev));
3770 			break;
3771 		case S_IFIFO: case S_IFSOCK:
3772 			error = vfs_mknod(path.dentry->d_inode,dentry,mode,0);
3773 			break;
3774 	}
3775 out:
3776 	done_path_create(&path, dentry);
3777 	if (retry_estale(error, lookup_flags)) {
3778 		lookup_flags |= LOOKUP_REVAL;
3779 		goto retry;
3780 	}
3781 	return error;
3782 }
3783 
3784 SYSCALL_DEFINE3(mknod, const char __user *, filename, umode_t, mode, unsigned, dev)
3785 {
3786 	return sys_mknodat(AT_FDCWD, filename, mode, dev);
3787 }
3788 
3789 int vfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
3790 {
3791 	int error = may_create(dir, dentry);
3792 	unsigned max_links = dir->i_sb->s_max_links;
3793 
3794 	if (error)
3795 		return error;
3796 
3797 	if (!dir->i_op->mkdir)
3798 		return -EPERM;
3799 
3800 	mode &= (S_IRWXUGO|S_ISVTX);
3801 	error = security_inode_mkdir(dir, dentry, mode);
3802 	if (error)
3803 		return error;
3804 
3805 	if (max_links && dir->i_nlink >= max_links)
3806 		return -EMLINK;
3807 
3808 	error = dir->i_op->mkdir(dir, dentry, mode);
3809 	if (!error)
3810 		fsnotify_mkdir(dir, dentry);
3811 	return error;
3812 }
3813 EXPORT_SYMBOL(vfs_mkdir);
3814 
3815 SYSCALL_DEFINE3(mkdirat, int, dfd, const char __user *, pathname, umode_t, mode)
3816 {
3817 	struct dentry *dentry;
3818 	struct path path;
3819 	int error;
3820 	unsigned int lookup_flags = LOOKUP_DIRECTORY;
3821 
3822 retry:
3823 	dentry = user_path_create(dfd, pathname, &path, lookup_flags);
3824 	if (IS_ERR(dentry))
3825 		return PTR_ERR(dentry);
3826 
3827 	if (!IS_POSIXACL(path.dentry->d_inode))
3828 		mode &= ~current_umask();
3829 	error = security_path_mkdir(&path, dentry, mode);
3830 	if (!error)
3831 		error = vfs_mkdir(path.dentry->d_inode, dentry, mode);
3832 	done_path_create(&path, dentry);
3833 	if (retry_estale(error, lookup_flags)) {
3834 		lookup_flags |= LOOKUP_REVAL;
3835 		goto retry;
3836 	}
3837 	return error;
3838 }
3839 
3840 SYSCALL_DEFINE2(mkdir, const char __user *, pathname, umode_t, mode)
3841 {
3842 	return sys_mkdirat(AT_FDCWD, pathname, mode);
3843 }
3844 
3845 int vfs_rmdir(struct inode *dir, struct dentry *dentry)
3846 {
3847 	int error = may_delete(dir, dentry, 1);
3848 
3849 	if (error)
3850 		return error;
3851 
3852 	if (!dir->i_op->rmdir)
3853 		return -EPERM;
3854 
3855 	dget(dentry);
3856 	inode_lock(dentry->d_inode);
3857 
3858 	error = -EBUSY;
3859 	if (is_local_mountpoint(dentry))
3860 		goto out;
3861 
3862 	error = security_inode_rmdir(dir, dentry);
3863 	if (error)
3864 		goto out;
3865 
3866 	shrink_dcache_parent(dentry);
3867 	error = dir->i_op->rmdir(dir, dentry);
3868 	if (error)
3869 		goto out;
3870 
3871 	dentry->d_inode->i_flags |= S_DEAD;
3872 	dont_mount(dentry);
3873 	detach_mounts(dentry);
3874 
3875 out:
3876 	inode_unlock(dentry->d_inode);
3877 	dput(dentry);
3878 	if (!error)
3879 		d_delete(dentry);
3880 	return error;
3881 }
3882 EXPORT_SYMBOL(vfs_rmdir);
3883 
3884 static long do_rmdir(int dfd, const char __user *pathname)
3885 {
3886 	int error = 0;
3887 	struct filename *name;
3888 	struct dentry *dentry;
3889 	struct path path;
3890 	struct qstr last;
3891 	int type;
3892 	unsigned int lookup_flags = 0;
3893 retry:
3894 	name = filename_parentat(dfd, getname(pathname), lookup_flags,
3895 				&path, &last, &type);
3896 	if (IS_ERR(name))
3897 		return PTR_ERR(name);
3898 
3899 	switch (type) {
3900 	case LAST_DOTDOT:
3901 		error = -ENOTEMPTY;
3902 		goto exit1;
3903 	case LAST_DOT:
3904 		error = -EINVAL;
3905 		goto exit1;
3906 	case LAST_ROOT:
3907 		error = -EBUSY;
3908 		goto exit1;
3909 	}
3910 
3911 	error = mnt_want_write(path.mnt);
3912 	if (error)
3913 		goto exit1;
3914 
3915 	inode_lock_nested(path.dentry->d_inode, I_MUTEX_PARENT);
3916 	dentry = __lookup_hash(&last, path.dentry, lookup_flags);
3917 	error = PTR_ERR(dentry);
3918 	if (IS_ERR(dentry))
3919 		goto exit2;
3920 	if (!dentry->d_inode) {
3921 		error = -ENOENT;
3922 		goto exit3;
3923 	}
3924 	error = security_path_rmdir(&path, dentry);
3925 	if (error)
3926 		goto exit3;
3927 	error = vfs_rmdir(path.dentry->d_inode, dentry);
3928 exit3:
3929 	dput(dentry);
3930 exit2:
3931 	inode_unlock(path.dentry->d_inode);
3932 	mnt_drop_write(path.mnt);
3933 exit1:
3934 	path_put(&path);
3935 	putname(name);
3936 	if (retry_estale(error, lookup_flags)) {
3937 		lookup_flags |= LOOKUP_REVAL;
3938 		goto retry;
3939 	}
3940 	return error;
3941 }
3942 
3943 SYSCALL_DEFINE1(rmdir, const char __user *, pathname)
3944 {
3945 	return do_rmdir(AT_FDCWD, pathname);
3946 }
3947 
3948 /**
3949  * vfs_unlink - unlink a filesystem object
3950  * @dir:	parent directory
3951  * @dentry:	victim
3952  * @delegated_inode: returns victim inode, if the inode is delegated.
3953  *
3954  * The caller must hold dir->i_mutex.
3955  *
3956  * If vfs_unlink discovers a delegation, it will return -EWOULDBLOCK and
3957  * return a reference to the inode in delegated_inode.  The caller
3958  * should then break the delegation on that inode and retry.  Because
3959  * breaking a delegation may take a long time, the caller should drop
3960  * dir->i_mutex before doing so.
3961  *
3962  * Alternatively, a caller may pass NULL for delegated_inode.  This may
3963  * be appropriate for callers that expect the underlying filesystem not
3964  * to be NFS exported.
3965  */
3966 int vfs_unlink(struct inode *dir, struct dentry *dentry, struct inode **delegated_inode)
3967 {
3968 	struct inode *target = dentry->d_inode;
3969 	int error = may_delete(dir, dentry, 0);
3970 
3971 	if (error)
3972 		return error;
3973 
3974 	if (!dir->i_op->unlink)
3975 		return -EPERM;
3976 
3977 	inode_lock(target);
3978 	if (is_local_mountpoint(dentry))
3979 		error = -EBUSY;
3980 	else {
3981 		error = security_inode_unlink(dir, dentry);
3982 		if (!error) {
3983 			error = try_break_deleg(target, delegated_inode);
3984 			if (error)
3985 				goto out;
3986 			error = dir->i_op->unlink(dir, dentry);
3987 			if (!error) {
3988 				dont_mount(dentry);
3989 				detach_mounts(dentry);
3990 			}
3991 		}
3992 	}
3993 out:
3994 	inode_unlock(target);
3995 
3996 	/* We don't d_delete() NFS sillyrenamed files--they still exist. */
3997 	if (!error && !(dentry->d_flags & DCACHE_NFSFS_RENAMED)) {
3998 		fsnotify_link_count(target);
3999 		d_delete(dentry);
4000 	}
4001 
4002 	return error;
4003 }
4004 EXPORT_SYMBOL(vfs_unlink);
4005 
4006 /*
4007  * Make sure that the actual truncation of the file will occur outside its
4008  * directory's i_mutex.  Truncate can take a long time if there is a lot of
4009  * writeout happening, and we don't want to prevent access to the directory
4010  * while waiting on the I/O.
4011  */
4012 static long do_unlinkat(int dfd, const char __user *pathname)
4013 {
4014 	int error;
4015 	struct filename *name;
4016 	struct dentry *dentry;
4017 	struct path path;
4018 	struct qstr last;
4019 	int type;
4020 	struct inode *inode = NULL;
4021 	struct inode *delegated_inode = NULL;
4022 	unsigned int lookup_flags = 0;
4023 retry:
4024 	name = filename_parentat(dfd, getname(pathname), lookup_flags,
4025 				&path, &last, &type);
4026 	if (IS_ERR(name))
4027 		return PTR_ERR(name);
4028 
4029 	error = -EISDIR;
4030 	if (type != LAST_NORM)
4031 		goto exit1;
4032 
4033 	error = mnt_want_write(path.mnt);
4034 	if (error)
4035 		goto exit1;
4036 retry_deleg:
4037 	inode_lock_nested(path.dentry->d_inode, I_MUTEX_PARENT);
4038 	dentry = __lookup_hash(&last, path.dentry, lookup_flags);
4039 	error = PTR_ERR(dentry);
4040 	if (!IS_ERR(dentry)) {
4041 		/* Why not before? Because we want correct error value */
4042 		if (last.name[last.len])
4043 			goto slashes;
4044 		inode = dentry->d_inode;
4045 		if (d_is_negative(dentry))
4046 			goto slashes;
4047 		ihold(inode);
4048 		error = security_path_unlink(&path, dentry);
4049 		if (error)
4050 			goto exit2;
4051 		error = vfs_unlink(path.dentry->d_inode, dentry, &delegated_inode);
4052 exit2:
4053 		dput(dentry);
4054 	}
4055 	inode_unlock(path.dentry->d_inode);
4056 	if (inode)
4057 		iput(inode);	/* truncate the inode here */
4058 	inode = NULL;
4059 	if (delegated_inode) {
4060 		error = break_deleg_wait(&delegated_inode);
4061 		if (!error)
4062 			goto retry_deleg;
4063 	}
4064 	mnt_drop_write(path.mnt);
4065 exit1:
4066 	path_put(&path);
4067 	putname(name);
4068 	if (retry_estale(error, lookup_flags)) {
4069 		lookup_flags |= LOOKUP_REVAL;
4070 		inode = NULL;
4071 		goto retry;
4072 	}
4073 	return error;
4074 
4075 slashes:
4076 	if (d_is_negative(dentry))
4077 		error = -ENOENT;
4078 	else if (d_is_dir(dentry))
4079 		error = -EISDIR;
4080 	else
4081 		error = -ENOTDIR;
4082 	goto exit2;
4083 }
4084 
4085 SYSCALL_DEFINE3(unlinkat, int, dfd, const char __user *, pathname, int, flag)
4086 {
4087 	if ((flag & ~AT_REMOVEDIR) != 0)
4088 		return -EINVAL;
4089 
4090 	if (flag & AT_REMOVEDIR)
4091 		return do_rmdir(dfd, pathname);
4092 
4093 	return do_unlinkat(dfd, pathname);
4094 }
4095 
4096 SYSCALL_DEFINE1(unlink, const char __user *, pathname)
4097 {
4098 	return do_unlinkat(AT_FDCWD, pathname);
4099 }
4100 
4101 int vfs_symlink(struct inode *dir, struct dentry *dentry, const char *oldname)
4102 {
4103 	int error = may_create(dir, dentry);
4104 
4105 	if (error)
4106 		return error;
4107 
4108 	if (!dir->i_op->symlink)
4109 		return -EPERM;
4110 
4111 	error = security_inode_symlink(dir, dentry, oldname);
4112 	if (error)
4113 		return error;
4114 
4115 	error = dir->i_op->symlink(dir, dentry, oldname);
4116 	if (!error)
4117 		fsnotify_create(dir, dentry);
4118 	return error;
4119 }
4120 EXPORT_SYMBOL(vfs_symlink);
4121 
4122 SYSCALL_DEFINE3(symlinkat, const char __user *, oldname,
4123 		int, newdfd, const char __user *, newname)
4124 {
4125 	int error;
4126 	struct filename *from;
4127 	struct dentry *dentry;
4128 	struct path path;
4129 	unsigned int lookup_flags = 0;
4130 
4131 	from = getname(oldname);
4132 	if (IS_ERR(from))
4133 		return PTR_ERR(from);
4134 retry:
4135 	dentry = user_path_create(newdfd, newname, &path, lookup_flags);
4136 	error = PTR_ERR(dentry);
4137 	if (IS_ERR(dentry))
4138 		goto out_putname;
4139 
4140 	error = security_path_symlink(&path, dentry, from->name);
4141 	if (!error)
4142 		error = vfs_symlink(path.dentry->d_inode, dentry, from->name);
4143 	done_path_create(&path, dentry);
4144 	if (retry_estale(error, lookup_flags)) {
4145 		lookup_flags |= LOOKUP_REVAL;
4146 		goto retry;
4147 	}
4148 out_putname:
4149 	putname(from);
4150 	return error;
4151 }
4152 
4153 SYSCALL_DEFINE2(symlink, const char __user *, oldname, const char __user *, newname)
4154 {
4155 	return sys_symlinkat(oldname, AT_FDCWD, newname);
4156 }
4157 
4158 /**
4159  * vfs_link - create a new link
4160  * @old_dentry:	object to be linked
4161  * @dir:	new parent
4162  * @new_dentry:	where to create the new link
4163  * @delegated_inode: returns inode needing a delegation break
4164  *
4165  * The caller must hold dir->i_mutex
4166  *
4167  * If vfs_link discovers a delegation on the to-be-linked file in need
4168  * of breaking, it will return -EWOULDBLOCK and return a reference to the
4169  * inode in delegated_inode.  The caller should then break the delegation
4170  * and retry.  Because breaking a delegation may take a long time, the
4171  * caller should drop the i_mutex before doing so.
4172  *
4173  * Alternatively, a caller may pass NULL for delegated_inode.  This may
4174  * be appropriate for callers that expect the underlying filesystem not
4175  * to be NFS exported.
4176  */
4177 int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_dentry, struct inode **delegated_inode)
4178 {
4179 	struct inode *inode = old_dentry->d_inode;
4180 	unsigned max_links = dir->i_sb->s_max_links;
4181 	int error;
4182 
4183 	if (!inode)
4184 		return -ENOENT;
4185 
4186 	error = may_create(dir, new_dentry);
4187 	if (error)
4188 		return error;
4189 
4190 	if (dir->i_sb != inode->i_sb)
4191 		return -EXDEV;
4192 
4193 	/*
4194 	 * A link to an append-only or immutable file cannot be created.
4195 	 */
4196 	if (IS_APPEND(inode) || IS_IMMUTABLE(inode))
4197 		return -EPERM;
4198 	/*
4199 	 * Updating the link count will likely cause i_uid and i_gid to
4200 	 * be writen back improperly if their true value is unknown to
4201 	 * the vfs.
4202 	 */
4203 	if (HAS_UNMAPPED_ID(inode))
4204 		return -EPERM;
4205 	if (!dir->i_op->link)
4206 		return -EPERM;
4207 	if (S_ISDIR(inode->i_mode))
4208 		return -EPERM;
4209 
4210 	error = security_inode_link(old_dentry, dir, new_dentry);
4211 	if (error)
4212 		return error;
4213 
4214 	inode_lock(inode);
4215 	/* Make sure we don't allow creating hardlink to an unlinked file */
4216 	if (inode->i_nlink == 0 && !(inode->i_state & I_LINKABLE))
4217 		error =  -ENOENT;
4218 	else if (max_links && inode->i_nlink >= max_links)
4219 		error = -EMLINK;
4220 	else {
4221 		error = try_break_deleg(inode, delegated_inode);
4222 		if (!error)
4223 			error = dir->i_op->link(old_dentry, dir, new_dentry);
4224 	}
4225 
4226 	if (!error && (inode->i_state & I_LINKABLE)) {
4227 		spin_lock(&inode->i_lock);
4228 		inode->i_state &= ~I_LINKABLE;
4229 		spin_unlock(&inode->i_lock);
4230 	}
4231 	inode_unlock(inode);
4232 	if (!error)
4233 		fsnotify_link(dir, inode, new_dentry);
4234 	return error;
4235 }
4236 EXPORT_SYMBOL(vfs_link);
4237 
4238 /*
4239  * Hardlinks are often used in delicate situations.  We avoid
4240  * security-related surprises by not following symlinks on the
4241  * newname.  --KAB
4242  *
4243  * We don't follow them on the oldname either to be compatible
4244  * with linux 2.0, and to avoid hard-linking to directories
4245  * and other special files.  --ADM
4246  */
4247 SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
4248 		int, newdfd, const char __user *, newname, int, flags)
4249 {
4250 	struct dentry *new_dentry;
4251 	struct path old_path, new_path;
4252 	struct inode *delegated_inode = NULL;
4253 	int how = 0;
4254 	int error;
4255 
4256 	if ((flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
4257 		return -EINVAL;
4258 	/*
4259 	 * To use null names we require CAP_DAC_READ_SEARCH
4260 	 * This ensures that not everyone will be able to create
4261 	 * handlink using the passed filedescriptor.
4262 	 */
4263 	if (flags & AT_EMPTY_PATH) {
4264 		if (!capable(CAP_DAC_READ_SEARCH))
4265 			return -ENOENT;
4266 		how = LOOKUP_EMPTY;
4267 	}
4268 
4269 	if (flags & AT_SYMLINK_FOLLOW)
4270 		how |= LOOKUP_FOLLOW;
4271 retry:
4272 	error = user_path_at(olddfd, oldname, how, &old_path);
4273 	if (error)
4274 		return error;
4275 
4276 	new_dentry = user_path_create(newdfd, newname, &new_path,
4277 					(how & LOOKUP_REVAL));
4278 	error = PTR_ERR(new_dentry);
4279 	if (IS_ERR(new_dentry))
4280 		goto out;
4281 
4282 	error = -EXDEV;
4283 	if (old_path.mnt != new_path.mnt)
4284 		goto out_dput;
4285 	error = may_linkat(&old_path);
4286 	if (unlikely(error))
4287 		goto out_dput;
4288 	error = security_path_link(old_path.dentry, &new_path, new_dentry);
4289 	if (error)
4290 		goto out_dput;
4291 	error = vfs_link(old_path.dentry, new_path.dentry->d_inode, new_dentry, &delegated_inode);
4292 out_dput:
4293 	done_path_create(&new_path, new_dentry);
4294 	if (delegated_inode) {
4295 		error = break_deleg_wait(&delegated_inode);
4296 		if (!error) {
4297 			path_put(&old_path);
4298 			goto retry;
4299 		}
4300 	}
4301 	if (retry_estale(error, how)) {
4302 		path_put(&old_path);
4303 		how |= LOOKUP_REVAL;
4304 		goto retry;
4305 	}
4306 out:
4307 	path_put(&old_path);
4308 
4309 	return error;
4310 }
4311 
4312 SYSCALL_DEFINE2(link, const char __user *, oldname, const char __user *, newname)
4313 {
4314 	return sys_linkat(AT_FDCWD, oldname, AT_FDCWD, newname, 0);
4315 }
4316 
4317 /**
4318  * vfs_rename - rename a filesystem object
4319  * @old_dir:	parent of source
4320  * @old_dentry:	source
4321  * @new_dir:	parent of destination
4322  * @new_dentry:	destination
4323  * @delegated_inode: returns an inode needing a delegation break
4324  * @flags:	rename flags
4325  *
4326  * The caller must hold multiple mutexes--see lock_rename()).
4327  *
4328  * If vfs_rename discovers a delegation in need of breaking at either
4329  * the source or destination, it will return -EWOULDBLOCK and return a
4330  * reference to the inode in delegated_inode.  The caller should then
4331  * break the delegation and retry.  Because breaking a delegation may
4332  * take a long time, the caller should drop all locks before doing
4333  * so.
4334  *
4335  * Alternatively, a caller may pass NULL for delegated_inode.  This may
4336  * be appropriate for callers that expect the underlying filesystem not
4337  * to be NFS exported.
4338  *
4339  * The worst of all namespace operations - renaming directory. "Perverted"
4340  * doesn't even start to describe it. Somebody in UCB had a heck of a trip...
4341  * Problems:
4342  *
4343  *	a) we can get into loop creation.
4344  *	b) race potential - two innocent renames can create a loop together.
4345  *	   That's where 4.4 screws up. Current fix: serialization on
4346  *	   sb->s_vfs_rename_mutex. We might be more accurate, but that's another
4347  *	   story.
4348  *	c) we have to lock _four_ objects - parents and victim (if it exists),
4349  *	   and source (if it is not a directory).
4350  *	   And that - after we got ->i_mutex on parents (until then we don't know
4351  *	   whether the target exists).  Solution: try to be smart with locking
4352  *	   order for inodes.  We rely on the fact that tree topology may change
4353  *	   only under ->s_vfs_rename_mutex _and_ that parent of the object we
4354  *	   move will be locked.  Thus we can rank directories by the tree
4355  *	   (ancestors first) and rank all non-directories after them.
4356  *	   That works since everybody except rename does "lock parent, lookup,
4357  *	   lock child" and rename is under ->s_vfs_rename_mutex.
4358  *	   HOWEVER, it relies on the assumption that any object with ->lookup()
4359  *	   has no more than 1 dentry.  If "hybrid" objects will ever appear,
4360  *	   we'd better make sure that there's no link(2) for them.
4361  *	d) conversion from fhandle to dentry may come in the wrong moment - when
4362  *	   we are removing the target. Solution: we will have to grab ->i_mutex
4363  *	   in the fhandle_to_dentry code. [FIXME - current nfsfh.c relies on
4364  *	   ->i_mutex on parents, which works but leads to some truly excessive
4365  *	   locking].
4366  */
4367 int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
4368 	       struct inode *new_dir, struct dentry *new_dentry,
4369 	       struct inode **delegated_inode, unsigned int flags)
4370 {
4371 	int error;
4372 	bool is_dir = d_is_dir(old_dentry);
4373 	struct inode *source = old_dentry->d_inode;
4374 	struct inode *target = new_dentry->d_inode;
4375 	bool new_is_dir = false;
4376 	unsigned max_links = new_dir->i_sb->s_max_links;
4377 	struct name_snapshot old_name;
4378 
4379 	if (source == target)
4380 		return 0;
4381 
4382 	error = may_delete(old_dir, old_dentry, is_dir);
4383 	if (error)
4384 		return error;
4385 
4386 	if (!target) {
4387 		error = may_create(new_dir, new_dentry);
4388 	} else {
4389 		new_is_dir = d_is_dir(new_dentry);
4390 
4391 		if (!(flags & RENAME_EXCHANGE))
4392 			error = may_delete(new_dir, new_dentry, is_dir);
4393 		else
4394 			error = may_delete(new_dir, new_dentry, new_is_dir);
4395 	}
4396 	if (error)
4397 		return error;
4398 
4399 	if (!old_dir->i_op->rename)
4400 		return -EPERM;
4401 
4402 	/*
4403 	 * If we are going to change the parent - check write permissions,
4404 	 * we'll need to flip '..'.
4405 	 */
4406 	if (new_dir != old_dir) {
4407 		if (is_dir) {
4408 			error = inode_permission(source, MAY_WRITE);
4409 			if (error)
4410 				return error;
4411 		}
4412 		if ((flags & RENAME_EXCHANGE) && new_is_dir) {
4413 			error = inode_permission(target, MAY_WRITE);
4414 			if (error)
4415 				return error;
4416 		}
4417 	}
4418 
4419 	error = security_inode_rename(old_dir, old_dentry, new_dir, new_dentry,
4420 				      flags);
4421 	if (error)
4422 		return error;
4423 
4424 	take_dentry_name_snapshot(&old_name, old_dentry);
4425 	dget(new_dentry);
4426 	if (!is_dir || (flags & RENAME_EXCHANGE))
4427 		lock_two_nondirectories(source, target);
4428 	else if (target)
4429 		inode_lock(target);
4430 
4431 	error = -EBUSY;
4432 	if (is_local_mountpoint(old_dentry) || is_local_mountpoint(new_dentry))
4433 		goto out;
4434 
4435 	if (max_links && new_dir != old_dir) {
4436 		error = -EMLINK;
4437 		if (is_dir && !new_is_dir && new_dir->i_nlink >= max_links)
4438 			goto out;
4439 		if ((flags & RENAME_EXCHANGE) && !is_dir && new_is_dir &&
4440 		    old_dir->i_nlink >= max_links)
4441 			goto out;
4442 	}
4443 	if (is_dir && !(flags & RENAME_EXCHANGE) && target)
4444 		shrink_dcache_parent(new_dentry);
4445 	if (!is_dir) {
4446 		error = try_break_deleg(source, delegated_inode);
4447 		if (error)
4448 			goto out;
4449 	}
4450 	if (target && !new_is_dir) {
4451 		error = try_break_deleg(target, delegated_inode);
4452 		if (error)
4453 			goto out;
4454 	}
4455 	error = old_dir->i_op->rename(old_dir, old_dentry,
4456 				       new_dir, new_dentry, flags);
4457 	if (error)
4458 		goto out;
4459 
4460 	if (!(flags & RENAME_EXCHANGE) && target) {
4461 		if (is_dir)
4462 			target->i_flags |= S_DEAD;
4463 		dont_mount(new_dentry);
4464 		detach_mounts(new_dentry);
4465 	}
4466 	if (!(old_dir->i_sb->s_type->fs_flags & FS_RENAME_DOES_D_MOVE)) {
4467 		if (!(flags & RENAME_EXCHANGE))
4468 			d_move(old_dentry, new_dentry);
4469 		else
4470 			d_exchange(old_dentry, new_dentry);
4471 	}
4472 out:
4473 	if (!is_dir || (flags & RENAME_EXCHANGE))
4474 		unlock_two_nondirectories(source, target);
4475 	else if (target)
4476 		inode_unlock(target);
4477 	dput(new_dentry);
4478 	if (!error) {
4479 		fsnotify_move(old_dir, new_dir, old_name.name, is_dir,
4480 			      !(flags & RENAME_EXCHANGE) ? target : NULL, old_dentry);
4481 		if (flags & RENAME_EXCHANGE) {
4482 			fsnotify_move(new_dir, old_dir, old_dentry->d_name.name,
4483 				      new_is_dir, NULL, new_dentry);
4484 		}
4485 	}
4486 	release_dentry_name_snapshot(&old_name);
4487 
4488 	return error;
4489 }
4490 EXPORT_SYMBOL(vfs_rename);
4491 
4492 SYSCALL_DEFINE5(renameat2, int, olddfd, const char __user *, oldname,
4493 		int, newdfd, const char __user *, newname, unsigned int, flags)
4494 {
4495 	struct dentry *old_dentry, *new_dentry;
4496 	struct dentry *trap;
4497 	struct path old_path, new_path;
4498 	struct qstr old_last, new_last;
4499 	int old_type, new_type;
4500 	struct inode *delegated_inode = NULL;
4501 	struct filename *from;
4502 	struct filename *to;
4503 	unsigned int lookup_flags = 0, target_flags = LOOKUP_RENAME_TARGET;
4504 	bool should_retry = false;
4505 	int error;
4506 
4507 	if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE | RENAME_WHITEOUT))
4508 		return -EINVAL;
4509 
4510 	if ((flags & (RENAME_NOREPLACE | RENAME_WHITEOUT)) &&
4511 	    (flags & RENAME_EXCHANGE))
4512 		return -EINVAL;
4513 
4514 	if ((flags & RENAME_WHITEOUT) && !capable(CAP_MKNOD))
4515 		return -EPERM;
4516 
4517 	if (flags & RENAME_EXCHANGE)
4518 		target_flags = 0;
4519 
4520 retry:
4521 	from = filename_parentat(olddfd, getname(oldname), lookup_flags,
4522 				&old_path, &old_last, &old_type);
4523 	if (IS_ERR(from)) {
4524 		error = PTR_ERR(from);
4525 		goto exit;
4526 	}
4527 
4528 	to = filename_parentat(newdfd, getname(newname), lookup_flags,
4529 				&new_path, &new_last, &new_type);
4530 	if (IS_ERR(to)) {
4531 		error = PTR_ERR(to);
4532 		goto exit1;
4533 	}
4534 
4535 	error = -EXDEV;
4536 	if (old_path.mnt != new_path.mnt)
4537 		goto exit2;
4538 
4539 	error = -EBUSY;
4540 	if (old_type != LAST_NORM)
4541 		goto exit2;
4542 
4543 	if (flags & RENAME_NOREPLACE)
4544 		error = -EEXIST;
4545 	if (new_type != LAST_NORM)
4546 		goto exit2;
4547 
4548 	error = mnt_want_write(old_path.mnt);
4549 	if (error)
4550 		goto exit2;
4551 
4552 retry_deleg:
4553 	trap = lock_rename(new_path.dentry, old_path.dentry);
4554 
4555 	old_dentry = __lookup_hash(&old_last, old_path.dentry, lookup_flags);
4556 	error = PTR_ERR(old_dentry);
4557 	if (IS_ERR(old_dentry))
4558 		goto exit3;
4559 	/* source must exist */
4560 	error = -ENOENT;
4561 	if (d_is_negative(old_dentry))
4562 		goto exit4;
4563 	new_dentry = __lookup_hash(&new_last, new_path.dentry, lookup_flags | target_flags);
4564 	error = PTR_ERR(new_dentry);
4565 	if (IS_ERR(new_dentry))
4566 		goto exit4;
4567 	error = -EEXIST;
4568 	if ((flags & RENAME_NOREPLACE) && d_is_positive(new_dentry))
4569 		goto exit5;
4570 	if (flags & RENAME_EXCHANGE) {
4571 		error = -ENOENT;
4572 		if (d_is_negative(new_dentry))
4573 			goto exit5;
4574 
4575 		if (!d_is_dir(new_dentry)) {
4576 			error = -ENOTDIR;
4577 			if (new_last.name[new_last.len])
4578 				goto exit5;
4579 		}
4580 	}
4581 	/* unless the source is a directory trailing slashes give -ENOTDIR */
4582 	if (!d_is_dir(old_dentry)) {
4583 		error = -ENOTDIR;
4584 		if (old_last.name[old_last.len])
4585 			goto exit5;
4586 		if (!(flags & RENAME_EXCHANGE) && new_last.name[new_last.len])
4587 			goto exit5;
4588 	}
4589 	/* source should not be ancestor of target */
4590 	error = -EINVAL;
4591 	if (old_dentry == trap)
4592 		goto exit5;
4593 	/* target should not be an ancestor of source */
4594 	if (!(flags & RENAME_EXCHANGE))
4595 		error = -ENOTEMPTY;
4596 	if (new_dentry == trap)
4597 		goto exit5;
4598 
4599 	error = security_path_rename(&old_path, old_dentry,
4600 				     &new_path, new_dentry, flags);
4601 	if (error)
4602 		goto exit5;
4603 	error = vfs_rename(old_path.dentry->d_inode, old_dentry,
4604 			   new_path.dentry->d_inode, new_dentry,
4605 			   &delegated_inode, flags);
4606 exit5:
4607 	dput(new_dentry);
4608 exit4:
4609 	dput(old_dentry);
4610 exit3:
4611 	unlock_rename(new_path.dentry, old_path.dentry);
4612 	if (delegated_inode) {
4613 		error = break_deleg_wait(&delegated_inode);
4614 		if (!error)
4615 			goto retry_deleg;
4616 	}
4617 	mnt_drop_write(old_path.mnt);
4618 exit2:
4619 	if (retry_estale(error, lookup_flags))
4620 		should_retry = true;
4621 	path_put(&new_path);
4622 	putname(to);
4623 exit1:
4624 	path_put(&old_path);
4625 	putname(from);
4626 	if (should_retry) {
4627 		should_retry = false;
4628 		lookup_flags |= LOOKUP_REVAL;
4629 		goto retry;
4630 	}
4631 exit:
4632 	return error;
4633 }
4634 
4635 SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname,
4636 		int, newdfd, const char __user *, newname)
4637 {
4638 	return sys_renameat2(olddfd, oldname, newdfd, newname, 0);
4639 }
4640 
4641 SYSCALL_DEFINE2(rename, const char __user *, oldname, const char __user *, newname)
4642 {
4643 	return sys_renameat2(AT_FDCWD, oldname, AT_FDCWD, newname, 0);
4644 }
4645 
4646 int vfs_whiteout(struct inode *dir, struct dentry *dentry)
4647 {
4648 	int error = may_create(dir, dentry);
4649 	if (error)
4650 		return error;
4651 
4652 	if (!dir->i_op->mknod)
4653 		return -EPERM;
4654 
4655 	return dir->i_op->mknod(dir, dentry,
4656 				S_IFCHR | WHITEOUT_MODE, WHITEOUT_DEV);
4657 }
4658 EXPORT_SYMBOL(vfs_whiteout);
4659 
4660 int readlink_copy(char __user *buffer, int buflen, const char *link)
4661 {
4662 	int len = PTR_ERR(link);
4663 	if (IS_ERR(link))
4664 		goto out;
4665 
4666 	len = strlen(link);
4667 	if (len > (unsigned) buflen)
4668 		len = buflen;
4669 	if (copy_to_user(buffer, link, len))
4670 		len = -EFAULT;
4671 out:
4672 	return len;
4673 }
4674 
4675 /*
4676  * A helper for ->readlink().  This should be used *ONLY* for symlinks that
4677  * have ->get_link() not calling nd_jump_link().  Using (or not using) it
4678  * for any given inode is up to filesystem.
4679  */
4680 static int generic_readlink(struct dentry *dentry, char __user *buffer,
4681 			    int buflen)
4682 {
4683 	DEFINE_DELAYED_CALL(done);
4684 	struct inode *inode = d_inode(dentry);
4685 	const char *link = inode->i_link;
4686 	int res;
4687 
4688 	if (!link) {
4689 		link = inode->i_op->get_link(dentry, inode, &done);
4690 		if (IS_ERR(link))
4691 			return PTR_ERR(link);
4692 	}
4693 	res = readlink_copy(buffer, buflen, link);
4694 	do_delayed_call(&done);
4695 	return res;
4696 }
4697 
4698 /**
4699  * vfs_readlink - copy symlink body into userspace buffer
4700  * @dentry: dentry on which to get symbolic link
4701  * @buffer: user memory pointer
4702  * @buflen: size of buffer
4703  *
4704  * Does not touch atime.  That's up to the caller if necessary
4705  *
4706  * Does not call security hook.
4707  */
4708 int vfs_readlink(struct dentry *dentry, char __user *buffer, int buflen)
4709 {
4710 	struct inode *inode = d_inode(dentry);
4711 
4712 	if (unlikely(!(inode->i_opflags & IOP_DEFAULT_READLINK))) {
4713 		if (unlikely(inode->i_op->readlink))
4714 			return inode->i_op->readlink(dentry, buffer, buflen);
4715 
4716 		if (!d_is_symlink(dentry))
4717 			return -EINVAL;
4718 
4719 		spin_lock(&inode->i_lock);
4720 		inode->i_opflags |= IOP_DEFAULT_READLINK;
4721 		spin_unlock(&inode->i_lock);
4722 	}
4723 
4724 	return generic_readlink(dentry, buffer, buflen);
4725 }
4726 EXPORT_SYMBOL(vfs_readlink);
4727 
4728 /**
4729  * vfs_get_link - get symlink body
4730  * @dentry: dentry on which to get symbolic link
4731  * @done: caller needs to free returned data with this
4732  *
4733  * Calls security hook and i_op->get_link() on the supplied inode.
4734  *
4735  * It does not touch atime.  That's up to the caller if necessary.
4736  *
4737  * Does not work on "special" symlinks like /proc/$$/fd/N
4738  */
4739 const char *vfs_get_link(struct dentry *dentry, struct delayed_call *done)
4740 {
4741 	const char *res = ERR_PTR(-EINVAL);
4742 	struct inode *inode = d_inode(dentry);
4743 
4744 	if (d_is_symlink(dentry)) {
4745 		res = ERR_PTR(security_inode_readlink(dentry));
4746 		if (!res)
4747 			res = inode->i_op->get_link(dentry, inode, done);
4748 	}
4749 	return res;
4750 }
4751 EXPORT_SYMBOL(vfs_get_link);
4752 
4753 /* get the link contents into pagecache */
4754 const char *page_get_link(struct dentry *dentry, struct inode *inode,
4755 			  struct delayed_call *callback)
4756 {
4757 	char *kaddr;
4758 	struct page *page;
4759 	struct address_space *mapping = inode->i_mapping;
4760 
4761 	if (!dentry) {
4762 		page = find_get_page(mapping, 0);
4763 		if (!page)
4764 			return ERR_PTR(-ECHILD);
4765 		if (!PageUptodate(page)) {
4766 			put_page(page);
4767 			return ERR_PTR(-ECHILD);
4768 		}
4769 	} else {
4770 		page = read_mapping_page(mapping, 0, NULL);
4771 		if (IS_ERR(page))
4772 			return (char*)page;
4773 	}
4774 	set_delayed_call(callback, page_put_link, page);
4775 	BUG_ON(mapping_gfp_mask(mapping) & __GFP_HIGHMEM);
4776 	kaddr = page_address(page);
4777 	nd_terminate_link(kaddr, inode->i_size, PAGE_SIZE - 1);
4778 	return kaddr;
4779 }
4780 
4781 EXPORT_SYMBOL(page_get_link);
4782 
4783 void page_put_link(void *arg)
4784 {
4785 	put_page(arg);
4786 }
4787 EXPORT_SYMBOL(page_put_link);
4788 
4789 int page_readlink(struct dentry *dentry, char __user *buffer, int buflen)
4790 {
4791 	DEFINE_DELAYED_CALL(done);
4792 	int res = readlink_copy(buffer, buflen,
4793 				page_get_link(dentry, d_inode(dentry),
4794 					      &done));
4795 	do_delayed_call(&done);
4796 	return res;
4797 }
4798 EXPORT_SYMBOL(page_readlink);
4799 
4800 /*
4801  * The nofs argument instructs pagecache_write_begin to pass AOP_FLAG_NOFS
4802  */
4803 int __page_symlink(struct inode *inode, const char *symname, int len, int nofs)
4804 {
4805 	struct address_space *mapping = inode->i_mapping;
4806 	struct page *page;
4807 	void *fsdata;
4808 	int err;
4809 	unsigned int flags = 0;
4810 	if (nofs)
4811 		flags |= AOP_FLAG_NOFS;
4812 
4813 retry:
4814 	err = pagecache_write_begin(NULL, mapping, 0, len-1,
4815 				flags, &page, &fsdata);
4816 	if (err)
4817 		goto fail;
4818 
4819 	memcpy(page_address(page), symname, len-1);
4820 
4821 	err = pagecache_write_end(NULL, mapping, 0, len-1, len-1,
4822 							page, fsdata);
4823 	if (err < 0)
4824 		goto fail;
4825 	if (err < len-1)
4826 		goto retry;
4827 
4828 	mark_inode_dirty(inode);
4829 	return 0;
4830 fail:
4831 	return err;
4832 }
4833 EXPORT_SYMBOL(__page_symlink);
4834 
4835 int page_symlink(struct inode *inode, const char *symname, int len)
4836 {
4837 	return __page_symlink(inode, symname, len,
4838 			!mapping_gfp_constraint(inode->i_mapping, __GFP_FS));
4839 }
4840 EXPORT_SYMBOL(page_symlink);
4841 
4842 const struct inode_operations page_symlink_inode_operations = {
4843 	.get_link	= page_get_link,
4844 };
4845 EXPORT_SYMBOL(page_symlink_inode_operations);
4846