xref: /openbmc/linux/fs/namespace.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
1 /*
2  *  linux/fs/namespace.c
3  *
4  * (C) Copyright Al Viro 2000, 2001
5  *	Released under GPL v2.
6  *
7  * Based on code from fs/super.c, copyright Linus Torvalds and others.
8  * Heavily rewritten.
9  */
10 
11 #include <linux/syscalls.h>
12 #include <linux/slab.h>
13 #include <linux/sched.h>
14 #include <linux/smp_lock.h>
15 #include <linux/init.h>
16 #include <linux/kernel.h>
17 #include <linux/quotaops.h>
18 #include <linux/acct.h>
19 #include <linux/capability.h>
20 #include <linux/module.h>
21 #include <linux/sysfs.h>
22 #include <linux/seq_file.h>
23 #include <linux/mnt_namespace.h>
24 #include <linux/namei.h>
25 #include <linux/security.h>
26 #include <linux/mount.h>
27 #include <linux/ramfs.h>
28 #include <asm/uaccess.h>
29 #include <asm/unistd.h>
30 #include "pnode.h"
31 
32 /* spinlock for vfsmount related operations, inplace of dcache_lock */
33 __cacheline_aligned_in_smp DEFINE_SPINLOCK(vfsmount_lock);
34 
35 static int event;
36 
37 static struct list_head *mount_hashtable __read_mostly;
38 static int hash_mask __read_mostly, hash_bits __read_mostly;
39 static struct kmem_cache *mnt_cache __read_mostly;
40 static struct rw_semaphore namespace_sem;
41 
42 /* /sys/fs */
43 decl_subsys(fs, NULL, NULL);
44 EXPORT_SYMBOL_GPL(fs_subsys);
45 
46 static inline unsigned long hash(struct vfsmount *mnt, struct dentry *dentry)
47 {
48 	unsigned long tmp = ((unsigned long)mnt / L1_CACHE_BYTES);
49 	tmp += ((unsigned long)dentry / L1_CACHE_BYTES);
50 	tmp = tmp + (tmp >> hash_bits);
51 	return tmp & hash_mask;
52 }
53 
54 struct vfsmount *alloc_vfsmnt(const char *name)
55 {
56 	struct vfsmount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
57 	if (mnt) {
58 		atomic_set(&mnt->mnt_count, 1);
59 		INIT_LIST_HEAD(&mnt->mnt_hash);
60 		INIT_LIST_HEAD(&mnt->mnt_child);
61 		INIT_LIST_HEAD(&mnt->mnt_mounts);
62 		INIT_LIST_HEAD(&mnt->mnt_list);
63 		INIT_LIST_HEAD(&mnt->mnt_expire);
64 		INIT_LIST_HEAD(&mnt->mnt_share);
65 		INIT_LIST_HEAD(&mnt->mnt_slave_list);
66 		INIT_LIST_HEAD(&mnt->mnt_slave);
67 		if (name) {
68 			int size = strlen(name) + 1;
69 			char *newname = kmalloc(size, GFP_KERNEL);
70 			if (newname) {
71 				memcpy(newname, name, size);
72 				mnt->mnt_devname = newname;
73 			}
74 		}
75 	}
76 	return mnt;
77 }
78 
79 int simple_set_mnt(struct vfsmount *mnt, struct super_block *sb)
80 {
81 	mnt->mnt_sb = sb;
82 	mnt->mnt_root = dget(sb->s_root);
83 	return 0;
84 }
85 
86 EXPORT_SYMBOL(simple_set_mnt);
87 
88 void free_vfsmnt(struct vfsmount *mnt)
89 {
90 	kfree(mnt->mnt_devname);
91 	kmem_cache_free(mnt_cache, mnt);
92 }
93 
94 /*
95  * find the first or last mount at @dentry on vfsmount @mnt depending on
96  * @dir. If @dir is set return the first mount else return the last mount.
97  */
98 struct vfsmount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry,
99 			      int dir)
100 {
101 	struct list_head *head = mount_hashtable + hash(mnt, dentry);
102 	struct list_head *tmp = head;
103 	struct vfsmount *p, *found = NULL;
104 
105 	for (;;) {
106 		tmp = dir ? tmp->next : tmp->prev;
107 		p = NULL;
108 		if (tmp == head)
109 			break;
110 		p = list_entry(tmp, struct vfsmount, mnt_hash);
111 		if (p->mnt_parent == mnt && p->mnt_mountpoint == dentry) {
112 			found = p;
113 			break;
114 		}
115 	}
116 	return found;
117 }
118 
119 /*
120  * lookup_mnt increments the ref count before returning
121  * the vfsmount struct.
122  */
123 struct vfsmount *lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
124 {
125 	struct vfsmount *child_mnt;
126 	spin_lock(&vfsmount_lock);
127 	if ((child_mnt = __lookup_mnt(mnt, dentry, 1)))
128 		mntget(child_mnt);
129 	spin_unlock(&vfsmount_lock);
130 	return child_mnt;
131 }
132 
133 static inline int check_mnt(struct vfsmount *mnt)
134 {
135 	return mnt->mnt_ns == current->nsproxy->mnt_ns;
136 }
137 
138 static void touch_mnt_namespace(struct mnt_namespace *ns)
139 {
140 	if (ns) {
141 		ns->event = ++event;
142 		wake_up_interruptible(&ns->poll);
143 	}
144 }
145 
146 static void __touch_mnt_namespace(struct mnt_namespace *ns)
147 {
148 	if (ns && ns->event != event) {
149 		ns->event = event;
150 		wake_up_interruptible(&ns->poll);
151 	}
152 }
153 
154 static void detach_mnt(struct vfsmount *mnt, struct nameidata *old_nd)
155 {
156 	old_nd->dentry = mnt->mnt_mountpoint;
157 	old_nd->mnt = mnt->mnt_parent;
158 	mnt->mnt_parent = mnt;
159 	mnt->mnt_mountpoint = mnt->mnt_root;
160 	list_del_init(&mnt->mnt_child);
161 	list_del_init(&mnt->mnt_hash);
162 	old_nd->dentry->d_mounted--;
163 }
164 
165 void mnt_set_mountpoint(struct vfsmount *mnt, struct dentry *dentry,
166 			struct vfsmount *child_mnt)
167 {
168 	child_mnt->mnt_parent = mntget(mnt);
169 	child_mnt->mnt_mountpoint = dget(dentry);
170 	dentry->d_mounted++;
171 }
172 
173 static void attach_mnt(struct vfsmount *mnt, struct nameidata *nd)
174 {
175 	mnt_set_mountpoint(nd->mnt, nd->dentry, mnt);
176 	list_add_tail(&mnt->mnt_hash, mount_hashtable +
177 			hash(nd->mnt, nd->dentry));
178 	list_add_tail(&mnt->mnt_child, &nd->mnt->mnt_mounts);
179 }
180 
181 /*
182  * the caller must hold vfsmount_lock
183  */
184 static void commit_tree(struct vfsmount *mnt)
185 {
186 	struct vfsmount *parent = mnt->mnt_parent;
187 	struct vfsmount *m;
188 	LIST_HEAD(head);
189 	struct mnt_namespace *n = parent->mnt_ns;
190 
191 	BUG_ON(parent == mnt);
192 
193 	list_add_tail(&head, &mnt->mnt_list);
194 	list_for_each_entry(m, &head, mnt_list)
195 		m->mnt_ns = n;
196 	list_splice(&head, n->list.prev);
197 
198 	list_add_tail(&mnt->mnt_hash, mount_hashtable +
199 				hash(parent, mnt->mnt_mountpoint));
200 	list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
201 	touch_mnt_namespace(n);
202 }
203 
204 static struct vfsmount *next_mnt(struct vfsmount *p, struct vfsmount *root)
205 {
206 	struct list_head *next = p->mnt_mounts.next;
207 	if (next == &p->mnt_mounts) {
208 		while (1) {
209 			if (p == root)
210 				return NULL;
211 			next = p->mnt_child.next;
212 			if (next != &p->mnt_parent->mnt_mounts)
213 				break;
214 			p = p->mnt_parent;
215 		}
216 	}
217 	return list_entry(next, struct vfsmount, mnt_child);
218 }
219 
220 static struct vfsmount *skip_mnt_tree(struct vfsmount *p)
221 {
222 	struct list_head *prev = p->mnt_mounts.prev;
223 	while (prev != &p->mnt_mounts) {
224 		p = list_entry(prev, struct vfsmount, mnt_child);
225 		prev = p->mnt_mounts.prev;
226 	}
227 	return p;
228 }
229 
230 static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
231 					int flag)
232 {
233 	struct super_block *sb = old->mnt_sb;
234 	struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
235 
236 	if (mnt) {
237 		mnt->mnt_flags = old->mnt_flags;
238 		atomic_inc(&sb->s_active);
239 		mnt->mnt_sb = sb;
240 		mnt->mnt_root = dget(root);
241 		mnt->mnt_mountpoint = mnt->mnt_root;
242 		mnt->mnt_parent = mnt;
243 
244 		if (flag & CL_SLAVE) {
245 			list_add(&mnt->mnt_slave, &old->mnt_slave_list);
246 			mnt->mnt_master = old;
247 			CLEAR_MNT_SHARED(mnt);
248 		} else {
249 			if ((flag & CL_PROPAGATION) || IS_MNT_SHARED(old))
250 				list_add(&mnt->mnt_share, &old->mnt_share);
251 			if (IS_MNT_SLAVE(old))
252 				list_add(&mnt->mnt_slave, &old->mnt_slave);
253 			mnt->mnt_master = old->mnt_master;
254 		}
255 		if (flag & CL_MAKE_SHARED)
256 			set_mnt_shared(mnt);
257 
258 		/* stick the duplicate mount on the same expiry list
259 		 * as the original if that was on one */
260 		if (flag & CL_EXPIRE) {
261 			spin_lock(&vfsmount_lock);
262 			if (!list_empty(&old->mnt_expire))
263 				list_add(&mnt->mnt_expire, &old->mnt_expire);
264 			spin_unlock(&vfsmount_lock);
265 		}
266 	}
267 	return mnt;
268 }
269 
270 static inline void __mntput(struct vfsmount *mnt)
271 {
272 	struct super_block *sb = mnt->mnt_sb;
273 	dput(mnt->mnt_root);
274 	free_vfsmnt(mnt);
275 	deactivate_super(sb);
276 }
277 
278 void mntput_no_expire(struct vfsmount *mnt)
279 {
280 repeat:
281 	if (atomic_dec_and_lock(&mnt->mnt_count, &vfsmount_lock)) {
282 		if (likely(!mnt->mnt_pinned)) {
283 			spin_unlock(&vfsmount_lock);
284 			__mntput(mnt);
285 			return;
286 		}
287 		atomic_add(mnt->mnt_pinned + 1, &mnt->mnt_count);
288 		mnt->mnt_pinned = 0;
289 		spin_unlock(&vfsmount_lock);
290 		acct_auto_close_mnt(mnt);
291 		security_sb_umount_close(mnt);
292 		goto repeat;
293 	}
294 }
295 
296 EXPORT_SYMBOL(mntput_no_expire);
297 
298 void mnt_pin(struct vfsmount *mnt)
299 {
300 	spin_lock(&vfsmount_lock);
301 	mnt->mnt_pinned++;
302 	spin_unlock(&vfsmount_lock);
303 }
304 
305 EXPORT_SYMBOL(mnt_pin);
306 
307 void mnt_unpin(struct vfsmount *mnt)
308 {
309 	spin_lock(&vfsmount_lock);
310 	if (mnt->mnt_pinned) {
311 		atomic_inc(&mnt->mnt_count);
312 		mnt->mnt_pinned--;
313 	}
314 	spin_unlock(&vfsmount_lock);
315 }
316 
317 EXPORT_SYMBOL(mnt_unpin);
318 
319 /* iterator */
320 static void *m_start(struct seq_file *m, loff_t *pos)
321 {
322 	struct mnt_namespace *n = m->private;
323 	struct list_head *p;
324 	loff_t l = *pos;
325 
326 	down_read(&namespace_sem);
327 	list_for_each(p, &n->list)
328 		if (!l--)
329 			return list_entry(p, struct vfsmount, mnt_list);
330 	return NULL;
331 }
332 
333 static void *m_next(struct seq_file *m, void *v, loff_t *pos)
334 {
335 	struct mnt_namespace *n = m->private;
336 	struct list_head *p = ((struct vfsmount *)v)->mnt_list.next;
337 	(*pos)++;
338 	return p == &n->list ? NULL : list_entry(p, struct vfsmount, mnt_list);
339 }
340 
341 static void m_stop(struct seq_file *m, void *v)
342 {
343 	up_read(&namespace_sem);
344 }
345 
346 static inline void mangle(struct seq_file *m, const char *s)
347 {
348 	seq_escape(m, s, " \t\n\\");
349 }
350 
351 static int show_vfsmnt(struct seq_file *m, void *v)
352 {
353 	struct vfsmount *mnt = v;
354 	int err = 0;
355 	static struct proc_fs_info {
356 		int flag;
357 		char *str;
358 	} fs_info[] = {
359 		{ MS_SYNCHRONOUS, ",sync" },
360 		{ MS_DIRSYNC, ",dirsync" },
361 		{ MS_MANDLOCK, ",mand" },
362 		{ 0, NULL }
363 	};
364 	static struct proc_fs_info mnt_info[] = {
365 		{ MNT_NOSUID, ",nosuid" },
366 		{ MNT_NODEV, ",nodev" },
367 		{ MNT_NOEXEC, ",noexec" },
368 		{ MNT_NOATIME, ",noatime" },
369 		{ MNT_NODIRATIME, ",nodiratime" },
370 		{ MNT_RELATIME, ",relatime" },
371 		{ 0, NULL }
372 	};
373 	struct proc_fs_info *fs_infop;
374 
375 	mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
376 	seq_putc(m, ' ');
377 	seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
378 	seq_putc(m, ' ');
379 	mangle(m, mnt->mnt_sb->s_type->name);
380 	if (mnt->mnt_sb->s_subtype && mnt->mnt_sb->s_subtype[0]) {
381 		seq_putc(m, '.');
382 		mangle(m, mnt->mnt_sb->s_subtype);
383 	}
384 	seq_puts(m, mnt->mnt_sb->s_flags & MS_RDONLY ? " ro" : " rw");
385 	for (fs_infop = fs_info; fs_infop->flag; fs_infop++) {
386 		if (mnt->mnt_sb->s_flags & fs_infop->flag)
387 			seq_puts(m, fs_infop->str);
388 	}
389 	for (fs_infop = mnt_info; fs_infop->flag; fs_infop++) {
390 		if (mnt->mnt_flags & fs_infop->flag)
391 			seq_puts(m, fs_infop->str);
392 	}
393 	if (mnt->mnt_sb->s_op->show_options)
394 		err = mnt->mnt_sb->s_op->show_options(m, mnt);
395 	seq_puts(m, " 0 0\n");
396 	return err;
397 }
398 
399 struct seq_operations mounts_op = {
400 	.start	= m_start,
401 	.next	= m_next,
402 	.stop	= m_stop,
403 	.show	= show_vfsmnt
404 };
405 
406 static int show_vfsstat(struct seq_file *m, void *v)
407 {
408 	struct vfsmount *mnt = v;
409 	int err = 0;
410 
411 	/* device */
412 	if (mnt->mnt_devname) {
413 		seq_puts(m, "device ");
414 		mangle(m, mnt->mnt_devname);
415 	} else
416 		seq_puts(m, "no device");
417 
418 	/* mount point */
419 	seq_puts(m, " mounted on ");
420 	seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
421 	seq_putc(m, ' ');
422 
423 	/* file system type */
424 	seq_puts(m, "with fstype ");
425 	mangle(m, mnt->mnt_sb->s_type->name);
426 
427 	/* optional statistics */
428 	if (mnt->mnt_sb->s_op->show_stats) {
429 		seq_putc(m, ' ');
430 		err = mnt->mnt_sb->s_op->show_stats(m, mnt);
431 	}
432 
433 	seq_putc(m, '\n');
434 	return err;
435 }
436 
437 struct seq_operations mountstats_op = {
438 	.start	= m_start,
439 	.next	= m_next,
440 	.stop	= m_stop,
441 	.show	= show_vfsstat,
442 };
443 
444 /**
445  * may_umount_tree - check if a mount tree is busy
446  * @mnt: root of mount tree
447  *
448  * This is called to check if a tree of mounts has any
449  * open files, pwds, chroots or sub mounts that are
450  * busy.
451  */
452 int may_umount_tree(struct vfsmount *mnt)
453 {
454 	int actual_refs = 0;
455 	int minimum_refs = 0;
456 	struct vfsmount *p;
457 
458 	spin_lock(&vfsmount_lock);
459 	for (p = mnt; p; p = next_mnt(p, mnt)) {
460 		actual_refs += atomic_read(&p->mnt_count);
461 		minimum_refs += 2;
462 	}
463 	spin_unlock(&vfsmount_lock);
464 
465 	if (actual_refs > minimum_refs)
466 		return 0;
467 
468 	return 1;
469 }
470 
471 EXPORT_SYMBOL(may_umount_tree);
472 
473 /**
474  * may_umount - check if a mount point is busy
475  * @mnt: root of mount
476  *
477  * This is called to check if a mount point has any
478  * open files, pwds, chroots or sub mounts. If the
479  * mount has sub mounts this will return busy
480  * regardless of whether the sub mounts are busy.
481  *
482  * Doesn't take quota and stuff into account. IOW, in some cases it will
483  * give false negatives. The main reason why it's here is that we need
484  * a non-destructive way to look for easily umountable filesystems.
485  */
486 int may_umount(struct vfsmount *mnt)
487 {
488 	int ret = 1;
489 	spin_lock(&vfsmount_lock);
490 	if (propagate_mount_busy(mnt, 2))
491 		ret = 0;
492 	spin_unlock(&vfsmount_lock);
493 	return ret;
494 }
495 
496 EXPORT_SYMBOL(may_umount);
497 
498 void release_mounts(struct list_head *head)
499 {
500 	struct vfsmount *mnt;
501 	while (!list_empty(head)) {
502 		mnt = list_first_entry(head, struct vfsmount, mnt_hash);
503 		list_del_init(&mnt->mnt_hash);
504 		if (mnt->mnt_parent != mnt) {
505 			struct dentry *dentry;
506 			struct vfsmount *m;
507 			spin_lock(&vfsmount_lock);
508 			dentry = mnt->mnt_mountpoint;
509 			m = mnt->mnt_parent;
510 			mnt->mnt_mountpoint = mnt->mnt_root;
511 			mnt->mnt_parent = mnt;
512 			spin_unlock(&vfsmount_lock);
513 			dput(dentry);
514 			mntput(m);
515 		}
516 		mntput(mnt);
517 	}
518 }
519 
520 void umount_tree(struct vfsmount *mnt, int propagate, struct list_head *kill)
521 {
522 	struct vfsmount *p;
523 
524 	for (p = mnt; p; p = next_mnt(p, mnt))
525 		list_move(&p->mnt_hash, kill);
526 
527 	if (propagate)
528 		propagate_umount(kill);
529 
530 	list_for_each_entry(p, kill, mnt_hash) {
531 		list_del_init(&p->mnt_expire);
532 		list_del_init(&p->mnt_list);
533 		__touch_mnt_namespace(p->mnt_ns);
534 		p->mnt_ns = NULL;
535 		list_del_init(&p->mnt_child);
536 		if (p->mnt_parent != p)
537 			p->mnt_mountpoint->d_mounted--;
538 		change_mnt_propagation(p, MS_PRIVATE);
539 	}
540 }
541 
542 static int do_umount(struct vfsmount *mnt, int flags)
543 {
544 	struct super_block *sb = mnt->mnt_sb;
545 	int retval;
546 	LIST_HEAD(umount_list);
547 
548 	retval = security_sb_umount(mnt, flags);
549 	if (retval)
550 		return retval;
551 
552 	/*
553 	 * Allow userspace to request a mountpoint be expired rather than
554 	 * unmounting unconditionally. Unmount only happens if:
555 	 *  (1) the mark is already set (the mark is cleared by mntput())
556 	 *  (2) the usage count == 1 [parent vfsmount] + 1 [sys_umount]
557 	 */
558 	if (flags & MNT_EXPIRE) {
559 		if (mnt == current->fs->rootmnt ||
560 		    flags & (MNT_FORCE | MNT_DETACH))
561 			return -EINVAL;
562 
563 		if (atomic_read(&mnt->mnt_count) != 2)
564 			return -EBUSY;
565 
566 		if (!xchg(&mnt->mnt_expiry_mark, 1))
567 			return -EAGAIN;
568 	}
569 
570 	/*
571 	 * If we may have to abort operations to get out of this
572 	 * mount, and they will themselves hold resources we must
573 	 * allow the fs to do things. In the Unix tradition of
574 	 * 'Gee thats tricky lets do it in userspace' the umount_begin
575 	 * might fail to complete on the first run through as other tasks
576 	 * must return, and the like. Thats for the mount program to worry
577 	 * about for the moment.
578 	 */
579 
580 	lock_kernel();
581 	if (sb->s_op->umount_begin)
582 		sb->s_op->umount_begin(mnt, flags);
583 	unlock_kernel();
584 
585 	/*
586 	 * No sense to grab the lock for this test, but test itself looks
587 	 * somewhat bogus. Suggestions for better replacement?
588 	 * Ho-hum... In principle, we might treat that as umount + switch
589 	 * to rootfs. GC would eventually take care of the old vfsmount.
590 	 * Actually it makes sense, especially if rootfs would contain a
591 	 * /reboot - static binary that would close all descriptors and
592 	 * call reboot(9). Then init(8) could umount root and exec /reboot.
593 	 */
594 	if (mnt == current->fs->rootmnt && !(flags & MNT_DETACH)) {
595 		/*
596 		 * Special case for "unmounting" root ...
597 		 * we just try to remount it readonly.
598 		 */
599 		down_write(&sb->s_umount);
600 		if (!(sb->s_flags & MS_RDONLY)) {
601 			lock_kernel();
602 			DQUOT_OFF(sb);
603 			retval = do_remount_sb(sb, MS_RDONLY, NULL, 0);
604 			unlock_kernel();
605 		}
606 		up_write(&sb->s_umount);
607 		return retval;
608 	}
609 
610 	down_write(&namespace_sem);
611 	spin_lock(&vfsmount_lock);
612 	event++;
613 
614 	retval = -EBUSY;
615 	if (flags & MNT_DETACH || !propagate_mount_busy(mnt, 2)) {
616 		if (!list_empty(&mnt->mnt_list))
617 			umount_tree(mnt, 1, &umount_list);
618 		retval = 0;
619 	}
620 	spin_unlock(&vfsmount_lock);
621 	if (retval)
622 		security_sb_umount_busy(mnt);
623 	up_write(&namespace_sem);
624 	release_mounts(&umount_list);
625 	return retval;
626 }
627 
628 /*
629  * Now umount can handle mount points as well as block devices.
630  * This is important for filesystems which use unnamed block devices.
631  *
632  * We now support a flag for forced unmount like the other 'big iron'
633  * unixes. Our API is identical to OSF/1 to avoid making a mess of AMD
634  */
635 
636 asmlinkage long sys_umount(char __user * name, int flags)
637 {
638 	struct nameidata nd;
639 	int retval;
640 
641 	retval = __user_walk(name, LOOKUP_FOLLOW, &nd);
642 	if (retval)
643 		goto out;
644 	retval = -EINVAL;
645 	if (nd.dentry != nd.mnt->mnt_root)
646 		goto dput_and_out;
647 	if (!check_mnt(nd.mnt))
648 		goto dput_and_out;
649 
650 	retval = -EPERM;
651 	if (!capable(CAP_SYS_ADMIN))
652 		goto dput_and_out;
653 
654 	retval = do_umount(nd.mnt, flags);
655 dput_and_out:
656 	path_release_on_umount(&nd);
657 out:
658 	return retval;
659 }
660 
661 #ifdef __ARCH_WANT_SYS_OLDUMOUNT
662 
663 /*
664  *	The 2.0 compatible umount. No flags.
665  */
666 asmlinkage long sys_oldumount(char __user * name)
667 {
668 	return sys_umount(name, 0);
669 }
670 
671 #endif
672 
673 static int mount_is_safe(struct nameidata *nd)
674 {
675 	if (capable(CAP_SYS_ADMIN))
676 		return 0;
677 	return -EPERM;
678 #ifdef notyet
679 	if (S_ISLNK(nd->dentry->d_inode->i_mode))
680 		return -EPERM;
681 	if (nd->dentry->d_inode->i_mode & S_ISVTX) {
682 		if (current->uid != nd->dentry->d_inode->i_uid)
683 			return -EPERM;
684 	}
685 	if (vfs_permission(nd, MAY_WRITE))
686 		return -EPERM;
687 	return 0;
688 #endif
689 }
690 
691 static int lives_below_in_same_fs(struct dentry *d, struct dentry *dentry)
692 {
693 	while (1) {
694 		if (d == dentry)
695 			return 1;
696 		if (d == NULL || d == d->d_parent)
697 			return 0;
698 		d = d->d_parent;
699 	}
700 }
701 
702 struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
703 					int flag)
704 {
705 	struct vfsmount *res, *p, *q, *r, *s;
706 	struct nameidata nd;
707 
708 	if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(mnt))
709 		return NULL;
710 
711 	res = q = clone_mnt(mnt, dentry, flag);
712 	if (!q)
713 		goto Enomem;
714 	q->mnt_mountpoint = mnt->mnt_mountpoint;
715 
716 	p = mnt;
717 	list_for_each_entry(r, &mnt->mnt_mounts, mnt_child) {
718 		if (!lives_below_in_same_fs(r->mnt_mountpoint, dentry))
719 			continue;
720 
721 		for (s = r; s; s = next_mnt(s, r)) {
722 			if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(s)) {
723 				s = skip_mnt_tree(s);
724 				continue;
725 			}
726 			while (p != s->mnt_parent) {
727 				p = p->mnt_parent;
728 				q = q->mnt_parent;
729 			}
730 			p = s;
731 			nd.mnt = q;
732 			nd.dentry = p->mnt_mountpoint;
733 			q = clone_mnt(p, p->mnt_root, flag);
734 			if (!q)
735 				goto Enomem;
736 			spin_lock(&vfsmount_lock);
737 			list_add_tail(&q->mnt_list, &res->mnt_list);
738 			attach_mnt(q, &nd);
739 			spin_unlock(&vfsmount_lock);
740 		}
741 	}
742 	return res;
743 Enomem:
744 	if (res) {
745 		LIST_HEAD(umount_list);
746 		spin_lock(&vfsmount_lock);
747 		umount_tree(res, 0, &umount_list);
748 		spin_unlock(&vfsmount_lock);
749 		release_mounts(&umount_list);
750 	}
751 	return NULL;
752 }
753 
754 /*
755  *  @source_mnt : mount tree to be attached
756  *  @nd         : place the mount tree @source_mnt is attached
757  *  @parent_nd  : if non-null, detach the source_mnt from its parent and
758  *  		   store the parent mount and mountpoint dentry.
759  *  		   (done when source_mnt is moved)
760  *
761  *  NOTE: in the table below explains the semantics when a source mount
762  *  of a given type is attached to a destination mount of a given type.
763  * ---------------------------------------------------------------------------
764  * |         BIND MOUNT OPERATION                                            |
765  * |**************************************************************************
766  * | source-->| shared        |       private  |       slave    | unbindable |
767  * | dest     |               |                |                |            |
768  * |   |      |               |                |                |            |
769  * |   v      |               |                |                |            |
770  * |**************************************************************************
771  * |  shared  | shared (++)   |     shared (+) |     shared(+++)|  invalid   |
772  * |          |               |                |                |            |
773  * |non-shared| shared (+)    |      private   |      slave (*) |  invalid   |
774  * ***************************************************************************
775  * A bind operation clones the source mount and mounts the clone on the
776  * destination mount.
777  *
778  * (++)  the cloned mount is propagated to all the mounts in the propagation
779  * 	 tree of the destination mount and the cloned mount is added to
780  * 	 the peer group of the source mount.
781  * (+)   the cloned mount is created under the destination mount and is marked
782  *       as shared. The cloned mount is added to the peer group of the source
783  *       mount.
784  * (+++) the mount is propagated to all the mounts in the propagation tree
785  *       of the destination mount and the cloned mount is made slave
786  *       of the same master as that of the source mount. The cloned mount
787  *       is marked as 'shared and slave'.
788  * (*)   the cloned mount is made a slave of the same master as that of the
789  * 	 source mount.
790  *
791  * ---------------------------------------------------------------------------
792  * |         		MOVE MOUNT OPERATION                                 |
793  * |**************************************************************************
794  * | source-->| shared        |       private  |       slave    | unbindable |
795  * | dest     |               |                |                |            |
796  * |   |      |               |                |                |            |
797  * |   v      |               |                |                |            |
798  * |**************************************************************************
799  * |  shared  | shared (+)    |     shared (+) |    shared(+++) |  invalid   |
800  * |          |               |                |                |            |
801  * |non-shared| shared (+*)   |      private   |    slave (*)   | unbindable |
802  * ***************************************************************************
803  *
804  * (+)  the mount is moved to the destination. And is then propagated to
805  * 	all the mounts in the propagation tree of the destination mount.
806  * (+*)  the mount is moved to the destination.
807  * (+++)  the mount is moved to the destination and is then propagated to
808  * 	all the mounts belonging to the destination mount's propagation tree.
809  * 	the mount is marked as 'shared and slave'.
810  * (*)	the mount continues to be a slave at the new location.
811  *
812  * if the source mount is a tree, the operations explained above is
813  * applied to each mount in the tree.
814  * Must be called without spinlocks held, since this function can sleep
815  * in allocations.
816  */
817 static int attach_recursive_mnt(struct vfsmount *source_mnt,
818 			struct nameidata *nd, struct nameidata *parent_nd)
819 {
820 	LIST_HEAD(tree_list);
821 	struct vfsmount *dest_mnt = nd->mnt;
822 	struct dentry *dest_dentry = nd->dentry;
823 	struct vfsmount *child, *p;
824 
825 	if (propagate_mnt(dest_mnt, dest_dentry, source_mnt, &tree_list))
826 		return -EINVAL;
827 
828 	if (IS_MNT_SHARED(dest_mnt)) {
829 		for (p = source_mnt; p; p = next_mnt(p, source_mnt))
830 			set_mnt_shared(p);
831 	}
832 
833 	spin_lock(&vfsmount_lock);
834 	if (parent_nd) {
835 		detach_mnt(source_mnt, parent_nd);
836 		attach_mnt(source_mnt, nd);
837 		touch_mnt_namespace(current->nsproxy->mnt_ns);
838 	} else {
839 		mnt_set_mountpoint(dest_mnt, dest_dentry, source_mnt);
840 		commit_tree(source_mnt);
841 	}
842 
843 	list_for_each_entry_safe(child, p, &tree_list, mnt_hash) {
844 		list_del_init(&child->mnt_hash);
845 		commit_tree(child);
846 	}
847 	spin_unlock(&vfsmount_lock);
848 	return 0;
849 }
850 
851 static int graft_tree(struct vfsmount *mnt, struct nameidata *nd)
852 {
853 	int err;
854 	if (mnt->mnt_sb->s_flags & MS_NOUSER)
855 		return -EINVAL;
856 
857 	if (S_ISDIR(nd->dentry->d_inode->i_mode) !=
858 	      S_ISDIR(mnt->mnt_root->d_inode->i_mode))
859 		return -ENOTDIR;
860 
861 	err = -ENOENT;
862 	mutex_lock(&nd->dentry->d_inode->i_mutex);
863 	if (IS_DEADDIR(nd->dentry->d_inode))
864 		goto out_unlock;
865 
866 	err = security_sb_check_sb(mnt, nd);
867 	if (err)
868 		goto out_unlock;
869 
870 	err = -ENOENT;
871 	if (IS_ROOT(nd->dentry) || !d_unhashed(nd->dentry))
872 		err = attach_recursive_mnt(mnt, nd, NULL);
873 out_unlock:
874 	mutex_unlock(&nd->dentry->d_inode->i_mutex);
875 	if (!err)
876 		security_sb_post_addmount(mnt, nd);
877 	return err;
878 }
879 
880 /*
881  * recursively change the type of the mountpoint.
882  */
883 static int do_change_type(struct nameidata *nd, int flag)
884 {
885 	struct vfsmount *m, *mnt = nd->mnt;
886 	int recurse = flag & MS_REC;
887 	int type = flag & ~MS_REC;
888 
889 	if (!capable(CAP_SYS_ADMIN))
890 		return -EPERM;
891 
892 	if (nd->dentry != nd->mnt->mnt_root)
893 		return -EINVAL;
894 
895 	down_write(&namespace_sem);
896 	spin_lock(&vfsmount_lock);
897 	for (m = mnt; m; m = (recurse ? next_mnt(m, mnt) : NULL))
898 		change_mnt_propagation(m, type);
899 	spin_unlock(&vfsmount_lock);
900 	up_write(&namespace_sem);
901 	return 0;
902 }
903 
904 /*
905  * do loopback mount.
906  */
907 static int do_loopback(struct nameidata *nd, char *old_name, int recurse)
908 {
909 	struct nameidata old_nd;
910 	struct vfsmount *mnt = NULL;
911 	int err = mount_is_safe(nd);
912 	if (err)
913 		return err;
914 	if (!old_name || !*old_name)
915 		return -EINVAL;
916 	err = path_lookup(old_name, LOOKUP_FOLLOW, &old_nd);
917 	if (err)
918 		return err;
919 
920 	down_write(&namespace_sem);
921 	err = -EINVAL;
922 	if (IS_MNT_UNBINDABLE(old_nd.mnt))
923  		goto out;
924 
925 	if (!check_mnt(nd->mnt) || !check_mnt(old_nd.mnt))
926 		goto out;
927 
928 	err = -ENOMEM;
929 	if (recurse)
930 		mnt = copy_tree(old_nd.mnt, old_nd.dentry, 0);
931 	else
932 		mnt = clone_mnt(old_nd.mnt, old_nd.dentry, 0);
933 
934 	if (!mnt)
935 		goto out;
936 
937 	err = graft_tree(mnt, nd);
938 	if (err) {
939 		LIST_HEAD(umount_list);
940 		spin_lock(&vfsmount_lock);
941 		umount_tree(mnt, 0, &umount_list);
942 		spin_unlock(&vfsmount_lock);
943 		release_mounts(&umount_list);
944 	}
945 
946 out:
947 	up_write(&namespace_sem);
948 	path_release(&old_nd);
949 	return err;
950 }
951 
952 /*
953  * change filesystem flags. dir should be a physical root of filesystem.
954  * If you've mounted a non-root directory somewhere and want to do remount
955  * on it - tough luck.
956  */
957 static int do_remount(struct nameidata *nd, int flags, int mnt_flags,
958 		      void *data)
959 {
960 	int err;
961 	struct super_block *sb = nd->mnt->mnt_sb;
962 
963 	if (!capable(CAP_SYS_ADMIN))
964 		return -EPERM;
965 
966 	if (!check_mnt(nd->mnt))
967 		return -EINVAL;
968 
969 	if (nd->dentry != nd->mnt->mnt_root)
970 		return -EINVAL;
971 
972 	down_write(&sb->s_umount);
973 	err = do_remount_sb(sb, flags, data, 0);
974 	if (!err)
975 		nd->mnt->mnt_flags = mnt_flags;
976 	up_write(&sb->s_umount);
977 	if (!err)
978 		security_sb_post_remount(nd->mnt, flags, data);
979 	return err;
980 }
981 
982 static inline int tree_contains_unbindable(struct vfsmount *mnt)
983 {
984 	struct vfsmount *p;
985 	for (p = mnt; p; p = next_mnt(p, mnt)) {
986 		if (IS_MNT_UNBINDABLE(p))
987 			return 1;
988 	}
989 	return 0;
990 }
991 
992 static int do_move_mount(struct nameidata *nd, char *old_name)
993 {
994 	struct nameidata old_nd, parent_nd;
995 	struct vfsmount *p;
996 	int err = 0;
997 	if (!capable(CAP_SYS_ADMIN))
998 		return -EPERM;
999 	if (!old_name || !*old_name)
1000 		return -EINVAL;
1001 	err = path_lookup(old_name, LOOKUP_FOLLOW, &old_nd);
1002 	if (err)
1003 		return err;
1004 
1005 	down_write(&namespace_sem);
1006 	while (d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
1007 		;
1008 	err = -EINVAL;
1009 	if (!check_mnt(nd->mnt) || !check_mnt(old_nd.mnt))
1010 		goto out;
1011 
1012 	err = -ENOENT;
1013 	mutex_lock(&nd->dentry->d_inode->i_mutex);
1014 	if (IS_DEADDIR(nd->dentry->d_inode))
1015 		goto out1;
1016 
1017 	if (!IS_ROOT(nd->dentry) && d_unhashed(nd->dentry))
1018 		goto out1;
1019 
1020 	err = -EINVAL;
1021 	if (old_nd.dentry != old_nd.mnt->mnt_root)
1022 		goto out1;
1023 
1024 	if (old_nd.mnt == old_nd.mnt->mnt_parent)
1025 		goto out1;
1026 
1027 	if (S_ISDIR(nd->dentry->d_inode->i_mode) !=
1028 	      S_ISDIR(old_nd.dentry->d_inode->i_mode))
1029 		goto out1;
1030 	/*
1031 	 * Don't move a mount residing in a shared parent.
1032 	 */
1033 	if (old_nd.mnt->mnt_parent && IS_MNT_SHARED(old_nd.mnt->mnt_parent))
1034 		goto out1;
1035 	/*
1036 	 * Don't move a mount tree containing unbindable mounts to a destination
1037 	 * mount which is shared.
1038 	 */
1039 	if (IS_MNT_SHARED(nd->mnt) && tree_contains_unbindable(old_nd.mnt))
1040 		goto out1;
1041 	err = -ELOOP;
1042 	for (p = nd->mnt; p->mnt_parent != p; p = p->mnt_parent)
1043 		if (p == old_nd.mnt)
1044 			goto out1;
1045 
1046 	if ((err = attach_recursive_mnt(old_nd.mnt, nd, &parent_nd)))
1047 		goto out1;
1048 
1049 	spin_lock(&vfsmount_lock);
1050 	/* if the mount is moved, it should no longer be expire
1051 	 * automatically */
1052 	list_del_init(&old_nd.mnt->mnt_expire);
1053 	spin_unlock(&vfsmount_lock);
1054 out1:
1055 	mutex_unlock(&nd->dentry->d_inode->i_mutex);
1056 out:
1057 	up_write(&namespace_sem);
1058 	if (!err)
1059 		path_release(&parent_nd);
1060 	path_release(&old_nd);
1061 	return err;
1062 }
1063 
1064 /*
1065  * create a new mount for userspace and request it to be added into the
1066  * namespace's tree
1067  */
1068 static int do_new_mount(struct nameidata *nd, char *type, int flags,
1069 			int mnt_flags, char *name, void *data)
1070 {
1071 	struct vfsmount *mnt;
1072 
1073 	if (!type || !memchr(type, 0, PAGE_SIZE))
1074 		return -EINVAL;
1075 
1076 	/* we need capabilities... */
1077 	if (!capable(CAP_SYS_ADMIN))
1078 		return -EPERM;
1079 
1080 	mnt = do_kern_mount(type, flags, name, data);
1081 	if (IS_ERR(mnt))
1082 		return PTR_ERR(mnt);
1083 
1084 	return do_add_mount(mnt, nd, mnt_flags, NULL);
1085 }
1086 
1087 /*
1088  * add a mount into a namespace's mount tree
1089  * - provide the option of adding the new mount to an expiration list
1090  */
1091 int do_add_mount(struct vfsmount *newmnt, struct nameidata *nd,
1092 		 int mnt_flags, struct list_head *fslist)
1093 {
1094 	int err;
1095 
1096 	down_write(&namespace_sem);
1097 	/* Something was mounted here while we slept */
1098 	while (d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
1099 		;
1100 	err = -EINVAL;
1101 	if (!check_mnt(nd->mnt))
1102 		goto unlock;
1103 
1104 	/* Refuse the same filesystem on the same mount point */
1105 	err = -EBUSY;
1106 	if (nd->mnt->mnt_sb == newmnt->mnt_sb &&
1107 	    nd->mnt->mnt_root == nd->dentry)
1108 		goto unlock;
1109 
1110 	err = -EINVAL;
1111 	if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode))
1112 		goto unlock;
1113 
1114 	newmnt->mnt_flags = mnt_flags;
1115 	if ((err = graft_tree(newmnt, nd)))
1116 		goto unlock;
1117 
1118 	if (fslist) {
1119 		/* add to the specified expiration list */
1120 		spin_lock(&vfsmount_lock);
1121 		list_add_tail(&newmnt->mnt_expire, fslist);
1122 		spin_unlock(&vfsmount_lock);
1123 	}
1124 	up_write(&namespace_sem);
1125 	return 0;
1126 
1127 unlock:
1128 	up_write(&namespace_sem);
1129 	mntput(newmnt);
1130 	return err;
1131 }
1132 
1133 EXPORT_SYMBOL_GPL(do_add_mount);
1134 
1135 static void expire_mount(struct vfsmount *mnt, struct list_head *mounts,
1136 				struct list_head *umounts)
1137 {
1138 	spin_lock(&vfsmount_lock);
1139 
1140 	/*
1141 	 * Check if mount is still attached, if not, let whoever holds it deal
1142 	 * with the sucker
1143 	 */
1144 	if (mnt->mnt_parent == mnt) {
1145 		spin_unlock(&vfsmount_lock);
1146 		return;
1147 	}
1148 
1149 	/*
1150 	 * Check that it is still dead: the count should now be 2 - as
1151 	 * contributed by the vfsmount parent and the mntget above
1152 	 */
1153 	if (!propagate_mount_busy(mnt, 2)) {
1154 		/* delete from the namespace */
1155 		touch_mnt_namespace(mnt->mnt_ns);
1156 		list_del_init(&mnt->mnt_list);
1157 		mnt->mnt_ns = NULL;
1158 		umount_tree(mnt, 1, umounts);
1159 		spin_unlock(&vfsmount_lock);
1160 	} else {
1161 		/*
1162 		 * Someone brought it back to life whilst we didn't have any
1163 		 * locks held so return it to the expiration list
1164 		 */
1165 		list_add_tail(&mnt->mnt_expire, mounts);
1166 		spin_unlock(&vfsmount_lock);
1167 	}
1168 }
1169 
1170 /*
1171  * go through the vfsmounts we've just consigned to the graveyard to
1172  * - check that they're still dead
1173  * - delete the vfsmount from the appropriate namespace under lock
1174  * - dispose of the corpse
1175  */
1176 static void expire_mount_list(struct list_head *graveyard, struct list_head *mounts)
1177 {
1178 	struct mnt_namespace *ns;
1179 	struct vfsmount *mnt;
1180 
1181 	while (!list_empty(graveyard)) {
1182 		LIST_HEAD(umounts);
1183 		mnt = list_first_entry(graveyard, struct vfsmount, mnt_expire);
1184 		list_del_init(&mnt->mnt_expire);
1185 
1186 		/* don't do anything if the namespace is dead - all the
1187 		 * vfsmounts from it are going away anyway */
1188 		ns = mnt->mnt_ns;
1189 		if (!ns || !ns->root)
1190 			continue;
1191 		get_mnt_ns(ns);
1192 
1193 		spin_unlock(&vfsmount_lock);
1194 		down_write(&namespace_sem);
1195 		expire_mount(mnt, mounts, &umounts);
1196 		up_write(&namespace_sem);
1197 		release_mounts(&umounts);
1198 		mntput(mnt);
1199 		put_mnt_ns(ns);
1200 		spin_lock(&vfsmount_lock);
1201 	}
1202 }
1203 
1204 /*
1205  * process a list of expirable mountpoints with the intent of discarding any
1206  * mountpoints that aren't in use and haven't been touched since last we came
1207  * here
1208  */
1209 void mark_mounts_for_expiry(struct list_head *mounts)
1210 {
1211 	struct vfsmount *mnt, *next;
1212 	LIST_HEAD(graveyard);
1213 
1214 	if (list_empty(mounts))
1215 		return;
1216 
1217 	spin_lock(&vfsmount_lock);
1218 
1219 	/* extract from the expiration list every vfsmount that matches the
1220 	 * following criteria:
1221 	 * - only referenced by its parent vfsmount
1222 	 * - still marked for expiry (marked on the last call here; marks are
1223 	 *   cleared by mntput())
1224 	 */
1225 	list_for_each_entry_safe(mnt, next, mounts, mnt_expire) {
1226 		if (!xchg(&mnt->mnt_expiry_mark, 1) ||
1227 		    atomic_read(&mnt->mnt_count) != 1)
1228 			continue;
1229 
1230 		mntget(mnt);
1231 		list_move(&mnt->mnt_expire, &graveyard);
1232 	}
1233 
1234 	expire_mount_list(&graveyard, mounts);
1235 
1236 	spin_unlock(&vfsmount_lock);
1237 }
1238 
1239 EXPORT_SYMBOL_GPL(mark_mounts_for_expiry);
1240 
1241 /*
1242  * Ripoff of 'select_parent()'
1243  *
1244  * search the list of submounts for a given mountpoint, and move any
1245  * shrinkable submounts to the 'graveyard' list.
1246  */
1247 static int select_submounts(struct vfsmount *parent, struct list_head *graveyard)
1248 {
1249 	struct vfsmount *this_parent = parent;
1250 	struct list_head *next;
1251 	int found = 0;
1252 
1253 repeat:
1254 	next = this_parent->mnt_mounts.next;
1255 resume:
1256 	while (next != &this_parent->mnt_mounts) {
1257 		struct list_head *tmp = next;
1258 		struct vfsmount *mnt = list_entry(tmp, struct vfsmount, mnt_child);
1259 
1260 		next = tmp->next;
1261 		if (!(mnt->mnt_flags & MNT_SHRINKABLE))
1262 			continue;
1263 		/*
1264 		 * Descend a level if the d_mounts list is non-empty.
1265 		 */
1266 		if (!list_empty(&mnt->mnt_mounts)) {
1267 			this_parent = mnt;
1268 			goto repeat;
1269 		}
1270 
1271 		if (!propagate_mount_busy(mnt, 1)) {
1272 			mntget(mnt);
1273 			list_move_tail(&mnt->mnt_expire, graveyard);
1274 			found++;
1275 		}
1276 	}
1277 	/*
1278 	 * All done at this level ... ascend and resume the search
1279 	 */
1280 	if (this_parent != parent) {
1281 		next = this_parent->mnt_child.next;
1282 		this_parent = this_parent->mnt_parent;
1283 		goto resume;
1284 	}
1285 	return found;
1286 }
1287 
1288 /*
1289  * process a list of expirable mountpoints with the intent of discarding any
1290  * submounts of a specific parent mountpoint
1291  */
1292 void shrink_submounts(struct vfsmount *mountpoint, struct list_head *mounts)
1293 {
1294 	LIST_HEAD(graveyard);
1295 	int found;
1296 
1297 	spin_lock(&vfsmount_lock);
1298 
1299 	/* extract submounts of 'mountpoint' from the expiration list */
1300 	while ((found = select_submounts(mountpoint, &graveyard)) != 0)
1301 		expire_mount_list(&graveyard, mounts);
1302 
1303 	spin_unlock(&vfsmount_lock);
1304 }
1305 
1306 EXPORT_SYMBOL_GPL(shrink_submounts);
1307 
1308 /*
1309  * Some copy_from_user() implementations do not return the exact number of
1310  * bytes remaining to copy on a fault.  But copy_mount_options() requires that.
1311  * Note that this function differs from copy_from_user() in that it will oops
1312  * on bad values of `to', rather than returning a short copy.
1313  */
1314 static long exact_copy_from_user(void *to, const void __user * from,
1315 				 unsigned long n)
1316 {
1317 	char *t = to;
1318 	const char __user *f = from;
1319 	char c;
1320 
1321 	if (!access_ok(VERIFY_READ, from, n))
1322 		return n;
1323 
1324 	while (n) {
1325 		if (__get_user(c, f)) {
1326 			memset(t, 0, n);
1327 			break;
1328 		}
1329 		*t++ = c;
1330 		f++;
1331 		n--;
1332 	}
1333 	return n;
1334 }
1335 
1336 int copy_mount_options(const void __user * data, unsigned long *where)
1337 {
1338 	int i;
1339 	unsigned long page;
1340 	unsigned long size;
1341 
1342 	*where = 0;
1343 	if (!data)
1344 		return 0;
1345 
1346 	if (!(page = __get_free_page(GFP_KERNEL)))
1347 		return -ENOMEM;
1348 
1349 	/* We only care that *some* data at the address the user
1350 	 * gave us is valid.  Just in case, we'll zero
1351 	 * the remainder of the page.
1352 	 */
1353 	/* copy_from_user cannot cross TASK_SIZE ! */
1354 	size = TASK_SIZE - (unsigned long)data;
1355 	if (size > PAGE_SIZE)
1356 		size = PAGE_SIZE;
1357 
1358 	i = size - exact_copy_from_user((void *)page, data, size);
1359 	if (!i) {
1360 		free_page(page);
1361 		return -EFAULT;
1362 	}
1363 	if (i != PAGE_SIZE)
1364 		memset((char *)page + i, 0, PAGE_SIZE - i);
1365 	*where = page;
1366 	return 0;
1367 }
1368 
1369 /*
1370  * Flags is a 32-bit value that allows up to 31 non-fs dependent flags to
1371  * be given to the mount() call (ie: read-only, no-dev, no-suid etc).
1372  *
1373  * data is a (void *) that can point to any structure up to
1374  * PAGE_SIZE-1 bytes, which can contain arbitrary fs-dependent
1375  * information (or be NULL).
1376  *
1377  * Pre-0.97 versions of mount() didn't have a flags word.
1378  * When the flags word was introduced its top half was required
1379  * to have the magic value 0xC0ED, and this remained so until 2.4.0-test9.
1380  * Therefore, if this magic number is present, it carries no information
1381  * and must be discarded.
1382  */
1383 long do_mount(char *dev_name, char *dir_name, char *type_page,
1384 		  unsigned long flags, void *data_page)
1385 {
1386 	struct nameidata nd;
1387 	int retval = 0;
1388 	int mnt_flags = 0;
1389 
1390 	/* Discard magic */
1391 	if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
1392 		flags &= ~MS_MGC_MSK;
1393 
1394 	/* Basic sanity checks */
1395 
1396 	if (!dir_name || !*dir_name || !memchr(dir_name, 0, PAGE_SIZE))
1397 		return -EINVAL;
1398 	if (dev_name && !memchr(dev_name, 0, PAGE_SIZE))
1399 		return -EINVAL;
1400 
1401 	if (data_page)
1402 		((char *)data_page)[PAGE_SIZE - 1] = 0;
1403 
1404 	/* Separate the per-mountpoint flags */
1405 	if (flags & MS_NOSUID)
1406 		mnt_flags |= MNT_NOSUID;
1407 	if (flags & MS_NODEV)
1408 		mnt_flags |= MNT_NODEV;
1409 	if (flags & MS_NOEXEC)
1410 		mnt_flags |= MNT_NOEXEC;
1411 	if (flags & MS_NOATIME)
1412 		mnt_flags |= MNT_NOATIME;
1413 	if (flags & MS_NODIRATIME)
1414 		mnt_flags |= MNT_NODIRATIME;
1415 	if (flags & MS_RELATIME)
1416 		mnt_flags |= MNT_RELATIME;
1417 
1418 	flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE |
1419 		   MS_NOATIME | MS_NODIRATIME | MS_RELATIME);
1420 
1421 	/* ... and get the mountpoint */
1422 	retval = path_lookup(dir_name, LOOKUP_FOLLOW, &nd);
1423 	if (retval)
1424 		return retval;
1425 
1426 	retval = security_sb_mount(dev_name, &nd, type_page, flags, data_page);
1427 	if (retval)
1428 		goto dput_out;
1429 
1430 	if (flags & MS_REMOUNT)
1431 		retval = do_remount(&nd, flags & ~MS_REMOUNT, mnt_flags,
1432 				    data_page);
1433 	else if (flags & MS_BIND)
1434 		retval = do_loopback(&nd, dev_name, flags & MS_REC);
1435 	else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
1436 		retval = do_change_type(&nd, flags);
1437 	else if (flags & MS_MOVE)
1438 		retval = do_move_mount(&nd, dev_name);
1439 	else
1440 		retval = do_new_mount(&nd, type_page, flags, mnt_flags,
1441 				      dev_name, data_page);
1442 dput_out:
1443 	path_release(&nd);
1444 	return retval;
1445 }
1446 
1447 /*
1448  * Allocate a new namespace structure and populate it with contents
1449  * copied from the namespace of the passed in task structure.
1450  */
1451 static struct mnt_namespace *dup_mnt_ns(struct mnt_namespace *mnt_ns,
1452 		struct fs_struct *fs)
1453 {
1454 	struct mnt_namespace *new_ns;
1455 	struct vfsmount *rootmnt = NULL, *pwdmnt = NULL, *altrootmnt = NULL;
1456 	struct vfsmount *p, *q;
1457 
1458 	new_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
1459 	if (!new_ns)
1460 		return NULL;
1461 
1462 	atomic_set(&new_ns->count, 1);
1463 	INIT_LIST_HEAD(&new_ns->list);
1464 	init_waitqueue_head(&new_ns->poll);
1465 	new_ns->event = 0;
1466 
1467 	down_write(&namespace_sem);
1468 	/* First pass: copy the tree topology */
1469 	new_ns->root = copy_tree(mnt_ns->root, mnt_ns->root->mnt_root,
1470 					CL_COPY_ALL | CL_EXPIRE);
1471 	if (!new_ns->root) {
1472 		up_write(&namespace_sem);
1473 		kfree(new_ns);
1474 		return NULL;
1475 	}
1476 	spin_lock(&vfsmount_lock);
1477 	list_add_tail(&new_ns->list, &new_ns->root->mnt_list);
1478 	spin_unlock(&vfsmount_lock);
1479 
1480 	/*
1481 	 * Second pass: switch the tsk->fs->* elements and mark new vfsmounts
1482 	 * as belonging to new namespace.  We have already acquired a private
1483 	 * fs_struct, so tsk->fs->lock is not needed.
1484 	 */
1485 	p = mnt_ns->root;
1486 	q = new_ns->root;
1487 	while (p) {
1488 		q->mnt_ns = new_ns;
1489 		if (fs) {
1490 			if (p == fs->rootmnt) {
1491 				rootmnt = p;
1492 				fs->rootmnt = mntget(q);
1493 			}
1494 			if (p == fs->pwdmnt) {
1495 				pwdmnt = p;
1496 				fs->pwdmnt = mntget(q);
1497 			}
1498 			if (p == fs->altrootmnt) {
1499 				altrootmnt = p;
1500 				fs->altrootmnt = mntget(q);
1501 			}
1502 		}
1503 		p = next_mnt(p, mnt_ns->root);
1504 		q = next_mnt(q, new_ns->root);
1505 	}
1506 	up_write(&namespace_sem);
1507 
1508 	if (rootmnt)
1509 		mntput(rootmnt);
1510 	if (pwdmnt)
1511 		mntput(pwdmnt);
1512 	if (altrootmnt)
1513 		mntput(altrootmnt);
1514 
1515 	return new_ns;
1516 }
1517 
1518 struct mnt_namespace *copy_mnt_ns(int flags, struct mnt_namespace *ns,
1519 		struct fs_struct *new_fs)
1520 {
1521 	struct mnt_namespace *new_ns;
1522 
1523 	BUG_ON(!ns);
1524 	get_mnt_ns(ns);
1525 
1526 	if (!(flags & CLONE_NEWNS))
1527 		return ns;
1528 
1529 	new_ns = dup_mnt_ns(ns, new_fs);
1530 
1531 	put_mnt_ns(ns);
1532 	return new_ns;
1533 }
1534 
1535 asmlinkage long sys_mount(char __user * dev_name, char __user * dir_name,
1536 			  char __user * type, unsigned long flags,
1537 			  void __user * data)
1538 {
1539 	int retval;
1540 	unsigned long data_page;
1541 	unsigned long type_page;
1542 	unsigned long dev_page;
1543 	char *dir_page;
1544 
1545 	retval = copy_mount_options(type, &type_page);
1546 	if (retval < 0)
1547 		return retval;
1548 
1549 	dir_page = getname(dir_name);
1550 	retval = PTR_ERR(dir_page);
1551 	if (IS_ERR(dir_page))
1552 		goto out1;
1553 
1554 	retval = copy_mount_options(dev_name, &dev_page);
1555 	if (retval < 0)
1556 		goto out2;
1557 
1558 	retval = copy_mount_options(data, &data_page);
1559 	if (retval < 0)
1560 		goto out3;
1561 
1562 	lock_kernel();
1563 	retval = do_mount((char *)dev_page, dir_page, (char *)type_page,
1564 			  flags, (void *)data_page);
1565 	unlock_kernel();
1566 	free_page(data_page);
1567 
1568 out3:
1569 	free_page(dev_page);
1570 out2:
1571 	putname(dir_page);
1572 out1:
1573 	free_page(type_page);
1574 	return retval;
1575 }
1576 
1577 /*
1578  * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
1579  * It can block. Requires the big lock held.
1580  */
1581 void set_fs_root(struct fs_struct *fs, struct vfsmount *mnt,
1582 		 struct dentry *dentry)
1583 {
1584 	struct dentry *old_root;
1585 	struct vfsmount *old_rootmnt;
1586 	write_lock(&fs->lock);
1587 	old_root = fs->root;
1588 	old_rootmnt = fs->rootmnt;
1589 	fs->rootmnt = mntget(mnt);
1590 	fs->root = dget(dentry);
1591 	write_unlock(&fs->lock);
1592 	if (old_root) {
1593 		dput(old_root);
1594 		mntput(old_rootmnt);
1595 	}
1596 }
1597 
1598 /*
1599  * Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values.
1600  * It can block. Requires the big lock held.
1601  */
1602 void set_fs_pwd(struct fs_struct *fs, struct vfsmount *mnt,
1603 		struct dentry *dentry)
1604 {
1605 	struct dentry *old_pwd;
1606 	struct vfsmount *old_pwdmnt;
1607 
1608 	write_lock(&fs->lock);
1609 	old_pwd = fs->pwd;
1610 	old_pwdmnt = fs->pwdmnt;
1611 	fs->pwdmnt = mntget(mnt);
1612 	fs->pwd = dget(dentry);
1613 	write_unlock(&fs->lock);
1614 
1615 	if (old_pwd) {
1616 		dput(old_pwd);
1617 		mntput(old_pwdmnt);
1618 	}
1619 }
1620 
1621 static void chroot_fs_refs(struct nameidata *old_nd, struct nameidata *new_nd)
1622 {
1623 	struct task_struct *g, *p;
1624 	struct fs_struct *fs;
1625 
1626 	read_lock(&tasklist_lock);
1627 	do_each_thread(g, p) {
1628 		task_lock(p);
1629 		fs = p->fs;
1630 		if (fs) {
1631 			atomic_inc(&fs->count);
1632 			task_unlock(p);
1633 			if (fs->root == old_nd->dentry
1634 			    && fs->rootmnt == old_nd->mnt)
1635 				set_fs_root(fs, new_nd->mnt, new_nd->dentry);
1636 			if (fs->pwd == old_nd->dentry
1637 			    && fs->pwdmnt == old_nd->mnt)
1638 				set_fs_pwd(fs, new_nd->mnt, new_nd->dentry);
1639 			put_fs_struct(fs);
1640 		} else
1641 			task_unlock(p);
1642 	} while_each_thread(g, p);
1643 	read_unlock(&tasklist_lock);
1644 }
1645 
1646 /*
1647  * pivot_root Semantics:
1648  * Moves the root file system of the current process to the directory put_old,
1649  * makes new_root as the new root file system of the current process, and sets
1650  * root/cwd of all processes which had them on the current root to new_root.
1651  *
1652  * Restrictions:
1653  * The new_root and put_old must be directories, and  must not be on the
1654  * same file  system as the current process root. The put_old  must  be
1655  * underneath new_root,  i.e. adding a non-zero number of /.. to the string
1656  * pointed to by put_old must yield the same directory as new_root. No other
1657  * file system may be mounted on put_old. After all, new_root is a mountpoint.
1658  *
1659  * Also, the current root cannot be on the 'rootfs' (initial ramfs) filesystem.
1660  * See Documentation/filesystems/ramfs-rootfs-initramfs.txt for alternatives
1661  * in this situation.
1662  *
1663  * Notes:
1664  *  - we don't move root/cwd if they are not at the root (reason: if something
1665  *    cared enough to change them, it's probably wrong to force them elsewhere)
1666  *  - it's okay to pick a root that isn't the root of a file system, e.g.
1667  *    /nfs/my_root where /nfs is the mount point. It must be a mountpoint,
1668  *    though, so you may need to say mount --bind /nfs/my_root /nfs/my_root
1669  *    first.
1670  */
1671 asmlinkage long sys_pivot_root(const char __user * new_root,
1672 			       const char __user * put_old)
1673 {
1674 	struct vfsmount *tmp;
1675 	struct nameidata new_nd, old_nd, parent_nd, root_parent, user_nd;
1676 	int error;
1677 
1678 	if (!capable(CAP_SYS_ADMIN))
1679 		return -EPERM;
1680 
1681 	lock_kernel();
1682 
1683 	error = __user_walk(new_root, LOOKUP_FOLLOW | LOOKUP_DIRECTORY,
1684 			    &new_nd);
1685 	if (error)
1686 		goto out0;
1687 	error = -EINVAL;
1688 	if (!check_mnt(new_nd.mnt))
1689 		goto out1;
1690 
1691 	error = __user_walk(put_old, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &old_nd);
1692 	if (error)
1693 		goto out1;
1694 
1695 	error = security_sb_pivotroot(&old_nd, &new_nd);
1696 	if (error) {
1697 		path_release(&old_nd);
1698 		goto out1;
1699 	}
1700 
1701 	read_lock(&current->fs->lock);
1702 	user_nd.mnt = mntget(current->fs->rootmnt);
1703 	user_nd.dentry = dget(current->fs->root);
1704 	read_unlock(&current->fs->lock);
1705 	down_write(&namespace_sem);
1706 	mutex_lock(&old_nd.dentry->d_inode->i_mutex);
1707 	error = -EINVAL;
1708 	if (IS_MNT_SHARED(old_nd.mnt) ||
1709 		IS_MNT_SHARED(new_nd.mnt->mnt_parent) ||
1710 		IS_MNT_SHARED(user_nd.mnt->mnt_parent))
1711 		goto out2;
1712 	if (!check_mnt(user_nd.mnt))
1713 		goto out2;
1714 	error = -ENOENT;
1715 	if (IS_DEADDIR(new_nd.dentry->d_inode))
1716 		goto out2;
1717 	if (d_unhashed(new_nd.dentry) && !IS_ROOT(new_nd.dentry))
1718 		goto out2;
1719 	if (d_unhashed(old_nd.dentry) && !IS_ROOT(old_nd.dentry))
1720 		goto out2;
1721 	error = -EBUSY;
1722 	if (new_nd.mnt == user_nd.mnt || old_nd.mnt == user_nd.mnt)
1723 		goto out2; /* loop, on the same file system  */
1724 	error = -EINVAL;
1725 	if (user_nd.mnt->mnt_root != user_nd.dentry)
1726 		goto out2; /* not a mountpoint */
1727 	if (user_nd.mnt->mnt_parent == user_nd.mnt)
1728 		goto out2; /* not attached */
1729 	if (new_nd.mnt->mnt_root != new_nd.dentry)
1730 		goto out2; /* not a mountpoint */
1731 	if (new_nd.mnt->mnt_parent == new_nd.mnt)
1732 		goto out2; /* not attached */
1733 	tmp = old_nd.mnt; /* make sure we can reach put_old from new_root */
1734 	spin_lock(&vfsmount_lock);
1735 	if (tmp != new_nd.mnt) {
1736 		for (;;) {
1737 			if (tmp->mnt_parent == tmp)
1738 				goto out3; /* already mounted on put_old */
1739 			if (tmp->mnt_parent == new_nd.mnt)
1740 				break;
1741 			tmp = tmp->mnt_parent;
1742 		}
1743 		if (!is_subdir(tmp->mnt_mountpoint, new_nd.dentry))
1744 			goto out3;
1745 	} else if (!is_subdir(old_nd.dentry, new_nd.dentry))
1746 		goto out3;
1747 	detach_mnt(new_nd.mnt, &parent_nd);
1748 	detach_mnt(user_nd.mnt, &root_parent);
1749 	attach_mnt(user_nd.mnt, &old_nd);     /* mount old root on put_old */
1750 	attach_mnt(new_nd.mnt, &root_parent); /* mount new_root on / */
1751 	touch_mnt_namespace(current->nsproxy->mnt_ns);
1752 	spin_unlock(&vfsmount_lock);
1753 	chroot_fs_refs(&user_nd, &new_nd);
1754 	security_sb_post_pivotroot(&user_nd, &new_nd);
1755 	error = 0;
1756 	path_release(&root_parent);
1757 	path_release(&parent_nd);
1758 out2:
1759 	mutex_unlock(&old_nd.dentry->d_inode->i_mutex);
1760 	up_write(&namespace_sem);
1761 	path_release(&user_nd);
1762 	path_release(&old_nd);
1763 out1:
1764 	path_release(&new_nd);
1765 out0:
1766 	unlock_kernel();
1767 	return error;
1768 out3:
1769 	spin_unlock(&vfsmount_lock);
1770 	goto out2;
1771 }
1772 
1773 static void __init init_mount_tree(void)
1774 {
1775 	struct vfsmount *mnt;
1776 	struct mnt_namespace *ns;
1777 
1778 	mnt = do_kern_mount("rootfs", 0, "rootfs", NULL);
1779 	if (IS_ERR(mnt))
1780 		panic("Can't create rootfs");
1781 	ns = kmalloc(sizeof(*ns), GFP_KERNEL);
1782 	if (!ns)
1783 		panic("Can't allocate initial namespace");
1784 	atomic_set(&ns->count, 1);
1785 	INIT_LIST_HEAD(&ns->list);
1786 	init_waitqueue_head(&ns->poll);
1787 	ns->event = 0;
1788 	list_add(&mnt->mnt_list, &ns->list);
1789 	ns->root = mnt;
1790 	mnt->mnt_ns = ns;
1791 
1792 	init_task.nsproxy->mnt_ns = ns;
1793 	get_mnt_ns(ns);
1794 
1795 	set_fs_pwd(current->fs, ns->root, ns->root->mnt_root);
1796 	set_fs_root(current->fs, ns->root, ns->root->mnt_root);
1797 }
1798 
1799 void __init mnt_init(unsigned long mempages)
1800 {
1801 	struct list_head *d;
1802 	unsigned int nr_hash;
1803 	int i;
1804 	int err;
1805 
1806 	init_rwsem(&namespace_sem);
1807 
1808 	mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct vfsmount),
1809 			0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL, NULL);
1810 
1811 	mount_hashtable = (struct list_head *)__get_free_page(GFP_ATOMIC);
1812 
1813 	if (!mount_hashtable)
1814 		panic("Failed to allocate mount hash table\n");
1815 
1816 	/*
1817 	 * Find the power-of-two list-heads that can fit into the allocation..
1818 	 * We don't guarantee that "sizeof(struct list_head)" is necessarily
1819 	 * a power-of-two.
1820 	 */
1821 	nr_hash = PAGE_SIZE / sizeof(struct list_head);
1822 	hash_bits = 0;
1823 	do {
1824 		hash_bits++;
1825 	} while ((nr_hash >> hash_bits) != 0);
1826 	hash_bits--;
1827 
1828 	/*
1829 	 * Re-calculate the actual number of entries and the mask
1830 	 * from the number of bits we can fit.
1831 	 */
1832 	nr_hash = 1UL << hash_bits;
1833 	hash_mask = nr_hash - 1;
1834 
1835 	printk("Mount-cache hash table entries: %d\n", nr_hash);
1836 
1837 	/* And initialize the newly allocated array */
1838 	d = mount_hashtable;
1839 	i = nr_hash;
1840 	do {
1841 		INIT_LIST_HEAD(d);
1842 		d++;
1843 		i--;
1844 	} while (i);
1845 	err = sysfs_init();
1846 	if (err)
1847 		printk(KERN_WARNING "%s: sysfs_init error: %d\n",
1848 			__FUNCTION__, err);
1849 	err = subsystem_register(&fs_subsys);
1850 	if (err)
1851 		printk(KERN_WARNING "%s: subsystem_register error: %d\n",
1852 			__FUNCTION__, err);
1853 	init_rootfs();
1854 	init_mount_tree();
1855 }
1856 
1857 void __put_mnt_ns(struct mnt_namespace *ns)
1858 {
1859 	struct vfsmount *root = ns->root;
1860 	LIST_HEAD(umount_list);
1861 	ns->root = NULL;
1862 	spin_unlock(&vfsmount_lock);
1863 	down_write(&namespace_sem);
1864 	spin_lock(&vfsmount_lock);
1865 	umount_tree(root, 0, &umount_list);
1866 	spin_unlock(&vfsmount_lock);
1867 	up_write(&namespace_sem);
1868 	release_mounts(&umount_list);
1869 	kfree(ns);
1870 }
1871