xref: /openbmc/linux/fs/devpts/inode.c (revision a319b01d) 
1 /* -*- linux-c -*- --------------------------------------------------------- *
2  *
3  * linux/fs/devpts/inode.c
4  *
5  *  Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved
6  *
7  * This file is part of the Linux kernel and is made available under
8  * the terms of the GNU General Public License, version 2, or at your
9  * option, any later version, incorporated herein by reference.
10  *
11  * ------------------------------------------------------------------------- */
12 
13 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
14 
15 #include <linux/module.h>
16 #include <linux/init.h>
17 #include <linux/fs.h>
18 #include <linux/sched.h>
19 #include <linux/namei.h>
20 #include <linux/slab.h>
21 #include <linux/mount.h>
22 #include <linux/tty.h>
23 #include <linux/mutex.h>
24 #include <linux/magic.h>
25 #include <linux/idr.h>
26 #include <linux/devpts_fs.h>
27 #include <linux/parser.h>
28 #include <linux/fsnotify.h>
29 #include <linux/seq_file.h>
30 
31 #define DEVPTS_DEFAULT_MODE 0600
32 /*
33  * ptmx is a new node in /dev/pts and will be unused in legacy (single-
34  * instance) mode. To prevent surprises in user space, set permissions of
35  * ptmx to 0. Use 'chmod' or remount with '-o ptmxmode' to set meaningful
36  * permissions.
37  */
38 #define DEVPTS_DEFAULT_PTMX_MODE 0000
39 #define PTMX_MINOR	2
40 
41 /*
42  * sysctl support for setting limits on the number of Unix98 ptys allocated.
43  * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
44  */
45 static int pty_limit = NR_UNIX98_PTY_DEFAULT;
46 static int pty_reserve = NR_UNIX98_PTY_RESERVE;
47 static int pty_limit_min;
48 static int pty_limit_max = INT_MAX;
49 static int pty_count;
50 
51 static struct ctl_table pty_table[] = {
52 	{
53 		.procname	= "max",
54 		.maxlen		= sizeof(int),
55 		.mode		= 0644,
56 		.data		= &pty_limit,
57 		.proc_handler	= proc_dointvec_minmax,
58 		.extra1		= &pty_limit_min,
59 		.extra2		= &pty_limit_max,
60 	}, {
61 		.procname	= "reserve",
62 		.maxlen		= sizeof(int),
63 		.mode		= 0644,
64 		.data		= &pty_reserve,
65 		.proc_handler	= proc_dointvec_minmax,
66 		.extra1		= &pty_limit_min,
67 		.extra2		= &pty_limit_max,
68 	}, {
69 		.procname	= "nr",
70 		.maxlen		= sizeof(int),
71 		.mode		= 0444,
72 		.data		= &pty_count,
73 		.proc_handler	= proc_dointvec,
74 	},
75 	{}
76 };
77 
78 static struct ctl_table pty_kern_table[] = {
79 	{
80 		.procname	= "pty",
81 		.mode		= 0555,
82 		.child		= pty_table,
83 	},
84 	{}
85 };
86 
87 static struct ctl_table pty_root_table[] = {
88 	{
89 		.procname	= "kernel",
90 		.mode		= 0555,
91 		.child		= pty_kern_table,
92 	},
93 	{}
94 };
95 
96 static DEFINE_MUTEX(allocated_ptys_lock);
97 
98 struct pts_mount_opts {
99 	int setuid;
100 	int setgid;
101 	kuid_t   uid;
102 	kgid_t   gid;
103 	umode_t mode;
104 	umode_t ptmxmode;
105 	int reserve;
106 	int max;
107 };
108 
109 enum {
110 	Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance,  Opt_max,
111 	Opt_err
112 };
113 
114 static const match_table_t tokens = {
115 	{Opt_uid, "uid=%u"},
116 	{Opt_gid, "gid=%u"},
117 	{Opt_mode, "mode=%o"},
118 	{Opt_ptmxmode, "ptmxmode=%o"},
119 	{Opt_newinstance, "newinstance"},
120 	{Opt_max, "max=%d"},
121 	{Opt_err, NULL}
122 };
123 
124 struct pts_fs_info {
125 	struct ida allocated_ptys;
126 	struct pts_mount_opts mount_opts;
127 	struct super_block *sb;
128 	struct dentry *ptmx_dentry;
129 };
130 
131 static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
132 {
133 	return sb->s_fs_info;
134 }
135 
136 static int devpts_ptmx_path(struct path *path)
137 {
138 	struct super_block *sb;
139 	int err;
140 
141 	/* Is a devpts filesystem at "pts" in the same directory? */
142 	err = path_pts(path);
143 	if (err)
144 		return err;
145 
146 	/* Is the path the root of a devpts filesystem? */
147 	sb = path->mnt->mnt_sb;
148 	if ((sb->s_magic != DEVPTS_SUPER_MAGIC) ||
149 	    (path->mnt->mnt_root != sb->s_root))
150 		return -ENODEV;
151 
152 	return 0;
153 }
154 
155 struct vfsmount *devpts_mntget(struct file *filp, struct pts_fs_info *fsi)
156 {
157 	struct path path;
158 	int err = 0;
159 
160 	path = filp->f_path;
161 	path_get(&path);
162 
163 	/* Walk upward while the start point is a bind mount of
164 	 * a single file.
165 	 */
166 	while (path.mnt->mnt_root == path.dentry)
167 		if (follow_up(&path) == 0)
168 			break;
169 
170 	/* devpts_ptmx_path() finds a devpts fs or returns an error. */
171 	if ((path.mnt->mnt_sb->s_magic != DEVPTS_SUPER_MAGIC) ||
172 	    (DEVPTS_SB(path.mnt->mnt_sb) != fsi))
173 		err = devpts_ptmx_path(&path);
174 	dput(path.dentry);
175 	if (!err) {
176 		if (DEVPTS_SB(path.mnt->mnt_sb) == fsi)
177 			return path.mnt;
178 
179 		err = -ENODEV;
180 	}
181 
182 	mntput(path.mnt);
183 	return ERR_PTR(err);
184 }
185 
186 struct pts_fs_info *devpts_acquire(struct file *filp)
187 {
188 	struct pts_fs_info *result;
189 	struct path path;
190 	struct super_block *sb;
191 
192 	path = filp->f_path;
193 	path_get(&path);
194 
195 	/* Has the devpts filesystem already been found? */
196 	if (path.mnt->mnt_sb->s_magic != DEVPTS_SUPER_MAGIC) {
197 		int err;
198 
199 		err = devpts_ptmx_path(&path);
200 		if (err) {
201 			result = ERR_PTR(err);
202 			goto out;
203 		}
204 	}
205 
206 	/*
207 	 * pty code needs to hold extra references in case of last /dev/tty close
208 	 */
209 	sb = path.mnt->mnt_sb;
210 	atomic_inc(&sb->s_active);
211 	result = DEVPTS_SB(sb);
212 
213 out:
214 	path_put(&path);
215 	return result;
216 }
217 
218 void devpts_release(struct pts_fs_info *fsi)
219 {
220 	deactivate_super(fsi->sb);
221 }
222 
223 #define PARSE_MOUNT	0
224 #define PARSE_REMOUNT	1
225 
226 /*
227  * parse_mount_options():
228  *	Set @opts to mount options specified in @data. If an option is not
229  *	specified in @data, set it to its default value.
230  *
231  * Note: @data may be NULL (in which case all options are set to default).
232  */
233 static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
234 {
235 	char *p;
236 	kuid_t uid;
237 	kgid_t gid;
238 
239 	opts->setuid  = 0;
240 	opts->setgid  = 0;
241 	opts->uid     = GLOBAL_ROOT_UID;
242 	opts->gid     = GLOBAL_ROOT_GID;
243 	opts->mode    = DEVPTS_DEFAULT_MODE;
244 	opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
245 	opts->max     = NR_UNIX98_PTY_MAX;
246 
247 	/* Only allow instances mounted from the initial mount
248 	 * namespace to tap the reserve pool of ptys.
249 	 */
250 	if (op == PARSE_MOUNT)
251 		opts->reserve =
252 			(current->nsproxy->mnt_ns == init_task.nsproxy->mnt_ns);
253 
254 	while ((p = strsep(&data, ",")) != NULL) {
255 		substring_t args[MAX_OPT_ARGS];
256 		int token;
257 		int option;
258 
259 		if (!*p)
260 			continue;
261 
262 		token = match_token(p, tokens, args);
263 		switch (token) {
264 		case Opt_uid:
265 			if (match_int(&args[0], &option))
266 				return -EINVAL;
267 			uid = make_kuid(current_user_ns(), option);
268 			if (!uid_valid(uid))
269 				return -EINVAL;
270 			opts->uid = uid;
271 			opts->setuid = 1;
272 			break;
273 		case Opt_gid:
274 			if (match_int(&args[0], &option))
275 				return -EINVAL;
276 			gid = make_kgid(current_user_ns(), option);
277 			if (!gid_valid(gid))
278 				return -EINVAL;
279 			opts->gid = gid;
280 			opts->setgid = 1;
281 			break;
282 		case Opt_mode:
283 			if (match_octal(&args[0], &option))
284 				return -EINVAL;
285 			opts->mode = option & S_IALLUGO;
286 			break;
287 		case Opt_ptmxmode:
288 			if (match_octal(&args[0], &option))
289 				return -EINVAL;
290 			opts->ptmxmode = option & S_IALLUGO;
291 			break;
292 		case Opt_newinstance:
293 			break;
294 		case Opt_max:
295 			if (match_int(&args[0], &option) ||
296 			    option < 0 || option > NR_UNIX98_PTY_MAX)
297 				return -EINVAL;
298 			opts->max = option;
299 			break;
300 		default:
301 			pr_err("called with bogus options\n");
302 			return -EINVAL;
303 		}
304 	}
305 
306 	return 0;
307 }
308 
309 static int mknod_ptmx(struct super_block *sb)
310 {
311 	int mode;
312 	int rc = -ENOMEM;
313 	struct dentry *dentry;
314 	struct inode *inode;
315 	struct dentry *root = sb->s_root;
316 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
317 	struct pts_mount_opts *opts = &fsi->mount_opts;
318 	kuid_t ptmx_uid = current_fsuid();
319 	kgid_t ptmx_gid = current_fsgid();
320 
321 	inode_lock(d_inode(root));
322 
323 	/* If we have already created ptmx node, return */
324 	if (fsi->ptmx_dentry) {
325 		rc = 0;
326 		goto out;
327 	}
328 
329 	dentry = d_alloc_name(root, "ptmx");
330 	if (!dentry) {
331 		pr_err("Unable to alloc dentry for ptmx node\n");
332 		goto out;
333 	}
334 
335 	/*
336 	 * Create a new 'ptmx' node in this mount of devpts.
337 	 */
338 	inode = new_inode(sb);
339 	if (!inode) {
340 		pr_err("Unable to alloc inode for ptmx node\n");
341 		dput(dentry);
342 		goto out;
343 	}
344 
345 	inode->i_ino = 2;
346 	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
347 
348 	mode = S_IFCHR|opts->ptmxmode;
349 	init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
350 	inode->i_uid = ptmx_uid;
351 	inode->i_gid = ptmx_gid;
352 
353 	d_add(dentry, inode);
354 
355 	fsi->ptmx_dentry = dentry;
356 	rc = 0;
357 out:
358 	inode_unlock(d_inode(root));
359 	return rc;
360 }
361 
362 static void update_ptmx_mode(struct pts_fs_info *fsi)
363 {
364 	struct inode *inode;
365 	if (fsi->ptmx_dentry) {
366 		inode = d_inode(fsi->ptmx_dentry);
367 		inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
368 	}
369 }
370 
371 static int devpts_remount(struct super_block *sb, int *flags, char *data)
372 {
373 	int err;
374 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
375 	struct pts_mount_opts *opts = &fsi->mount_opts;
376 
377 	err = parse_mount_options(data, PARSE_REMOUNT, opts);
378 
379 	/*
380 	 * parse_mount_options() restores options to default values
381 	 * before parsing and may have changed ptmxmode. So, update the
382 	 * mode in the inode too. Bogus options don't fail the remount,
383 	 * so do this even on error return.
384 	 */
385 	update_ptmx_mode(fsi);
386 
387 	return err;
388 }
389 
390 static int devpts_show_options(struct seq_file *seq, struct dentry *root)
391 {
392 	struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
393 	struct pts_mount_opts *opts = &fsi->mount_opts;
394 
395 	if (opts->setuid)
396 		seq_printf(seq, ",uid=%u",
397 			   from_kuid_munged(&init_user_ns, opts->uid));
398 	if (opts->setgid)
399 		seq_printf(seq, ",gid=%u",
400 			   from_kgid_munged(&init_user_ns, opts->gid));
401 	seq_printf(seq, ",mode=%03o", opts->mode);
402 	seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
403 	if (opts->max < NR_UNIX98_PTY_MAX)
404 		seq_printf(seq, ",max=%d", opts->max);
405 
406 	return 0;
407 }
408 
409 static const struct super_operations devpts_sops = {
410 	.statfs		= simple_statfs,
411 	.remount_fs	= devpts_remount,
412 	.show_options	= devpts_show_options,
413 };
414 
415 static void *new_pts_fs_info(struct super_block *sb)
416 {
417 	struct pts_fs_info *fsi;
418 
419 	fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
420 	if (!fsi)
421 		return NULL;
422 
423 	ida_init(&fsi->allocated_ptys);
424 	fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
425 	fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
426 	fsi->sb = sb;
427 
428 	return fsi;
429 }
430 
431 static int
432 devpts_fill_super(struct super_block *s, void *data, int silent)
433 {
434 	struct inode *inode;
435 	int error;
436 
437 	s->s_iflags &= ~SB_I_NODEV;
438 	s->s_blocksize = 1024;
439 	s->s_blocksize_bits = 10;
440 	s->s_magic = DEVPTS_SUPER_MAGIC;
441 	s->s_op = &devpts_sops;
442 	s->s_time_gran = 1;
443 
444 	error = -ENOMEM;
445 	s->s_fs_info = new_pts_fs_info(s);
446 	if (!s->s_fs_info)
447 		goto fail;
448 
449 	error = parse_mount_options(data, PARSE_MOUNT, &DEVPTS_SB(s)->mount_opts);
450 	if (error)
451 		goto fail;
452 
453 	error = -ENOMEM;
454 	inode = new_inode(s);
455 	if (!inode)
456 		goto fail;
457 	inode->i_ino = 1;
458 	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
459 	inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
460 	inode->i_op = &simple_dir_inode_operations;
461 	inode->i_fop = &simple_dir_operations;
462 	set_nlink(inode, 2);
463 
464 	s->s_root = d_make_root(inode);
465 	if (!s->s_root) {
466 		pr_err("get root dentry failed\n");
467 		goto fail;
468 	}
469 
470 	error = mknod_ptmx(s);
471 	if (error)
472 		goto fail_dput;
473 
474 	return 0;
475 fail_dput:
476 	dput(s->s_root);
477 	s->s_root = NULL;
478 fail:
479 	return error;
480 }
481 
482 /*
483  * devpts_mount()
484  *
485  *     Mount a new (private) instance of devpts.  PTYs created in this
486  *     instance are independent of the PTYs in other devpts instances.
487  */
488 static struct dentry *devpts_mount(struct file_system_type *fs_type,
489 	int flags, const char *dev_name, void *data)
490 {
491 	return mount_nodev(fs_type, flags, data, devpts_fill_super);
492 }
493 
494 static void devpts_kill_sb(struct super_block *sb)
495 {
496 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
497 
498 	if (fsi)
499 		ida_destroy(&fsi->allocated_ptys);
500 	kfree(fsi);
501 	kill_litter_super(sb);
502 }
503 
504 static struct file_system_type devpts_fs_type = {
505 	.name		= "devpts",
506 	.mount		= devpts_mount,
507 	.kill_sb	= devpts_kill_sb,
508 	.fs_flags	= FS_USERNS_MOUNT,
509 };
510 
511 /*
512  * The normal naming convention is simply /dev/pts/<number>; this conforms
513  * to the System V naming convention
514  */
515 
516 int devpts_new_index(struct pts_fs_info *fsi)
517 {
518 	int index;
519 	int ida_ret;
520 
521 retry:
522 	if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
523 		return -ENOMEM;
524 
525 	mutex_lock(&allocated_ptys_lock);
526 	if (pty_count >= (pty_limit -
527 			  (fsi->mount_opts.reserve ? 0 : pty_reserve))) {
528 		mutex_unlock(&allocated_ptys_lock);
529 		return -ENOSPC;
530 	}
531 
532 	ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
533 	if (ida_ret < 0) {
534 		mutex_unlock(&allocated_ptys_lock);
535 		if (ida_ret == -EAGAIN)
536 			goto retry;
537 		return -EIO;
538 	}
539 
540 	if (index >= fsi->mount_opts.max) {
541 		ida_remove(&fsi->allocated_ptys, index);
542 		mutex_unlock(&allocated_ptys_lock);
543 		return -ENOSPC;
544 	}
545 	pty_count++;
546 	mutex_unlock(&allocated_ptys_lock);
547 	return index;
548 }
549 
550 void devpts_kill_index(struct pts_fs_info *fsi, int idx)
551 {
552 	mutex_lock(&allocated_ptys_lock);
553 	ida_remove(&fsi->allocated_ptys, idx);
554 	pty_count--;
555 	mutex_unlock(&allocated_ptys_lock);
556 }
557 
558 /**
559  * devpts_pty_new -- create a new inode in /dev/pts/
560  * @ptmx_inode: inode of the master
561  * @device: major+minor of the node to be created
562  * @index: used as a name of the node
563  * @priv: what's given back by devpts_get_priv
564  *
565  * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
566  */
567 struct dentry *devpts_pty_new(struct pts_fs_info *fsi, int index, void *priv)
568 {
569 	struct dentry *dentry;
570 	struct super_block *sb = fsi->sb;
571 	struct inode *inode;
572 	struct dentry *root;
573 	struct pts_mount_opts *opts;
574 	char s[12];
575 
576 	root = sb->s_root;
577 	opts = &fsi->mount_opts;
578 
579 	inode = new_inode(sb);
580 	if (!inode)
581 		return ERR_PTR(-ENOMEM);
582 
583 	inode->i_ino = index + 3;
584 	inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
585 	inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
586 	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
587 	init_special_inode(inode, S_IFCHR|opts->mode, MKDEV(UNIX98_PTY_SLAVE_MAJOR, index));
588 
589 	sprintf(s, "%d", index);
590 
591 	dentry = d_alloc_name(root, s);
592 	if (dentry) {
593 		dentry->d_fsdata = priv;
594 		d_add(dentry, inode);
595 		fsnotify_create(d_inode(root), dentry);
596 	} else {
597 		iput(inode);
598 		dentry = ERR_PTR(-ENOMEM);
599 	}
600 
601 	return dentry;
602 }
603 
604 /**
605  * devpts_get_priv -- get private data for a slave
606  * @pts_inode: inode of the slave
607  *
608  * Returns whatever was passed as priv in devpts_pty_new for a given inode.
609  */
610 void *devpts_get_priv(struct dentry *dentry)
611 {
612 	if (dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC)
613 		return NULL;
614 	return dentry->d_fsdata;
615 }
616 
617 /**
618  * devpts_pty_kill -- remove inode form /dev/pts/
619  * @inode: inode of the slave to be removed
620  *
621  * This is an inverse operation of devpts_pty_new.
622  */
623 void devpts_pty_kill(struct dentry *dentry)
624 {
625 	WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);
626 
627 	dentry->d_fsdata = NULL;
628 	drop_nlink(dentry->d_inode);
629 	d_delete(dentry);
630 	dput(dentry);	/* d_alloc_name() in devpts_pty_new() */
631 }
632 
633 static int __init init_devpts_fs(void)
634 {
635 	int err = register_filesystem(&devpts_fs_type);
636 	if (!err) {
637 		register_sysctl_table(pty_root_table);
638 	}
639 	return err;
640 }
641 module_init(init_devpts_fs)
642