xref: /openbmc/linux/fs/devpts/inode.c (revision 311fc65c) 
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 	/* Has the devpts filesystem already been found? */
142 	if (path->mnt->mnt_sb->s_magic == DEVPTS_SUPER_MAGIC)
143 		return 0;
144 
145 	/* Is a devpts filesystem at "pts" in the same directory? */
146 	err = path_pts(path);
147 	if (err)
148 		return err;
149 
150 	/* Is the path the root of a devpts filesystem? */
151 	sb = path->mnt->mnt_sb;
152 	if ((sb->s_magic != DEVPTS_SUPER_MAGIC) ||
153 	    (path->mnt->mnt_root != sb->s_root))
154 		return -ENODEV;
155 
156 	return 0;
157 }
158 
159 struct vfsmount *devpts_mntget(struct file *filp, struct pts_fs_info *fsi)
160 {
161 	struct path path;
162 	int err;
163 
164 	path = filp->f_path;
165 	path_get(&path);
166 
167 	err = devpts_ptmx_path(&path);
168 	dput(path.dentry);
169 	if (err) {
170 		mntput(path.mnt);
171 		path.mnt = ERR_PTR(err);
172 	}
173 	if (DEVPTS_SB(path.mnt->mnt_sb) != fsi) {
174 		mntput(path.mnt);
175 		path.mnt = ERR_PTR(-ENODEV);
176 	}
177 	return path.mnt;
178 }
179 
180 struct pts_fs_info *devpts_acquire(struct file *filp)
181 {
182 	struct pts_fs_info *result;
183 	struct path path;
184 	struct super_block *sb;
185 	int err;
186 
187 	path = filp->f_path;
188 	path_get(&path);
189 
190 	err = devpts_ptmx_path(&path);
191 	if (err) {
192 		result = ERR_PTR(err);
193 		goto out;
194 	}
195 
196 	/*
197 	 * pty code needs to hold extra references in case of last /dev/tty close
198 	 */
199 	sb = path.mnt->mnt_sb;
200 	atomic_inc(&sb->s_active);
201 	result = DEVPTS_SB(sb);
202 
203 out:
204 	path_put(&path);
205 	return result;
206 }
207 
208 void devpts_release(struct pts_fs_info *fsi)
209 {
210 	deactivate_super(fsi->sb);
211 }
212 
213 #define PARSE_MOUNT	0
214 #define PARSE_REMOUNT	1
215 
216 /*
217  * parse_mount_options():
218  *	Set @opts to mount options specified in @data. If an option is not
219  *	specified in @data, set it to its default value.
220  *
221  * Note: @data may be NULL (in which case all options are set to default).
222  */
223 static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
224 {
225 	char *p;
226 	kuid_t uid;
227 	kgid_t gid;
228 
229 	opts->setuid  = 0;
230 	opts->setgid  = 0;
231 	opts->uid     = GLOBAL_ROOT_UID;
232 	opts->gid     = GLOBAL_ROOT_GID;
233 	opts->mode    = DEVPTS_DEFAULT_MODE;
234 	opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
235 	opts->max     = NR_UNIX98_PTY_MAX;
236 
237 	/* Only allow instances mounted from the initial mount
238 	 * namespace to tap the reserve pool of ptys.
239 	 */
240 	if (op == PARSE_MOUNT)
241 		opts->reserve =
242 			(current->nsproxy->mnt_ns == init_task.nsproxy->mnt_ns);
243 
244 	while ((p = strsep(&data, ",")) != NULL) {
245 		substring_t args[MAX_OPT_ARGS];
246 		int token;
247 		int option;
248 
249 		if (!*p)
250 			continue;
251 
252 		token = match_token(p, tokens, args);
253 		switch (token) {
254 		case Opt_uid:
255 			if (match_int(&args[0], &option))
256 				return -EINVAL;
257 			uid = make_kuid(current_user_ns(), option);
258 			if (!uid_valid(uid))
259 				return -EINVAL;
260 			opts->uid = uid;
261 			opts->setuid = 1;
262 			break;
263 		case Opt_gid:
264 			if (match_int(&args[0], &option))
265 				return -EINVAL;
266 			gid = make_kgid(current_user_ns(), option);
267 			if (!gid_valid(gid))
268 				return -EINVAL;
269 			opts->gid = gid;
270 			opts->setgid = 1;
271 			break;
272 		case Opt_mode:
273 			if (match_octal(&args[0], &option))
274 				return -EINVAL;
275 			opts->mode = option & S_IALLUGO;
276 			break;
277 		case Opt_ptmxmode:
278 			if (match_octal(&args[0], &option))
279 				return -EINVAL;
280 			opts->ptmxmode = option & S_IALLUGO;
281 			break;
282 		case Opt_newinstance:
283 			break;
284 		case Opt_max:
285 			if (match_int(&args[0], &option) ||
286 			    option < 0 || option > NR_UNIX98_PTY_MAX)
287 				return -EINVAL;
288 			opts->max = option;
289 			break;
290 		default:
291 			pr_err("called with bogus options\n");
292 			return -EINVAL;
293 		}
294 	}
295 
296 	return 0;
297 }
298 
299 static int mknod_ptmx(struct super_block *sb)
300 {
301 	int mode;
302 	int rc = -ENOMEM;
303 	struct dentry *dentry;
304 	struct inode *inode;
305 	struct dentry *root = sb->s_root;
306 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
307 	struct pts_mount_opts *opts = &fsi->mount_opts;
308 	kuid_t ptmx_uid = current_fsuid();
309 	kgid_t ptmx_gid = current_fsgid();
310 
311 	inode_lock(d_inode(root));
312 
313 	/* If we have already created ptmx node, return */
314 	if (fsi->ptmx_dentry) {
315 		rc = 0;
316 		goto out;
317 	}
318 
319 	dentry = d_alloc_name(root, "ptmx");
320 	if (!dentry) {
321 		pr_err("Unable to alloc dentry for ptmx node\n");
322 		goto out;
323 	}
324 
325 	/*
326 	 * Create a new 'ptmx' node in this mount of devpts.
327 	 */
328 	inode = new_inode(sb);
329 	if (!inode) {
330 		pr_err("Unable to alloc inode for ptmx node\n");
331 		dput(dentry);
332 		goto out;
333 	}
334 
335 	inode->i_ino = 2;
336 	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
337 
338 	mode = S_IFCHR|opts->ptmxmode;
339 	init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
340 	inode->i_uid = ptmx_uid;
341 	inode->i_gid = ptmx_gid;
342 
343 	d_add(dentry, inode);
344 
345 	fsi->ptmx_dentry = dentry;
346 	rc = 0;
347 out:
348 	inode_unlock(d_inode(root));
349 	return rc;
350 }
351 
352 static void update_ptmx_mode(struct pts_fs_info *fsi)
353 {
354 	struct inode *inode;
355 	if (fsi->ptmx_dentry) {
356 		inode = d_inode(fsi->ptmx_dentry);
357 		inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
358 	}
359 }
360 
361 static int devpts_remount(struct super_block *sb, int *flags, char *data)
362 {
363 	int err;
364 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
365 	struct pts_mount_opts *opts = &fsi->mount_opts;
366 
367 	err = parse_mount_options(data, PARSE_REMOUNT, opts);
368 
369 	/*
370 	 * parse_mount_options() restores options to default values
371 	 * before parsing and may have changed ptmxmode. So, update the
372 	 * mode in the inode too. Bogus options don't fail the remount,
373 	 * so do this even on error return.
374 	 */
375 	update_ptmx_mode(fsi);
376 
377 	return err;
378 }
379 
380 static int devpts_show_options(struct seq_file *seq, struct dentry *root)
381 {
382 	struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
383 	struct pts_mount_opts *opts = &fsi->mount_opts;
384 
385 	if (opts->setuid)
386 		seq_printf(seq, ",uid=%u",
387 			   from_kuid_munged(&init_user_ns, opts->uid));
388 	if (opts->setgid)
389 		seq_printf(seq, ",gid=%u",
390 			   from_kgid_munged(&init_user_ns, opts->gid));
391 	seq_printf(seq, ",mode=%03o", opts->mode);
392 	seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
393 	if (opts->max < NR_UNIX98_PTY_MAX)
394 		seq_printf(seq, ",max=%d", opts->max);
395 
396 	return 0;
397 }
398 
399 static const struct super_operations devpts_sops = {
400 	.statfs		= simple_statfs,
401 	.remount_fs	= devpts_remount,
402 	.show_options	= devpts_show_options,
403 };
404 
405 static void *new_pts_fs_info(struct super_block *sb)
406 {
407 	struct pts_fs_info *fsi;
408 
409 	fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
410 	if (!fsi)
411 		return NULL;
412 
413 	ida_init(&fsi->allocated_ptys);
414 	fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
415 	fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
416 	fsi->sb = sb;
417 
418 	return fsi;
419 }
420 
421 static int
422 devpts_fill_super(struct super_block *s, void *data, int silent)
423 {
424 	struct inode *inode;
425 	int error;
426 
427 	s->s_iflags &= ~SB_I_NODEV;
428 	s->s_blocksize = 1024;
429 	s->s_blocksize_bits = 10;
430 	s->s_magic = DEVPTS_SUPER_MAGIC;
431 	s->s_op = &devpts_sops;
432 	s->s_time_gran = 1;
433 
434 	error = -ENOMEM;
435 	s->s_fs_info = new_pts_fs_info(s);
436 	if (!s->s_fs_info)
437 		goto fail;
438 
439 	error = parse_mount_options(data, PARSE_MOUNT, &DEVPTS_SB(s)->mount_opts);
440 	if (error)
441 		goto fail;
442 
443 	error = -ENOMEM;
444 	inode = new_inode(s);
445 	if (!inode)
446 		goto fail;
447 	inode->i_ino = 1;
448 	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
449 	inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
450 	inode->i_op = &simple_dir_inode_operations;
451 	inode->i_fop = &simple_dir_operations;
452 	set_nlink(inode, 2);
453 
454 	s->s_root = d_make_root(inode);
455 	if (!s->s_root) {
456 		pr_err("get root dentry failed\n");
457 		goto fail;
458 	}
459 
460 	error = mknod_ptmx(s);
461 	if (error)
462 		goto fail_dput;
463 
464 	return 0;
465 fail_dput:
466 	dput(s->s_root);
467 	s->s_root = NULL;
468 fail:
469 	return error;
470 }
471 
472 /*
473  * devpts_mount()
474  *
475  *     Mount a new (private) instance of devpts.  PTYs created in this
476  *     instance are independent of the PTYs in other devpts instances.
477  */
478 static struct dentry *devpts_mount(struct file_system_type *fs_type,
479 	int flags, const char *dev_name, void *data)
480 {
481 	return mount_nodev(fs_type, flags, data, devpts_fill_super);
482 }
483 
484 static void devpts_kill_sb(struct super_block *sb)
485 {
486 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
487 
488 	if (fsi)
489 		ida_destroy(&fsi->allocated_ptys);
490 	kfree(fsi);
491 	kill_litter_super(sb);
492 }
493 
494 static struct file_system_type devpts_fs_type = {
495 	.name		= "devpts",
496 	.mount		= devpts_mount,
497 	.kill_sb	= devpts_kill_sb,
498 	.fs_flags	= FS_USERNS_MOUNT,
499 };
500 
501 /*
502  * The normal naming convention is simply /dev/pts/<number>; this conforms
503  * to the System V naming convention
504  */
505 
506 int devpts_new_index(struct pts_fs_info *fsi)
507 {
508 	int index;
509 	int ida_ret;
510 
511 retry:
512 	if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
513 		return -ENOMEM;
514 
515 	mutex_lock(&allocated_ptys_lock);
516 	if (pty_count >= (pty_limit -
517 			  (fsi->mount_opts.reserve ? 0 : pty_reserve))) {
518 		mutex_unlock(&allocated_ptys_lock);
519 		return -ENOSPC;
520 	}
521 
522 	ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
523 	if (ida_ret < 0) {
524 		mutex_unlock(&allocated_ptys_lock);
525 		if (ida_ret == -EAGAIN)
526 			goto retry;
527 		return -EIO;
528 	}
529 
530 	if (index >= fsi->mount_opts.max) {
531 		ida_remove(&fsi->allocated_ptys, index);
532 		mutex_unlock(&allocated_ptys_lock);
533 		return -ENOSPC;
534 	}
535 	pty_count++;
536 	mutex_unlock(&allocated_ptys_lock);
537 	return index;
538 }
539 
540 void devpts_kill_index(struct pts_fs_info *fsi, int idx)
541 {
542 	mutex_lock(&allocated_ptys_lock);
543 	ida_remove(&fsi->allocated_ptys, idx);
544 	pty_count--;
545 	mutex_unlock(&allocated_ptys_lock);
546 }
547 
548 /**
549  * devpts_pty_new -- create a new inode in /dev/pts/
550  * @ptmx_inode: inode of the master
551  * @device: major+minor of the node to be created
552  * @index: used as a name of the node
553  * @priv: what's given back by devpts_get_priv
554  *
555  * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
556  */
557 struct dentry *devpts_pty_new(struct pts_fs_info *fsi, int index, void *priv)
558 {
559 	struct dentry *dentry;
560 	struct super_block *sb = fsi->sb;
561 	struct inode *inode;
562 	struct dentry *root;
563 	struct pts_mount_opts *opts;
564 	char s[12];
565 
566 	root = sb->s_root;
567 	opts = &fsi->mount_opts;
568 
569 	inode = new_inode(sb);
570 	if (!inode)
571 		return ERR_PTR(-ENOMEM);
572 
573 	inode->i_ino = index + 3;
574 	inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
575 	inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
576 	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
577 	init_special_inode(inode, S_IFCHR|opts->mode, MKDEV(UNIX98_PTY_SLAVE_MAJOR, index));
578 
579 	sprintf(s, "%d", index);
580 
581 	dentry = d_alloc_name(root, s);
582 	if (dentry) {
583 		dentry->d_fsdata = priv;
584 		d_add(dentry, inode);
585 		fsnotify_create(d_inode(root), dentry);
586 	} else {
587 		iput(inode);
588 		dentry = ERR_PTR(-ENOMEM);
589 	}
590 
591 	return dentry;
592 }
593 
594 /**
595  * devpts_get_priv -- get private data for a slave
596  * @pts_inode: inode of the slave
597  *
598  * Returns whatever was passed as priv in devpts_pty_new for a given inode.
599  */
600 void *devpts_get_priv(struct dentry *dentry)
601 {
602 	if (dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC)
603 		return NULL;
604 	return dentry->d_fsdata;
605 }
606 
607 /**
608  * devpts_pty_kill -- remove inode form /dev/pts/
609  * @inode: inode of the slave to be removed
610  *
611  * This is an inverse operation of devpts_pty_new.
612  */
613 void devpts_pty_kill(struct dentry *dentry)
614 {
615 	WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);
616 
617 	dentry->d_fsdata = NULL;
618 	drop_nlink(dentry->d_inode);
619 	d_delete(dentry);
620 	dput(dentry);	/* d_alloc_name() in devpts_pty_new() */
621 }
622 
623 static int __init init_devpts_fs(void)
624 {
625 	int err = register_filesystem(&devpts_fs_type);
626 	if (!err) {
627 		register_sysctl_table(pty_root_table);
628 	}
629 	return err;
630 }
631 module_init(init_devpts_fs)
632