xref: /openbmc/linux/fs/devpts/inode.c (revision bc5aa3a0) 
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 struct pts_fs_info *devpts_acquire(struct file *filp)
137 {
138 	struct pts_fs_info *result;
139 	struct path path;
140 	struct super_block *sb;
141 	int err;
142 
143 	path = filp->f_path;
144 	path_get(&path);
145 
146 	/* Has the devpts filesystem already been found? */
147 	sb = path.mnt->mnt_sb;
148 	if (sb->s_magic != DEVPTS_SUPER_MAGIC) {
149 		/* Is a devpts filesystem at "pts" in the same directory? */
150 		err = path_pts(&path);
151 		if (err) {
152 			result = ERR_PTR(err);
153 			goto out;
154 		}
155 
156 		/* Is the path the root of a devpts filesystem? */
157 		result = ERR_PTR(-ENODEV);
158 		sb = path.mnt->mnt_sb;
159 		if ((sb->s_magic != DEVPTS_SUPER_MAGIC) ||
160 		    (path.mnt->mnt_root != sb->s_root))
161 			goto out;
162 	}
163 
164 	/*
165 	 * pty code needs to hold extra references in case of last /dev/tty close
166 	 */
167 	atomic_inc(&sb->s_active);
168 	result = DEVPTS_SB(sb);
169 
170 out:
171 	path_put(&path);
172 	return result;
173 }
174 
175 void devpts_release(struct pts_fs_info *fsi)
176 {
177 	deactivate_super(fsi->sb);
178 }
179 
180 #define PARSE_MOUNT	0
181 #define PARSE_REMOUNT	1
182 
183 /*
184  * parse_mount_options():
185  *	Set @opts to mount options specified in @data. If an option is not
186  *	specified in @data, set it to its default value.
187  *
188  * Note: @data may be NULL (in which case all options are set to default).
189  */
190 static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
191 {
192 	char *p;
193 	kuid_t uid;
194 	kgid_t gid;
195 
196 	opts->setuid  = 0;
197 	opts->setgid  = 0;
198 	opts->uid     = GLOBAL_ROOT_UID;
199 	opts->gid     = GLOBAL_ROOT_GID;
200 	opts->mode    = DEVPTS_DEFAULT_MODE;
201 	opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
202 	opts->max     = NR_UNIX98_PTY_MAX;
203 
204 	/* Only allow instances mounted from the initial mount
205 	 * namespace to tap the reserve pool of ptys.
206 	 */
207 	if (op == PARSE_MOUNT)
208 		opts->reserve =
209 			(current->nsproxy->mnt_ns == init_task.nsproxy->mnt_ns);
210 
211 	while ((p = strsep(&data, ",")) != NULL) {
212 		substring_t args[MAX_OPT_ARGS];
213 		int token;
214 		int option;
215 
216 		if (!*p)
217 			continue;
218 
219 		token = match_token(p, tokens, args);
220 		switch (token) {
221 		case Opt_uid:
222 			if (match_int(&args[0], &option))
223 				return -EINVAL;
224 			uid = make_kuid(current_user_ns(), option);
225 			if (!uid_valid(uid))
226 				return -EINVAL;
227 			opts->uid = uid;
228 			opts->setuid = 1;
229 			break;
230 		case Opt_gid:
231 			if (match_int(&args[0], &option))
232 				return -EINVAL;
233 			gid = make_kgid(current_user_ns(), option);
234 			if (!gid_valid(gid))
235 				return -EINVAL;
236 			opts->gid = gid;
237 			opts->setgid = 1;
238 			break;
239 		case Opt_mode:
240 			if (match_octal(&args[0], &option))
241 				return -EINVAL;
242 			opts->mode = option & S_IALLUGO;
243 			break;
244 		case Opt_ptmxmode:
245 			if (match_octal(&args[0], &option))
246 				return -EINVAL;
247 			opts->ptmxmode = option & S_IALLUGO;
248 			break;
249 		case Opt_newinstance:
250 			break;
251 		case Opt_max:
252 			if (match_int(&args[0], &option) ||
253 			    option < 0 || option > NR_UNIX98_PTY_MAX)
254 				return -EINVAL;
255 			opts->max = option;
256 			break;
257 		default:
258 			pr_err("called with bogus options\n");
259 			return -EINVAL;
260 		}
261 	}
262 
263 	return 0;
264 }
265 
266 static int mknod_ptmx(struct super_block *sb)
267 {
268 	int mode;
269 	int rc = -ENOMEM;
270 	struct dentry *dentry;
271 	struct inode *inode;
272 	struct dentry *root = sb->s_root;
273 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
274 	struct pts_mount_opts *opts = &fsi->mount_opts;
275 	kuid_t root_uid;
276 	kgid_t root_gid;
277 
278 	root_uid = make_kuid(current_user_ns(), 0);
279 	root_gid = make_kgid(current_user_ns(), 0);
280 	if (!uid_valid(root_uid) || !gid_valid(root_gid))
281 		return -EINVAL;
282 
283 	inode_lock(d_inode(root));
284 
285 	/* If we have already created ptmx node, return */
286 	if (fsi->ptmx_dentry) {
287 		rc = 0;
288 		goto out;
289 	}
290 
291 	dentry = d_alloc_name(root, "ptmx");
292 	if (!dentry) {
293 		pr_err("Unable to alloc dentry for ptmx node\n");
294 		goto out;
295 	}
296 
297 	/*
298 	 * Create a new 'ptmx' node in this mount of devpts.
299 	 */
300 	inode = new_inode(sb);
301 	if (!inode) {
302 		pr_err("Unable to alloc inode for ptmx node\n");
303 		dput(dentry);
304 		goto out;
305 	}
306 
307 	inode->i_ino = 2;
308 	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
309 
310 	mode = S_IFCHR|opts->ptmxmode;
311 	init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
312 	inode->i_uid = root_uid;
313 	inode->i_gid = root_gid;
314 
315 	d_add(dentry, inode);
316 
317 	fsi->ptmx_dentry = dentry;
318 	rc = 0;
319 out:
320 	inode_unlock(d_inode(root));
321 	return rc;
322 }
323 
324 static void update_ptmx_mode(struct pts_fs_info *fsi)
325 {
326 	struct inode *inode;
327 	if (fsi->ptmx_dentry) {
328 		inode = d_inode(fsi->ptmx_dentry);
329 		inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
330 	}
331 }
332 
333 static int devpts_remount(struct super_block *sb, int *flags, char *data)
334 {
335 	int err;
336 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
337 	struct pts_mount_opts *opts = &fsi->mount_opts;
338 
339 	sync_filesystem(sb);
340 	err = parse_mount_options(data, PARSE_REMOUNT, opts);
341 
342 	/*
343 	 * parse_mount_options() restores options to default values
344 	 * before parsing and may have changed ptmxmode. So, update the
345 	 * mode in the inode too. Bogus options don't fail the remount,
346 	 * so do this even on error return.
347 	 */
348 	update_ptmx_mode(fsi);
349 
350 	return err;
351 }
352 
353 static int devpts_show_options(struct seq_file *seq, struct dentry *root)
354 {
355 	struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
356 	struct pts_mount_opts *opts = &fsi->mount_opts;
357 
358 	if (opts->setuid)
359 		seq_printf(seq, ",uid=%u",
360 			   from_kuid_munged(&init_user_ns, opts->uid));
361 	if (opts->setgid)
362 		seq_printf(seq, ",gid=%u",
363 			   from_kgid_munged(&init_user_ns, opts->gid));
364 	seq_printf(seq, ",mode=%03o", opts->mode);
365 	seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
366 	if (opts->max < NR_UNIX98_PTY_MAX)
367 		seq_printf(seq, ",max=%d", opts->max);
368 
369 	return 0;
370 }
371 
372 static const struct super_operations devpts_sops = {
373 	.statfs		= simple_statfs,
374 	.remount_fs	= devpts_remount,
375 	.show_options	= devpts_show_options,
376 };
377 
378 static void *new_pts_fs_info(struct super_block *sb)
379 {
380 	struct pts_fs_info *fsi;
381 
382 	fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
383 	if (!fsi)
384 		return NULL;
385 
386 	ida_init(&fsi->allocated_ptys);
387 	fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
388 	fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
389 	fsi->sb = sb;
390 
391 	return fsi;
392 }
393 
394 static int
395 devpts_fill_super(struct super_block *s, void *data, int silent)
396 {
397 	struct inode *inode;
398 
399 	s->s_iflags &= ~SB_I_NODEV;
400 	s->s_blocksize = 1024;
401 	s->s_blocksize_bits = 10;
402 	s->s_magic = DEVPTS_SUPER_MAGIC;
403 	s->s_op = &devpts_sops;
404 	s->s_time_gran = 1;
405 
406 	s->s_fs_info = new_pts_fs_info(s);
407 	if (!s->s_fs_info)
408 		goto fail;
409 
410 	inode = new_inode(s);
411 	if (!inode)
412 		goto fail;
413 	inode->i_ino = 1;
414 	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
415 	inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
416 	inode->i_op = &simple_dir_inode_operations;
417 	inode->i_fop = &simple_dir_operations;
418 	set_nlink(inode, 2);
419 
420 	s->s_root = d_make_root(inode);
421 	if (s->s_root)
422 		return 0;
423 
424 	pr_err("get root dentry failed\n");
425 
426 fail:
427 	return -ENOMEM;
428 }
429 
430 /*
431  * devpts_mount()
432  *
433  *     Mount a new (private) instance of devpts.  PTYs created in this
434  *     instance are independent of the PTYs in other devpts instances.
435  */
436 static struct dentry *devpts_mount(struct file_system_type *fs_type,
437 	int flags, const char *dev_name, void *data)
438 {
439 	int error;
440 	struct pts_mount_opts opts;
441 	struct super_block *s;
442 
443 	error = parse_mount_options(data, PARSE_MOUNT, &opts);
444 	if (error)
445 		return ERR_PTR(error);
446 
447 	s = sget(fs_type, NULL, set_anon_super, flags, NULL);
448 	if (IS_ERR(s))
449 		return ERR_CAST(s);
450 
451 	if (!s->s_root) {
452 		error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
453 		if (error)
454 			goto out_undo_sget;
455 		s->s_flags |= MS_ACTIVE;
456 	}
457 
458 	memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts));
459 
460 	error = mknod_ptmx(s);
461 	if (error)
462 		goto out_undo_sget;
463 
464 	return dget(s->s_root);
465 
466 out_undo_sget:
467 	deactivate_locked_super(s);
468 	return ERR_PTR(error);
469 }
470 
471 static void devpts_kill_sb(struct super_block *sb)
472 {
473 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
474 
475 	ida_destroy(&fsi->allocated_ptys);
476 	kfree(fsi);
477 	kill_litter_super(sb);
478 }
479 
480 static struct file_system_type devpts_fs_type = {
481 	.name		= "devpts",
482 	.mount		= devpts_mount,
483 	.kill_sb	= devpts_kill_sb,
484 	.fs_flags	= FS_USERNS_MOUNT,
485 };
486 
487 /*
488  * The normal naming convention is simply /dev/pts/<number>; this conforms
489  * to the System V naming convention
490  */
491 
492 int devpts_new_index(struct pts_fs_info *fsi)
493 {
494 	int index;
495 	int ida_ret;
496 
497 retry:
498 	if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
499 		return -ENOMEM;
500 
501 	mutex_lock(&allocated_ptys_lock);
502 	if (pty_count >= (pty_limit -
503 			  (fsi->mount_opts.reserve ? 0 : pty_reserve))) {
504 		mutex_unlock(&allocated_ptys_lock);
505 		return -ENOSPC;
506 	}
507 
508 	ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
509 	if (ida_ret < 0) {
510 		mutex_unlock(&allocated_ptys_lock);
511 		if (ida_ret == -EAGAIN)
512 			goto retry;
513 		return -EIO;
514 	}
515 
516 	if (index >= fsi->mount_opts.max) {
517 		ida_remove(&fsi->allocated_ptys, index);
518 		mutex_unlock(&allocated_ptys_lock);
519 		return -ENOSPC;
520 	}
521 	pty_count++;
522 	mutex_unlock(&allocated_ptys_lock);
523 	return index;
524 }
525 
526 void devpts_kill_index(struct pts_fs_info *fsi, int idx)
527 {
528 	mutex_lock(&allocated_ptys_lock);
529 	ida_remove(&fsi->allocated_ptys, idx);
530 	pty_count--;
531 	mutex_unlock(&allocated_ptys_lock);
532 }
533 
534 /**
535  * devpts_pty_new -- create a new inode in /dev/pts/
536  * @ptmx_inode: inode of the master
537  * @device: major+minor of the node to be created
538  * @index: used as a name of the node
539  * @priv: what's given back by devpts_get_priv
540  *
541  * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
542  */
543 struct dentry *devpts_pty_new(struct pts_fs_info *fsi, int index, void *priv)
544 {
545 	struct dentry *dentry;
546 	struct super_block *sb = fsi->sb;
547 	struct inode *inode;
548 	struct dentry *root;
549 	struct pts_mount_opts *opts;
550 	char s[12];
551 
552 	root = sb->s_root;
553 	opts = &fsi->mount_opts;
554 
555 	inode = new_inode(sb);
556 	if (!inode)
557 		return ERR_PTR(-ENOMEM);
558 
559 	inode->i_ino = index + 3;
560 	inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
561 	inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
562 	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
563 	init_special_inode(inode, S_IFCHR|opts->mode, MKDEV(UNIX98_PTY_SLAVE_MAJOR, index));
564 
565 	sprintf(s, "%d", index);
566 
567 	dentry = d_alloc_name(root, s);
568 	if (dentry) {
569 		dentry->d_fsdata = priv;
570 		d_add(dentry, inode);
571 		fsnotify_create(d_inode(root), dentry);
572 	} else {
573 		iput(inode);
574 		dentry = ERR_PTR(-ENOMEM);
575 	}
576 
577 	return dentry;
578 }
579 
580 /**
581  * devpts_get_priv -- get private data for a slave
582  * @pts_inode: inode of the slave
583  *
584  * Returns whatever was passed as priv in devpts_pty_new for a given inode.
585  */
586 void *devpts_get_priv(struct dentry *dentry)
587 {
588 	if (dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC)
589 		return NULL;
590 	return dentry->d_fsdata;
591 }
592 
593 /**
594  * devpts_pty_kill -- remove inode form /dev/pts/
595  * @inode: inode of the slave to be removed
596  *
597  * This is an inverse operation of devpts_pty_new.
598  */
599 void devpts_pty_kill(struct dentry *dentry)
600 {
601 	WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);
602 
603 	dentry->d_fsdata = NULL;
604 	drop_nlink(dentry->d_inode);
605 	d_delete(dentry);
606 	dput(dentry);	/* d_alloc_name() in devpts_pty_new() */
607 }
608 
609 static int __init init_devpts_fs(void)
610 {
611 	int err = register_filesystem(&devpts_fs_type);
612 	if (!err) {
613 		register_sysctl_table(pty_root_table);
614 	}
615 	return err;
616 }
617 module_init(init_devpts_fs)
618