xref: /openbmc/linux/fs/devpts/inode.c (revision c8dbaa22) 
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, struct vfsmount **ptsmnt)
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 	*ptsmnt = NULL;
146 
147 	/* Has the devpts filesystem already been found? */
148 	sb = path.mnt->mnt_sb;
149 	if (sb->s_magic != DEVPTS_SUPER_MAGIC) {
150 		/* Is a devpts filesystem at "pts" in the same directory? */
151 		err = path_pts(&path);
152 		if (err) {
153 			result = ERR_PTR(err);
154 			goto out;
155 		}
156 
157 		/* Is the path the root of a devpts filesystem? */
158 		result = ERR_PTR(-ENODEV);
159 		sb = path.mnt->mnt_sb;
160 		if ((sb->s_magic != DEVPTS_SUPER_MAGIC) ||
161 		    (path.mnt->mnt_root != sb->s_root))
162 			goto out;
163 	}
164 
165 	/*
166 	 * pty code needs to hold extra references in case of last /dev/tty close
167 	 */
168 	atomic_inc(&sb->s_active);
169 	*ptsmnt = mntget(path.mnt);
170 	result = DEVPTS_SB(sb);
171 
172 out:
173 	path_put(&path);
174 	return result;
175 }
176 
177 void devpts_release(struct pts_fs_info *fsi)
178 {
179 	deactivate_super(fsi->sb);
180 }
181 
182 #define PARSE_MOUNT	0
183 #define PARSE_REMOUNT	1
184 
185 /*
186  * parse_mount_options():
187  *	Set @opts to mount options specified in @data. If an option is not
188  *	specified in @data, set it to its default value.
189  *
190  * Note: @data may be NULL (in which case all options are set to default).
191  */
192 static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
193 {
194 	char *p;
195 	kuid_t uid;
196 	kgid_t gid;
197 
198 	opts->setuid  = 0;
199 	opts->setgid  = 0;
200 	opts->uid     = GLOBAL_ROOT_UID;
201 	opts->gid     = GLOBAL_ROOT_GID;
202 	opts->mode    = DEVPTS_DEFAULT_MODE;
203 	opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
204 	opts->max     = NR_UNIX98_PTY_MAX;
205 
206 	/* Only allow instances mounted from the initial mount
207 	 * namespace to tap the reserve pool of ptys.
208 	 */
209 	if (op == PARSE_MOUNT)
210 		opts->reserve =
211 			(current->nsproxy->mnt_ns == init_task.nsproxy->mnt_ns);
212 
213 	while ((p = strsep(&data, ",")) != NULL) {
214 		substring_t args[MAX_OPT_ARGS];
215 		int token;
216 		int option;
217 
218 		if (!*p)
219 			continue;
220 
221 		token = match_token(p, tokens, args);
222 		switch (token) {
223 		case Opt_uid:
224 			if (match_int(&args[0], &option))
225 				return -EINVAL;
226 			uid = make_kuid(current_user_ns(), option);
227 			if (!uid_valid(uid))
228 				return -EINVAL;
229 			opts->uid = uid;
230 			opts->setuid = 1;
231 			break;
232 		case Opt_gid:
233 			if (match_int(&args[0], &option))
234 				return -EINVAL;
235 			gid = make_kgid(current_user_ns(), option);
236 			if (!gid_valid(gid))
237 				return -EINVAL;
238 			opts->gid = gid;
239 			opts->setgid = 1;
240 			break;
241 		case Opt_mode:
242 			if (match_octal(&args[0], &option))
243 				return -EINVAL;
244 			opts->mode = option & S_IALLUGO;
245 			break;
246 		case Opt_ptmxmode:
247 			if (match_octal(&args[0], &option))
248 				return -EINVAL;
249 			opts->ptmxmode = option & S_IALLUGO;
250 			break;
251 		case Opt_newinstance:
252 			break;
253 		case Opt_max:
254 			if (match_int(&args[0], &option) ||
255 			    option < 0 || option > NR_UNIX98_PTY_MAX)
256 				return -EINVAL;
257 			opts->max = option;
258 			break;
259 		default:
260 			pr_err("called with bogus options\n");
261 			return -EINVAL;
262 		}
263 	}
264 
265 	return 0;
266 }
267 
268 static int mknod_ptmx(struct super_block *sb)
269 {
270 	int mode;
271 	int rc = -ENOMEM;
272 	struct dentry *dentry;
273 	struct inode *inode;
274 	struct dentry *root = sb->s_root;
275 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
276 	struct pts_mount_opts *opts = &fsi->mount_opts;
277 	kuid_t ptmx_uid = current_fsuid();
278 	kgid_t ptmx_gid = current_fsgid();
279 
280 	inode_lock(d_inode(root));
281 
282 	/* If we have already created ptmx node, return */
283 	if (fsi->ptmx_dentry) {
284 		rc = 0;
285 		goto out;
286 	}
287 
288 	dentry = d_alloc_name(root, "ptmx");
289 	if (!dentry) {
290 		pr_err("Unable to alloc dentry for ptmx node\n");
291 		goto out;
292 	}
293 
294 	/*
295 	 * Create a new 'ptmx' node in this mount of devpts.
296 	 */
297 	inode = new_inode(sb);
298 	if (!inode) {
299 		pr_err("Unable to alloc inode for ptmx node\n");
300 		dput(dentry);
301 		goto out;
302 	}
303 
304 	inode->i_ino = 2;
305 	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
306 
307 	mode = S_IFCHR|opts->ptmxmode;
308 	init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
309 	inode->i_uid = ptmx_uid;
310 	inode->i_gid = ptmx_gid;
311 
312 	d_add(dentry, inode);
313 
314 	fsi->ptmx_dentry = dentry;
315 	rc = 0;
316 out:
317 	inode_unlock(d_inode(root));
318 	return rc;
319 }
320 
321 static void update_ptmx_mode(struct pts_fs_info *fsi)
322 {
323 	struct inode *inode;
324 	if (fsi->ptmx_dentry) {
325 		inode = d_inode(fsi->ptmx_dentry);
326 		inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
327 	}
328 }
329 
330 static int devpts_remount(struct super_block *sb, int *flags, char *data)
331 {
332 	int err;
333 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
334 	struct pts_mount_opts *opts = &fsi->mount_opts;
335 
336 	err = parse_mount_options(data, PARSE_REMOUNT, opts);
337 
338 	/*
339 	 * parse_mount_options() restores options to default values
340 	 * before parsing and may have changed ptmxmode. So, update the
341 	 * mode in the inode too. Bogus options don't fail the remount,
342 	 * so do this even on error return.
343 	 */
344 	update_ptmx_mode(fsi);
345 
346 	return err;
347 }
348 
349 static int devpts_show_options(struct seq_file *seq, struct dentry *root)
350 {
351 	struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
352 	struct pts_mount_opts *opts = &fsi->mount_opts;
353 
354 	if (opts->setuid)
355 		seq_printf(seq, ",uid=%u",
356 			   from_kuid_munged(&init_user_ns, opts->uid));
357 	if (opts->setgid)
358 		seq_printf(seq, ",gid=%u",
359 			   from_kgid_munged(&init_user_ns, opts->gid));
360 	seq_printf(seq, ",mode=%03o", opts->mode);
361 	seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
362 	if (opts->max < NR_UNIX98_PTY_MAX)
363 		seq_printf(seq, ",max=%d", opts->max);
364 
365 	return 0;
366 }
367 
368 static const struct super_operations devpts_sops = {
369 	.statfs		= simple_statfs,
370 	.remount_fs	= devpts_remount,
371 	.show_options	= devpts_show_options,
372 };
373 
374 static void *new_pts_fs_info(struct super_block *sb)
375 {
376 	struct pts_fs_info *fsi;
377 
378 	fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
379 	if (!fsi)
380 		return NULL;
381 
382 	ida_init(&fsi->allocated_ptys);
383 	fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
384 	fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
385 	fsi->sb = sb;
386 
387 	return fsi;
388 }
389 
390 static int
391 devpts_fill_super(struct super_block *s, void *data, int silent)
392 {
393 	struct inode *inode;
394 	int error;
395 
396 	s->s_iflags &= ~SB_I_NODEV;
397 	s->s_blocksize = 1024;
398 	s->s_blocksize_bits = 10;
399 	s->s_magic = DEVPTS_SUPER_MAGIC;
400 	s->s_op = &devpts_sops;
401 	s->s_time_gran = 1;
402 
403 	error = -ENOMEM;
404 	s->s_fs_info = new_pts_fs_info(s);
405 	if (!s->s_fs_info)
406 		goto fail;
407 
408 	error = parse_mount_options(data, PARSE_MOUNT, &DEVPTS_SB(s)->mount_opts);
409 	if (error)
410 		goto fail;
411 
412 	error = -ENOMEM;
413 	inode = new_inode(s);
414 	if (!inode)
415 		goto fail;
416 	inode->i_ino = 1;
417 	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
418 	inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
419 	inode->i_op = &simple_dir_inode_operations;
420 	inode->i_fop = &simple_dir_operations;
421 	set_nlink(inode, 2);
422 
423 	s->s_root = d_make_root(inode);
424 	if (!s->s_root) {
425 		pr_err("get root dentry failed\n");
426 		goto fail;
427 	}
428 
429 	error = mknod_ptmx(s);
430 	if (error)
431 		goto fail_dput;
432 
433 	return 0;
434 fail_dput:
435 	dput(s->s_root);
436 	s->s_root = NULL;
437 fail:
438 	return error;
439 }
440 
441 /*
442  * devpts_mount()
443  *
444  *     Mount a new (private) instance of devpts.  PTYs created in this
445  *     instance are independent of the PTYs in other devpts instances.
446  */
447 static struct dentry *devpts_mount(struct file_system_type *fs_type,
448 	int flags, const char *dev_name, void *data)
449 {
450 	return mount_nodev(fs_type, flags, data, devpts_fill_super);
451 }
452 
453 static void devpts_kill_sb(struct super_block *sb)
454 {
455 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
456 
457 	if (fsi)
458 		ida_destroy(&fsi->allocated_ptys);
459 	kfree(fsi);
460 	kill_litter_super(sb);
461 }
462 
463 static struct file_system_type devpts_fs_type = {
464 	.name		= "devpts",
465 	.mount		= devpts_mount,
466 	.kill_sb	= devpts_kill_sb,
467 	.fs_flags	= FS_USERNS_MOUNT,
468 };
469 
470 /*
471  * The normal naming convention is simply /dev/pts/<number>; this conforms
472  * to the System V naming convention
473  */
474 
475 int devpts_new_index(struct pts_fs_info *fsi)
476 {
477 	int index;
478 	int ida_ret;
479 
480 retry:
481 	if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
482 		return -ENOMEM;
483 
484 	mutex_lock(&allocated_ptys_lock);
485 	if (pty_count >= (pty_limit -
486 			  (fsi->mount_opts.reserve ? 0 : pty_reserve))) {
487 		mutex_unlock(&allocated_ptys_lock);
488 		return -ENOSPC;
489 	}
490 
491 	ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
492 	if (ida_ret < 0) {
493 		mutex_unlock(&allocated_ptys_lock);
494 		if (ida_ret == -EAGAIN)
495 			goto retry;
496 		return -EIO;
497 	}
498 
499 	if (index >= fsi->mount_opts.max) {
500 		ida_remove(&fsi->allocated_ptys, index);
501 		mutex_unlock(&allocated_ptys_lock);
502 		return -ENOSPC;
503 	}
504 	pty_count++;
505 	mutex_unlock(&allocated_ptys_lock);
506 	return index;
507 }
508 
509 void devpts_kill_index(struct pts_fs_info *fsi, int idx)
510 {
511 	mutex_lock(&allocated_ptys_lock);
512 	ida_remove(&fsi->allocated_ptys, idx);
513 	pty_count--;
514 	mutex_unlock(&allocated_ptys_lock);
515 }
516 
517 /**
518  * devpts_pty_new -- create a new inode in /dev/pts/
519  * @ptmx_inode: inode of the master
520  * @device: major+minor of the node to be created
521  * @index: used as a name of the node
522  * @priv: what's given back by devpts_get_priv
523  *
524  * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
525  */
526 struct dentry *devpts_pty_new(struct pts_fs_info *fsi, int index, void *priv)
527 {
528 	struct dentry *dentry;
529 	struct super_block *sb = fsi->sb;
530 	struct inode *inode;
531 	struct dentry *root;
532 	struct pts_mount_opts *opts;
533 	char s[12];
534 
535 	root = sb->s_root;
536 	opts = &fsi->mount_opts;
537 
538 	inode = new_inode(sb);
539 	if (!inode)
540 		return ERR_PTR(-ENOMEM);
541 
542 	inode->i_ino = index + 3;
543 	inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
544 	inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
545 	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
546 	init_special_inode(inode, S_IFCHR|opts->mode, MKDEV(UNIX98_PTY_SLAVE_MAJOR, index));
547 
548 	sprintf(s, "%d", index);
549 
550 	dentry = d_alloc_name(root, s);
551 	if (dentry) {
552 		dentry->d_fsdata = priv;
553 		d_add(dentry, inode);
554 		fsnotify_create(d_inode(root), dentry);
555 	} else {
556 		iput(inode);
557 		dentry = ERR_PTR(-ENOMEM);
558 	}
559 
560 	return dentry;
561 }
562 
563 /**
564  * devpts_get_priv -- get private data for a slave
565  * @pts_inode: inode of the slave
566  *
567  * Returns whatever was passed as priv in devpts_pty_new for a given inode.
568  */
569 void *devpts_get_priv(struct dentry *dentry)
570 {
571 	if (dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC)
572 		return NULL;
573 	return dentry->d_fsdata;
574 }
575 
576 /**
577  * devpts_pty_kill -- remove inode form /dev/pts/
578  * @inode: inode of the slave to be removed
579  *
580  * This is an inverse operation of devpts_pty_new.
581  */
582 void devpts_pty_kill(struct dentry *dentry)
583 {
584 	WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);
585 
586 	dentry->d_fsdata = NULL;
587 	drop_nlink(dentry->d_inode);
588 	d_delete(dentry);
589 	dput(dentry);	/* d_alloc_name() in devpts_pty_new() */
590 }
591 
592 static int __init init_devpts_fs(void)
593 {
594 	int err = register_filesystem(&devpts_fs_type);
595 	if (!err) {
596 		register_sysctl_table(pty_root_table);
597 	}
598 	return err;
599 }
600 module_init(init_devpts_fs)
601