xref: /openbmc/linux/fs/devpts/inode.c (revision 7d71109d) 
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 	/* Has the devpts filesystem already been found? */
164 	if (path.mnt->mnt_sb->s_magic != DEVPTS_SUPER_MAGIC)
165 		err = devpts_ptmx_path(&path);
166 	dput(path.dentry);
167 	if (err) {
168 		mntput(path.mnt);
169 		return ERR_PTR(err);
170 	}
171 
172 	if (DEVPTS_SB(path.mnt->mnt_sb) != fsi) {
173 		mntput(path.mnt);
174 		return ERR_PTR(-ENODEV);
175 	}
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 
186 	path = filp->f_path;
187 	path_get(&path);
188 
189 	/* Has the devpts filesystem already been found? */
190 	if (path.mnt->mnt_sb->s_magic != DEVPTS_SUPER_MAGIC) {
191 		int err;
192 
193 		err = devpts_ptmx_path(&path);
194 		if (err) {
195 			result = ERR_PTR(err);
196 			goto out;
197 		}
198 	}
199 
200 	/*
201 	 * pty code needs to hold extra references in case of last /dev/tty close
202 	 */
203 	sb = path.mnt->mnt_sb;
204 	atomic_inc(&sb->s_active);
205 	result = DEVPTS_SB(sb);
206 
207 out:
208 	path_put(&path);
209 	return result;
210 }
211 
212 void devpts_release(struct pts_fs_info *fsi)
213 {
214 	deactivate_super(fsi->sb);
215 }
216 
217 #define PARSE_MOUNT	0
218 #define PARSE_REMOUNT	1
219 
220 /*
221  * parse_mount_options():
222  *	Set @opts to mount options specified in @data. If an option is not
223  *	specified in @data, set it to its default value.
224  *
225  * Note: @data may be NULL (in which case all options are set to default).
226  */
227 static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
228 {
229 	char *p;
230 	kuid_t uid;
231 	kgid_t gid;
232 
233 	opts->setuid  = 0;
234 	opts->setgid  = 0;
235 	opts->uid     = GLOBAL_ROOT_UID;
236 	opts->gid     = GLOBAL_ROOT_GID;
237 	opts->mode    = DEVPTS_DEFAULT_MODE;
238 	opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
239 	opts->max     = NR_UNIX98_PTY_MAX;
240 
241 	/* Only allow instances mounted from the initial mount
242 	 * namespace to tap the reserve pool of ptys.
243 	 */
244 	if (op == PARSE_MOUNT)
245 		opts->reserve =
246 			(current->nsproxy->mnt_ns == init_task.nsproxy->mnt_ns);
247 
248 	while ((p = strsep(&data, ",")) != NULL) {
249 		substring_t args[MAX_OPT_ARGS];
250 		int token;
251 		int option;
252 
253 		if (!*p)
254 			continue;
255 
256 		token = match_token(p, tokens, args);
257 		switch (token) {
258 		case Opt_uid:
259 			if (match_int(&args[0], &option))
260 				return -EINVAL;
261 			uid = make_kuid(current_user_ns(), option);
262 			if (!uid_valid(uid))
263 				return -EINVAL;
264 			opts->uid = uid;
265 			opts->setuid = 1;
266 			break;
267 		case Opt_gid:
268 			if (match_int(&args[0], &option))
269 				return -EINVAL;
270 			gid = make_kgid(current_user_ns(), option);
271 			if (!gid_valid(gid))
272 				return -EINVAL;
273 			opts->gid = gid;
274 			opts->setgid = 1;
275 			break;
276 		case Opt_mode:
277 			if (match_octal(&args[0], &option))
278 				return -EINVAL;
279 			opts->mode = option & S_IALLUGO;
280 			break;
281 		case Opt_ptmxmode:
282 			if (match_octal(&args[0], &option))
283 				return -EINVAL;
284 			opts->ptmxmode = option & S_IALLUGO;
285 			break;
286 		case Opt_newinstance:
287 			break;
288 		case Opt_max:
289 			if (match_int(&args[0], &option) ||
290 			    option < 0 || option > NR_UNIX98_PTY_MAX)
291 				return -EINVAL;
292 			opts->max = option;
293 			break;
294 		default:
295 			pr_err("called with bogus options\n");
296 			return -EINVAL;
297 		}
298 	}
299 
300 	return 0;
301 }
302 
303 static int mknod_ptmx(struct super_block *sb)
304 {
305 	int mode;
306 	int rc = -ENOMEM;
307 	struct dentry *dentry;
308 	struct inode *inode;
309 	struct dentry *root = sb->s_root;
310 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
311 	struct pts_mount_opts *opts = &fsi->mount_opts;
312 	kuid_t ptmx_uid = current_fsuid();
313 	kgid_t ptmx_gid = current_fsgid();
314 
315 	inode_lock(d_inode(root));
316 
317 	/* If we have already created ptmx node, return */
318 	if (fsi->ptmx_dentry) {
319 		rc = 0;
320 		goto out;
321 	}
322 
323 	dentry = d_alloc_name(root, "ptmx");
324 	if (!dentry) {
325 		pr_err("Unable to alloc dentry for ptmx node\n");
326 		goto out;
327 	}
328 
329 	/*
330 	 * Create a new 'ptmx' node in this mount of devpts.
331 	 */
332 	inode = new_inode(sb);
333 	if (!inode) {
334 		pr_err("Unable to alloc inode for ptmx node\n");
335 		dput(dentry);
336 		goto out;
337 	}
338 
339 	inode->i_ino = 2;
340 	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
341 
342 	mode = S_IFCHR|opts->ptmxmode;
343 	init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
344 	inode->i_uid = ptmx_uid;
345 	inode->i_gid = ptmx_gid;
346 
347 	d_add(dentry, inode);
348 
349 	fsi->ptmx_dentry = dentry;
350 	rc = 0;
351 out:
352 	inode_unlock(d_inode(root));
353 	return rc;
354 }
355 
356 static void update_ptmx_mode(struct pts_fs_info *fsi)
357 {
358 	struct inode *inode;
359 	if (fsi->ptmx_dentry) {
360 		inode = d_inode(fsi->ptmx_dentry);
361 		inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
362 	}
363 }
364 
365 static int devpts_remount(struct super_block *sb, int *flags, char *data)
366 {
367 	int err;
368 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
369 	struct pts_mount_opts *opts = &fsi->mount_opts;
370 
371 	err = parse_mount_options(data, PARSE_REMOUNT, opts);
372 
373 	/*
374 	 * parse_mount_options() restores options to default values
375 	 * before parsing and may have changed ptmxmode. So, update the
376 	 * mode in the inode too. Bogus options don't fail the remount,
377 	 * so do this even on error return.
378 	 */
379 	update_ptmx_mode(fsi);
380 
381 	return err;
382 }
383 
384 static int devpts_show_options(struct seq_file *seq, struct dentry *root)
385 {
386 	struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
387 	struct pts_mount_opts *opts = &fsi->mount_opts;
388 
389 	if (opts->setuid)
390 		seq_printf(seq, ",uid=%u",
391 			   from_kuid_munged(&init_user_ns, opts->uid));
392 	if (opts->setgid)
393 		seq_printf(seq, ",gid=%u",
394 			   from_kgid_munged(&init_user_ns, opts->gid));
395 	seq_printf(seq, ",mode=%03o", opts->mode);
396 	seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
397 	if (opts->max < NR_UNIX98_PTY_MAX)
398 		seq_printf(seq, ",max=%d", opts->max);
399 
400 	return 0;
401 }
402 
403 static const struct super_operations devpts_sops = {
404 	.statfs		= simple_statfs,
405 	.remount_fs	= devpts_remount,
406 	.show_options	= devpts_show_options,
407 };
408 
409 static void *new_pts_fs_info(struct super_block *sb)
410 {
411 	struct pts_fs_info *fsi;
412 
413 	fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
414 	if (!fsi)
415 		return NULL;
416 
417 	ida_init(&fsi->allocated_ptys);
418 	fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
419 	fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
420 	fsi->sb = sb;
421 
422 	return fsi;
423 }
424 
425 static int
426 devpts_fill_super(struct super_block *s, void *data, int silent)
427 {
428 	struct inode *inode;
429 	int error;
430 
431 	s->s_iflags &= ~SB_I_NODEV;
432 	s->s_blocksize = 1024;
433 	s->s_blocksize_bits = 10;
434 	s->s_magic = DEVPTS_SUPER_MAGIC;
435 	s->s_op = &devpts_sops;
436 	s->s_time_gran = 1;
437 
438 	error = -ENOMEM;
439 	s->s_fs_info = new_pts_fs_info(s);
440 	if (!s->s_fs_info)
441 		goto fail;
442 
443 	error = parse_mount_options(data, PARSE_MOUNT, &DEVPTS_SB(s)->mount_opts);
444 	if (error)
445 		goto fail;
446 
447 	error = -ENOMEM;
448 	inode = new_inode(s);
449 	if (!inode)
450 		goto fail;
451 	inode->i_ino = 1;
452 	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
453 	inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
454 	inode->i_op = &simple_dir_inode_operations;
455 	inode->i_fop = &simple_dir_operations;
456 	set_nlink(inode, 2);
457 
458 	s->s_root = d_make_root(inode);
459 	if (!s->s_root) {
460 		pr_err("get root dentry failed\n");
461 		goto fail;
462 	}
463 
464 	error = mknod_ptmx(s);
465 	if (error)
466 		goto fail_dput;
467 
468 	return 0;
469 fail_dput:
470 	dput(s->s_root);
471 	s->s_root = NULL;
472 fail:
473 	return error;
474 }
475 
476 /*
477  * devpts_mount()
478  *
479  *     Mount a new (private) instance of devpts.  PTYs created in this
480  *     instance are independent of the PTYs in other devpts instances.
481  */
482 static struct dentry *devpts_mount(struct file_system_type *fs_type,
483 	int flags, const char *dev_name, void *data)
484 {
485 	return mount_nodev(fs_type, flags, data, devpts_fill_super);
486 }
487 
488 static void devpts_kill_sb(struct super_block *sb)
489 {
490 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
491 
492 	if (fsi)
493 		ida_destroy(&fsi->allocated_ptys);
494 	kfree(fsi);
495 	kill_litter_super(sb);
496 }
497 
498 static struct file_system_type devpts_fs_type = {
499 	.name		= "devpts",
500 	.mount		= devpts_mount,
501 	.kill_sb	= devpts_kill_sb,
502 	.fs_flags	= FS_USERNS_MOUNT,
503 };
504 
505 /*
506  * The normal naming convention is simply /dev/pts/<number>; this conforms
507  * to the System V naming convention
508  */
509 
510 int devpts_new_index(struct pts_fs_info *fsi)
511 {
512 	int index;
513 	int ida_ret;
514 
515 retry:
516 	if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
517 		return -ENOMEM;
518 
519 	mutex_lock(&allocated_ptys_lock);
520 	if (pty_count >= (pty_limit -
521 			  (fsi->mount_opts.reserve ? 0 : pty_reserve))) {
522 		mutex_unlock(&allocated_ptys_lock);
523 		return -ENOSPC;
524 	}
525 
526 	ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
527 	if (ida_ret < 0) {
528 		mutex_unlock(&allocated_ptys_lock);
529 		if (ida_ret == -EAGAIN)
530 			goto retry;
531 		return -EIO;
532 	}
533 
534 	if (index >= fsi->mount_opts.max) {
535 		ida_remove(&fsi->allocated_ptys, index);
536 		mutex_unlock(&allocated_ptys_lock);
537 		return -ENOSPC;
538 	}
539 	pty_count++;
540 	mutex_unlock(&allocated_ptys_lock);
541 	return index;
542 }
543 
544 void devpts_kill_index(struct pts_fs_info *fsi, int idx)
545 {
546 	mutex_lock(&allocated_ptys_lock);
547 	ida_remove(&fsi->allocated_ptys, idx);
548 	pty_count--;
549 	mutex_unlock(&allocated_ptys_lock);
550 }
551 
552 /**
553  * devpts_pty_new -- create a new inode in /dev/pts/
554  * @ptmx_inode: inode of the master
555  * @device: major+minor of the node to be created
556  * @index: used as a name of the node
557  * @priv: what's given back by devpts_get_priv
558  *
559  * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
560  */
561 struct dentry *devpts_pty_new(struct pts_fs_info *fsi, int index, void *priv)
562 {
563 	struct dentry *dentry;
564 	struct super_block *sb = fsi->sb;
565 	struct inode *inode;
566 	struct dentry *root;
567 	struct pts_mount_opts *opts;
568 	char s[12];
569 
570 	root = sb->s_root;
571 	opts = &fsi->mount_opts;
572 
573 	inode = new_inode(sb);
574 	if (!inode)
575 		return ERR_PTR(-ENOMEM);
576 
577 	inode->i_ino = index + 3;
578 	inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
579 	inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
580 	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
581 	init_special_inode(inode, S_IFCHR|opts->mode, MKDEV(UNIX98_PTY_SLAVE_MAJOR, index));
582 
583 	sprintf(s, "%d", index);
584 
585 	dentry = d_alloc_name(root, s);
586 	if (dentry) {
587 		dentry->d_fsdata = priv;
588 		d_add(dentry, inode);
589 		fsnotify_create(d_inode(root), dentry);
590 	} else {
591 		iput(inode);
592 		dentry = ERR_PTR(-ENOMEM);
593 	}
594 
595 	return dentry;
596 }
597 
598 /**
599  * devpts_get_priv -- get private data for a slave
600  * @pts_inode: inode of the slave
601  *
602  * Returns whatever was passed as priv in devpts_pty_new for a given inode.
603  */
604 void *devpts_get_priv(struct dentry *dentry)
605 {
606 	if (dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC)
607 		return NULL;
608 	return dentry->d_fsdata;
609 }
610 
611 /**
612  * devpts_pty_kill -- remove inode form /dev/pts/
613  * @inode: inode of the slave to be removed
614  *
615  * This is an inverse operation of devpts_pty_new.
616  */
617 void devpts_pty_kill(struct dentry *dentry)
618 {
619 	WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);
620 
621 	dentry->d_fsdata = NULL;
622 	drop_nlink(dentry->d_inode);
623 	d_delete(dentry);
624 	dput(dentry);	/* d_alloc_name() in devpts_pty_new() */
625 }
626 
627 static int __init init_devpts_fs(void)
628 {
629 	int err = register_filesystem(&devpts_fs_type);
630 	if (!err) {
631 		register_sysctl_table(pty_root_table);
632 	}
633 	return err;
634 }
635 module_init(init_devpts_fs)
636