Line data Source code
1 : // SPDX-License-Identifier: GPL-2.0-or-later
2 : /* -*- linux-c -*- --------------------------------------------------------- *
3 : *
4 : * linux/fs/devpts/inode.c
5 : *
6 : * Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved
7 : *
8 : * ------------------------------------------------------------------------- */
9 :
10 : #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
11 :
12 : #include <linux/module.h>
13 : #include <linux/init.h>
14 : #include <linux/fs.h>
15 : #include <linux/sched.h>
16 : #include <linux/namei.h>
17 : #include <linux/slab.h>
18 : #include <linux/mount.h>
19 : #include <linux/tty.h>
20 : #include <linux/mutex.h>
21 : #include <linux/magic.h>
22 : #include <linux/idr.h>
23 : #include <linux/devpts_fs.h>
24 : #include <linux/parser.h>
25 : #include <linux/fsnotify.h>
26 : #include <linux/seq_file.h>
27 :
28 : #define DEVPTS_DEFAULT_MODE 0600
29 : /*
30 : * ptmx is a new node in /dev/pts and will be unused in legacy (single-
31 : * instance) mode. To prevent surprises in user space, set permissions of
32 : * ptmx to 0. Use 'chmod' or remount with '-o ptmxmode' to set meaningful
33 : * permissions.
34 : */
35 : #define DEVPTS_DEFAULT_PTMX_MODE 0000
36 : #define PTMX_MINOR 2
37 :
38 : /*
39 : * sysctl support for setting limits on the number of Unix98 ptys allocated.
40 : * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
41 : */
42 : static int pty_limit = NR_UNIX98_PTY_DEFAULT;
43 : static int pty_reserve = NR_UNIX98_PTY_RESERVE;
44 : static int pty_limit_min;
45 : static int pty_limit_max = INT_MAX;
46 : static atomic_t pty_count = ATOMIC_INIT(0);
47 :
48 : static struct ctl_table pty_table[] = {
49 : {
50 : .procname = "max",
51 : .maxlen = sizeof(int),
52 : .mode = 0644,
53 : .data = &pty_limit,
54 : .proc_handler = proc_dointvec_minmax,
55 : .extra1 = &pty_limit_min,
56 : .extra2 = &pty_limit_max,
57 : }, {
58 : .procname = "reserve",
59 : .maxlen = sizeof(int),
60 : .mode = 0644,
61 : .data = &pty_reserve,
62 : .proc_handler = proc_dointvec_minmax,
63 : .extra1 = &pty_limit_min,
64 : .extra2 = &pty_limit_max,
65 : }, {
66 : .procname = "nr",
67 : .maxlen = sizeof(int),
68 : .mode = 0444,
69 : .data = &pty_count,
70 : .proc_handler = proc_dointvec,
71 : },
72 : {}
73 : };
74 :
75 : struct pts_mount_opts {
76 : int setuid;
77 : int setgid;
78 : kuid_t uid;
79 : kgid_t gid;
80 : umode_t mode;
81 : umode_t ptmxmode;
82 : int reserve;
83 : int max;
84 : };
85 :
86 : enum {
87 : Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance, Opt_max,
88 : Opt_err
89 : };
90 :
91 : static const match_table_t tokens = {
92 : {Opt_uid, "uid=%u"},
93 : {Opt_gid, "gid=%u"},
94 : {Opt_mode, "mode=%o"},
95 : {Opt_ptmxmode, "ptmxmode=%o"},
96 : {Opt_newinstance, "newinstance"},
97 : {Opt_max, "max=%d"},
98 : {Opt_err, NULL}
99 : };
100 :
101 : struct pts_fs_info {
102 : struct ida allocated_ptys;
103 : struct pts_mount_opts mount_opts;
104 : struct super_block *sb;
105 : struct dentry *ptmx_dentry;
106 : };
107 :
108 : static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
109 : {
110 : return sb->s_fs_info;
111 : }
112 :
113 0 : static int devpts_ptmx_path(struct path *path)
114 : {
115 : struct super_block *sb;
116 : int err;
117 :
118 : /* Is a devpts filesystem at "pts" in the same directory? */
119 0 : err = path_pts(path);
120 0 : if (err)
121 : return err;
122 :
123 : /* Is the path the root of a devpts filesystem? */
124 0 : sb = path->mnt->mnt_sb;
125 0 : if ((sb->s_magic != DEVPTS_SUPER_MAGIC) ||
126 0 : (path->mnt->mnt_root != sb->s_root))
127 : return -ENODEV;
128 :
129 0 : return 0;
130 : }
131 :
132 : /*
133 : * Try to find a suitable devpts filesystem. We support the following
134 : * scenarios:
135 : * - The ptmx device node is located in the same directory as the devpts
136 : * mount where the pts device nodes are located.
137 : * This is e.g. the case when calling open on the /dev/pts/ptmx device
138 : * node when the devpts filesystem is mounted at /dev/pts.
139 : * - The ptmx device node is located outside the devpts filesystem mount
140 : * where the pts device nodes are located. For example, the ptmx device
141 : * is a symlink, separate device node, or bind-mount.
142 : * A supported scenario is bind-mounting /dev/pts/ptmx to /dev/ptmx and
143 : * then calling open on /dev/ptmx. In this case a suitable pts
144 : * subdirectory can be found in the common parent directory /dev of the
145 : * devpts mount and the ptmx bind-mount, after resolving the /dev/ptmx
146 : * bind-mount.
147 : * If no suitable pts subdirectory can be found this function will fail.
148 : * This is e.g. the case when bind-mounting /dev/pts/ptmx to /ptmx.
149 : */
150 0 : struct vfsmount *devpts_mntget(struct file *filp, struct pts_fs_info *fsi)
151 : {
152 : struct path path;
153 0 : int err = 0;
154 :
155 0 : path = filp->f_path;
156 0 : path_get(&path);
157 :
158 : /* Walk upward while the start point is a bind mount of
159 : * a single file.
160 : */
161 0 : while (path.mnt->mnt_root == path.dentry)
162 0 : if (follow_up(&path) == 0)
163 : break;
164 :
165 : /* devpts_ptmx_path() finds a devpts fs or returns an error. */
166 0 : if ((path.mnt->mnt_sb->s_magic != DEVPTS_SUPER_MAGIC) ||
167 0 : (DEVPTS_SB(path.mnt->mnt_sb) != fsi))
168 0 : err = devpts_ptmx_path(&path);
169 0 : dput(path.dentry);
170 0 : if (!err) {
171 0 : if (DEVPTS_SB(path.mnt->mnt_sb) == fsi)
172 : return path.mnt;
173 :
174 : err = -ENODEV;
175 : }
176 :
177 0 : mntput(path.mnt);
178 0 : return ERR_PTR(err);
179 : }
180 :
181 0 : struct pts_fs_info *devpts_acquire(struct file *filp)
182 : {
183 : struct pts_fs_info *result;
184 : struct path path;
185 : struct super_block *sb;
186 :
187 0 : path = filp->f_path;
188 0 : path_get(&path);
189 :
190 : /* Has the devpts filesystem already been found? */
191 0 : if (path.mnt->mnt_sb->s_magic != DEVPTS_SUPER_MAGIC) {
192 : int err;
193 :
194 0 : err = devpts_ptmx_path(&path);
195 0 : if (err) {
196 0 : result = ERR_PTR(err);
197 0 : goto out;
198 : }
199 : }
200 :
201 : /*
202 : * pty code needs to hold extra references in case of last /dev/tty close
203 : */
204 0 : sb = path.mnt->mnt_sb;
205 0 : atomic_inc(&sb->s_active);
206 0 : result = DEVPTS_SB(sb);
207 :
208 : out:
209 0 : path_put(&path);
210 0 : return result;
211 : }
212 :
213 0 : void devpts_release(struct pts_fs_info *fsi)
214 : {
215 0 : deactivate_super(fsi->sb);
216 0 : }
217 :
218 : #define PARSE_MOUNT 0
219 : #define PARSE_REMOUNT 1
220 :
221 : /*
222 : * parse_mount_options():
223 : * Set @opts to mount options specified in @data. If an option is not
224 : * specified in @data, set it to its default value.
225 : *
226 : * Note: @data may be NULL (in which case all options are set to default).
227 : */
228 0 : static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
229 : {
230 : char *p;
231 : kuid_t uid;
232 : kgid_t gid;
233 :
234 0 : opts->setuid = 0;
235 0 : opts->setgid = 0;
236 0 : opts->uid = GLOBAL_ROOT_UID;
237 0 : opts->gid = GLOBAL_ROOT_GID;
238 0 : opts->mode = DEVPTS_DEFAULT_MODE;
239 0 : opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
240 0 : opts->max = NR_UNIX98_PTY_MAX;
241 :
242 : /* Only allow instances mounted from the initial mount
243 : * namespace to tap the reserve pool of ptys.
244 : */
245 0 : if (op == PARSE_MOUNT)
246 0 : opts->reserve =
247 0 : (current->nsproxy->mnt_ns == init_task.nsproxy->mnt_ns);
248 :
249 0 : while ((p = strsep(&data, ",")) != NULL) {
250 : substring_t args[MAX_OPT_ARGS];
251 : int token;
252 : int option;
253 :
254 0 : if (!*p)
255 0 : continue;
256 :
257 0 : token = match_token(p, tokens, args);
258 0 : switch (token) {
259 : case Opt_uid:
260 0 : if (match_int(&args[0], &option))
261 0 : return -EINVAL;
262 0 : uid = make_kuid(current_user_ns(), option);
263 0 : if (!uid_valid(uid))
264 : return -EINVAL;
265 0 : opts->uid = uid;
266 0 : opts->setuid = 1;
267 0 : break;
268 : case Opt_gid:
269 0 : if (match_int(&args[0], &option))
270 : return -EINVAL;
271 0 : gid = make_kgid(current_user_ns(), option);
272 0 : if (!gid_valid(gid))
273 : return -EINVAL;
274 0 : opts->gid = gid;
275 0 : opts->setgid = 1;
276 0 : break;
277 : case Opt_mode:
278 0 : if (match_octal(&args[0], &option))
279 : return -EINVAL;
280 0 : opts->mode = option & S_IALLUGO;
281 0 : break;
282 : case Opt_ptmxmode:
283 0 : if (match_octal(&args[0], &option))
284 : return -EINVAL;
285 0 : opts->ptmxmode = option & S_IALLUGO;
286 0 : break;
287 : case Opt_newinstance:
288 : break;
289 : case Opt_max:
290 0 : if (match_int(&args[0], &option) ||
291 0 : option < 0 || option > NR_UNIX98_PTY_MAX)
292 : return -EINVAL;
293 0 : opts->max = option;
294 0 : break;
295 : default:
296 0 : pr_err("called with bogus options\n");
297 0 : return -EINVAL;
298 : }
299 : }
300 :
301 : return 0;
302 : }
303 :
304 0 : static int mknod_ptmx(struct super_block *sb)
305 : {
306 : int mode;
307 0 : int rc = -ENOMEM;
308 : struct dentry *dentry;
309 : struct inode *inode;
310 0 : struct dentry *root = sb->s_root;
311 0 : struct pts_fs_info *fsi = DEVPTS_SB(sb);
312 0 : struct pts_mount_opts *opts = &fsi->mount_opts;
313 0 : kuid_t ptmx_uid = current_fsuid();
314 0 : kgid_t ptmx_gid = current_fsgid();
315 :
316 0 : inode_lock(d_inode(root));
317 :
318 : /* If we have already created ptmx node, return */
319 0 : if (fsi->ptmx_dentry) {
320 : rc = 0;
321 : goto out;
322 : }
323 :
324 0 : dentry = d_alloc_name(root, "ptmx");
325 0 : if (!dentry) {
326 0 : pr_err("Unable to alloc dentry for ptmx node\n");
327 0 : goto out;
328 : }
329 :
330 : /*
331 : * Create a new 'ptmx' node in this mount of devpts.
332 : */
333 0 : inode = new_inode(sb);
334 0 : if (!inode) {
335 0 : pr_err("Unable to alloc inode for ptmx node\n");
336 0 : dput(dentry);
337 0 : goto out;
338 : }
339 :
340 0 : inode->i_ino = 2;
341 0 : inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
342 :
343 0 : mode = S_IFCHR|opts->ptmxmode;
344 0 : init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
345 0 : inode->i_uid = ptmx_uid;
346 0 : inode->i_gid = ptmx_gid;
347 :
348 0 : d_add(dentry, inode);
349 :
350 0 : fsi->ptmx_dentry = dentry;
351 0 : rc = 0;
352 : out:
353 0 : inode_unlock(d_inode(root));
354 0 : return rc;
355 : }
356 :
357 : static void update_ptmx_mode(struct pts_fs_info *fsi)
358 : {
359 : struct inode *inode;
360 0 : if (fsi->ptmx_dentry) {
361 0 : inode = d_inode(fsi->ptmx_dentry);
362 0 : inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
363 : }
364 : }
365 :
366 0 : static int devpts_remount(struct super_block *sb, int *flags, char *data)
367 : {
368 : int err;
369 0 : struct pts_fs_info *fsi = DEVPTS_SB(sb);
370 0 : struct pts_mount_opts *opts = &fsi->mount_opts;
371 :
372 0 : err = parse_mount_options(data, PARSE_REMOUNT, opts);
373 :
374 : /*
375 : * parse_mount_options() restores options to default values
376 : * before parsing and may have changed ptmxmode. So, update the
377 : * mode in the inode too. Bogus options don't fail the remount,
378 : * so do this even on error return.
379 : */
380 : update_ptmx_mode(fsi);
381 :
382 0 : return err;
383 : }
384 :
385 0 : static int devpts_show_options(struct seq_file *seq, struct dentry *root)
386 : {
387 0 : struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
388 0 : struct pts_mount_opts *opts = &fsi->mount_opts;
389 :
390 0 : if (opts->setuid)
391 0 : seq_printf(seq, ",uid=%u",
392 : from_kuid_munged(&init_user_ns, opts->uid));
393 0 : if (opts->setgid)
394 0 : seq_printf(seq, ",gid=%u",
395 : from_kgid_munged(&init_user_ns, opts->gid));
396 0 : seq_printf(seq, ",mode=%03o", opts->mode);
397 0 : seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
398 0 : if (opts->max < NR_UNIX98_PTY_MAX)
399 0 : seq_printf(seq, ",max=%d", opts->max);
400 :
401 0 : return 0;
402 : }
403 :
404 : static const struct super_operations devpts_sops = {
405 : .statfs = simple_statfs,
406 : .remount_fs = devpts_remount,
407 : .show_options = devpts_show_options,
408 : };
409 :
410 0 : static void *new_pts_fs_info(struct super_block *sb)
411 : {
412 : struct pts_fs_info *fsi;
413 :
414 0 : fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
415 0 : if (!fsi)
416 : return NULL;
417 :
418 0 : ida_init(&fsi->allocated_ptys);
419 0 : fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
420 0 : fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
421 0 : fsi->sb = sb;
422 :
423 0 : return fsi;
424 : }
425 :
426 : static int
427 0 : devpts_fill_super(struct super_block *s, void *data, int silent)
428 : {
429 : struct inode *inode;
430 : int error;
431 :
432 0 : s->s_iflags &= ~SB_I_NODEV;
433 0 : s->s_blocksize = 1024;
434 0 : s->s_blocksize_bits = 10;
435 0 : s->s_magic = DEVPTS_SUPER_MAGIC;
436 0 : s->s_op = &devpts_sops;
437 0 : s->s_d_op = &simple_dentry_operations;
438 0 : s->s_time_gran = 1;
439 :
440 0 : error = -ENOMEM;
441 0 : s->s_fs_info = new_pts_fs_info(s);
442 0 : if (!s->s_fs_info)
443 : goto fail;
444 :
445 0 : error = parse_mount_options(data, PARSE_MOUNT, &DEVPTS_SB(s)->mount_opts);
446 0 : if (error)
447 : goto fail;
448 :
449 0 : error = -ENOMEM;
450 0 : inode = new_inode(s);
451 0 : if (!inode)
452 : goto fail;
453 0 : inode->i_ino = 1;
454 0 : inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
455 0 : inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
456 0 : inode->i_op = &simple_dir_inode_operations;
457 0 : inode->i_fop = &simple_dir_operations;
458 0 : set_nlink(inode, 2);
459 :
460 0 : s->s_root = d_make_root(inode);
461 0 : if (!s->s_root) {
462 0 : pr_err("get root dentry failed\n");
463 0 : goto fail;
464 : }
465 :
466 0 : error = mknod_ptmx(s);
467 0 : if (error)
468 : goto fail_dput;
469 :
470 : return 0;
471 : fail_dput:
472 0 : dput(s->s_root);
473 0 : s->s_root = NULL;
474 : fail:
475 : return error;
476 : }
477 :
478 : /*
479 : * devpts_mount()
480 : *
481 : * Mount a new (private) instance of devpts. PTYs created in this
482 : * instance are independent of the PTYs in other devpts instances.
483 : */
484 0 : static struct dentry *devpts_mount(struct file_system_type *fs_type,
485 : int flags, const char *dev_name, void *data)
486 : {
487 0 : return mount_nodev(fs_type, flags, data, devpts_fill_super);
488 : }
489 :
490 0 : static void devpts_kill_sb(struct super_block *sb)
491 : {
492 0 : struct pts_fs_info *fsi = DEVPTS_SB(sb);
493 :
494 0 : if (fsi)
495 0 : ida_destroy(&fsi->allocated_ptys);
496 0 : kfree(fsi);
497 0 : kill_litter_super(sb);
498 0 : }
499 :
500 : static struct file_system_type devpts_fs_type = {
501 : .name = "devpts",
502 : .mount = devpts_mount,
503 : .kill_sb = devpts_kill_sb,
504 : .fs_flags = FS_USERNS_MOUNT,
505 : };
506 :
507 : /*
508 : * The normal naming convention is simply /dev/pts/<number>; this conforms
509 : * to the System V naming convention
510 : */
511 :
512 0 : int devpts_new_index(struct pts_fs_info *fsi)
513 : {
514 0 : int index = -ENOSPC;
515 :
516 0 : if (atomic_inc_return(&pty_count) >= (pty_limit -
517 0 : (fsi->mount_opts.reserve ? 0 : pty_reserve)))
518 : goto out;
519 :
520 0 : index = ida_alloc_max(&fsi->allocated_ptys, fsi->mount_opts.max - 1,
521 : GFP_KERNEL);
522 :
523 : out:
524 0 : if (index < 0)
525 : atomic_dec(&pty_count);
526 0 : return index;
527 : }
528 :
529 0 : void devpts_kill_index(struct pts_fs_info *fsi, int idx)
530 : {
531 0 : ida_free(&fsi->allocated_ptys, idx);
532 0 : atomic_dec(&pty_count);
533 0 : }
534 :
535 : /**
536 : * devpts_pty_new -- create a new inode in /dev/pts/
537 : * @ptmx_inode: inode of the master
538 : * @device: major+minor of the node to be created
539 : * @index: used as a name of the node
540 : * @priv: what's given back by devpts_get_priv
541 : *
542 : * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
543 : */
544 0 : struct dentry *devpts_pty_new(struct pts_fs_info *fsi, int index, void *priv)
545 : {
546 : struct dentry *dentry;
547 0 : struct super_block *sb = fsi->sb;
548 : struct inode *inode;
549 : struct dentry *root;
550 : struct pts_mount_opts *opts;
551 : char s[12];
552 :
553 0 : root = sb->s_root;
554 0 : opts = &fsi->mount_opts;
555 :
556 0 : inode = new_inode(sb);
557 0 : if (!inode)
558 : return ERR_PTR(-ENOMEM);
559 :
560 0 : inode->i_ino = index + 3;
561 0 : inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
562 0 : inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
563 0 : inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
564 0 : init_special_inode(inode, S_IFCHR|opts->mode, MKDEV(UNIX98_PTY_SLAVE_MAJOR, index));
565 :
566 0 : sprintf(s, "%d", index);
567 :
568 0 : dentry = d_alloc_name(root, s);
569 0 : if (dentry) {
570 0 : dentry->d_fsdata = priv;
571 0 : d_add(dentry, inode);
572 0 : fsnotify_create(d_inode(root), dentry);
573 : } else {
574 0 : iput(inode);
575 0 : dentry = ERR_PTR(-ENOMEM);
576 : }
577 :
578 : return dentry;
579 : }
580 :
581 : /**
582 : * devpts_get_priv -- get private data for a slave
583 : * @pts_inode: inode of the slave
584 : *
585 : * Returns whatever was passed as priv in devpts_pty_new for a given inode.
586 : */
587 0 : void *devpts_get_priv(struct dentry *dentry)
588 : {
589 0 : if (dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC)
590 : return NULL;
591 0 : return dentry->d_fsdata;
592 : }
593 :
594 : /**
595 : * devpts_pty_kill -- remove inode form /dev/pts/
596 : * @inode: inode of the slave to be removed
597 : *
598 : * This is an inverse operation of devpts_pty_new.
599 : */
600 0 : void devpts_pty_kill(struct dentry *dentry)
601 : {
602 0 : WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);
603 :
604 0 : dentry->d_fsdata = NULL;
605 0 : drop_nlink(dentry->d_inode);
606 0 : d_drop(dentry);
607 0 : fsnotify_unlink(d_inode(dentry->d_parent), dentry);
608 0 : dput(dentry); /* d_alloc_name() in devpts_pty_new() */
609 0 : }
610 :
611 1 : static int __init init_devpts_fs(void)
612 : {
613 1 : int err = register_filesystem(&devpts_fs_type);
614 1 : if (!err) {
615 1 : register_sysctl("kernel/pty", pty_table);
616 : }
617 1 : return err;
618 : }
619 : module_init(init_devpts_fs)
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