Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
[linux/fpc-iii.git] / fs / devpts / inode.c
blob42e5a766d33c7d1fea3ca9c05be73639c38c421e
1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* -*- linux-c -*- --------------------------------------------------------- *
4 * linux/fs/devpts/inode.c
6 * Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved
8 * ------------------------------------------------------------------------- */
10 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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>
28 #define DEVPTS_DEFAULT_MODE 0600
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.
35 #define DEVPTS_DEFAULT_PTMX_MODE 0000
36 #define PTMX_MINOR 2
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.
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);
48 static struct ctl_table pty_table[] = {
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,
75 static struct ctl_table pty_kern_table[] = {
77 .procname = "pty",
78 .mode = 0555,
79 .child = pty_table,
84 static struct ctl_table pty_root_table[] = {
86 .procname = "kernel",
87 .mode = 0555,
88 .child = pty_kern_table,
93 struct pts_mount_opts {
94 int setuid;
95 int setgid;
96 kuid_t uid;
97 kgid_t gid;
98 umode_t mode;
99 umode_t ptmxmode;
100 int reserve;
101 int max;
104 enum {
105 Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance, Opt_max,
106 Opt_err
109 static const match_table_t tokens = {
110 {Opt_uid, "uid=%u"},
111 {Opt_gid, "gid=%u"},
112 {Opt_mode, "mode=%o"},
113 {Opt_ptmxmode, "ptmxmode=%o"},
114 {Opt_newinstance, "newinstance"},
115 {Opt_max, "max=%d"},
116 {Opt_err, NULL}
119 struct pts_fs_info {
120 struct ida allocated_ptys;
121 struct pts_mount_opts mount_opts;
122 struct super_block *sb;
123 struct dentry *ptmx_dentry;
126 static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
128 return sb->s_fs_info;
131 static int devpts_ptmx_path(struct path *path)
133 struct super_block *sb;
134 int err;
136 /* Is a devpts filesystem at "pts" in the same directory? */
137 err = path_pts(path);
138 if (err)
139 return err;
141 /* Is the path the root of a devpts filesystem? */
142 sb = path->mnt->mnt_sb;
143 if ((sb->s_magic != DEVPTS_SUPER_MAGIC) ||
144 (path->mnt->mnt_root != sb->s_root))
145 return -ENODEV;
147 return 0;
151 * Try to find a suitable devpts filesystem. We support the following
152 * scenarios:
153 * - The ptmx device node is located in the same directory as the devpts
154 * mount where the pts device nodes are located.
155 * This is e.g. the case when calling open on the /dev/pts/ptmx device
156 * node when the devpts filesystem is mounted at /dev/pts.
157 * - The ptmx device node is located outside the devpts filesystem mount
158 * where the pts device nodes are located. For example, the ptmx device
159 * is a symlink, separate device node, or bind-mount.
160 * A supported scenario is bind-mounting /dev/pts/ptmx to /dev/ptmx and
161 * then calling open on /dev/ptmx. In this case a suitable pts
162 * subdirectory can be found in the common parent directory /dev of the
163 * devpts mount and the ptmx bind-mount, after resolving the /dev/ptmx
164 * bind-mount.
165 * If no suitable pts subdirectory can be found this function will fail.
166 * This is e.g. the case when bind-mounting /dev/pts/ptmx to /ptmx.
168 struct vfsmount *devpts_mntget(struct file *filp, struct pts_fs_info *fsi)
170 struct path path;
171 int err = 0;
173 path = filp->f_path;
174 path_get(&path);
176 /* Walk upward while the start point is a bind mount of
177 * a single file.
179 while (path.mnt->mnt_root == path.dentry)
180 if (follow_up(&path) == 0)
181 break;
183 /* devpts_ptmx_path() finds a devpts fs or returns an error. */
184 if ((path.mnt->mnt_sb->s_magic != DEVPTS_SUPER_MAGIC) ||
185 (DEVPTS_SB(path.mnt->mnt_sb) != fsi))
186 err = devpts_ptmx_path(&path);
187 dput(path.dentry);
188 if (!err) {
189 if (DEVPTS_SB(path.mnt->mnt_sb) == fsi)
190 return path.mnt;
192 err = -ENODEV;
195 mntput(path.mnt);
196 return ERR_PTR(err);
199 struct pts_fs_info *devpts_acquire(struct file *filp)
201 struct pts_fs_info *result;
202 struct path path;
203 struct super_block *sb;
205 path = filp->f_path;
206 path_get(&path);
208 /* Has the devpts filesystem already been found? */
209 if (path.mnt->mnt_sb->s_magic != DEVPTS_SUPER_MAGIC) {
210 int err;
212 err = devpts_ptmx_path(&path);
213 if (err) {
214 result = ERR_PTR(err);
215 goto out;
220 * pty code needs to hold extra references in case of last /dev/tty close
222 sb = path.mnt->mnt_sb;
223 atomic_inc(&sb->s_active);
224 result = DEVPTS_SB(sb);
226 out:
227 path_put(&path);
228 return result;
231 void devpts_release(struct pts_fs_info *fsi)
233 deactivate_super(fsi->sb);
236 #define PARSE_MOUNT 0
237 #define PARSE_REMOUNT 1
240 * parse_mount_options():
241 * Set @opts to mount options specified in @data. If an option is not
242 * specified in @data, set it to its default value.
244 * Note: @data may be NULL (in which case all options are set to default).
246 static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
248 char *p;
249 kuid_t uid;
250 kgid_t gid;
252 opts->setuid = 0;
253 opts->setgid = 0;
254 opts->uid = GLOBAL_ROOT_UID;
255 opts->gid = GLOBAL_ROOT_GID;
256 opts->mode = DEVPTS_DEFAULT_MODE;
257 opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
258 opts->max = NR_UNIX98_PTY_MAX;
260 /* Only allow instances mounted from the initial mount
261 * namespace to tap the reserve pool of ptys.
263 if (op == PARSE_MOUNT)
264 opts->reserve =
265 (current->nsproxy->mnt_ns == init_task.nsproxy->mnt_ns);
267 while ((p = strsep(&data, ",")) != NULL) {
268 substring_t args[MAX_OPT_ARGS];
269 int token;
270 int option;
272 if (!*p)
273 continue;
275 token = match_token(p, tokens, args);
276 switch (token) {
277 case Opt_uid:
278 if (match_int(&args[0], &option))
279 return -EINVAL;
280 uid = make_kuid(current_user_ns(), option);
281 if (!uid_valid(uid))
282 return -EINVAL;
283 opts->uid = uid;
284 opts->setuid = 1;
285 break;
286 case Opt_gid:
287 if (match_int(&args[0], &option))
288 return -EINVAL;
289 gid = make_kgid(current_user_ns(), option);
290 if (!gid_valid(gid))
291 return -EINVAL;
292 opts->gid = gid;
293 opts->setgid = 1;
294 break;
295 case Opt_mode:
296 if (match_octal(&args[0], &option))
297 return -EINVAL;
298 opts->mode = option & S_IALLUGO;
299 break;
300 case Opt_ptmxmode:
301 if (match_octal(&args[0], &option))
302 return -EINVAL;
303 opts->ptmxmode = option & S_IALLUGO;
304 break;
305 case Opt_newinstance:
306 break;
307 case Opt_max:
308 if (match_int(&args[0], &option) ||
309 option < 0 || option > NR_UNIX98_PTY_MAX)
310 return -EINVAL;
311 opts->max = option;
312 break;
313 default:
314 pr_err("called with bogus options\n");
315 return -EINVAL;
319 return 0;
322 static int mknod_ptmx(struct super_block *sb)
324 int mode;
325 int rc = -ENOMEM;
326 struct dentry *dentry;
327 struct inode *inode;
328 struct dentry *root = sb->s_root;
329 struct pts_fs_info *fsi = DEVPTS_SB(sb);
330 struct pts_mount_opts *opts = &fsi->mount_opts;
331 kuid_t ptmx_uid = current_fsuid();
332 kgid_t ptmx_gid = current_fsgid();
334 inode_lock(d_inode(root));
336 /* If we have already created ptmx node, return */
337 if (fsi->ptmx_dentry) {
338 rc = 0;
339 goto out;
342 dentry = d_alloc_name(root, "ptmx");
343 if (!dentry) {
344 pr_err("Unable to alloc dentry for ptmx node\n");
345 goto out;
349 * Create a new 'ptmx' node in this mount of devpts.
351 inode = new_inode(sb);
352 if (!inode) {
353 pr_err("Unable to alloc inode for ptmx node\n");
354 dput(dentry);
355 goto out;
358 inode->i_ino = 2;
359 inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
361 mode = S_IFCHR|opts->ptmxmode;
362 init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
363 inode->i_uid = ptmx_uid;
364 inode->i_gid = ptmx_gid;
366 d_add(dentry, inode);
368 fsi->ptmx_dentry = dentry;
369 rc = 0;
370 out:
371 inode_unlock(d_inode(root));
372 return rc;
375 static void update_ptmx_mode(struct pts_fs_info *fsi)
377 struct inode *inode;
378 if (fsi->ptmx_dentry) {
379 inode = d_inode(fsi->ptmx_dentry);
380 inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
384 static int devpts_remount(struct super_block *sb, int *flags, char *data)
386 int err;
387 struct pts_fs_info *fsi = DEVPTS_SB(sb);
388 struct pts_mount_opts *opts = &fsi->mount_opts;
390 err = parse_mount_options(data, PARSE_REMOUNT, opts);
393 * parse_mount_options() restores options to default values
394 * before parsing and may have changed ptmxmode. So, update the
395 * mode in the inode too. Bogus options don't fail the remount,
396 * so do this even on error return.
398 update_ptmx_mode(fsi);
400 return err;
403 static int devpts_show_options(struct seq_file *seq, struct dentry *root)
405 struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
406 struct pts_mount_opts *opts = &fsi->mount_opts;
408 if (opts->setuid)
409 seq_printf(seq, ",uid=%u",
410 from_kuid_munged(&init_user_ns, opts->uid));
411 if (opts->setgid)
412 seq_printf(seq, ",gid=%u",
413 from_kgid_munged(&init_user_ns, opts->gid));
414 seq_printf(seq, ",mode=%03o", opts->mode);
415 seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
416 if (opts->max < NR_UNIX98_PTY_MAX)
417 seq_printf(seq, ",max=%d", opts->max);
419 return 0;
422 static const struct super_operations devpts_sops = {
423 .statfs = simple_statfs,
424 .remount_fs = devpts_remount,
425 .show_options = devpts_show_options,
428 static void *new_pts_fs_info(struct super_block *sb)
430 struct pts_fs_info *fsi;
432 fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
433 if (!fsi)
434 return NULL;
436 ida_init(&fsi->allocated_ptys);
437 fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
438 fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
439 fsi->sb = sb;
441 return fsi;
444 static int
445 devpts_fill_super(struct super_block *s, void *data, int silent)
447 struct inode *inode;
448 int error;
450 s->s_iflags &= ~SB_I_NODEV;
451 s->s_blocksize = 1024;
452 s->s_blocksize_bits = 10;
453 s->s_magic = DEVPTS_SUPER_MAGIC;
454 s->s_op = &devpts_sops;
455 s->s_d_op = &simple_dentry_operations;
456 s->s_time_gran = 1;
458 error = -ENOMEM;
459 s->s_fs_info = new_pts_fs_info(s);
460 if (!s->s_fs_info)
461 goto fail;
463 error = parse_mount_options(data, PARSE_MOUNT, &DEVPTS_SB(s)->mount_opts);
464 if (error)
465 goto fail;
467 error = -ENOMEM;
468 inode = new_inode(s);
469 if (!inode)
470 goto fail;
471 inode->i_ino = 1;
472 inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
473 inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
474 inode->i_op = &simple_dir_inode_operations;
475 inode->i_fop = &simple_dir_operations;
476 set_nlink(inode, 2);
478 s->s_root = d_make_root(inode);
479 if (!s->s_root) {
480 pr_err("get root dentry failed\n");
481 goto fail;
484 error = mknod_ptmx(s);
485 if (error)
486 goto fail_dput;
488 return 0;
489 fail_dput:
490 dput(s->s_root);
491 s->s_root = NULL;
492 fail:
493 return error;
497 * devpts_mount()
499 * Mount a new (private) instance of devpts. PTYs created in this
500 * instance are independent of the PTYs in other devpts instances.
502 static struct dentry *devpts_mount(struct file_system_type *fs_type,
503 int flags, const char *dev_name, void *data)
505 return mount_nodev(fs_type, flags, data, devpts_fill_super);
508 static void devpts_kill_sb(struct super_block *sb)
510 struct pts_fs_info *fsi = DEVPTS_SB(sb);
512 if (fsi)
513 ida_destroy(&fsi->allocated_ptys);
514 kfree(fsi);
515 kill_litter_super(sb);
518 static struct file_system_type devpts_fs_type = {
519 .name = "devpts",
520 .mount = devpts_mount,
521 .kill_sb = devpts_kill_sb,
522 .fs_flags = FS_USERNS_MOUNT,
526 * The normal naming convention is simply /dev/pts/<number>; this conforms
527 * to the System V naming convention
530 int devpts_new_index(struct pts_fs_info *fsi)
532 int index = -ENOSPC;
534 if (atomic_inc_return(&pty_count) >= (pty_limit -
535 (fsi->mount_opts.reserve ? 0 : pty_reserve)))
536 goto out;
538 index = ida_alloc_max(&fsi->allocated_ptys, fsi->mount_opts.max - 1,
539 GFP_KERNEL);
541 out:
542 if (index < 0)
543 atomic_dec(&pty_count);
544 return index;
547 void devpts_kill_index(struct pts_fs_info *fsi, int idx)
549 ida_free(&fsi->allocated_ptys, idx);
550 atomic_dec(&pty_count);
554 * devpts_pty_new -- create a new inode in /dev/pts/
555 * @ptmx_inode: inode of the master
556 * @device: major+minor of the node to be created
557 * @index: used as a name of the node
558 * @priv: what's given back by devpts_get_priv
560 * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
562 struct dentry *devpts_pty_new(struct pts_fs_info *fsi, int index, void *priv)
564 struct dentry *dentry;
565 struct super_block *sb = fsi->sb;
566 struct inode *inode;
567 struct dentry *root;
568 struct pts_mount_opts *opts;
569 char s[12];
571 root = sb->s_root;
572 opts = &fsi->mount_opts;
574 inode = new_inode(sb);
575 if (!inode)
576 return ERR_PTR(-ENOMEM);
578 inode->i_ino = index + 3;
579 inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
580 inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
581 inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
582 init_special_inode(inode, S_IFCHR|opts->mode, MKDEV(UNIX98_PTY_SLAVE_MAJOR, index));
584 sprintf(s, "%d", index);
586 dentry = d_alloc_name(root, s);
587 if (dentry) {
588 dentry->d_fsdata = priv;
589 d_add(dentry, inode);
590 fsnotify_create(d_inode(root), dentry);
591 } else {
592 iput(inode);
593 dentry = ERR_PTR(-ENOMEM);
596 return dentry;
600 * devpts_get_priv -- get private data for a slave
601 * @pts_inode: inode of the slave
603 * Returns whatever was passed as priv in devpts_pty_new for a given inode.
605 void *devpts_get_priv(struct dentry *dentry)
607 if (dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC)
608 return NULL;
609 return dentry->d_fsdata;
613 * devpts_pty_kill -- remove inode form /dev/pts/
614 * @inode: inode of the slave to be removed
616 * This is an inverse operation of devpts_pty_new.
618 void devpts_pty_kill(struct dentry *dentry)
620 WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);
622 dentry->d_fsdata = NULL;
623 drop_nlink(dentry->d_inode);
624 fsnotify_unlink(d_inode(dentry->d_parent), dentry);
625 d_drop(dentry);
626 dput(dentry); /* d_alloc_name() in devpts_pty_new() */
629 static int __init init_devpts_fs(void)
631 int err = register_filesystem(&devpts_fs_type);
632 if (!err) {
633 register_sysctl_table(pty_root_table);
635 return err;
637 module_init(init_devpts_fs)