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>
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
35 #define DEVPTS_DEFAULT_PTMX_MODE 0000
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[] = {
51 .maxlen = sizeof(int),
54 .proc_handler = proc_dointvec_minmax,
55 .extra1 = &pty_limit_min,
56 .extra2 = &pty_limit_max,
58 .procname = "reserve",
59 .maxlen = sizeof(int),
62 .proc_handler = proc_dointvec_minmax,
63 .extra1 = &pty_limit_min,
64 .extra2 = &pty_limit_max,
67 .maxlen = sizeof(int),
70 .proc_handler = proc_dointvec,
75 struct pts_mount_opts {
87 Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance, Opt_max,
91 static const match_table_t tokens = {
94 {Opt_mode, "mode=%o"},
95 {Opt_ptmxmode, "ptmxmode=%o"},
96 {Opt_newinstance, "newinstance"},
102 struct ida allocated_ptys;
103 struct pts_mount_opts mount_opts;
104 struct super_block *sb;
105 struct dentry *ptmx_dentry;
108 static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
110 return sb->s_fs_info;
113 static int devpts_ptmx_path(struct path *path)
115 struct super_block *sb;
118 /* Is a devpts filesystem at "pts" in the same directory? */
119 err = path_pts(path);
123 /* Is the path the root of a devpts filesystem? */
124 sb = path->mnt->mnt_sb;
125 if ((sb->s_magic != DEVPTS_SUPER_MAGIC) ||
126 (path->mnt->mnt_root != sb->s_root))
133 * Try to find a suitable devpts filesystem. We support the following
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
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.
150 struct vfsmount *devpts_mntget(struct file *filp, struct pts_fs_info *fsi)
158 /* Walk upward while the start point is a bind mount of
161 while (path.mnt->mnt_root == path.dentry)
162 if (follow_up(&path) == 0)
165 /* devpts_ptmx_path() finds a devpts fs or returns an error. */
166 if ((path.mnt->mnt_sb->s_magic != DEVPTS_SUPER_MAGIC) ||
167 (DEVPTS_SB(path.mnt->mnt_sb) != fsi))
168 err = devpts_ptmx_path(&path);
171 if (DEVPTS_SB(path.mnt->mnt_sb) == fsi)
181 struct pts_fs_info *devpts_acquire(struct file *filp)
183 struct pts_fs_info *result;
185 struct super_block *sb;
190 /* Has the devpts filesystem already been found? */
191 if (path.mnt->mnt_sb->s_magic != DEVPTS_SUPER_MAGIC) {
194 err = devpts_ptmx_path(&path);
196 result = ERR_PTR(err);
202 * pty code needs to hold extra references in case of last /dev/tty close
204 sb = path.mnt->mnt_sb;
205 atomic_inc(&sb->s_active);
206 result = DEVPTS_SB(sb);
213 void devpts_release(struct pts_fs_info *fsi)
215 deactivate_super(fsi->sb);
218 #define PARSE_MOUNT 0
219 #define PARSE_REMOUNT 1
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.
226 * Note: @data may be NULL (in which case all options are set to default).
228 static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
236 opts->uid = GLOBAL_ROOT_UID;
237 opts->gid = GLOBAL_ROOT_GID;
238 opts->mode = DEVPTS_DEFAULT_MODE;
239 opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
240 opts->max = NR_UNIX98_PTY_MAX;
242 /* Only allow instances mounted from the initial mount
243 * namespace to tap the reserve pool of ptys.
245 if (op == PARSE_MOUNT)
247 (current->nsproxy->mnt_ns == init_task.nsproxy->mnt_ns);
249 while ((p = strsep(&data, ",")) != NULL) {
250 substring_t args[MAX_OPT_ARGS];
257 token = match_token(p, tokens, args);
260 if (match_int(&args[0], &option))
262 uid = make_kuid(current_user_ns(), option);
269 if (match_int(&args[0], &option))
271 gid = make_kgid(current_user_ns(), option);
278 if (match_octal(&args[0], &option))
280 opts->mode = option & S_IALLUGO;
283 if (match_octal(&args[0], &option))
285 opts->ptmxmode = option & S_IALLUGO;
287 case Opt_newinstance:
290 if (match_int(&args[0], &option) ||
291 option < 0 || option > NR_UNIX98_PTY_MAX)
296 pr_err("called with bogus options\n");
304 static int mknod_ptmx(struct super_block *sb)
308 struct dentry *dentry;
310 struct dentry *root = sb->s_root;
311 struct pts_fs_info *fsi = DEVPTS_SB(sb);
312 struct pts_mount_opts *opts = &fsi->mount_opts;
313 kuid_t ptmx_uid = current_fsuid();
314 kgid_t ptmx_gid = current_fsgid();
316 inode_lock(d_inode(root));
318 /* If we have already created ptmx node, return */
319 if (fsi->ptmx_dentry) {
324 dentry = d_alloc_name(root, "ptmx");
326 pr_err("Unable to alloc dentry for ptmx node\n");
331 * Create a new 'ptmx' node in this mount of devpts.
333 inode = new_inode(sb);
335 pr_err("Unable to alloc inode for ptmx node\n");
341 inode->i_mtime = inode->i_atime = inode_set_ctime_current(inode);
343 mode = S_IFCHR|opts->ptmxmode;
344 init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
345 inode->i_uid = ptmx_uid;
346 inode->i_gid = ptmx_gid;
348 d_add(dentry, inode);
350 fsi->ptmx_dentry = dentry;
353 inode_unlock(d_inode(root));
357 static void update_ptmx_mode(struct pts_fs_info *fsi)
360 if (fsi->ptmx_dentry) {
361 inode = d_inode(fsi->ptmx_dentry);
362 inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
366 static int devpts_remount(struct super_block *sb, int *flags, char *data)
369 struct pts_fs_info *fsi = DEVPTS_SB(sb);
370 struct pts_mount_opts *opts = &fsi->mount_opts;
372 err = parse_mount_options(data, PARSE_REMOUNT, opts);
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.
380 update_ptmx_mode(fsi);
385 static int devpts_show_options(struct seq_file *seq, struct dentry *root)
387 struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
388 struct pts_mount_opts *opts = &fsi->mount_opts;
391 seq_printf(seq, ",uid=%u",
392 from_kuid_munged(&init_user_ns, opts->uid));
394 seq_printf(seq, ",gid=%u",
395 from_kgid_munged(&init_user_ns, opts->gid));
396 seq_printf(seq, ",mode=%03o", opts->mode);
397 seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
398 if (opts->max < NR_UNIX98_PTY_MAX)
399 seq_printf(seq, ",max=%d", opts->max);
404 static const struct super_operations devpts_sops = {
405 .statfs = simple_statfs,
406 .remount_fs = devpts_remount,
407 .show_options = devpts_show_options,
410 static void *new_pts_fs_info(struct super_block *sb)
412 struct pts_fs_info *fsi;
414 fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
418 ida_init(&fsi->allocated_ptys);
419 fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
420 fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
427 devpts_fill_super(struct super_block *s, void *data, int silent)
432 s->s_iflags &= ~SB_I_NODEV;
433 s->s_blocksize = 1024;
434 s->s_blocksize_bits = 10;
435 s->s_magic = DEVPTS_SUPER_MAGIC;
436 s->s_op = &devpts_sops;
437 s->s_d_op = &simple_dentry_operations;
441 s->s_fs_info = new_pts_fs_info(s);
445 error = parse_mount_options(data, PARSE_MOUNT, &DEVPTS_SB(s)->mount_opts);
450 inode = new_inode(s);
454 inode->i_mtime = inode->i_atime = inode_set_ctime_current(inode);
455 inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
456 inode->i_op = &simple_dir_inode_operations;
457 inode->i_fop = &simple_dir_operations;
460 s->s_root = d_make_root(inode);
462 pr_err("get root dentry failed\n");
466 error = mknod_ptmx(s);
481 * Mount a new (private) instance of devpts. PTYs created in this
482 * instance are independent of the PTYs in other devpts instances.
484 static struct dentry *devpts_mount(struct file_system_type *fs_type,
485 int flags, const char *dev_name, void *data)
487 return mount_nodev(fs_type, flags, data, devpts_fill_super);
490 static void devpts_kill_sb(struct super_block *sb)
492 struct pts_fs_info *fsi = DEVPTS_SB(sb);
495 ida_destroy(&fsi->allocated_ptys);
497 kill_litter_super(sb);
500 static struct file_system_type devpts_fs_type = {
502 .mount = devpts_mount,
503 .kill_sb = devpts_kill_sb,
504 .fs_flags = FS_USERNS_MOUNT,
508 * The normal naming convention is simply /dev/pts/<number>; this conforms
509 * to the System V naming convention
512 int devpts_new_index(struct pts_fs_info *fsi)
516 if (atomic_inc_return(&pty_count) >= (pty_limit -
517 (fsi->mount_opts.reserve ? 0 : pty_reserve)))
520 index = ida_alloc_max(&fsi->allocated_ptys, fsi->mount_opts.max - 1,
525 atomic_dec(&pty_count);
529 void devpts_kill_index(struct pts_fs_info *fsi, int idx)
531 ida_free(&fsi->allocated_ptys, idx);
532 atomic_dec(&pty_count);
536 * devpts_pty_new -- create a new inode in /dev/pts/
537 * @fsi: Filesystem info for this instance.
538 * @index: used as a name of the node
539 * @priv: what's given back by devpts_get_priv
541 * The dentry for the created inode is returned.
542 * Remove it from /dev/pts/ with devpts_pty_kill().
544 struct dentry *devpts_pty_new(struct pts_fs_info *fsi, int index, void *priv)
546 struct dentry *dentry;
547 struct super_block *sb = fsi->sb;
550 struct pts_mount_opts *opts;
554 opts = &fsi->mount_opts;
556 inode = new_inode(sb);
558 return ERR_PTR(-ENOMEM);
560 inode->i_ino = index + 3;
561 inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
562 inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
563 inode->i_mtime = inode->i_atime = inode_set_ctime_current(inode);
564 init_special_inode(inode, S_IFCHR|opts->mode, MKDEV(UNIX98_PTY_SLAVE_MAJOR, index));
566 sprintf(s, "%d", index);
568 dentry = d_alloc_name(root, s);
570 dentry->d_fsdata = priv;
571 d_add(dentry, inode);
572 fsnotify_create(d_inode(root), dentry);
575 dentry = ERR_PTR(-ENOMEM);
582 * devpts_get_priv -- get private data for a slave
583 * @dentry: dentry of the slave
585 * Returns whatever was passed as priv in devpts_pty_new for a given inode.
587 void *devpts_get_priv(struct dentry *dentry)
589 if (dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC)
591 return dentry->d_fsdata;
595 * devpts_pty_kill -- remove inode form /dev/pts/
596 * @dentry: dentry of the slave to be removed
598 * This is an inverse operation of devpts_pty_new.
600 void devpts_pty_kill(struct dentry *dentry)
602 WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);
604 dentry->d_fsdata = NULL;
605 drop_nlink(dentry->d_inode);
607 fsnotify_unlink(d_inode(dentry->d_parent), dentry);
608 dput(dentry); /* d_alloc_name() in devpts_pty_new() */
611 static int __init init_devpts_fs(void)
613 int err = register_filesystem(&devpts_fs_type);
615 register_sysctl("kernel/pty", pty_table);
619 module_init(init_devpts_fs)