1 /* -*- linux-c -*- --------------------------------------------------------- *
3 * linux/fs/devpts/inode.c
5 * Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved
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.
11 * ------------------------------------------------------------------------- */
13 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
15 #include <linux/module.h>
16 #include <linux/init.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>
31 #define DEVPTS_DEFAULT_MODE 0600
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
38 #define DEVPTS_DEFAULT_PTMX_MODE 0000
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.
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;
51 static struct ctl_table pty_table[] = {
54 .maxlen = sizeof(int),
57 .proc_handler = proc_dointvec_minmax,
58 .extra1 = &pty_limit_min,
59 .extra2 = &pty_limit_max,
61 .procname = "reserve",
62 .maxlen = sizeof(int),
65 .proc_handler = proc_dointvec_minmax,
66 .extra1 = &pty_limit_min,
67 .extra2 = &pty_limit_max,
70 .maxlen = sizeof(int),
73 .proc_handler = proc_dointvec,
78 static struct ctl_table pty_kern_table[] = {
87 static struct ctl_table pty_root_table[] = {
91 .child = pty_kern_table,
96 static DEFINE_MUTEX(allocated_ptys_lock);
98 struct pts_mount_opts {
110 Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance, Opt_max,
114 static const match_table_t tokens = {
117 {Opt_mode, "mode=%o"},
118 {Opt_ptmxmode, "ptmxmode=%o"},
119 {Opt_newinstance, "newinstance"},
125 struct ida allocated_ptys;
126 struct pts_mount_opts mount_opts;
127 struct super_block *sb;
128 struct dentry *ptmx_dentry;
131 static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
133 return sb->s_fs_info;
136 struct pts_fs_info *devpts_acquire(struct file *filp, struct vfsmount **ptsmnt)
138 struct pts_fs_info *result;
140 struct super_block *sb;
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);
153 result = ERR_PTR(err);
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))
166 * pty code needs to hold extra references in case of last /dev/tty close
168 atomic_inc(&sb->s_active);
169 *ptsmnt = mntget(path.mnt);
170 result = DEVPTS_SB(sb);
177 void devpts_release(struct pts_fs_info *fsi)
179 deactivate_super(fsi->sb);
182 #define PARSE_MOUNT 0
183 #define PARSE_REMOUNT 1
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.
190 * Note: @data may be NULL (in which case all options are set to default).
192 static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
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;
206 /* Only allow instances mounted from the initial mount
207 * namespace to tap the reserve pool of ptys.
209 if (op == PARSE_MOUNT)
211 (current->nsproxy->mnt_ns == init_task.nsproxy->mnt_ns);
213 while ((p = strsep(&data, ",")) != NULL) {
214 substring_t args[MAX_OPT_ARGS];
221 token = match_token(p, tokens, args);
224 if (match_int(&args[0], &option))
226 uid = make_kuid(current_user_ns(), option);
233 if (match_int(&args[0], &option))
235 gid = make_kgid(current_user_ns(), option);
242 if (match_octal(&args[0], &option))
244 opts->mode = option & S_IALLUGO;
247 if (match_octal(&args[0], &option))
249 opts->ptmxmode = option & S_IALLUGO;
251 case Opt_newinstance:
254 if (match_int(&args[0], &option) ||
255 option < 0 || option > NR_UNIX98_PTY_MAX)
260 pr_err("called with bogus options\n");
268 static int mknod_ptmx(struct super_block *sb)
272 struct dentry *dentry;
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();
280 inode_lock(d_inode(root));
282 /* If we have already created ptmx node, return */
283 if (fsi->ptmx_dentry) {
288 dentry = d_alloc_name(root, "ptmx");
290 pr_err("Unable to alloc dentry for ptmx node\n");
295 * Create a new 'ptmx' node in this mount of devpts.
297 inode = new_inode(sb);
299 pr_err("Unable to alloc inode for ptmx node\n");
305 inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
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;
312 d_add(dentry, inode);
314 fsi->ptmx_dentry = dentry;
317 inode_unlock(d_inode(root));
321 static void update_ptmx_mode(struct pts_fs_info *fsi)
324 if (fsi->ptmx_dentry) {
325 inode = d_inode(fsi->ptmx_dentry);
326 inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
330 static int devpts_remount(struct super_block *sb, int *flags, char *data)
333 struct pts_fs_info *fsi = DEVPTS_SB(sb);
334 struct pts_mount_opts *opts = &fsi->mount_opts;
336 err = parse_mount_options(data, PARSE_REMOUNT, opts);
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.
344 update_ptmx_mode(fsi);
349 static int devpts_show_options(struct seq_file *seq, struct dentry *root)
351 struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
352 struct pts_mount_opts *opts = &fsi->mount_opts;
355 seq_printf(seq, ",uid=%u",
356 from_kuid_munged(&init_user_ns, opts->uid));
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);
368 static const struct super_operations devpts_sops = {
369 .statfs = simple_statfs,
370 .remount_fs = devpts_remount,
371 .show_options = devpts_show_options,
374 static void *new_pts_fs_info(struct super_block *sb)
376 struct pts_fs_info *fsi;
378 fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
382 ida_init(&fsi->allocated_ptys);
383 fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
384 fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
391 devpts_fill_super(struct super_block *s, void *data, int silent)
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;
404 s->s_fs_info = new_pts_fs_info(s);
408 error = parse_mount_options(data, PARSE_MOUNT, &DEVPTS_SB(s)->mount_opts);
413 inode = new_inode(s);
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;
423 s->s_root = d_make_root(inode);
425 pr_err("get root dentry failed\n");
429 error = mknod_ptmx(s);
444 * Mount a new (private) instance of devpts. PTYs created in this
445 * instance are independent of the PTYs in other devpts instances.
447 static struct dentry *devpts_mount(struct file_system_type *fs_type,
448 int flags, const char *dev_name, void *data)
450 return mount_nodev(fs_type, flags, data, devpts_fill_super);
453 static void devpts_kill_sb(struct super_block *sb)
455 struct pts_fs_info *fsi = DEVPTS_SB(sb);
458 ida_destroy(&fsi->allocated_ptys);
460 kill_litter_super(sb);
463 static struct file_system_type devpts_fs_type = {
465 .mount = devpts_mount,
466 .kill_sb = devpts_kill_sb,
467 .fs_flags = FS_USERNS_MOUNT,
471 * The normal naming convention is simply /dev/pts/<number>; this conforms
472 * to the System V naming convention
475 int devpts_new_index(struct pts_fs_info *fsi)
481 if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
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);
491 ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
493 mutex_unlock(&allocated_ptys_lock);
494 if (ida_ret == -EAGAIN)
499 if (index >= fsi->mount_opts.max) {
500 ida_remove(&fsi->allocated_ptys, index);
501 mutex_unlock(&allocated_ptys_lock);
505 mutex_unlock(&allocated_ptys_lock);
509 void devpts_kill_index(struct pts_fs_info *fsi, int idx)
511 mutex_lock(&allocated_ptys_lock);
512 ida_remove(&fsi->allocated_ptys, idx);
514 mutex_unlock(&allocated_ptys_lock);
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
524 * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
526 struct dentry *devpts_pty_new(struct pts_fs_info *fsi, int index, void *priv)
528 struct dentry *dentry;
529 struct super_block *sb = fsi->sb;
532 struct pts_mount_opts *opts;
536 opts = &fsi->mount_opts;
538 inode = new_inode(sb);
540 return ERR_PTR(-ENOMEM);
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));
548 sprintf(s, "%d", index);
550 dentry = d_alloc_name(root, s);
552 dentry->d_fsdata = priv;
553 d_add(dentry, inode);
554 fsnotify_create(d_inode(root), dentry);
557 dentry = ERR_PTR(-ENOMEM);
564 * devpts_get_priv -- get private data for a slave
565 * @pts_inode: inode of the slave
567 * Returns whatever was passed as priv in devpts_pty_new for a given inode.
569 void *devpts_get_priv(struct dentry *dentry)
571 if (dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC)
573 return dentry->d_fsdata;
577 * devpts_pty_kill -- remove inode form /dev/pts/
578 * @inode: inode of the slave to be removed
580 * This is an inverse operation of devpts_pty_new.
582 void devpts_pty_kill(struct dentry *dentry)
584 WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);
586 dentry->d_fsdata = NULL;
587 drop_nlink(dentry->d_inode);
589 dput(dentry); /* d_alloc_name() in devpts_pty_new() */
592 static int __init init_devpts_fs(void)
594 int err = register_filesystem(&devpts_fs_type);
596 register_sysctl_table(pty_root_table);
600 module_init(init_devpts_fs)