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 static struct ctl_table pty_kern_table
[] = {
84 static struct ctl_table pty_root_table
[] = {
88 .child
= pty_kern_table
,
93 struct pts_mount_opts
{
105 Opt_uid
, Opt_gid
, Opt_mode
, Opt_ptmxmode
, Opt_newinstance
, Opt_max
,
109 static const match_table_t tokens
= {
112 {Opt_mode
, "mode=%o"},
113 {Opt_ptmxmode
, "ptmxmode=%o"},
114 {Opt_newinstance
, "newinstance"},
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
;
136 /* Is a devpts filesystem at "pts" in the same directory? */
137 err
= path_pts(path
);
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
))
151 * Try to find a suitable devpts filesystem. We support the following
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
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
)
176 /* Walk upward while the start point is a bind mount of
179 while (path
.mnt
->mnt_root
== path
.dentry
)
180 if (follow_up(&path
) == 0)
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
);
189 if (DEVPTS_SB(path
.mnt
->mnt_sb
) == fsi
)
199 struct pts_fs_info
*devpts_acquire(struct file
*filp
)
201 struct pts_fs_info
*result
;
203 struct super_block
*sb
;
208 /* Has the devpts filesystem already been found? */
209 if (path
.mnt
->mnt_sb
->s_magic
!= DEVPTS_SUPER_MAGIC
) {
212 err
= devpts_ptmx_path(&path
);
214 result
= ERR_PTR(err
);
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
);
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
)
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
)
265 (current
->nsproxy
->mnt_ns
== init_task
.nsproxy
->mnt_ns
);
267 while ((p
= strsep(&data
, ",")) != NULL
) {
268 substring_t args
[MAX_OPT_ARGS
];
275 token
= match_token(p
, tokens
, args
);
278 if (match_int(&args
[0], &option
))
280 uid
= make_kuid(current_user_ns(), option
);
287 if (match_int(&args
[0], &option
))
289 gid
= make_kgid(current_user_ns(), option
);
296 if (match_octal(&args
[0], &option
))
298 opts
->mode
= option
& S_IALLUGO
;
301 if (match_octal(&args
[0], &option
))
303 opts
->ptmxmode
= option
& S_IALLUGO
;
305 case Opt_newinstance
:
308 if (match_int(&args
[0], &option
) ||
309 option
< 0 || option
> NR_UNIX98_PTY_MAX
)
314 pr_err("called with bogus options\n");
322 static int mknod_ptmx(struct super_block
*sb
)
326 struct dentry
*dentry
;
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
) {
342 dentry
= d_alloc_name(root
, "ptmx");
344 pr_err("Unable to alloc dentry for ptmx node\n");
349 * Create a new 'ptmx' node in this mount of devpts.
351 inode
= new_inode(sb
);
353 pr_err("Unable to alloc inode for ptmx node\n");
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
;
371 inode_unlock(d_inode(root
));
375 static void update_ptmx_mode(struct pts_fs_info
*fsi
)
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
)
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
);
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
;
409 seq_printf(seq
, ",uid=%u",
410 from_kuid_munged(&init_user_ns
, opts
->uid
));
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
);
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
);
436 ida_init(&fsi
->allocated_ptys
);
437 fsi
->mount_opts
.mode
= DEVPTS_DEFAULT_MODE
;
438 fsi
->mount_opts
.ptmxmode
= DEVPTS_DEFAULT_PTMX_MODE
;
445 devpts_fill_super(struct super_block
*s
, void *data
, int silent
)
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
;
459 s
->s_fs_info
= new_pts_fs_info(s
);
463 error
= parse_mount_options(data
, PARSE_MOUNT
, &DEVPTS_SB(s
)->mount_opts
);
468 inode
= new_inode(s
);
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
;
478 s
->s_root
= d_make_root(inode
);
480 pr_err("get root dentry failed\n");
484 error
= mknod_ptmx(s
);
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
);
513 ida_destroy(&fsi
->allocated_ptys
);
515 kill_litter_super(sb
);
518 static struct file_system_type devpts_fs_type
= {
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
)
534 if (atomic_inc_return(&pty_count
) >= (pty_limit
-
535 (fsi
->mount_opts
.reserve
? 0 : pty_reserve
)))
538 index
= ida_alloc_max(&fsi
->allocated_ptys
, fsi
->mount_opts
.max
- 1,
543 atomic_dec(&pty_count
);
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
;
568 struct pts_mount_opts
*opts
;
572 opts
= &fsi
->mount_opts
;
574 inode
= new_inode(sb
);
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
);
588 dentry
->d_fsdata
= priv
;
589 d_add(dentry
, inode
);
590 fsnotify_create(d_inode(root
), dentry
);
593 dentry
= ERR_PTR(-ENOMEM
);
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
)
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
);
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
);
633 register_sysctl_table(pty_root_table
);
637 module_init(init_devpts_fs
)