// SPDX-License-Identifier: GPL-2.0-or-later
/* -*- linux-c -*- --------------------------------------------------------- *
*
* linux/fs/devpts/inode.c
*
* Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved
*
* ------------------------------------------------------------------------- */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/namei.h>
#include <linux/slab.h>
#include <linux/mount.h>
#include <linux/tty.h>
#include <linux/mutex.h>
#include <linux/magic.h>
#include <linux/idr.h>
#include <linux/devpts_fs.h>
#include <linux/parser.h>
#include <linux/fsnotify.h>
#include <linux/seq_file.h>
#define DEVPTS_DEFAULT_MODE 0600
/*
* ptmx is a new node in /dev/pts and will be unused in legacy (single-
* instance) mode. To prevent surprises in user space, set permissions of
* ptmx to 0. Use 'chmod' or remount with '-o ptmxmode' to set meaningful
* permissions.
*/
#define DEVPTS_DEFAULT_PTMX_MODE 0000
#define PTMX_MINOR 2
/*
* sysctl support for setting limits on the number of Unix98 ptys allocated.
* Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
*/
static int pty_limit = NR_UNIX98_PTY_DEFAULT;
static int pty_reserve = NR_UNIX98_PTY_RESERVE;
static int pty_limit_min;
static int pty_limit_max = INT_MAX;
static atomic_t pty_count = ATOMIC_INIT(0);
static struct ctl_table pty_table[] = {
{
.procname = "max",
.maxlen = sizeof(int),
.mode = 0644,
.data = &pty_limit,
.proc_handler = proc_dointvec_minmax,
.extra1 = &pty_limit_min,
.extra2 = &pty_limit_max,
}, {
.procname = "reserve",
.maxlen = sizeof(int),
.mode = 0644,
.data = &pty_reserve,
.proc_handler = proc_dointvec_minmax,
.extra1 = &pty_limit_min,
.extra2 = &pty_limit_max,
}, {
.procname = "nr",
.maxlen = sizeof(int),
.mode = 0444,
.data = &pty_count,
.proc_handler = proc_dointvec,
},
};
struct pts_mount_opts {
int setuid;
int setgid;
kuid_t uid;
kgid_t gid;
umode_t mode;
umode_t ptmxmode;
int reserve;
int max;
};
enum {
Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance, Opt_max,
Opt_err
};
static const match_table_t tokens = {
{Opt_uid, "uid=%u"},
{Opt_gid, "gid=%u"},
{Opt_mode, "mode=%o"},
{Opt_ptmxmode, "ptmxmode=%o"},
{Opt_newinstance, "newinstance"},
{Opt_max, "max=%d"},
{Opt_err, NULL}
};
struct pts_fs_info {
struct ida allocated_ptys;
struct pts_mount_opts mount_opts;
struct super_block *sb;
struct dentry *ptmx_dentry;
};
static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
{
return sb->s_fs_info;
}
static int devpts_ptmx_path(struct path *path)
{
struct super_block *sb;
int err;
/* Is a devpts filesystem at "pts" in the same directory? */
err = path_pts(path);
if (err)
return err;
/* Is the path the root of a devpts filesystem? */
sb = path->mnt->mnt_sb;
if ((sb->s_magic != DEVPTS_SUPER_MAGIC) ||
(path->mnt->mnt_root != sb->s_root))
return -ENODEV;
return 0;
}
/*
* Try to find a suitable devpts filesystem. We support the following
* scenarios:
* - The ptmx device node is located in the same directory as the devpts
* mount where the pts device nodes are located.
* This is e.g. the case when calling open on the /dev/pts/ptmx device
* node when the devpts filesystem is mounted at /dev/pts.
* - The ptmx device node is located outside the devpts filesystem mount
* where the pts device nodes are located. For example, the ptmx device
* is a symlink, separate device node, or bind-mount.
* A supported scenario is bind-mounting /dev/pts/ptmx to /dev/ptmx and
* then calling open on /dev/ptmx. In this case a suitable pts
* subdirectory can be found in the common parent directory /dev of the
* devpts mount and the ptmx bind-mount, after resolving the /dev/ptmx
* bind-mount.
* If no suitable pts subdirectory can be found this function will fail.
* This is e.g. the case when bind-mounting /dev/pts/ptmx to /ptmx.
*/
struct vfsmount *devpts_mntget(struct file *filp, struct pts_fs_info *fsi)
{
struct path path;
int err = 0;
path = filp->f_path;
path_get(&path);
/* Walk upward while the start point is a bind mount of
* a single file.
*/
while (path.mnt->mnt_root == path.dentry)
if (follow_up(&path) == 0)
break;
/* devpts_ptmx_path() finds a devpts fs or returns an error. */
if ((path.mnt->mnt_sb->s_magic != DEVPTS_SUPER_MAGIC) ||
(DEVPTS_SB(path.mnt->mnt_sb) != fsi))
err = devpts_ptmx_path(&path);
dput(path.dentry);
if (!err) {
if (DEVPTS_SB(path.mnt->mnt_sb) == fsi)
return path.mnt;
err = -ENODEV;
}
mntput(path.mnt);
return ERR_PTR(err);
}
struct pts_fs_info *devpts_acquire(struct file *filp)
{
struct pts_fs_info *result;
struct path path;
struct super_block *sb;
path = filp->f_path;
path_get(&path);
/* Has the devpts filesystem already been found? */
if (path.mnt->mnt_sb->s_magic != DEVPTS_SUPER_MAGIC) {
int err;
err = devpts_ptmx_path(&path);
if (err) {
result = ERR_PTR(err);
goto out;
}
}
/*
* pty code needs to hold extra references in case of last /dev/tty close
*/
sb = path.mnt->mnt_sb;
atomic_inc(&sb->s_active);
result = DEVPTS_SB(sb);
out:
path_put(&path);
return result;
}
void devpts_release(struct pts_fs_info *fsi)
{
deactivate_super(fsi->sb);
}
#define PARSE_MOUNT 0
#define PARSE_REMOUNT 1
/*
* parse_mount_options():
* Set @opts to mount options specified in @data. If an option is not
* specified in @data, set it to its default value.
*
* Note: @data may be NULL (in which case all options are set to default).
*/
static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
{
char *p;
kuid_t uid;
kgid_t gid;
opts->setuid = 0;
opts->setgid = 0;
opts->uid = GLOBAL_ROOT_UID;
opts->gid = GLOBAL_ROOT_GID;
opts->mode = DEVPTS_DEFAULT_MODE;
opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
opts->max = NR_UNIX98_PTY_MAX;
/* Only allow instances mounted from the initial mount
* namespace to tap the reserve pool of ptys.
*/
if (op == PARSE_MOUNT)
opts->reserve =
(current->nsproxy->mnt_ns == init_task.nsproxy->mnt_ns);
while ((p = strsep(&data, ",")) != NULL) {
substring_t args[MAX_OPT_ARGS];
int token;
int option;
if (!*p)
continue;
token = match_token(p, tokens, args);
switch (token) {
case Opt_uid:
if (match_int(&args[0], &option))
return -EINVAL;
uid = make_kuid(current_user_ns(), option);
if (!uid_valid(uid))
return -EINVAL;
opts->uid = uid;
opts->setuid = 1;
break;
case Opt_gid:
if (match_int(&args[0], &option))
return -EINVAL;
gid = make_kgid(current_user_ns(), option);
if (!gid_valid(gid))
return -EINVAL;
opts->gid = gid;
opts->setgid = 1;
break;
case Opt_mode:
if (match_octal(&args[0], &option))
return -EINVAL;
opts->mode = option & S_IALLUGO;
break;
case Opt_ptmxmode:
if (match_octal(&args[0], &option))
return -EINVAL;
opts->ptmxmode = option & S_IALLUGO;
break;
case Opt_newinstance:
break;
case Opt_max:
if (match_int(&args[0], &option) ||
option < 0 || option > NR_UNIX98_PTY_MAX)
return -EINVAL;
opts->max = option;
break;
default:
pr_err("called with bogus options\n");
return -EINVAL;
}
}
return 0;
}
static int mknod_ptmx(struct super_block *sb)
{
int mode;
int rc = -ENOMEM;
struct dentry *dentry;
struct inode *inode;
struct dentry *root = sb->s_root;
struct pts_fs_info *fsi = DEVPTS_SB(sb);
struct pts_mount_opts *opts = &fsi->mount_opts;
kuid_t ptmx_uid = current_fsuid();
kgid_t ptmx_gid = current_fsgid();
inode_lock(d_inode(root));
/* If we have already created ptmx node, return */
if (fsi->ptmx_dentry) {
rc = 0;
goto out;
}
dentry = d_alloc_name(root, "ptmx");
if (!dentry) {
pr_err("Unable to alloc dentry for ptmx node\n");
goto out;
}
/*
* Create a new 'ptmx' node in this mount of devpts.
*/
inode = new_inode(sb);
if (!inode) {
pr_err("Unable to alloc inode for ptmx node\n");
dput(dentry);
goto out;
}
inode->i_ino = 2;
simple_inode_init_ts(inode);
mode = S_IFCHR|opts->ptmxmode;
init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
inode->i_uid = ptmx_uid;
inode->i_gid = ptmx_gid;
d_add(dentry, inode);
fsi->ptmx_dentry = dentry;
rc = 0;
out:
inode_unlock(d_inode(root));
return rc;
}
static void update_ptmx_mode(struct pts_fs_info *fsi)
{
struct inode *inode;
if (fsi->ptmx_dentry) {
inode = d_inode(fsi->ptmx_dentry);
inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
}
}
static int devpts_remount(struct super_block *sb, int *flags, char *data)
{
int err;
struct pts_fs_info *fsi = DEVPTS_SB(sb);
struct pts_mount_opts *opts = &fsi->mount_opts;
err = parse_mount_options(data, PARSE_REMOUNT, opts);
/*
* parse_mount_options() restores options to default values
* before parsing and may have changed ptmxmode. So, update the
* mode in the inode too. Bogus options don't fail the remount,
* so do this even on error return.
*/
update_ptmx_mode(fsi);
return err;
}
static int devpts_show_options(struct seq_file *seq, struct dentry *root)
{
struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
struct pts_mount_opts *opts = &fsi->mount_opts;
if (opts->setuid)
seq_printf(seq, ",uid=%u",
from_kuid_munged(&init_user_ns, opts->uid));
if (opts->setgid)
seq_printf(seq, ",gid=%u",
from_kgid_munged(&init_user_ns, opts->gid));
seq_printf(seq, ",mode=%03o", opts->mode);
seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
if (opts->max < NR_UNIX98_PTY_MAX)
seq_printf(seq, ",max=%d", opts->max);
return 0;
}
static const struct super_operations devpts_sops = {
.statfs = simple_statfs,
.remount_fs = devpts_remount,
.show_options = devpts_show_options,
};
static void *new_pts_fs_info(struct super_block *sb)
{
struct pts_fs_info *fsi;
fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
if (!fsi)
return NULL;
ida_init(&fsi->allocated_ptys);
fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
fsi->sb = sb;
return fsi;
}
static int
devpts_fill_super(struct super_block *s, void *data, int silent)
{
struct inode *inode;
int error;
s->s_iflags &= ~SB_I_NODEV;
s->s_blocksize = 1024;
s->s_blocksize_bits = 10;
s->s_magic = DEVPTS_SUPER_MAGIC;
s->s_op = &devpts_sops;
s->s_d_op = &simple_dentry_operations;
s->s_time_gran = 1;
error = -ENOMEM;
s->s_fs_info = new_pts_fs_info(s);
if (!s->s_fs_info)
goto fail;
error = parse_mount_options(data, PARSE_MOUNT, &DEVPTS_SB(s)->mount_opts);
if (error)
goto fail;
error = -ENOMEM;
inode = new_inode(s);
if (!inode)
goto fail;
inode->i_ino = 1;
simple_inode_init_ts(inode);
inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
inode->i_op = &simple_dir_inode_operations;
inode->i_fop = &simple_dir_operations;
set_nlink(inode, 2);
s->s_root = d_make_root(inode);
if (!s->s_root) {
pr_err("get root dentry failed\n");
goto fail;
}
error = mknod_ptmx(s);
if (error)
goto fail_dput;
return 0;
fail_dput:
dput(s->s_root);
s->s_root = NULL;
fail:
return error;
}
/*
* devpts_mount()
*
* Mount a new (private) instance of devpts. PTYs created in this
* instance are independent of the PTYs in other devpts instances.
*/
static struct dentry *devpts_mount(struct file_system_type *fs_type,
int flags, const char *dev_name, void *data)
{
return mount_nodev(fs_type, flags, data, devpts_fill_super);
}
static void devpts_kill_sb(struct super_block *sb)
{
struct pts_fs_info *fsi = DEVPTS_SB(sb);
if (fsi)
ida_destroy(&fsi->allocated_ptys);
kfree(fsi);
kill_litter_super(sb);
}
static struct file_system_type devpts_fs_type = {
.name = "devpts",
.mount = devpts_mount,
.kill_sb = devpts_kill_sb,
.fs_flags = FS_USERNS_MOUNT,
};
/*
* The normal naming convention is simply /dev/pts/<number>; this conforms
* to the System V naming convention
*/
int devpts_new_index(struct pts_fs_info *fsi)
{
int index = -ENOSPC;
if (atomic_inc_return(&pty_count) >= (pty_limit -
(fsi->mount_opts.reserve ? 0 : pty_reserve)))
goto out;
index = ida_alloc_max(&fsi->allocated_ptys, fsi->mount_opts.max - 1,
GFP_KERNEL);
out:
if (index < 0)
atomic_dec(&pty_count);
return index;
}
void devpts_kill_index(struct pts_fs_info *fsi, int idx)
{
ida_free(&fsi->allocated_ptys, idx);
atomic_dec(&pty_count);
}
/**
* devpts_pty_new -- create a new inode in /dev/pts/
* @fsi: Filesystem info for this instance.
* @index: used as a name of the node
* @priv: what's given back by devpts_get_priv
*
* The dentry for the created inode is returned.
* Remove it from /dev/pts/ with devpts_pty_kill().
*/
struct dentry *devpts_pty_new(struct pts_fs_info *fsi, int index, void *priv)
{
struct dentry *dentry;
struct super_block *sb = fsi->sb;
struct inode *inode;
struct dentry *root;
struct pts_mount_opts *opts;
char s[12];
root = sb->s_root;
opts = &fsi->mount_opts;
inode = new_inode(sb);
if (!inode)
return ERR_PTR(-ENOMEM);
inode->i_ino = index + 3;
inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
simple_inode_init_ts(inode);
init_special_inode(inode, S_IFCHR|opts->mode, MKDEV(UNIX98_PTY_SLAVE_MAJOR, index));
sprintf(s, "%d", index);
dentry = d_alloc_name(root, s);
if (dentry) {
dentry->d_fsdata = priv;
d_add(dentry, inode);
fsnotify_create(d_inode(root), dentry);
} else {
iput(inode);
dentry = ERR_PTR(-ENOMEM);
}
return dentry;
}
/**
* devpts_get_priv -- get private data for a slave
* @dentry: dentry of the slave
*
* Returns whatever was passed as priv in devpts_pty_new for a given inode.
*/
void *devpts_get_priv(struct dentry *dentry)
{
if (dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC)
return NULL;
return dentry->d_fsdata;
}
/**
* devpts_pty_kill -- remove inode form /dev/pts/
* @dentry: dentry of the slave to be removed
*
* This is an inverse operation of devpts_pty_new.
*/
void devpts_pty_kill(struct dentry *dentry)
{
WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);
dentry->d_fsdata = NULL;
drop_nlink(dentry->d_inode);
d_drop(dentry);
fsnotify_unlink(d_inode(dentry->d_parent), dentry);
dput(dentry); /* d_alloc_name() in devpts_pty_new() */
}
static int __init init_devpts_fs(void)
{
int err = register_filesystem(&devpts_fs_type);
if (!err) {
register_sysctl("kernel/pty", pty_table);
}
return err;
}
module_init(init_devpts_fs)
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