linux/fs/devpts/inode.c
Linus Torvalds 8ead9dd547 devpts: more pty driver interface cleanups
This is more prep-work for the upcoming pty changes.  Still just code
cleanup with no actual semantic changes.

This removes a bunch pointless complexity by just having the slave pty
side remember the dentry associated with the devpts slave rather than
the inode.  That allows us to remove all the "look up the dentry" code
for when we want to remove it again.

Together with moving the tty pointer from "inode->i_private" to
"dentry->d_fsdata" and getting rid of pointless inode locking, this
removes about 30 lines of code.  Not only is the end result smaller,
it's simpler and easier to understand.

The old code, for example, depended on the d_find_alias() to not just
find the dentry, but also to check that it is still hashed, which in
turn validated the tty pointer in the inode.

That is a _very_ roundabout way to say "invalidate the cached tty
pointer when the dentry is removed".

The new code just does

	dentry->d_fsdata = NULL;

in devpts_pty_kill() instead, invalidating the tty pointer rather more
directly and obviously.  Don't do something complex and subtle when the
obvious straightforward approach will do.

The rest of the patch (ie apart from code deletion and the above tty
pointer clearing) is just switching the calling convention to pass the
dentry or file pointer around instead of the inode.

Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Peter Anvin <hpa@zytor.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Serge Hallyn <serge.hallyn@ubuntu.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
Cc: Jann Horn <jann@thejh.net>
Cc: Greg KH <greg@kroah.com>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Florian Weimer <fw@deneb.enyo.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-04-26 15:47:32 -07:00

697 lines
16 KiB
C

/* -*- linux-c -*- --------------------------------------------------------- *
*
* linux/fs/devpts/inode.c
*
* Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved
*
* This file is part of the Linux kernel and is made available under
* the terms of the GNU General Public License, version 2, or at your
* option, any later version, incorporated herein by reference.
*
* ------------------------------------------------------------------------- */
#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 int pty_count;
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,
},
{}
};
static struct ctl_table pty_kern_table[] = {
{
.procname = "pty",
.mode = 0555,
.child = pty_table,
},
{}
};
static struct ctl_table pty_root_table[] = {
{
.procname = "kernel",
.mode = 0555,
.child = pty_kern_table,
},
{}
};
static DEFINE_MUTEX(allocated_ptys_lock);
static struct vfsmount *devpts_mnt;
struct pts_mount_opts {
int setuid;
int setgid;
kuid_t uid;
kgid_t gid;
umode_t mode;
umode_t ptmxmode;
int newinstance;
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"},
#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
{Opt_ptmxmode, "ptmxmode=%o"},
{Opt_newinstance, "newinstance"},
{Opt_max, "max=%d"},
#endif
{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 inline struct super_block *pts_sb_from_inode(struct inode *inode)
{
#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
if (inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
return inode->i_sb;
#endif
if (!devpts_mnt)
return NULL;
return devpts_mnt->mnt_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. The exception is
* 'newinstance' option which can only be set/cleared on a mount (i.e.
* cannot be changed during remount).
*
* 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;
/* newinstance makes sense only on initial mount */
if (op == PARSE_MOUNT)
opts->newinstance = 0;
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;
#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
case Opt_ptmxmode:
if (match_octal(&args[0], &option))
return -EINVAL;
opts->ptmxmode = option & S_IALLUGO;
break;
case Opt_newinstance:
/* newinstance makes sense only on initial mount */
if (op == PARSE_MOUNT)
opts->newinstance = 1;
break;
case Opt_max:
if (match_int(&args[0], &option) ||
option < 0 || option > NR_UNIX98_PTY_MAX)
return -EINVAL;
opts->max = option;
break;
#endif
default:
pr_err("called with bogus options\n");
return -EINVAL;
}
}
return 0;
}
#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
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 root_uid;
kgid_t root_gid;
root_uid = make_kuid(current_user_ns(), 0);
root_gid = make_kgid(current_user_ns(), 0);
if (!uid_valid(root_uid) || !gid_valid(root_gid))
return -EINVAL;
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;
inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
mode = S_IFCHR|opts->ptmxmode;
init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
inode->i_uid = root_uid;
inode->i_gid = root_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;
}
}
#else
static inline void update_ptmx_mode(struct pts_fs_info *fsi)
{
return;
}
#endif
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;
sync_filesystem(sb);
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);
#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
if (opts->max < NR_UNIX98_PTY_MAX)
seq_printf(seq, ",max=%d", opts->max);
#endif
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;
s->s_blocksize = 1024;
s->s_blocksize_bits = 10;
s->s_magic = DEVPTS_SUPER_MAGIC;
s->s_op = &devpts_sops;
s->s_time_gran = 1;
s->s_fs_info = new_pts_fs_info(s);
if (!s->s_fs_info)
goto fail;
inode = new_inode(s);
if (!inode)
goto fail;
inode->i_ino = 1;
inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
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)
return 0;
pr_err("get root dentry failed\n");
fail:
return -ENOMEM;
}
#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
static int compare_init_pts_sb(struct super_block *s, void *p)
{
if (devpts_mnt)
return devpts_mnt->mnt_sb == s;
return 0;
}
/*
* devpts_mount()
*
* If the '-o newinstance' mount option was specified, mount a new
* (private) instance of devpts. PTYs created in this instance are
* independent of the PTYs in other devpts instances.
*
* If the '-o newinstance' option was not specified, mount/remount the
* initial kernel mount of devpts. This type of mount gives the
* legacy, single-instance semantics.
*
* The 'newinstance' option is needed to support multiple namespace
* semantics in devpts while preserving backward compatibility of the
* current 'single-namespace' semantics. i.e all mounts of devpts
* without the 'newinstance' mount option should bind to the initial
* kernel mount, like mount_single().
*
* Mounts with 'newinstance' option create a new, private namespace.
*
* NOTE:
*
* For single-mount semantics, devpts cannot use mount_single(),
* because mount_single()/sget() find and use the super-block from
* the most recent mount of devpts. But that recent mount may be a
* 'newinstance' mount and mount_single() would pick the newinstance
* super-block instead of the initial super-block.
*/
static struct dentry *devpts_mount(struct file_system_type *fs_type,
int flags, const char *dev_name, void *data)
{
int error;
struct pts_mount_opts opts;
struct super_block *s;
error = parse_mount_options(data, PARSE_MOUNT, &opts);
if (error)
return ERR_PTR(error);
/* Require newinstance for all user namespace mounts to ensure
* the mount options are not changed.
*/
if ((current_user_ns() != &init_user_ns) && !opts.newinstance)
return ERR_PTR(-EINVAL);
if (opts.newinstance)
s = sget(fs_type, NULL, set_anon_super, flags, NULL);
else
s = sget(fs_type, compare_init_pts_sb, set_anon_super, flags,
NULL);
if (IS_ERR(s))
return ERR_CAST(s);
if (!s->s_root) {
error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
if (error)
goto out_undo_sget;
s->s_flags |= MS_ACTIVE;
}
memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts));
error = mknod_ptmx(s);
if (error)
goto out_undo_sget;
return dget(s->s_root);
out_undo_sget:
deactivate_locked_super(s);
return ERR_PTR(error);
}
#else
/*
* This supports only the legacy single-instance semantics (no
* multiple-instance semantics)
*/
static struct dentry *devpts_mount(struct file_system_type *fs_type, int flags,
const char *dev_name, void *data)
{
return mount_single(fs_type, flags, data, devpts_fill_super);
}
#endif
static void devpts_kill_sb(struct super_block *sb)
{
struct pts_fs_info *fsi = DEVPTS_SB(sb);
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,
#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
.fs_flags = FS_USERNS_MOUNT | FS_USERNS_DEV_MOUNT,
#endif
};
/*
* 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;
int ida_ret;
if (!fsi)
return -ENODEV;
retry:
if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
return -ENOMEM;
mutex_lock(&allocated_ptys_lock);
if (pty_count >= pty_limit -
(fsi->mount_opts.newinstance ? pty_reserve : 0)) {
mutex_unlock(&allocated_ptys_lock);
return -ENOSPC;
}
ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
if (ida_ret < 0) {
mutex_unlock(&allocated_ptys_lock);
if (ida_ret == -EAGAIN)
goto retry;
return -EIO;
}
if (index >= fsi->mount_opts.max) {
ida_remove(&fsi->allocated_ptys, index);
mutex_unlock(&allocated_ptys_lock);
return -ENOSPC;
}
pty_count++;
mutex_unlock(&allocated_ptys_lock);
return index;
}
void devpts_kill_index(struct pts_fs_info *fsi, int idx)
{
mutex_lock(&allocated_ptys_lock);
ida_remove(&fsi->allocated_ptys, idx);
pty_count--;
mutex_unlock(&allocated_ptys_lock);
}
/*
* pty code needs to hold extra references in case of last /dev/tty close
*/
struct pts_fs_info *devpts_get_ref(struct inode *ptmx_inode, struct file *file)
{
struct super_block *sb;
struct pts_fs_info *fsi;
sb = pts_sb_from_inode(ptmx_inode);
if (!sb)
return NULL;
fsi = DEVPTS_SB(sb);
if (!fsi)
return NULL;
atomic_inc(&sb->s_active);
return fsi;
}
void devpts_put_ref(struct pts_fs_info *fsi)
{
deactivate_super(fsi->sb);
}
/**
* devpts_pty_new -- create a new inode in /dev/pts/
* @ptmx_inode: inode of the master
* @device: major+minor of the node to be created
* @index: used as a name of the node
* @priv: what's given back by devpts_get_priv
*
* The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
*/
struct dentry *devpts_pty_new(struct pts_fs_info *fsi, int index, void *priv)
{
struct dentry *dentry;
struct super_block *sb;
struct inode *inode;
struct dentry *root;
struct pts_mount_opts *opts;
char s[12];
if (!fsi)
return ERR_PTR(-ENODEV);
sb = fsi->sb;
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();
inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
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
* @pts_inode: inode of the slave
*
* Returns whatever was passed as priv in devpts_pty_new for a given inode.
*/
void *devpts_get_priv(struct dentry *dentry)
{
WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);
return dentry->d_fsdata;
}
/**
* devpts_pty_kill -- remove inode form /dev/pts/
* @inode: inode 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_delete(dentry);
dput(dentry); /* d_alloc_name() in devpts_pty_new() */
}
static int __init init_devpts_fs(void)
{
int err = register_filesystem(&devpts_fs_type);
struct ctl_table_header *table;
if (!err) {
struct vfsmount *mnt;
table = register_sysctl_table(pty_root_table);
mnt = kern_mount(&devpts_fs_type);
if (IS_ERR(mnt)) {
err = PTR_ERR(mnt);
unregister_filesystem(&devpts_fs_type);
unregister_sysctl_table(table);
} else {
devpts_mnt = mnt;
}
}
return err;
}
module_init(init_devpts_fs)