linux/fs/overlayfs/super.c
Kees Cook a068acf2ee fs: create and use seq_show_option for escaping
Many file systems that implement the show_options hook fail to correctly
escape their output which could lead to unescaped characters (e.g.  new
lines) leaking into /proc/mounts and /proc/[pid]/mountinfo files.  This
could lead to confusion, spoofed entries (resulting in things like
systemd issuing false d-bus "mount" notifications), and who knows what
else.  This looks like it would only be the root user stepping on
themselves, but it's possible weird things could happen in containers or
in other situations with delegated mount privileges.

Here's an example using overlay with setuid fusermount trusting the
contents of /proc/mounts (via the /etc/mtab symlink).  Imagine the use
of "sudo" is something more sneaky:

  $ BASE="ovl"
  $ MNT="$BASE/mnt"
  $ LOW="$BASE/lower"
  $ UP="$BASE/upper"
  $ WORK="$BASE/work/ 0 0
  none /proc fuse.pwn user_id=1000"
  $ mkdir -p "$LOW" "$UP" "$WORK"
  $ sudo mount -t overlay -o "lowerdir=$LOW,upperdir=$UP,workdir=$WORK" none /mnt
  $ cat /proc/mounts
  none /root/ovl/mnt overlay rw,relatime,lowerdir=ovl/lower,upperdir=ovl/upper,workdir=ovl/work/ 0 0
  none /proc fuse.pwn user_id=1000 0 0
  $ fusermount -u /proc
  $ cat /proc/mounts
  cat: /proc/mounts: No such file or directory

This fixes the problem by adding new seq_show_option and
seq_show_option_n helpers, and updating the vulnerable show_option
handlers to use them as needed.  Some, like SELinux, need to be open
coded due to unusual existing escape mechanisms.

[akpm@linux-foundation.org: add lost chunk, per Kees]
[keescook@chromium.org: seq_show_option should be using const parameters]
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Acked-by: Jan Kara <jack@suse.com>
Acked-by: Paul Moore <paul@paul-moore.com>
Cc: J. R. Okajima <hooanon05g@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-09-04 16:54:41 -07:00

1115 lines
24 KiB
C

/*
*
* Copyright (C) 2011 Novell Inc.
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 as published by
* the Free Software Foundation.
*/
#include <linux/fs.h>
#include <linux/namei.h>
#include <linux/xattr.h>
#include <linux/security.h>
#include <linux/mount.h>
#include <linux/slab.h>
#include <linux/parser.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/statfs.h>
#include <linux/seq_file.h>
#include "overlayfs.h"
MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
MODULE_DESCRIPTION("Overlay filesystem");
MODULE_LICENSE("GPL");
#define OVERLAYFS_SUPER_MAGIC 0x794c7630
struct ovl_config {
char *lowerdir;
char *upperdir;
char *workdir;
};
/* private information held for overlayfs's superblock */
struct ovl_fs {
struct vfsmount *upper_mnt;
unsigned numlower;
struct vfsmount **lower_mnt;
struct dentry *workdir;
long lower_namelen;
/* pathnames of lower and upper dirs, for show_options */
struct ovl_config config;
};
struct ovl_dir_cache;
/* private information held for every overlayfs dentry */
struct ovl_entry {
struct dentry *__upperdentry;
struct ovl_dir_cache *cache;
union {
struct {
u64 version;
bool opaque;
};
struct rcu_head rcu;
};
unsigned numlower;
struct path lowerstack[];
};
#define OVL_MAX_STACK 500
static struct dentry *__ovl_dentry_lower(struct ovl_entry *oe)
{
return oe->numlower ? oe->lowerstack[0].dentry : NULL;
}
enum ovl_path_type ovl_path_type(struct dentry *dentry)
{
struct ovl_entry *oe = dentry->d_fsdata;
enum ovl_path_type type = 0;
if (oe->__upperdentry) {
type = __OVL_PATH_UPPER;
if (oe->numlower) {
if (S_ISDIR(dentry->d_inode->i_mode))
type |= __OVL_PATH_MERGE;
} else if (!oe->opaque) {
type |= __OVL_PATH_PURE;
}
} else {
if (oe->numlower > 1)
type |= __OVL_PATH_MERGE;
}
return type;
}
static struct dentry *ovl_upperdentry_dereference(struct ovl_entry *oe)
{
return lockless_dereference(oe->__upperdentry);
}
void ovl_path_upper(struct dentry *dentry, struct path *path)
{
struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
struct ovl_entry *oe = dentry->d_fsdata;
path->mnt = ofs->upper_mnt;
path->dentry = ovl_upperdentry_dereference(oe);
}
enum ovl_path_type ovl_path_real(struct dentry *dentry, struct path *path)
{
enum ovl_path_type type = ovl_path_type(dentry);
if (!OVL_TYPE_UPPER(type))
ovl_path_lower(dentry, path);
else
ovl_path_upper(dentry, path);
return type;
}
struct dentry *ovl_dentry_upper(struct dentry *dentry)
{
struct ovl_entry *oe = dentry->d_fsdata;
return ovl_upperdentry_dereference(oe);
}
struct dentry *ovl_dentry_lower(struct dentry *dentry)
{
struct ovl_entry *oe = dentry->d_fsdata;
return __ovl_dentry_lower(oe);
}
struct dentry *ovl_dentry_real(struct dentry *dentry)
{
struct ovl_entry *oe = dentry->d_fsdata;
struct dentry *realdentry;
realdentry = ovl_upperdentry_dereference(oe);
if (!realdentry)
realdentry = __ovl_dentry_lower(oe);
return realdentry;
}
struct dentry *ovl_entry_real(struct ovl_entry *oe, bool *is_upper)
{
struct dentry *realdentry;
realdentry = ovl_upperdentry_dereference(oe);
if (realdentry) {
*is_upper = true;
} else {
realdentry = __ovl_dentry_lower(oe);
*is_upper = false;
}
return realdentry;
}
struct ovl_dir_cache *ovl_dir_cache(struct dentry *dentry)
{
struct ovl_entry *oe = dentry->d_fsdata;
return oe->cache;
}
void ovl_set_dir_cache(struct dentry *dentry, struct ovl_dir_cache *cache)
{
struct ovl_entry *oe = dentry->d_fsdata;
oe->cache = cache;
}
void ovl_path_lower(struct dentry *dentry, struct path *path)
{
struct ovl_entry *oe = dentry->d_fsdata;
*path = oe->numlower ? oe->lowerstack[0] : (struct path) { NULL, NULL };
}
int ovl_want_write(struct dentry *dentry)
{
struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
return mnt_want_write(ofs->upper_mnt);
}
void ovl_drop_write(struct dentry *dentry)
{
struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
mnt_drop_write(ofs->upper_mnt);
}
struct dentry *ovl_workdir(struct dentry *dentry)
{
struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
return ofs->workdir;
}
bool ovl_dentry_is_opaque(struct dentry *dentry)
{
struct ovl_entry *oe = dentry->d_fsdata;
return oe->opaque;
}
void ovl_dentry_set_opaque(struct dentry *dentry, bool opaque)
{
struct ovl_entry *oe = dentry->d_fsdata;
oe->opaque = opaque;
}
void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry)
{
struct ovl_entry *oe = dentry->d_fsdata;
WARN_ON(!mutex_is_locked(&upperdentry->d_parent->d_inode->i_mutex));
WARN_ON(oe->__upperdentry);
BUG_ON(!upperdentry->d_inode);
/*
* Make sure upperdentry is consistent before making it visible to
* ovl_upperdentry_dereference().
*/
smp_wmb();
oe->__upperdentry = upperdentry;
}
void ovl_dentry_version_inc(struct dentry *dentry)
{
struct ovl_entry *oe = dentry->d_fsdata;
WARN_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
oe->version++;
}
u64 ovl_dentry_version_get(struct dentry *dentry)
{
struct ovl_entry *oe = dentry->d_fsdata;
WARN_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
return oe->version;
}
bool ovl_is_whiteout(struct dentry *dentry)
{
struct inode *inode = dentry->d_inode;
return inode && IS_WHITEOUT(inode);
}
static bool ovl_is_opaquedir(struct dentry *dentry)
{
int res;
char val;
struct inode *inode = dentry->d_inode;
if (!S_ISDIR(inode->i_mode) || !inode->i_op->getxattr)
return false;
res = inode->i_op->getxattr(dentry, OVL_XATTR_OPAQUE, &val, 1);
if (res == 1 && val == 'y')
return true;
return false;
}
static void ovl_dentry_release(struct dentry *dentry)
{
struct ovl_entry *oe = dentry->d_fsdata;
if (oe) {
unsigned int i;
dput(oe->__upperdentry);
for (i = 0; i < oe->numlower; i++)
dput(oe->lowerstack[i].dentry);
kfree_rcu(oe, rcu);
}
}
static int ovl_dentry_revalidate(struct dentry *dentry, unsigned int flags)
{
struct ovl_entry *oe = dentry->d_fsdata;
unsigned int i;
int ret = 1;
for (i = 0; i < oe->numlower; i++) {
struct dentry *d = oe->lowerstack[i].dentry;
if (d->d_flags & DCACHE_OP_REVALIDATE) {
ret = d->d_op->d_revalidate(d, flags);
if (ret < 0)
return ret;
if (!ret) {
if (!(flags & LOOKUP_RCU))
d_invalidate(d);
return -ESTALE;
}
}
}
return 1;
}
static int ovl_dentry_weak_revalidate(struct dentry *dentry, unsigned int flags)
{
struct ovl_entry *oe = dentry->d_fsdata;
unsigned int i;
int ret = 1;
for (i = 0; i < oe->numlower; i++) {
struct dentry *d = oe->lowerstack[i].dentry;
if (d->d_flags & DCACHE_OP_WEAK_REVALIDATE) {
ret = d->d_op->d_weak_revalidate(d, flags);
if (ret <= 0)
break;
}
}
return ret;
}
static const struct dentry_operations ovl_dentry_operations = {
.d_release = ovl_dentry_release,
.d_select_inode = ovl_d_select_inode,
};
static const struct dentry_operations ovl_reval_dentry_operations = {
.d_release = ovl_dentry_release,
.d_revalidate = ovl_dentry_revalidate,
.d_weak_revalidate = ovl_dentry_weak_revalidate,
};
static struct ovl_entry *ovl_alloc_entry(unsigned int numlower)
{
size_t size = offsetof(struct ovl_entry, lowerstack[numlower]);
struct ovl_entry *oe = kzalloc(size, GFP_KERNEL);
if (oe)
oe->numlower = numlower;
return oe;
}
static bool ovl_dentry_remote(struct dentry *dentry)
{
return dentry->d_flags &
(DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
}
static bool ovl_dentry_weird(struct dentry *dentry)
{
return dentry->d_flags & (DCACHE_NEED_AUTOMOUNT |
DCACHE_MANAGE_TRANSIT |
DCACHE_OP_HASH |
DCACHE_OP_COMPARE);
}
static inline struct dentry *ovl_lookup_real(struct dentry *dir,
struct qstr *name)
{
struct dentry *dentry;
mutex_lock(&dir->d_inode->i_mutex);
dentry = lookup_one_len(name->name, dir, name->len);
mutex_unlock(&dir->d_inode->i_mutex);
if (IS_ERR(dentry)) {
if (PTR_ERR(dentry) == -ENOENT)
dentry = NULL;
} else if (!dentry->d_inode) {
dput(dentry);
dentry = NULL;
} else if (ovl_dentry_weird(dentry)) {
dput(dentry);
/* Don't support traversing automounts and other weirdness */
dentry = ERR_PTR(-EREMOTE);
}
return dentry;
}
/*
* Returns next layer in stack starting from top.
* Returns -1 if this is the last layer.
*/
int ovl_path_next(int idx, struct dentry *dentry, struct path *path)
{
struct ovl_entry *oe = dentry->d_fsdata;
BUG_ON(idx < 0);
if (idx == 0) {
ovl_path_upper(dentry, path);
if (path->dentry)
return oe->numlower ? 1 : -1;
idx++;
}
BUG_ON(idx > oe->numlower);
*path = oe->lowerstack[idx - 1];
return (idx < oe->numlower) ? idx + 1 : -1;
}
struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
unsigned int flags)
{
struct ovl_entry *oe;
struct ovl_entry *poe = dentry->d_parent->d_fsdata;
struct path *stack = NULL;
struct dentry *upperdir, *upperdentry = NULL;
unsigned int ctr = 0;
struct inode *inode = NULL;
bool upperopaque = false;
struct dentry *this, *prev = NULL;
unsigned int i;
int err;
upperdir = ovl_upperdentry_dereference(poe);
if (upperdir) {
this = ovl_lookup_real(upperdir, &dentry->d_name);
err = PTR_ERR(this);
if (IS_ERR(this))
goto out;
if (this) {
if (unlikely(ovl_dentry_remote(this))) {
dput(this);
err = -EREMOTE;
goto out;
}
if (ovl_is_whiteout(this)) {
dput(this);
this = NULL;
upperopaque = true;
} else if (poe->numlower && ovl_is_opaquedir(this)) {
upperopaque = true;
}
}
upperdentry = prev = this;
}
if (!upperopaque && poe->numlower) {
err = -ENOMEM;
stack = kcalloc(poe->numlower, sizeof(struct path), GFP_KERNEL);
if (!stack)
goto out_put_upper;
}
for (i = 0; !upperopaque && i < poe->numlower; i++) {
bool opaque = false;
struct path lowerpath = poe->lowerstack[i];
this = ovl_lookup_real(lowerpath.dentry, &dentry->d_name);
err = PTR_ERR(this);
if (IS_ERR(this)) {
/*
* If it's positive, then treat ENAMETOOLONG as ENOENT.
*/
if (err == -ENAMETOOLONG && (upperdentry || ctr))
continue;
goto out_put;
}
if (!this)
continue;
if (ovl_is_whiteout(this)) {
dput(this);
break;
}
/*
* Only makes sense to check opaque dir if this is not the
* lowermost layer.
*/
if (i < poe->numlower - 1 && ovl_is_opaquedir(this))
opaque = true;
if (prev && (!S_ISDIR(prev->d_inode->i_mode) ||
!S_ISDIR(this->d_inode->i_mode))) {
/*
* FIXME: check for upper-opaqueness maybe better done
* in remove code.
*/
if (prev == upperdentry)
upperopaque = true;
dput(this);
break;
}
/*
* If this is a non-directory then stop here.
*/
if (!S_ISDIR(this->d_inode->i_mode))
opaque = true;
stack[ctr].dentry = this;
stack[ctr].mnt = lowerpath.mnt;
ctr++;
prev = this;
if (opaque)
break;
}
oe = ovl_alloc_entry(ctr);
err = -ENOMEM;
if (!oe)
goto out_put;
if (upperdentry || ctr) {
struct dentry *realdentry;
realdentry = upperdentry ? upperdentry : stack[0].dentry;
err = -ENOMEM;
inode = ovl_new_inode(dentry->d_sb, realdentry->d_inode->i_mode,
oe);
if (!inode)
goto out_free_oe;
ovl_copyattr(realdentry->d_inode, inode);
}
oe->opaque = upperopaque;
oe->__upperdentry = upperdentry;
memcpy(oe->lowerstack, stack, sizeof(struct path) * ctr);
kfree(stack);
dentry->d_fsdata = oe;
d_add(dentry, inode);
return NULL;
out_free_oe:
kfree(oe);
out_put:
for (i = 0; i < ctr; i++)
dput(stack[i].dentry);
kfree(stack);
out_put_upper:
dput(upperdentry);
out:
return ERR_PTR(err);
}
struct file *ovl_path_open(struct path *path, int flags)
{
return dentry_open(path, flags, current_cred());
}
static void ovl_put_super(struct super_block *sb)
{
struct ovl_fs *ufs = sb->s_fs_info;
unsigned i;
dput(ufs->workdir);
mntput(ufs->upper_mnt);
for (i = 0; i < ufs->numlower; i++)
mntput(ufs->lower_mnt[i]);
kfree(ufs->config.lowerdir);
kfree(ufs->config.upperdir);
kfree(ufs->config.workdir);
kfree(ufs);
}
/**
* ovl_statfs
* @sb: The overlayfs super block
* @buf: The struct kstatfs to fill in with stats
*
* Get the filesystem statistics. As writes always target the upper layer
* filesystem pass the statfs to the upper filesystem (if it exists)
*/
static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
{
struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
struct dentry *root_dentry = dentry->d_sb->s_root;
struct path path;
int err;
ovl_path_real(root_dentry, &path);
err = vfs_statfs(&path, buf);
if (!err) {
buf->f_namelen = max(buf->f_namelen, ofs->lower_namelen);
buf->f_type = OVERLAYFS_SUPER_MAGIC;
}
return err;
}
/**
* ovl_show_options
*
* Prints the mount options for a given superblock.
* Returns zero; does not fail.
*/
static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
{
struct super_block *sb = dentry->d_sb;
struct ovl_fs *ufs = sb->s_fs_info;
seq_show_option(m, "lowerdir", ufs->config.lowerdir);
if (ufs->config.upperdir) {
seq_show_option(m, "upperdir", ufs->config.upperdir);
seq_show_option(m, "workdir", ufs->config.workdir);
}
return 0;
}
static int ovl_remount(struct super_block *sb, int *flags, char *data)
{
struct ovl_fs *ufs = sb->s_fs_info;
if (!(*flags & MS_RDONLY) && (!ufs->upper_mnt || !ufs->workdir))
return -EROFS;
return 0;
}
static const struct super_operations ovl_super_operations = {
.put_super = ovl_put_super,
.statfs = ovl_statfs,
.show_options = ovl_show_options,
.remount_fs = ovl_remount,
};
enum {
OPT_LOWERDIR,
OPT_UPPERDIR,
OPT_WORKDIR,
OPT_ERR,
};
static const match_table_t ovl_tokens = {
{OPT_LOWERDIR, "lowerdir=%s"},
{OPT_UPPERDIR, "upperdir=%s"},
{OPT_WORKDIR, "workdir=%s"},
{OPT_ERR, NULL}
};
static char *ovl_next_opt(char **s)
{
char *sbegin = *s;
char *p;
if (sbegin == NULL)
return NULL;
for (p = sbegin; *p; p++) {
if (*p == '\\') {
p++;
if (!*p)
break;
} else if (*p == ',') {
*p = '\0';
*s = p + 1;
return sbegin;
}
}
*s = NULL;
return sbegin;
}
static int ovl_parse_opt(char *opt, struct ovl_config *config)
{
char *p;
while ((p = ovl_next_opt(&opt)) != NULL) {
int token;
substring_t args[MAX_OPT_ARGS];
if (!*p)
continue;
token = match_token(p, ovl_tokens, args);
switch (token) {
case OPT_UPPERDIR:
kfree(config->upperdir);
config->upperdir = match_strdup(&args[0]);
if (!config->upperdir)
return -ENOMEM;
break;
case OPT_LOWERDIR:
kfree(config->lowerdir);
config->lowerdir = match_strdup(&args[0]);
if (!config->lowerdir)
return -ENOMEM;
break;
case OPT_WORKDIR:
kfree(config->workdir);
config->workdir = match_strdup(&args[0]);
if (!config->workdir)
return -ENOMEM;
break;
default:
pr_err("overlayfs: unrecognized mount option \"%s\" or missing value\n", p);
return -EINVAL;
}
}
/* Workdir is useless in non-upper mount */
if (!config->upperdir && config->workdir) {
pr_info("overlayfs: option \"workdir=%s\" is useless in a non-upper mount, ignore\n",
config->workdir);
kfree(config->workdir);
config->workdir = NULL;
}
return 0;
}
#define OVL_WORKDIR_NAME "work"
static struct dentry *ovl_workdir_create(struct vfsmount *mnt,
struct dentry *dentry)
{
struct inode *dir = dentry->d_inode;
struct dentry *work;
int err;
bool retried = false;
err = mnt_want_write(mnt);
if (err)
return ERR_PTR(err);
mutex_lock_nested(&dir->i_mutex, I_MUTEX_PARENT);
retry:
work = lookup_one_len(OVL_WORKDIR_NAME, dentry,
strlen(OVL_WORKDIR_NAME));
if (!IS_ERR(work)) {
struct kstat stat = {
.mode = S_IFDIR | 0,
};
if (work->d_inode) {
err = -EEXIST;
if (retried)
goto out_dput;
retried = true;
ovl_cleanup(dir, work);
dput(work);
goto retry;
}
err = ovl_create_real(dir, work, &stat, NULL, NULL, true);
if (err)
goto out_dput;
}
out_unlock:
mutex_unlock(&dir->i_mutex);
mnt_drop_write(mnt);
return work;
out_dput:
dput(work);
work = ERR_PTR(err);
goto out_unlock;
}
static void ovl_unescape(char *s)
{
char *d = s;
for (;; s++, d++) {
if (*s == '\\')
s++;
*d = *s;
if (!*s)
break;
}
}
static int ovl_mount_dir_noesc(const char *name, struct path *path)
{
int err = -EINVAL;
if (!*name) {
pr_err("overlayfs: empty lowerdir\n");
goto out;
}
err = kern_path(name, LOOKUP_FOLLOW, path);
if (err) {
pr_err("overlayfs: failed to resolve '%s': %i\n", name, err);
goto out;
}
err = -EINVAL;
if (ovl_dentry_weird(path->dentry)) {
pr_err("overlayfs: filesystem on '%s' not supported\n", name);
goto out_put;
}
if (!S_ISDIR(path->dentry->d_inode->i_mode)) {
pr_err("overlayfs: '%s' not a directory\n", name);
goto out_put;
}
return 0;
out_put:
path_put(path);
out:
return err;
}
static int ovl_mount_dir(const char *name, struct path *path)
{
int err = -ENOMEM;
char *tmp = kstrdup(name, GFP_KERNEL);
if (tmp) {
ovl_unescape(tmp);
err = ovl_mount_dir_noesc(tmp, path);
if (!err)
if (ovl_dentry_remote(path->dentry)) {
pr_err("overlayfs: filesystem on '%s' not supported as upperdir\n",
tmp);
path_put(path);
err = -EINVAL;
}
kfree(tmp);
}
return err;
}
static int ovl_lower_dir(const char *name, struct path *path, long *namelen,
int *stack_depth, bool *remote)
{
int err;
struct kstatfs statfs;
err = ovl_mount_dir_noesc(name, path);
if (err)
goto out;
err = vfs_statfs(path, &statfs);
if (err) {
pr_err("overlayfs: statfs failed on '%s'\n", name);
goto out_put;
}
*namelen = max(*namelen, statfs.f_namelen);
*stack_depth = max(*stack_depth, path->mnt->mnt_sb->s_stack_depth);
if (ovl_dentry_remote(path->dentry))
*remote = true;
return 0;
out_put:
path_put(path);
out:
return err;
}
/* Workdir should not be subdir of upperdir and vice versa */
static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
{
bool ok = false;
if (workdir != upperdir) {
ok = (lock_rename(workdir, upperdir) == NULL);
unlock_rename(workdir, upperdir);
}
return ok;
}
static unsigned int ovl_split_lowerdirs(char *str)
{
unsigned int ctr = 1;
char *s, *d;
for (s = d = str;; s++, d++) {
if (*s == '\\') {
s++;
} else if (*s == ':') {
*d = '\0';
ctr++;
continue;
}
*d = *s;
if (!*s)
break;
}
return ctr;
}
static int ovl_fill_super(struct super_block *sb, void *data, int silent)
{
struct path upperpath = { NULL, NULL };
struct path workpath = { NULL, NULL };
struct dentry *root_dentry;
struct ovl_entry *oe;
struct ovl_fs *ufs;
struct path *stack = NULL;
char *lowertmp;
char *lower;
unsigned int numlower;
unsigned int stacklen = 0;
unsigned int i;
bool remote = false;
int err;
err = -ENOMEM;
ufs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
if (!ufs)
goto out;
err = ovl_parse_opt((char *) data, &ufs->config);
if (err)
goto out_free_config;
err = -EINVAL;
if (!ufs->config.lowerdir) {
pr_err("overlayfs: missing 'lowerdir'\n");
goto out_free_config;
}
sb->s_stack_depth = 0;
if (ufs->config.upperdir) {
if (!ufs->config.workdir) {
pr_err("overlayfs: missing 'workdir'\n");
goto out_free_config;
}
err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
if (err)
goto out_free_config;
/* Upper fs should not be r/o */
if (upperpath.mnt->mnt_sb->s_flags & MS_RDONLY) {
pr_err("overlayfs: upper fs is r/o, try multi-lower layers mount\n");
err = -EINVAL;
goto out_put_upperpath;
}
err = ovl_mount_dir(ufs->config.workdir, &workpath);
if (err)
goto out_put_upperpath;
err = -EINVAL;
if (upperpath.mnt != workpath.mnt) {
pr_err("overlayfs: workdir and upperdir must reside under the same mount\n");
goto out_put_workpath;
}
if (!ovl_workdir_ok(workpath.dentry, upperpath.dentry)) {
pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
goto out_put_workpath;
}
sb->s_stack_depth = upperpath.mnt->mnt_sb->s_stack_depth;
}
err = -ENOMEM;
lowertmp = kstrdup(ufs->config.lowerdir, GFP_KERNEL);
if (!lowertmp)
goto out_put_workpath;
err = -EINVAL;
stacklen = ovl_split_lowerdirs(lowertmp);
if (stacklen > OVL_MAX_STACK) {
pr_err("overlayfs: too many lower directries, limit is %d\n",
OVL_MAX_STACK);
goto out_free_lowertmp;
} else if (!ufs->config.upperdir && stacklen == 1) {
pr_err("overlayfs: at least 2 lowerdir are needed while upperdir nonexistent\n");
goto out_free_lowertmp;
}
stack = kcalloc(stacklen, sizeof(struct path), GFP_KERNEL);
if (!stack)
goto out_free_lowertmp;
lower = lowertmp;
for (numlower = 0; numlower < stacklen; numlower++) {
err = ovl_lower_dir(lower, &stack[numlower],
&ufs->lower_namelen, &sb->s_stack_depth,
&remote);
if (err)
goto out_put_lowerpath;
lower = strchr(lower, '\0') + 1;
}
err = -EINVAL;
sb->s_stack_depth++;
if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
pr_err("overlayfs: maximum fs stacking depth exceeded\n");
goto out_put_lowerpath;
}
if (ufs->config.upperdir) {
ufs->upper_mnt = clone_private_mount(&upperpath);
err = PTR_ERR(ufs->upper_mnt);
if (IS_ERR(ufs->upper_mnt)) {
pr_err("overlayfs: failed to clone upperpath\n");
goto out_put_lowerpath;
}
ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
err = PTR_ERR(ufs->workdir);
if (IS_ERR(ufs->workdir)) {
pr_warn("overlayfs: failed to create directory %s/%s (errno: %i); mounting read-only\n",
ufs->config.workdir, OVL_WORKDIR_NAME, -err);
sb->s_flags |= MS_RDONLY;
ufs->workdir = NULL;
}
}
err = -ENOMEM;
ufs->lower_mnt = kcalloc(numlower, sizeof(struct vfsmount *), GFP_KERNEL);
if (ufs->lower_mnt == NULL)
goto out_put_workdir;
for (i = 0; i < numlower; i++) {
struct vfsmount *mnt = clone_private_mount(&stack[i]);
err = PTR_ERR(mnt);
if (IS_ERR(mnt)) {
pr_err("overlayfs: failed to clone lowerpath\n");
goto out_put_lower_mnt;
}
/*
* Make lower_mnt R/O. That way fchmod/fchown on lower file
* will fail instead of modifying lower fs.
*/
mnt->mnt_flags |= MNT_READONLY;
ufs->lower_mnt[ufs->numlower] = mnt;
ufs->numlower++;
}
/* If the upper fs is nonexistent, we mark overlayfs r/o too */
if (!ufs->upper_mnt)
sb->s_flags |= MS_RDONLY;
if (remote)
sb->s_d_op = &ovl_reval_dentry_operations;
else
sb->s_d_op = &ovl_dentry_operations;
err = -ENOMEM;
oe = ovl_alloc_entry(numlower);
if (!oe)
goto out_put_lower_mnt;
root_dentry = d_make_root(ovl_new_inode(sb, S_IFDIR, oe));
if (!root_dentry)
goto out_free_oe;
mntput(upperpath.mnt);
for (i = 0; i < numlower; i++)
mntput(stack[i].mnt);
path_put(&workpath);
kfree(lowertmp);
oe->__upperdentry = upperpath.dentry;
for (i = 0; i < numlower; i++) {
oe->lowerstack[i].dentry = stack[i].dentry;
oe->lowerstack[i].mnt = ufs->lower_mnt[i];
}
root_dentry->d_fsdata = oe;
sb->s_magic = OVERLAYFS_SUPER_MAGIC;
sb->s_op = &ovl_super_operations;
sb->s_root = root_dentry;
sb->s_fs_info = ufs;
return 0;
out_free_oe:
kfree(oe);
out_put_lower_mnt:
for (i = 0; i < ufs->numlower; i++)
mntput(ufs->lower_mnt[i]);
kfree(ufs->lower_mnt);
out_put_workdir:
dput(ufs->workdir);
mntput(ufs->upper_mnt);
out_put_lowerpath:
for (i = 0; i < numlower; i++)
path_put(&stack[i]);
kfree(stack);
out_free_lowertmp:
kfree(lowertmp);
out_put_workpath:
path_put(&workpath);
out_put_upperpath:
path_put(&upperpath);
out_free_config:
kfree(ufs->config.lowerdir);
kfree(ufs->config.upperdir);
kfree(ufs->config.workdir);
kfree(ufs);
out:
return err;
}
static struct dentry *ovl_mount(struct file_system_type *fs_type, int flags,
const char *dev_name, void *raw_data)
{
return mount_nodev(fs_type, flags, raw_data, ovl_fill_super);
}
static struct file_system_type ovl_fs_type = {
.owner = THIS_MODULE,
.name = "overlay",
.mount = ovl_mount,
.kill_sb = kill_anon_super,
};
MODULE_ALIAS_FS("overlay");
static int __init ovl_init(void)
{
return register_filesystem(&ovl_fs_type);
}
static void __exit ovl_exit(void)
{
unregister_filesystem(&ovl_fs_type);
}
module_init(ovl_init);
module_exit(ovl_exit);