github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-09-12 04:23:03 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph

configfs: Fixes for v7.3-rc2

Browse Source 
- A symlink racing with rmdir of its target could reach a freed
   ->ci_dentry. The reference get_target() takes pins the config_item,
   not its dentry; the dentry is pinned by DCACHE_PERSISTENT, which
   configfs_remove_dir() drops while the item is still alive. Take the
   target's configfs_dirent under ->d_lock instead of chasing
   ->ci_dentry.
 
 - configfs_rmdir() left the dentry hashed across the final put of the
   item, and configfs_get_config_item() treats a hashed dentry as proof
   of a live item. A concurrent symlink could therefore resurrect a
   dying item and hit a use-after-free. Unhash in configfs_remove_dir(),
   while the item is still guaranteed to be there.
 
 Both issues were found by syzbot.
 -----BEGIN PGP SIGNATURE-----
 
 iQIzBAABCAAdFiEErIU5puj0ZwLKSkObNaOTn/x4d20FAmqe6GQACgkQNaOTn/x4
 d21unBAAqg0vIxjQAGhQ/hZnnqdFJ9es63NE93H4ZZJzkLa9J5xqMnbAVAOUoPwo
 BIbUs4uNVunJdhx3hgiPFSjEB9g+d9xxuoxNLHNPFptQe720QJ5ETC5X/QCmCrUc
 QUOVLFN0EomOXXN7HK8+hKKTbslIFHDN2SmLkICprHwL6YKygginhhHaHGukY8Oo
 Mfro0MTaFaVvQM6137r9EB3pnR+i+mtwEDjyWxBQFH3/KtyPW0RrUiyPM5uBP5ds
 ECr1UsqMNFJfeLDH8T6SQ80hz/dczByo5OHyrMrmdmeQWmZLNEtKS0Q9L7kveS5L
 l5PuAH2f6PHcF+cziflvB1hVy/zFWAZ6aOUMdKJY7HBImMWnWdjhm2p9ssVVe0zy
 GlrXbULTekq7W4o/X70948hnk0jU3auHkeFSTHc6T/u8pt1HmKVV+Bg/uYsj8cFh
 +DSeR5iZwj5LaYQ9mMocZQucjEBjT/Cqy/N2sT2gvKqnbyQ0w1mJEeuXMrU23NsV
 2oRSMcXYEraBw6Ccnq2E7LL97tKwLp4g7myUsUGjcAe6i1JSM8d1X9wDoyL9QaHs
 JTdHzIg0LoDX5hHjc7gBW2/Kj3cm8xvvs+lxjNM8aBIsszKTGVNakjA3IsI5UFax
 /1IhMMKiyhIGJO2APFlfAzViTPm04DuAkFM80zCdH9pRfvcD2DU=
 =kqSj
 -----END PGP SIGNATURE-----

Merge tag 'configfs-7.3-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/leitao/linux

Pull configfs fixes from Breno Leitao:

 - A symlink racing with rmdir of its target could reach a freed
   ->ci_dentry.

   The reference that get_target() takes pins the config_item, not
   its dentry; the dentry is pinned by DCACHE_PERSISTENT, which
   configfs_remove_dir() drops while the item is still alive.

   Take the target's configfs_dirent under ->d_lock instead of chasing
   ->ci_dentry.

 - configfs_rmdir() left the dentry hashed across the final put of the
   item, and configfs_get_config_item() treats a hashed dentry as proof
   of a live item. A concurrent symlink could therefore resurrect a
   dying item and hit a use-after-free.

   Unhash in configfs_remove_dir(), while the item is still guaranteed
   to be there.

Both issues were found by syzbot.

* tag 'configfs-7.3-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/leitao/linux:
  configfs: unhash the dentry before dropping the item in rmdir
  configfs: pin the symlink target's dirent instead of chasing ->ci_dentry
This commit is contained in:
Linus Torvalds 2026-09-07 10:01:38 -07:00
commit c297ed90fb
2 changed files with 29 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
fs/configfs/dir.c
View File

@ -416,6 +416,15 @@ static void configfs_remove_dir(struct dentry *d)
if (d_really_is_positive(d)) {
if (unlikely(simple_rmdir(d_inode(parent), d)))
pr_warn("remove_dir (%pd): attributes remain", d);
else
/*
* configfs_get_config_item() takes a hashed dentry as
* proof that ->s_element is still alive. Our caller
* is about to drop the last reference to the item and
* the VFS will not unhash until after we return, so
* unhash it here.
*/
d_drop(d);
}
pr_debug(" o %pd removing done (%d)\n", d, d_count(d));

24
fs/configfs/symlink.c
View File

@ -76,9 +76,9 @@ static int configfs_get_target_path(struct config_item *item,
static int create_link(struct config_item *parent_item,
struct config_item *item,
struct configfs_dirent *target_sd,
struct dentry *dentry)
{
struct configfs_dirent *target_sd = item->ci_dentry->d_fsdata;
char *body;
int ret;
@ -115,6 +115,7 @@ static int create_link(struct config_item *parent_item,
static int get_target(const char *symname, struct config_item **target,
struct configfs_dirent **target_sd,
struct super_block *sb)
{
struct path path __free(path_put) = {};
@ -125,7 +126,20 @@ static int get_target(const char *symname, struct config_item **target,
return ret;
if (path.dentry->d_sb != sb)
return -EPERM;
*target = configfs_get_config_item(path.dentry);
/*
* A hashed dentry guarantees that neither the item nor the dirent
* have been released yet, as removals unhash before dropping.
* Grab both references here. An item reference alone would not keep
* ->ci_dentry alive.
*/
spin_lock(&path.dentry->d_lock);
if (!d_unhashed(path.dentry)) {
struct configfs_dirent *sd = path.dentry->d_fsdata;
*target = config_item_get(sd->s_element);
*target_sd = configfs_get(sd);
}
spin_unlock(&path.dentry->d_lock);
if (!*target)
return -ENOENT;
return 0;
@ -139,6 +153,7 @@ int configfs_symlink(struct mnt_idmap *idmap, struct inode *dir,
struct configfs_dirent *sd;
struct config_item *parent_item;
struct config_item *target_item = NULL;
struct configfs_dirent *target_sd = NULL;
const struct config_item_type *type;
sd = dentry->d_parent->d_fsdata;
@ -182,7 +197,7 @@ int configfs_symlink(struct mnt_idmap *idmap, struct inode *dir,
* AV, a thoroughly annoyed bastard.
*/
inode_unlock(dir);
ret = get_target(symname, &target_item, dentry->d_sb);
ret = get_target(symname, &target_item, &target_sd, dentry->d_sb);
inode_lock(dir);
if (ret)
goto out_put;
@ -196,13 +211,14 @@ int configfs_symlink(struct mnt_idmap *idmap, struct inode *dir,
ret = type->ct_item_ops->allow_link(parent_item, target_item);
if (!ret) {
mutex_lock(&configfs_symlink_mutex);
ret = create_link(parent_item, target_item, dentry);
ret = create_link(parent_item, target_item, target_sd, dentry);
mutex_unlock(&configfs_symlink_mutex);
if (ret && type->ct_item_ops->drop_link)
type->ct_item_ops->drop_link(parent_item,
target_item);
}
configfs_put(target_sd);
config_item_put(target_item);
out_put: