github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-09-11 11:12:48 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph

configfs: unhash the dentry before dropping the item in rmdir

Browse Source 
configfs_get_config_item() treats a hashed dentry as proof that
sd->s_element is a live config_item.  configfs_rmdir() breaks that:
simple_rmdir() leaves the dentry hashed, the last reference to the item is
dropped right after, and the dentry is only unhashed by d_delete() once
->rmdir() has returned.  configfs_symlink() resolves its target holding no
lock on it, so get_target() can land in that window:

  BUG: KASAN: slab-use-after-free in config_item_get+0x26/0x90
   get_target fs/configfs/symlink.c:128 [inline]
   configfs_symlink+0x4ab/0x1030 fs/configfs/symlink.c:185

Unhash in configfs_remove_dir(), while the item is still guaranteed to be
there.  A reference obtained just before that stays harmless, as
create_link() rechecks CONFIGFS_USET_DROPPING, already set by
configfs_detach_prep().  Both configfs_unregister_subsystem() paths
d_drop() after detaching, so this only makes rmdir match them.

Reported-by: syzbot+6b16e3d085833cbf3e25@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=6b16e3d085833cbf3e25
Fixes: 7063fbf226 ("[PATCH] configfs: User-driven configuration filesystem")
Cc: stable@vger.kernel.org
Signed-off-by: Vasileios Almpanis <vasilisalmpanis@gmail.com>
Tested-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20260730093435.195441-3-vasilisalmpanis@gmail.com
Signed-off-by: Breno Leitao <leitao@debian.org>
This commit is contained in:
Vasileios Almpanis 2026-07-30 11:30:25 +02:00 committed by Breno Leitao
parent a7c1290eef
commit f06c2d26d1
1 changed files with 9 additions and 0 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));