From f06c2d26d1999d37e93299db0ecead04ca7d0b9f Mon Sep 17 00:00:00 2001 From: Vasileios Almpanis Date: Thu, 30 Jul 2026 11:30:25 +0200 Subject: configfs: unhash the dentry before dropping the item in rmdir 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: 7063fbf22611 ("[PATCH] configfs: User-driven configuration filesystem") Cc: stable@vger.kernel.org Signed-off-by: Vasileios Almpanis Tested-by: Breno Leitao Reviewed-by: Breno Leitao Link: https://patch.msgid.link/20260730093435.195441-3-vasilisalmpanis@gmail.com Signed-off-by: Breno Leitao --- fs/configfs/dir.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c index 3c88f13f1ca2..eda80c2a2d38 100644 --- a/fs/configfs/dir.c +++ b/fs/configfs/dir.c @@ -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)); -- cgit v1.2.3