Re: [PATCH] ovl: use I_MUTEX_PARENT when locking parent in ovl_create_temp()

On Thu, Aug 21, 2025 at 3:43 PM Amir Goldstein amir73il@gmail.com wrote:

From: NeilBrown neil@brown.name

commit 5f1c8965e748c150d580a2ea8fbee1bd80d07a24 upstream.

ovl_create_temp() treats "workdir" as a parent in which it creates an object so it should use I_MUTEX_PARENT.

Prior to the commit identified below the lock was taken by the caller which sometimes used I_MUTEX_PARENT and sometimes used I_MUTEX_NORMAL. The use of I_MUTEX_NORMAL was incorrect but unfortunately copied into ovl_create_temp().

Note to backporters: This patch only applies after the last Fixes given below (post v6.16). To fix the bug in v6.7 and later the inode_lock() call in ovl_copy_up_workdir() needs to nest using I_MUTEX_PARENT.

[Amir: backport to v6.16 when lock was taken by the callers]

Greg,

Forgot to mention stable version in subject line. This should apply cleanly to 6.16.y and 6.12.y.

Thanks, Amir.

Link: https://lore.kernel.org/all/67a72070.050a0220.3d72c.0022.GAE@google.com/ Cc: stable@vger.kernel.org Reported-by: syzbot+7836a68852a10ec3d790@syzkaller.appspotmail.com Tested-by: syzbot+7836a68852a10ec3d790@syzkaller.appspotmail.com Fixes: c63e56a4a652 ("ovl: do not open/llseek lower file with upper sb_writers held") Fixes: d2c995581c7c ("ovl: Call ovl_create_temp() without lock held.") Signed-off-by: NeilBrown neil@brown.name Signed-off-by: Amir Goldstein amir73il@gmail.com

---

fs/overlayfs/copy_up.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c index d7310fcf38881..c2263148ff20a 100644 --- a/fs/overlayfs/copy_up.c +++ b/fs/overlayfs/copy_up.c @@ -779,7 +779,7 @@ static int ovl_copy_up_workdir(struct ovl_copy_up_ctx *c) return err;

    ovl_start_write(c->dentry);

•   inode_lock(wdir);
  

•   inode_lock_nested(wdir, I_MUTEX_PARENT);
    temp = ovl_create_temp(ofs, c->workdir, &cattr);
    inode_unlock(wdir);
    ovl_end_write(c->dentry);
  

-- 2.50.1