Re: [bug report] ext4: Fix possible corruption when moving a directory

From: Jan Kara <jack@suse.cz>
To: Eric Biggers <ebiggers@kernel.org>
Cc: Dan Carpenter <error27@gmail.com>,
	jack@suse.cz, linux-ext4@vger.kernel.org
Subject: Re: [bug report] ext4: Fix possible corruption when moving a directory
Date: Wed, 8 Mar 2023 11:42:34 +0100	[thread overview]
Message-ID: <20230308104234.z7vmgmjz2smepwlg@quack3> (raw)
In-Reply-To: <ZAeOFzbhCNvskQ6b@gmail.com>

On Tue 07-03-23 19:18:47, Eric Biggers wrote:
> On Tue, Mar 07, 2023 at 06:56:28PM +0300, Dan Carpenter wrote:
> > Hello Jan Kara,
> > 
> > The patch 0813299c586b: "ext4: Fix possible corruption when moving a
> > directory" from Jan 26, 2023, leads to the following Smatch static
> > checker warning:
> > 
> > 	fs/ext4/namei.c:4017 ext4_rename()
> > 	error: double unlocked '&old.inode->i_rwsem' (orig line 3882)
> > 
> [...]
> >     3875                 /*
> >     3876                  * We need to protect against old.inode directory getting
> >     3877                  * converted from inline directory format into a normal one.
> >     3878                  */
> >     3879                 inode_lock_nested(old.inode, I_MUTEX_NONDIR2);
> >     3880                 retval = ext4_rename_dir_prepare(handle, &old);
> >     3881                 if (retval) {
> >     3882                         inode_unlock(old.inode);
> > 
> > The issue here is that ext4_rename_dir_prepare() sets old.dir_bh and
> > then returns -EFSCORRUPTED.  It results in an unlock here and then again
> > after the goto.
> 
> That analysis looks correct.  FYI, I think this is the same as the syzbot report
> "[ext4?] WARNING: bad unlock balance in ext4_rename2"
> (https://lore.kernel.org/linux-ext4/000000000000435c6905f639ae8e@google.com).

Good spotting! This should be fixed (along with the lock ordering problem)
by 3c92792da8506 ("ext4: Fix deadlock during directory rename") Ted has
just merged couple hours ago.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR