Re: [PATCH] ext4: fix mmp use after free during unmount

[Theodore Ts'o <tytso@mit.edu>]

On Thu, Oct 20, 2016 at 02:26:38PM -0600, Andreas Dilger wrote:
> On Oct 20, 2016, at 12:19 PM, Eric Sandeen <sandeen@redhat.com> wrote:
> > 
> > In ext4_put_super, we call brelse on the buffer head containing
> > the ext4 superblock, but then try to use it when we stop the
> > mmp thread, because when the thread shuts down it does:
> > 
> > write_mmp_block
> >  ext4_mmp_csum_set
> >    ext4_has_metadata_csum
> >      WARN_ON_ONCE(ext4_has_feature_metadata_csum(sb)...)
> > 
> > which reaches into sb->s_fs_info->s_es->s_feature_ro_compat,
> > which lives in the superblock buffer s_sbh which we just released.
> > 
> > Fix this by moving the brelse down to a point where we are no
> > longer using it.
> > 
> > Reported-by: Wang Shu <shuwang@redhat.com>
> > Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> 
> Reviewed-by: Andreas Dilger <adilger@dilger.ca>

Applied, thanks.

					- Ted