Re: [PATCH] xfs: fix use after free in buf log item unlock assert

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Fri, Mar 29, 2019 at 10:03:28AM -0400, Brian Foster wrote:
> On Wed, Feb 06, 2019 at 11:01:07AM -0500, Brian Foster wrote:
> > The xfs_buf_log_item ->iop_unlock() callback asserts that the buffer
> > is unlocked when either non-stale or aborted. This assert occurs
> > after the bli refcount has been dropped and the log item potentially
> > freed. The aborted check is thus a potential use after free. This
> > problem has been reproduced with KASAN enabled via generic/475.
> > 
> > Fix up xfs_buf_item_unlock() to query aborted state before the bli
> > reference is dropped to prevent a potential use after free.
> > 
> > Signed-off-by: Brian Foster <bfoster@redhat.com>
> > ---
> 
> Ping on this one.. looks like it was reviewed and maybe fell through the
> cracks?

Yep.  Spreadsheet says it's in 5.0-rc6, and ... totally not upstream. :(
Sorry about that.

--D

> Brian
> 
> >  fs/xfs/xfs_buf_item.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/xfs/xfs_buf_item.c b/fs/xfs/xfs_buf_item.c
> > index 010db5f8fb00..65b32acfa0f6 100644
> > --- a/fs/xfs/xfs_buf_item.c
> > +++ b/fs/xfs/xfs_buf_item.c
> > @@ -605,6 +605,8 @@ xfs_buf_item_unlock(
> >  #if defined(DEBUG) || defined(XFS_WARN)
> >  	bool			ordered = bip->bli_flags & XFS_BLI_ORDERED;
> >  	bool			dirty = bip->bli_flags & XFS_BLI_DIRTY;
> > +	bool			aborted = test_bit(XFS_LI_ABORTED,
> > +						   &lip->li_flags);
> >  #endif
> >  
> >  	trace_xfs_buf_item_unlock(bip);
> > @@ -633,7 +635,7 @@ xfs_buf_item_unlock(
> >  	released = xfs_buf_item_put(bip);
> >  	if (hold || (stale && !released))
> >  		return;
> > -	ASSERT(!stale || test_bit(XFS_LI_ABORTED, &lip->li_flags));
> > +	ASSERT(!stale || aborted);
> >  	xfs_buf_relse(bp);
> >  }
> >  
> > -- 
> > 2.17.2
> >