From: Bob Peterson Date: Tue, 10 Dec 2013 17:06:35 +0000 (-0500) Subject: GFS2: Fix use-after-free race when calling gfs2_remove_from_ail X-Git-Tag: v3.13-rc7~5^2~4 X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=9290a9a7c0bcf5400e8dbfbf9707fa68ea3fb338;p=linux-block.git GFS2: Fix use-after-free race when calling gfs2_remove_from_ail Function gfs2_remove_from_ail drops the reference on the bh via brelse. This patch fixes a race condition whereby bh is deferenced after the brelse when setting bd->bd_blkno = bh->b_blocknr; Under certain rare circumstances, bh might be gone or reused, and bd->bd_blkno is set to whatever that memory happens to be, which is often 0. Later, in gfs2_trans_add_unrevoke, that bd fails the test "bd->bd_blkno >= blkno" which causes it to never be freed. The end result is that the bd is never freed from the bufdata cache, which results in this error: slab error in kmem_cache_destroy(): cache `gfs2_bufdata': Can't free all objects Signed-off-by: Bob Peterson Signed-off-by: Steven Whitehouse --- diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c index 610613fb65b5..9dcb9777a5f8 100644 --- a/fs/gfs2/log.c +++ b/fs/gfs2/log.c @@ -551,10 +551,10 @@ void gfs2_add_revoke(struct gfs2_sbd *sdp, struct gfs2_bufdata *bd) struct buffer_head *bh = bd->bd_bh; struct gfs2_glock *gl = bd->bd_gl; - gfs2_remove_from_ail(bd); - bd->bd_bh = NULL; bh->b_private = NULL; bd->bd_blkno = bh->b_blocknr; + gfs2_remove_from_ail(bd); /* drops ref on bh */ + bd->bd_bh = NULL; bd->bd_ops = &gfs2_revoke_lops; sdp->sd_log_num_revoke++; atomic_inc(&gl->gl_revokes);