gfs2: fix use-after-free in trans_drain

This patch adds code to function trans_drain to remove drained
bd elements from the ail lists, if queued, before freeing the bd.
If we don't remove the bd from the ail, function ail_drain will
try to reference the bd after it has been freed by trans_drain.

Thanks to Andy Price for his analysis of the problem.

Reported-by: Andy Price <anprice@redhat.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index 16937ebb2a3e..760af666576c 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -998,12 +998,16 @@ static void trans_drain(struct gfs2_trans *tr)
 	while (!list_empty(head)) {
 		bd = list_first_entry(head, struct gfs2_bufdata, bd_list);
 		list_del_init(&bd->bd_list);
+		if (!list_empty(&bd->bd_ail_st_list))
+			gfs2_remove_from_ail(bd);
 		kmem_cache_free(gfs2_bufdata_cachep, bd);
 	}
 	head = &tr->tr_databuf;
 	while (!list_empty(head)) {
 		bd = list_first_entry(head, struct gfs2_bufdata, bd_list);
 		list_del_init(&bd->bd_list);
+		if (!list_empty(&bd->bd_ail_st_list))
+			gfs2_remove_from_ail(bd);
 		kmem_cache_free(gfs2_bufdata_cachep, bd);
 	}
 }