qcow2: Fix NULL dereference in qcow2_open() error path (CVE-2014-0146)

The qcow2 code assumes that s->snapshots is non-NULL if s->nb_snapshots
!= 0. By having the initialisation of both fields separated in
qcow2_open(), any error occuring in between would cause the error path
to dereference NULL in qcow2_free_snapshots() if the image had any
snapshots.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

diff --git a/block/qcow2.c b/block/qcow2.c
index c1ff31f4827c61067ab1a51454bc76339649994b..e40f733f02ff78d53737fd471c90cb6e33febd12 100644 (file)
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -403,9 +403,6 @@ static int qcow2_open(BlockDriverState *bs, int flags)
     s->refcount_table_size =
         header.refcount_table_clusters << (s->cluster_bits - 3);
 
-    s->snapshots_offset = header.snapshots_offset;
-    s->nb_snapshots = header.nb_snapshots;
-
     /* read the level 1 table */
     s->l1_size = header.l1_size;
     s->l1_vm_state_index = size_to_l1(s, header.size);
@@ -467,6 +464,10 @@ static int qcow2_open(BlockDriverState *bs, int flags)
         bs->backing_file[len] = '\0';
     }
 
+    /* Internal snapshots */
+    s->snapshots_offset = header.snapshots_offset;
+    s->nb_snapshots = header.nb_snapshots;
+
     ret = qcow2_read_snapshots(bs);
     if (ret < 0) {
         goto fail;