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>

1 files changed, 4 insertions, 3 deletions

diff --git a/block/qcow2.c b/block/qcow2.c
index b64564d171..be48a27afa 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -637,9 +637,6 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
 
-    s->snapshots_offset = header.snapshots_offset;
-    s->nb_snapshots = header.nb_snapshots;
-
     /* read the level 1 table */
     if (header.l1_size > 0x2000000) {
         /* 32 MB L1 table is enough for 2 PB images at 64k cluster size
@@ -734,6 +731,10 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, 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) {
         error_setg_errno(errp, -ret, "Could not read snapshots");