[Qemu-devel] [patch] qcow2: double free snapshots

[Zhang Haoyu]

In qcow2_open(), if qcow2_read_snapshots() failed, qcow2_open() -> 
qcow2_free_snapshots() will be called, NULL snapshots dereference happened.
because qcow2_free_snapshots has been performed before in the fail case of 
qcow2_read_snapshots().
shown as below callstack,
qcow2_open
|- qcow2_read_snapshots
|-- goto fail;
|-- qcow2_free_snapshots
|- goto fail;
|- qcow2_free_snapshots  /* on this case, NULL snapshots dereference happened.  
*/

Signed-off-by: Zhang Haoyu <address@hidden>
---
 block/qcow2-snapshot.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
index 0aa9def..15c0513 100644
--- a/block/qcow2-snapshot.c
+++ b/block/qcow2-snapshot.c
@@ -31,6 +31,10 @@ void qcow2_free_snapshots(BlockDriverState *bs)
     BDRVQcowState *s = bs->opaque;
     int i;
 
+    if (!s || !s->snapshots) {
+        return;
+    }
+
     for(i = 0; i < s->nb_snapshots; i++) {
         g_free(s->snapshots[i].name);
         g_free(s->snapshots[i].id_str);
-- 
1.9.4.msysgit.0