[libvirt] [PATCH] util: avoid null deref on qcowXGetBackingStore

[ajia at redhat.com]

From: Alex Jia <ajia at redhat.com>

Detected by Coverity. the only case is caller passes a NULL to 'format' variable,
then taking 'if (format)' false branch, the function qcow2GetBackingStoreFormat
will directly dereferences the NULL 'format' pointer variable.

Signed-off-by: Alex Jia <ajia at redhat.com>
---
 src/util/storage_file.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/src/util/storage_file.c b/src/util/storage_file.c
index f33ea74..ba9cfc5 100644
--- a/src/util/storage_file.c
+++ b/src/util/storage_file.c
@@ -333,7 +333,7 @@ qcowXGetBackingStore(char **res,
      * between the end of the header (QCOW2_HDR_TOTAL_SIZE)
      * and the start of the backingStoreName (offset)
      */
-    if (isQCow2)
+    if (isQCow2 && format)
         qcow2GetBackingStoreFormat(format, buf, buf_size, QCOW2_HDR_TOTAL_SIZE, offset);
 
     return BACKING_STORE_OK;
-- 
1.7.1