qemu-img rebase: Fix output image corruption

qemu-img rebase must always give clusters in the COW file priority over those
in the backing file. As it failed to use number of non-allocated clusters but
assumed the maximum, it was possible that allocated clusters were taken from
the backing file instead, leading to a corrupted output image.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/qemu-img.c b/qemu-img.c
index c21d9990e..d3c30a74f 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1136,7 +1136,7 @@ static int img_rebase(int argc, char **argv)
     if (!unsafe) {
         uint64_t num_sectors;
         uint64_t sector;
-        int n, n1;
+        int n;
         uint8_t * buf_old;
         uint8_t * buf_new;
 
@@ -1155,8 +1155,8 @@ static int img_rebase(int argc, char **argv)
             }
 
             /* If the cluster is allocated, we don't need to take action */
-            if (bdrv_is_allocated(bs, sector, n, &n1)) {
-                n = n1;
+            ret = bdrv_is_allocated(bs, sector, n, &n);
+            if (ret) {
                 continue;
             }