qcow2: Avoid making the L1 table too big

We refuse to open images whose L1 table we deem "too big". Consequently,
we should not produce such images ourselves.

Cc: qemu-stable@nongnu.org
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Message-id: 20160615153630.2116-3-mreitz@redhat.com
Reviewed-by: NEric Blake <eblake@redhat.com>
[mreitz: Added QEMU_BUILD_BUG_ON()]
Signed-off-by: NMax Reitz <mreitz@redhat.com>

(cherry picked from commit 84c26520)
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

block/qcow2-cluster.c

@@ -64,7 +64,8 @@ int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size,
         }
     }
 
-    if (new_l1_size > INT_MAX / sizeof(uint64_t)) {
+    QEMU_BUILD_BUG_ON(QCOW_MAX_L1_SIZE > INT_MAX);
+    if (new_l1_size > QCOW_MAX_L1_SIZE / sizeof(uint64_t)) {
         return -EFBIG;
     }