qcow2: reject unaligned offsets in write compressed

Misaligned compressed write is not supported.
Signed-off-by: NAnton Nefedov <anton.nefedov@virtuozzo.com>
Message-id: 1510654613-47868-2-git-send-email-anton.nefedov@virtuozzo.com
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>

block/qcow2.c

@@ -3358,6 +3358,10 @@ qcow2_co_pwritev_compressed(BlockDriverState *bs, uint64_t offset,
         return bdrv_truncate(bs->file, cluster_offset, PREALLOC_MODE_OFF, NULL);
     }
 
+    if (offset_into_cluster(s, offset)) {
+        return -EINVAL;
+    }
+
     buf = qemu_blockalign(bs, s->cluster_size);
     if (bytes != s->cluster_size) {
         if (bytes > s->cluster_size ||