We shouldn't try to copy bytes beyond EOF. Fix it.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
---
 block/backup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/backup.c b/block/backup.c
index 228ba9423c..d482d93458 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -155,7 +155,7 @@ static int coroutine_fn backup_cow_with_offload(BackupBlockJob *job,
     int ret;
     int nr_clusters;
     BlockBackend *blk = job->common.blk;
-    int nbytes = end - start;
+    int nbytes = MIN(end - start, job->len - start);
     int read_flags = is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0;
 
     assert(end - start < INT_MAX);
-- 
2.18.0