From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Date: Thu, 28 Sep 2017 12:03:00 +0000 (+0300)
Subject: block/mirror: check backing in bdrv_mirror_top_refresh_filename
X-Git-Tag: v2.11.0-rc0~61^2^2~4
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=18775ff32697ab6e1fd47989673bf1de54d0d942;p=thirdparty%2Fqemu.git

block/mirror: check backing in bdrv_mirror_top_refresh_filename

Backing may be zero after failed bdrv_attach_child in
bdrv_set_backing_hd, which leads to SIGSEGV.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-id: 20170928120300.58164-1-vsementsov@virtuozzo.com
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
---

diff --git a/block/mirror.c b/block/mirror.c
index 459b80f8f32..3b6f0c57722 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -1058,6 +1058,11 @@ static int coroutine_fn bdrv_mirror_top_pdiscard(BlockDriverState *bs,
 
 static void bdrv_mirror_top_refresh_filename(BlockDriverState *bs, QDict *opts)
 {
+    if (bs->backing == NULL) {
+        /* we can be here after failed bdrv_attach_child in
+         * bdrv_set_backing_hd */
+        return;
+    }
     bdrv_refresh_filename(bs->backing->bs);
     pstrcpy(bs->exact_filename, sizeof(bs->exact_filename),
             bs->backing->bs->filename);