From d8f974ead4b4c1f549441e7aac96262cf2b754ee Mon Sep 17 00:00:00 2001
From: Max Reitz <mreitz@redhat.com>
Date: Mon, 17 Mar 2014 22:45:29 +0100
Subject: [PATCH 4/6] qcow2: Check bs->drv in copy_sectors()

RH-Author: Max Reitz <mreitz@redhat.com>
Message-id: <1395096331-12610-2-git-send-email-mreitz@redhat.com>
Patchwork-id: 58119
O-Subject: [RHEL-7.0 qemu-kvm PATCH 1/3] qcow2: Check bs->drv in copy_sectors()
Bugzilla: 1048575
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
RH-Acked-by: Fam Zheng <famz@redhat.com>

BZ: 1048575

Before dereferencing bs->drv for a call to its member bdrv_co_readv(),
copy_sectors() should check whether that pointer is indeed valid, since
it may have been set to NULL by e.g. a concurrent write triggering the
corruption prevention mechanism.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
(cherry picked from commit dba2855572c746836ad90ce9154403b5929d996b)

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/qcow2-cluster.c | 4 ++++
 1 file changed, 4 insertions(+)

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 block/qcow2-cluster.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 862df0f..87c13ce 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -370,6 +370,10 @@ static int coroutine_fn copy_sectors(BlockDriverState *bs,
 
     BLKDBG_EVENT(bs->file, BLKDBG_COW_READ);
 
+    if (!bs->drv) {
+        return -ENOMEDIUM;
+    }
+
     /* Call .bdrv_co_readv() directly instead of using the public block-layer
      * interface.  This avoids double I/O throttling and request tracking,
      * which can lead to deadlock when block layer copy-on-read is enabled.
-- 
1.7.1