From 612017cc4834cd5eabc12afc7dd6cebf890b42e5 Mon Sep 17 00:00:00 2001
From: Xiao Wang <jasowang@redhat.com>
Date: Fri, 19 Aug 2016 09:24:25 +0200
Subject: [PATCH] virtio: validate the existence of handle_output before
 calling it

RH-Author: Xiao Wang <jasowang@redhat.com>
Message-id: <1471598665-23846-1-git-send-email-jasowang@redhat.com>
Patchwork-id: 72021
O-Subject: [RHEL7.3 qemu-kvm PATCH] virtio: validate the existence of handle_output before calling it
Bugzilla: 1367040
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: Fam Zheng <famz@redhat.com>
RH-Acked-by: Pankaj Gupta <pagupta@redhat.com>

Bugzilla: 1367040
Brew Build: https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=11620539
Test status: Tested by myself.

We don't validate the existence of handle_output which may let a buggy
guest to trigger a SIGSEV easily. E.g:

1) write 10 to queue_sel to a virtio net device with only 1 queue
2) setup an arbitrary pfn
3) then notify queue 10

Fixing this by validating the existence of handle_output before.

Cc: qemu-stable@nongnu.org
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Don Koch <dkoch@verizon.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
(cherry picked from commit 9e0f5b8108e248b78444c9a2ec41a8309825736c)
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 hw/virtio/virtio.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index a861870..e67337b 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -692,8 +692,9 @@ int virtio_queue_get_id(VirtQueue *vq)
 
 void virtio_queue_notify_vq(VirtQueue *vq)
 {
-    if (vq->vring.desc) {
+    if (vq->vring.desc && vq->handle_output) {
         VirtIODevice *vdev = vq->vdev;
+
         trace_virtio_queue_notify(vdev, vq - vdev->vq, vq);
         vq->handle_output(vdev, vq);
     }
-- 
1.8.3.1