[PATCH V2] virtio-net: check the existence of peer before accessing vDPA config

[Jason Wang]

We try to check whether a peer is VDPA in order to get config from
there - with no peer, this leads to a NULL
pointer dereference. Add a check before trying to access the peer
type. No peer means not VDPA.

Fixes: 108a64818e69b ("vhost-vdpa: introduce vhost-vdpa backend")
Cc: Cindy Lu <l...@redhat.com>
Tested-by: Cornelia Huck <coh...@redhat.com>
Reviewed-by: Cornelia Huck <coh...@redhat.com>
Signed-off-by: Jason Wang <jasow...@redhat.com>
---
Changes from V1:
- Tweak the log
- Add the comment in the code
---
 hw/net/virtio-net.c | 30 +++++++++++++++++++-----------
 1 file changed, 19 insertions(+), 11 deletions(-)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 4895af1cbe..a1fe9e9285 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -125,6 +125,7 @@ static void virtio_net_get_config(VirtIODevice *vdev, 
uint8_t *config)
 {
     VirtIONet *n = VIRTIO_NET(vdev);
     struct virtio_net_config netcfg;
+    NetClientState *nc = qemu_get_queue(n->nic);
 
     int ret = 0;
     memset(&netcfg, 0 , sizeof(struct virtio_net_config));
@@ -142,13 +143,16 @@ static void virtio_net_get_config(VirtIODevice *vdev, 
uint8_t *config)
                  VIRTIO_NET_RSS_SUPPORTED_HASHES);
     memcpy(config, &netcfg, n->config_size);
 
-    NetClientState *nc = qemu_get_queue(n->nic);
-    if (nc->peer->info->type == NET_CLIENT_DRIVER_VHOST_VDPA) {
+    /*
+     * Is this VDPA? No peer means not VDPA: there's no way to
+     * disconnect/reconnect a VDPA peer.
+     */
+    if (nc->peer && nc->peer->info->type == NET_CLIENT_DRIVER_VHOST_VDPA) {
         ret = vhost_net_get_config(get_vhost_net(nc->peer), (uint8_t *)&netcfg,
-                             n->config_size);
-    if (ret != -1) {
-        memcpy(config, &netcfg, n->config_size);
-    }
+                                   n->config_size);
+        if (ret != -1) {
+            memcpy(config, &netcfg, n->config_size);
+        }
     }
 }
 
@@ -156,6 +160,7 @@ static void virtio_net_set_config(VirtIODevice *vdev, const 
uint8_t *config)
 {
     VirtIONet *n = VIRTIO_NET(vdev);
     struct virtio_net_config netcfg = {};
+    NetClientState *nc = qemu_get_queue(n->nic);
 
     memcpy(&netcfg, config, n->config_size);
 
@@ -166,11 +171,14 @@ static void virtio_net_set_config(VirtIODevice *vdev, 
const uint8_t *config)
         qemu_format_nic_info_str(qemu_get_queue(n->nic), n->mac);
     }
 
-    NetClientState *nc = qemu_get_queue(n->nic);
-    if (nc->peer->info->type == NET_CLIENT_DRIVER_VHOST_VDPA) {
-        vhost_net_set_config(get_vhost_net(nc->peer), (uint8_t *)&netcfg,
-                               0, n->config_size,
-                        VHOST_SET_CONFIG_TYPE_MASTER);
+    /*
+     * Is this VDPA? No peer means not VDPA: there's no way to
+     * disconnect/reconnect a VDPA peer.
+     */
+    if (nc->peer && nc->peer->info->type == NET_CLIENT_DRIVER_VHOST_VDPA) {
+        vhost_net_set_config(get_vhost_net(nc->peer),
+                             (uint8_t *)&netcfg, 0, n->config_size,
+                             VHOST_SET_CONFIG_TYPE_MASTER);
       }
 }
 
-- 
2.20.1