netdev-dpdk: Fix vhost_driver_flags data race in destruct.

Coverity reports a data race where netdev_dpdk_vhost_destruct()
accesses vhost_driver_flags without holding dpdk_mutex, while
netdev_dpdk_vhost_client_reconfigure() writes to vhost_driver_flags
with the mutex held (as is done 4 out of 4 times when writing).

This could cause a race if another thread modifies vhost_driver_flags
through netdev_dpdk_vhost_client_reconfigure() at the same time the
destructor is running, potentially leading to incorrect socket cleanup.

Fix by capturing the flag value while holding dpdk_mutex, similar to how
vhost_id is already handled.

Fixes: c1ff66a ("netdev-dpdk: vHost client mode and reconnect")
Acked-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Acked-by: Mike Pattrick <mkp@redhat.com>
Signed-off-by: Eelco Chaudron <echaudro@redhat.com>

Author: chaudron

lib/netdev-dpdk.c

@@ -1822,6 +1822,7 @@ static void
 netdev_dpdk_vhost_destruct(struct netdev *netdev)
 {
     struct netdev_dpdk *dev = netdev_dpdk_cast(netdev);
+    bool is_client_mode;
     char *vhost_id;
 
     ovs_mutex_lock(&dpdk_mutex);
@@ -1836,6 +1837,7 @@ netdev_dpdk_vhost_destruct(struct netdev *netdev)
     }
 
     vhost_id = dev->vhost_id;
+    is_client_mode = dev->vhost_driver_flags & RTE_VHOST_USER_CLIENT;
     dev->vhost_id = NULL;
     rte_free(dev->vhost_rxq_enabled);
 
@@ -1850,7 +1852,7 @@ netdev_dpdk_vhost_destruct(struct netdev *netdev)
     if (dpdk_vhost_driver_unregister(dev, vhost_id)) {
         VLOG_ERR("%s: Unable to unregister vhost driver for socket '%s'.\n",
                  netdev->name, vhost_id);
-    } else if (!(dev->vhost_driver_flags & RTE_VHOST_USER_CLIENT)) {
+    } else if (!is_client_mode) {
         /* OVS server mode - remove this socket from list for deletion */
         fatal_signal_remove_file_to_unlink(vhost_id);
     }