virtio_net: fix use after free

commit 434f1d33383da5404d6421209ad34411b923fd90
    net: Remove ndo_xmit_flush netdev operation, use signalling instead.

added code that looks at skb->xmit_more after the skb has
been put in TX VQ. Since some paths process the ring and free the skb
immediately, this can cause use after free.

Fix by storing xmit_more in a local variable.

Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 3d0ce4468ce6b6a5cde558a9df6e8614150fc2ea..13d0a8bc8bf3558d666087a273ab87109f902b59 100644 (file)
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -920,6 +920,8 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
        int qnum = skb_get_queue_mapping(skb);
        struct send_queue *sq = &vi->sq[qnum];
        int err;
+       struct netdev_queue *txq = netdev_get_tx_queue(dev, qnum);
+       bool kick = !skb->xmit_more;
 
        /* Free up any pending old buffers before queueing new ones. */
        free_old_xmit_skbs(sq);
@@ -956,7 +958,7 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
                }
        }
 
-       if (__netif_subqueue_stopped(dev, qnum) || !skb->xmit_more)
+       if (kick || netif_xmit_stopped(txq))
                virtqueue_kick(sq->vq);
 
        return NETDEV_TX_OK;