On 10/31/2014 11:36 AM, Eric Dumazet wrote: > On Wed, 2014-10-15 at 16:23 +0300, Michael S. Tsirkin wrote: >> commit 0b725a2ca61bedc33a2a63d0451d528b268cf975 >> 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@xxxxxxxxxxxxx> >> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> >> --- >> >> David, am I using the API correctly? >> Seems to work for me. >> You used __netif_subqueue_stopped but that seems to use >> a slightly more expensive test_bit internally. >> The reason I added a variable for the txq here is because it's handy for >> BQL patch later on. >> >> >> drivers/net/virtio_net.c | 4 +++- >> 1 file changed, 3 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c >> index 3d0ce44..13d0a8b 100644 >> --- 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; > I must say I am kind of confused by this patch. > > Why the skb_orphan(skb) & nf_reset(skb) do not have the same issue ? > Since they are called before the possible free_old_xmit_skbs(), skb won't get freed at this time. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
