Re: [PATCH] virtio_net: fix use after free
From: Eric Dumazet <hidden>
Date: 2014-10-31 03:36:54
Also in:
lkml, netdev
Subsystem:
networking drivers, the rest, virtio net driver · Maintainers:
Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds, "Michael S. Tsirkin", Jason Wang
On Wed, 2014-10-15 at 16:23 +0300, Michael S. Tsirkin wrote:
quoted hunk ↗ jump to hunk
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@davemloft.net> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> --- 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 ? It looks like following patch is needed ?
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index ec2a8b41ed41..17cc42c6a559 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c@@ -927,6 +927,10 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev) /* Free up any pending old buffers before queueing new ones. */ free_old_xmit_skbs(sq); + /* Don't wait up for transmitted skbs to be freed. */ + skb_orphan(skb); + nf_reset(skb); + /* Try to transmit */ err = xmit_skb(sq, skb);
@@ -941,10 +945,6 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev) return NETDEV_TX_OK; } - /* Don't wait up for transmitted skbs to be freed. */ - skb_orphan(skb); - nf_reset(skb); - /* Apparently nice girls don't return TX_BUSY; stop the queue * before it gets out of hand. Naturally, this wastes entries. */ if (sq->vq->num_free < 2+MAX_SKB_FRAGS) {