| Message ID | 20100109123827.GB4386@del.dom.local |
|---|---|
| State | Changes Requested, archived |
| Delegated to: | David Miller |
| Headers | show |
From: Jarek Poplawski <jarkao2@gmail.com> Date: Sat, 9 Jan 2010 13:38:27 +0100 > tpacket_snd() can change and kfree an skb after dev_queue_xmit(), > which is illegal. > > With debugging by: Stephen Hemminger <shemminger@vyatta.com> > > Reported-by: Michael Breuer <mbreuer@majjas.com> > Tested-by: Michael Breuer <mbreuer@majjas.com> > Signed-off-by: Jarek Poplawski <jarkao2@gmail.com> > Acked-by: Stephen Hemminger <shemminger@vyatta.com> Jarek, if this code path triggers, it will deadlock the send ring with your changes. We will now leave the ring packet status in the "SENDING" state. That's not right. Then, if the application calls send again, we will just return immediately since we only make progress if the head ring entry is in SEND_REQUEST state. This is really bogus behavior. When the qdisc or mid-layer drops the packet, we should at least mark the packet state properly (which is what the current code would does, sans the "reference SKB after dev_queue_xmit()" issue). And advance the packet ring pointer. This way the user: 1) can see that the packet got dropped and couldn't be sent 2) can call send again to try sending the rest of the ring Fix the use after dev_queue_xmit() issue, but don't change other side effects which are important for correct AF_PACKET TX ring semantics. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Sun, Jan 10, 2010 at 01:51:35PM -0800, David Miller wrote: > From: Jarek Poplawski <jarkao2@gmail.com> > Date: Sat, 9 Jan 2010 13:38:27 +0100 > > > tpacket_snd() can change and kfree an skb after dev_queue_xmit(), > > which is illegal. > > > > With debugging by: Stephen Hemminger <shemminger@vyatta.com> > > > > Reported-by: Michael Breuer <mbreuer@majjas.com> > > Tested-by: Michael Breuer <mbreuer@majjas.com> > > Signed-off-by: Jarek Poplawski <jarkao2@gmail.com> > > Acked-by: Stephen Hemminger <shemminger@vyatta.com> > > Jarek, if this code path triggers, it will deadlock the > send ring with your changes. > > We will now leave the ring packet status in the "SENDING" state. > > That's not right. No, the destructor of this skb, tpacket_destruct_skb(), will clean this. (Just like for other skbs kfreed during dev_queue_xmit().) Jarek P. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index e0516a2..aba2049 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -1021,9 +1021,10 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg) status = TP_STATUS_SEND_REQUEST; err = dev_queue_xmit(skb); - if (unlikely(err > 0 && (err = net_xmit_errno(err)) != 0)) - goto out_xmit; packet_increment_head(&po->tx_ring); + if (unlikely(err > 0 && (err = net_xmit_errno(err)) != 0)) + goto out_put; + len_sum += tp_len; } while (likely((ph != NULL) || ((!(msg->msg_flags & MSG_DONTWAIT)) && @@ -1033,9 +1034,6 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg) err = len_sum; goto out_put; -out_xmit: - skb->destructor = sock_wfree; - atomic_dec(&po->tx_ring.pending); out_status: __packet_set_status(po, ph, status); kfree_skb(skb);