On 10-01-2010 22:51, David Miller wrote:Tested by: Michael Breuer
From: Jarek Poplawski<jarkao2@xxxxxxxxx>As I wrote already, I don't think this patch is wrong. Alas, we can't
Date: Sat, 9 Jan 2010 13:38:27 +0100
tpacket_snd() can change and kfree an skb after dev_queue_xmit(),Jarek, if this code path triggers, it will deadlock the
which is illegal.
With debugging by: Stephen Hemminger<shemminger@xxxxxxxxxx>
Reported-by: Michael Breuer<mbreuer@xxxxxxxxxx>
Tested-by: Michael Breuer<mbreuer@xxxxxxxxxx>
Signed-off-by: Jarek Poplawski<jarkao2@xxxxxxxxx>
Acked-by: Stephen Hemminger<shemminger@xxxxxxxxxx>
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.
both fix this bug and retain exactly current behaviour, at least
without deeper changes. And I doubt it's worth it if we ignore negative
dev_queue_xmit() return (drops also) at the same time.
Btw, there was an alternative fix (positively) tested - more radical,
but IMHO safe and appropriate at least as a temporary solution for
-stable:
http://permalink.gmane.org/gmane.linux.kernel/934761
Anyway, here is another try, with even more of the current semantics.
If you think it's better, I hope Michael can test it (and send his
Tested-by).
Thanks,
Jarek P.
----------------> (alternative 3)
Subject: af_packet: Don't use skb after dev_queue_xmit()
tpacket_snd() can change and kfree an skb after dev_queue_xmit(),
which is illegal.
With debugging by: Stephen Hemminger<shemminger@xxxxxxxxxx>
Reported-by: Michael Breuer<mbreuer@xxxxxxxxxx>
Signed-off-by: Jarek Poplawski<jarkao2@xxxxxxxxx>
Cc: Stephen Hemminger<shemminger@xxxxxxxxxx>
---
net/packet/af_packet.c | 19 ++++++++++++++-----
1 files changed, 14 insertions(+), 5 deletions(-)
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index e0516a2..f126d18 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1021,8 +1021,20 @@ 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;
+ if (unlikely(err> 0)) {
+ err = net_xmit_errno(err);
+ if (err&& __packet_get_status(po, ph) ==
+ TP_STATUS_AVAILABLE) {
+ /* skb was destructed already */
+ skb = NULL;
+ goto out_status;
+ }
+ /*
+ * skb was dropped but not destructed yet;
+ * let's treat it like congestion or err< 0
+ */
+ err = 0;
+ }
packet_increment_head(&po->tx_ring);
len_sum += tp_len;
} while (likely((ph != NULL) ||
@@ -1033,9 +1045,6 @@ 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);