Message ID | 1369724604.7764.1.camel@localhost |
---|---|
State | Changes Requested, archived |
Delegated to: | David Miller |
Headers | show |
Hi Jana, Thanks for the patch, and sorry for missing it the first time around! On Tue, May 28, 2013 at 09:03:24AM +0200, Jana Saout wrote: > Interestingly, the PPP over L2TP (with xl2tpd) is working fine when > using my Linux client, but a simple ping from my Android phone causes > the BUG on the first packet. It happens on the L2TP -> PPP path, as the > ping request never leaves the ppp devices to the local network. > > What *might* be different from other setups, is that the machine on > which the L2TP packets are decapsulated is a Xen VM, so the packets > arrive with CHECKSUM_PARTIAL set. Could you advise what Android client you're using? I'd like to attempt to reproduce this here. We do a lot of L2TP testing in VM environments (albeit not Xen), so I'm interested as to why we've not hit this. > I believe that since the L2TP checksum has already been checked and > everything, the decapsulated packet is supposedly "fine" and I also saw > the following line in l2tp_eth.c: > > /* checksums verified by L2TP */ > skb->ip_summed = CHECKSUM_NONE; > > which sounds to mike like the right thing to do, so I modified > l2tp_ppp.c accordingly and voila - no more crashes. In case it helps, I > would like to share that patch for inclusion or, in case I'm wrong, to > ask you to find the correct fix. :) I think your analysis is correct, but I'm not sure whether setting skb->ip_summed to CHECKSUM_NONE is the right thing to do. It seems like this would disable checksumming for the ICMP echo response. Although that may avoid the BUG, it may not be entirely ideal behaviour. I'll have a dig into the other tunnelling protocol implementation and see what they do.
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diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c index 637a341..53aabefb 100644 --- a/net/l2tp/l2tp_ppp.c +++ b/net/l2tp/l2tp_ppp.c @@ -250,6 +250,10 @@ static void pppol2tp_recv(struct l2tp_session *session, struct sk_buff *skb, int * to the inner packet either */ secpath_reset(skb); + + /* checksums verified by L2TP */ + skb->ip_summed = CHECKSUM_NONE; + skb_dst_drop(skb); nf_reset(skb);