Messages in this thread | | | Date | Mon, 9 Feb 2009 18:28:06 +1100 | From | Herbert Xu <> | Subject | Re: commit 64ff3b938ec6782e6585a83d5459b98b0c3f6eb8 breaks rlogin |
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On Mon, Feb 09, 2009 at 09:13:00AM +0200, Ilpo Järvinen wrote: > > Hmm, what happens if a opposite dir ACK gets sent (it's zero sized seqno > range will be above urgent sequence when urg is not yet acknowledged)? So > we'll take the later branch after your change and send bogus 0xffff urg? > I think you're change might have actually broken bidir tcp completely (and > probably window probing as well under some conditions). Congraz, two flies > with a single stroke :-). You would have needed an additional check that > the tcb->seq is below urg... > > ...Below is a patch but Jeff might need to revert the revert first if > he tests with the latest Linus' tree.
Good point! That would definitely explain this.
> [PATCH] tcp: check that we're still < urg instead of sending a bogus one > > Opposite dir ACK with zero sized seqno range can go into the > later condition once urg is in the outstanding window not > yet acknowledge (we're still in urg mode but seqno we sent in > the ack won't be below snd_up). Need to check that we never > advertize bogus urg for a segment which is after the snd_up. > > Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> > --- > net/ipv4/tcp_output.c | 3 ++- > 1 files changed, 2 insertions(+), 1 deletions(-) > > diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c > index 557fe16..c808d73 100644 > --- a/net/ipv4/tcp_output.c > +++ b/net/ipv4/tcp_output.c > @@ -667,7 +667,8 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it, > if (between(tp->snd_up, tcb->seq + 1, tcb->seq + 0xFFFF)) { > th->urg_ptr = htons(tp->snd_up - tcb->seq); > th->urg = 1; > - } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) { > + } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt) && > + before(tcb->seq, tcp->snd_up)) { > th->urg_ptr = 0xFFFF; > th->urg = 1; > }
We could rewrite this as
if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tcp->snd_up))) { if (before(tp->sndup, tcb->seq + 0x10000)) { th->urg_ptr = htons(tp->snd_up - tcb->seq); th->urg = 1; } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) { th->urg_ptr = 0xFFFF; th->urg = 1; } }
Thanks, -- Visit Openswan at http://www.openswan.org/ Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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