On Tue, May 01, 2007 at 09:57:18PM +0400, Evgeniy Polyakov ([EMAIL PROTECTED])
wrote:
> > I think if you will storm any system with acks lower than expected
> > unacknowledged number, result will be the same - ack, that it was bogus
> > message, if sending system sends wrong ack again, it will again receive
> > that it was bogus...
>
> Wrong syn number of course.
> I described not exactly correct case - likely broken side does not know
> that its messages were lost (or specially crafts such packets), so it
> retransmit the same bogus packet with wrong syn, which already was acked.
>
> As far as I can see, this is it:
>
> /* step 1: check sequence number */
> if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
> if (!th->rst)
> tcp_send_dupack(sk, skb);
> goto discard;
> }
And this is part of the RFC Linux follows:
There are four cases for the acceptability test for an incoming
segment:
Segment Receive Test
Length Window
------- ------- -------------------------------------------
0 0 SEG.SEQ = RCV.NXT
0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
>0 0 not acceptable
>0 >0 RCV.NXT =< SEG.SEQ < RCV.NXT+RCV.WND
or RCV.NXT =< SEG.SEQ+SEG.LEN-1 < RCV.NXT+RCV.WND
If the RCV.WND is zero, no segments will be acceptable, but
special allowance should be made to accept valid ACKs, URGs and
RSTs.
If an incoming segment is not acceptable, an acknowledgment
should be sent in reply (unless the RST bit is set, if so drop
the segment and return):
<SEQ=SND.NXT><ACK=RCV.NXT><CTL=ACK>
After sending the acknowledgment, drop the unacceptable segment
and return.
--
Evgeniy Polyakov
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