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Improve a comment to refer to the actual sections in the TCP

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specification for the comparisons made.
Thanks to lstewart@ for the suggestion.

MFC after:		4 weeks
Sponsored by:		Netflix, Inc.
Differential Revision:	https://reviews.freebsd.org/D17595
This commit is contained in:
Michael Tuexen 2018-11-01 11:35:28 +00:00
parent e403f9865d
commit 099ab39f44
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=339989
1 changed files with 18 additions and 4 deletions
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22
sys/netinet/tcp_syncache.c
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@ -581,15 +581,28 @@ syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m)
/*
* If the RST bit is set, check the sequence number to see
* if this is a valid reset segment.
*
* RFC 793 page 37:
* In all states except SYN-SENT, all reset (RST) segments
* are validated by checking their SEQ-fields. A reset is
* valid if its sequence number is in the window.
*
* The sequence number in the reset segment is normally an
* echo of our outgoing acknowlegement numbers, but some hosts
* send a reset with the sequence number at the rightmost edge
* of our receive window, and we have to handle this case.
* RFC 793 page 69:
* 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
*
* Note that when receiving a SYN segment in the LISTEN state,
* IRS is set to SEG.SEQ and RCV.NXT is set to SEG.SEQ+1, as
* described in RFC 793, page 66.
*/
if ((SEQ_GEQ(th->th_seq, sc->sc_irs + 1) &&
SEQ_LT(th->th_seq, sc->sc_irs + 1 + sc->sc_wnd)) ||
@ -1731,6 +1744,7 @@ syncache_respond(struct syncache *sc, struct syncache_head *sch,
th->th_seq = htonl(sc->sc_iss);
else
th->th_seq = htonl(sc->sc_iss + 1);
printf("SEG.SEQ=0x%x, ISS=0x%x.\n", ntohl(th->th_seq), sc->sc_iss);
th->th_ack = htonl(sc->sc_irs + 1);
th->th_off = sizeof(struct tcphdr) >> 2;
th->th_x2 = 0;