Date: Thu, 1 Nov 2018 11:35:28 +0000 (UTC) From: Michael Tuexen <tuexen@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r339989 - head/sys/netinet Message-ID: <201811011135.wA1BZSAL094335@repo.freebsd.org>
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Author: tuexen Date: Thu Nov 1 11:35:28 2018 New Revision: 339989 URL: https://svnweb.freebsd.org/changeset/base/339989 Log: Improve a comment to refer to the actual sections in the TCP 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 Modified: head/sys/netinet/tcp_syncache.c Modified: head/sys/netinet/tcp_syncache.c ============================================================================== --- head/sys/netinet/tcp_syncache.c Thu Nov 1 10:25:22 2018 (r339988) +++ head/sys/netinet/tcp_syncache.c Thu Nov 1 11:35:28 2018 (r339989) @@ -581,15 +581,28 @@ syncache_chkrst(struct in_conninfo *inc, struct tcphdr /* * 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_ 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;
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