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When retransmitting TCP SYN-ACK segments with the TCP timestamp option

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enabled use an updated timestamp instead of reusing the one used in
the initial TCP SYN-ACK segment.

This patch ensures that an updated timestamp is used when sending the
SYN-ACK from the syncache code. It was already done if the
SYN-ACK was retransmitted from the generic code.

This makes the behaviour consistent and also conformant with
the TCP specification.

Reviewed by:		jtl@, Jason Eggleston
MFC after:		1 month
Sponsored by:		Neflix, Inc.
Differential Revision:	https://reviews.freebsd.org/D15634
This commit is contained in:
Michael Tuexen 2018-06-15 12:28:43 +00:00
parent 725f388bdc
commit 43b223f42e
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=335194
2 changed files with 2 additions and 26 deletions
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27
sys/netinet/tcp_syncache.c
View File

@ -1168,25 +1168,6 @@ syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
}
}
/*
* If timestamps were negotiated, the reflected timestamp
* must be equal to what we actually sent in the SYN|ACK
* except in the case of 0. Some boxes are known for sending
* broken timestamp replies during the 3whs (and potentially
* during the connection also).
*
* Accept the final ACK of 3whs with reflected timestamp of 0
* instead of sending a RST and deleting the syncache entry.
*/
if ((to->to_flags & TOF_TS) && to->to_tsecr &&
to->to_tsecr != sc->sc_ts) {
if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
"segment rejected\n",
s, __func__, to->to_tsecr, sc->sc_ts);
goto failed;
}
*lsop = syncache_socket(sc, *lsop, m);
if (*lsop == NULL)
@ -1513,7 +1494,6 @@ syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
*/
if (to->to_flags & TOF_TS) {
sc->sc_tsreflect = to->to_tsval;
sc->sc_ts = tcp_ts_getticks();
sc->sc_flags |= SCF_TIMESTAMP;
}
if (to->to_flags & TOF_SCALE) {
@ -1742,8 +1722,7 @@ syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked,
to.to_flags |= TOF_SCALE;
}
if (sc->sc_flags & SCF_TIMESTAMP) {
/* Virgin timestamp or TCP cookie enhanced one. */
to.to_tsval = sc->sc_ts;
to.to_tsval = sc->sc_tsoff + tcp_ts_getticks();
to.to_tsecr = sc->sc_tsreflect;
to.to_flags |= TOF_TS;
}
@ -2050,8 +2029,7 @@ syncookie_generate(struct syncache_head *sch, struct syncache *sc)
/* Randomize the timestamp. */
if (sc->sc_flags & SCF_TIMESTAMP) {
sc->sc_ts = arc4random();
sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks();
sc->sc_tsoff = arc4random() - tcp_ts_getticks();
}
TCPSTAT_INC(tcps_sc_sendcookie);
@ -2140,7 +2118,6 @@ syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
if (to->to_flags & TOF_TS) {
sc->sc_flags |= SCF_TIMESTAMP;
sc->sc_tsreflect = to->to_tsval;
sc->sc_ts = to->to_tsecr;
sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks();
}

1
sys/netinet/tcp_syncache.h
View File

@ -56,7 +56,6 @@ struct syncache {
int sc_rxttime; /* retransmit time */
u_int16_t sc_rxmits; /* retransmit counter */
u_int32_t sc_tsreflect; /* timestamp to reflect */
u_int32_t sc_ts; /* our timestamp to send */
u_int32_t sc_tsoff; /* ts offset w/ syncookies */
u_int32_t sc_flowlabel; /* IPv6 flowlabel */
tcp_seq sc_irs; /* seq from peer */