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Enabling the IPPROTO_IPV6 level socket option IPV6_USE_MIN_MTU on a TCP

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socket resulted in sending fragmented IPV6 packets.

This is fixes by reducing the MSS to the appropriate value. In addtion,
if the socket option is set before the handshake happens, announce this
MSS to the peer. This is not stricly required, but done since TCP
is conservative.

PR:			173444
Reviewed by:		bz@, rrs@
MFC after:		1 month
Sponsored by:		Netflix, Inc.
Differential Revision:	https://reviews.freebsd.org/D16796
This commit is contained in:
Michael Tuexen 2018-08-21 14:12:30 +00:00
parent 7d4dcc36a8
commit 5dff1c3845
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=338138
4 changed files with 42 additions and 0 deletions
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1
sys/netinet/in_pcb.h
View File

@ -122,6 +122,7 @@ struct in_conninfo {
* Flags for inc_flags.
*/
#define INC_ISIPV6 0x01
#define INC_IPV6MINMTU 0x02
#define inc_fport inc_ie.ie_fport
#define inc_lport inc_ie.ie_lport

2
sys/netinet/tcp_input.c
View File

@ -1051,6 +1051,8 @@ tcp_input(struct mbuf **mp, int *offp, int proto)
#ifdef INET6
if (isipv6) {
inc.inc_flags |= INC_ISIPV6;
if (inp->inp_inc.inc_flags & INC_IPV6MINMTU)
inc.inc_flags |= INC_IPV6MINMTU;
inc.inc6_faddr = ip6->ip6_src;
inc.inc6_laddr = ip6->ip6_dst;
} else

3
sys/netinet/tcp_subr.c
View File

@ -2865,6 +2865,9 @@ tcp_maxmtu6(struct in_conninfo *inc, struct tcp_ifcap *cap)
KASSERT(inc != NULL, ("tcp_maxmtu6 with NULL in_conninfo pointer"));
if (inc->inc_flags & INC_IPV6MINMTU)
return (IPV6_MMTU);
if (!IN6_IS_ADDR_UNSPECIFIED(&inc->inc6_faddr)) {
in6_splitscope(&inc->inc6_faddr, &dst6, &scopeid);
if (fib6_lookup_nh_ext(inc->inc_fibnum, &dst6, scopeid, 0,

36
sys/netinet/tcp_usrreq.c
View File

@ -1584,6 +1584,42 @@ tcp_ctloutput(struct socket *so, struct sockopt *sopt)
if (inp->inp_vflag & INP_IPV6PROTO) {
INP_WUNLOCK(inp);
error = ip6_ctloutput(so, sopt);
/*
* In case of the IPV6_USE_MIN_MTU socket option,
* the INC_IPV6MINMTU flag to announce a corresponding
* MSS during the initial handshake.
* If the TCP connection is not in the front states,
* just reduce the MSS being used.
* This avoids the sending of TCP segments which will
* be fragmented at the IPv6 layer.
*/
if ((error == 0) &&
(sopt->sopt_dir == SOPT_SET) &&
(sopt->sopt_level == IPPROTO_IPV6) &&
(sopt->sopt_name == IPV6_USE_MIN_MTU)) {
INP_WLOCK(inp);
if ((inp->inp_flags &
(INP_TIMEWAIT | INP_DROPPED))) {
INP_WUNLOCK(inp);
return (ECONNRESET);
}
inp->inp_inc.inc_flags |= INC_IPV6MINMTU;
tp = intotcpcb(inp);
if ((tp->t_state >= TCPS_SYN_SENT) &&
(inp->inp_inc.inc_flags & INC_ISIPV6)) {
struct ip6_pktopts *opt;
opt = inp->in6p_outputopts;
if ((opt != NULL) &&
(opt->ip6po_minmtu ==
IP6PO_MINMTU_ALL)) {
if (tp->t_maxseg > TCP6_MSS) {
tp->t_maxseg = TCP6_MSS;
}
}
}
INP_WUNLOCK(inp);
}
}
#endif /* INET6 */
#if defined(INET6) && defined(INET)