From 47c62aa0b0b32c345bff946b9d20c22176e209a6 Mon Sep 17 00:00:00 2001 From: sbruno Date: Wed, 29 Oct 2014 22:17:45 +0000 Subject: MFC r272720, 273061, 273062, 273063, 273064 Implement PLPMTUD blackhole detection (RFC 4821), inspired by code from xnu sources. If we encounter a network where ICMP is blocked the Needs Frag indicator may not propagate back to us. Attempt to downshift the mss once to a preconfigured value. Note, this is turned off by default. --- sys/netinet/tcp_output.c | 17 +++++- sys/netinet/tcp_timer.c | 156 +++++++++++++++++++++++++++++++++++++++++++++++ sys/netinet/tcp_var.h | 11 +++- 3 files changed, 182 insertions(+), 2 deletions(-) (limited to 'sys/netinet') diff --git a/sys/netinet/tcp_output.c b/sys/netinet/tcp_output.c index 8c97c12..8abb16d 100644 --- a/sys/netinet/tcp_output.c +++ b/sys/netinet/tcp_output.c @@ -676,6 +676,12 @@ just_return: send: SOCKBUF_LOCK_ASSERT(&so->so_snd); + if (len > 0) { + if (len >= tp->t_maxseg) + tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT; + else + tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT; + } /* * Before ESTABLISHED, force sending of initial options * unless TCP set not to do any options. @@ -1184,6 +1190,11 @@ send: */ ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6)); + if (V_path_mtu_discovery && tp->t_maxopd > V_tcp_minmss) + tp->t_flags2 |= TF2_PLPMTU_PMTUD; + else + tp->t_flags2 &= ~TF2_PLPMTU_PMTUD; + if (tp->t_state == TCPS_SYN_SENT) TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th); @@ -1220,8 +1231,12 @@ send: * * NB: Don't set DF on small MTU/MSS to have a safe fallback. */ - if (V_path_mtu_discovery && tp->t_maxopd > V_tcp_minmss) + if (V_path_mtu_discovery && tp->t_maxopd > V_tcp_minmss) { ip->ip_off |= htons(IP_DF); + tp->t_flags2 |= TF2_PLPMTU_PMTUD; + } else { + tp->t_flags2 &= ~TF2_PLPMTU_PMTUD; + } if (tp->t_state == TCPS_SYN_SENT) TCP_PROBE5(connect__request, NULL, tp, ip, tp, th); diff --git a/sys/netinet/tcp_timer.c b/sys/netinet/tcp_timer.c index bde7503..00fcb22 100644 --- a/sys/netinet/tcp_timer.c +++ b/sys/netinet/tcp_timer.c @@ -63,6 +63,9 @@ __FBSDID("$FreeBSD$"); #include #include #include +#ifdef INET6 +#include +#endif #include #ifdef TCPDEBUG #include @@ -124,6 +127,54 @@ SYSCTL_INT(_net_inet_tcp, OID_AUTO, rexmit_drop_options, CTLFLAG_RW, &tcp_rexmit_drop_options, 0, "Drop TCP options from 3rd and later retransmitted SYN"); +static VNET_DEFINE(int, tcp_pmtud_blackhole_detect); +#define V_tcp_pmtud_blackhole_detect VNET(tcp_pmtud_blackhole_detect) +SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_detection, + CTLFLAG_RW, + &VNET_NAME(tcp_pmtud_blackhole_detect), 0, + "Path MTU Discovery Black Hole Detection Enabled"); + +static VNET_DEFINE(int, tcp_pmtud_blackhole_activated); +#define V_tcp_pmtud_blackhole_activated \ + VNET(tcp_pmtud_blackhole_activated) +SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_activated, + CTLFLAG_RD, + &VNET_NAME(tcp_pmtud_blackhole_activated), 0, + "Path MTU Discovery Black Hole Detection, Activation Count"); + +static VNET_DEFINE(int, tcp_pmtud_blackhole_activated_min_mss); +#define V_tcp_pmtud_blackhole_activated_min_mss \ + VNET(tcp_pmtud_blackhole_activated_min_mss) +SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_activated_min_mss, + CTLFLAG_RD, + &VNET_NAME(tcp_pmtud_blackhole_activated_min_mss), 0, + "Path MTU Discovery Black Hole Detection, Activation Count at min MSS"); + +static VNET_DEFINE(int, tcp_pmtud_blackhole_failed); +#define V_tcp_pmtud_blackhole_failed VNET(tcp_pmtud_blackhole_failed) +SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_failed, + CTLFLAG_RD, + &VNET_NAME(tcp_pmtud_blackhole_failed), 0, + "Path MTU Discovery Black Hole Detection, Failure Count"); + +#ifdef INET +static VNET_DEFINE(int, tcp_pmtud_blackhole_mss) = 1200; +#define V_tcp_pmtud_blackhole_mss VNET(tcp_pmtud_blackhole_mss) +SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_mss, + CTLFLAG_RW, + &VNET_NAME(tcp_pmtud_blackhole_mss), 0, + "Path MTU Discovery Black Hole Detection lowered MSS"); +#endif + +#ifdef INET6 +static VNET_DEFINE(int, tcp_v6pmtud_blackhole_mss) = 1220; +#define V_tcp_v6pmtud_blackhole_mss VNET(tcp_v6pmtud_blackhole_mss) +SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, v6pmtud_blackhole_mss, + CTLFLAG_RW, + &VNET_NAME(tcp_v6pmtud_blackhole_mss), 0, + "Path MTU Discovery IPv6 Black Hole Detection lowered MSS"); +#endif + static int per_cpu_timers = 0; SYSCTL_INT(_net_inet_tcp, OID_AUTO, per_cpu_timers, CTLFLAG_RW, &per_cpu_timers , 0, "run tcp timers on all cpus"); @@ -492,6 +543,7 @@ tcp_timer_rexmt(void * xtp) ostate = tp->t_state; #endif + INP_INFO_RLOCK(&V_tcbinfo); inp = tp->t_inpcb; /* @@ -593,6 +645,110 @@ tcp_timer_rexmt(void * xtp) rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift]; TCPT_RANGESET(tp->t_rxtcur, rexmt, tp->t_rttmin, TCPTV_REXMTMAX); + + /* + * We enter the path for PLMTUD if connection is established or, if + * connection is FIN_WAIT_1 status, reason for the last is that if + * amount of data we send is very small, we could send it in couple of + * packets and process straight to FIN. In that case we won't catch + * ESTABLISHED state. + */ + if (V_tcp_pmtud_blackhole_detect && (((tp->t_state == TCPS_ESTABLISHED)) + || (tp->t_state == TCPS_FIN_WAIT_1))) { + int optlen; +#ifdef INET6 + int isipv6; +#endif + + if (((tp->t_flags2 & (TF2_PLPMTU_PMTUD|TF2_PLPMTU_MAXSEGSNT)) == + (TF2_PLPMTU_PMTUD|TF2_PLPMTU_MAXSEGSNT)) && + (tp->t_rxtshift <= 2)) { + /* + * Enter Path MTU Black-hole Detection mechanism: + * - Disable Path MTU Discovery (IP "DF" bit). + * - Reduce MTU to lower value than what we + * negotiated with peer. + */ + /* Record that we may have found a black hole. */ + tp->t_flags2 |= TF2_PLPMTU_BLACKHOLE; + + /* Keep track of previous MSS. */ + optlen = tp->t_maxopd - tp->t_maxseg; + tp->t_pmtud_saved_maxopd = tp->t_maxopd; + + /* + * Reduce the MSS to blackhole value or to the default + * in an attempt to retransmit. + */ +#ifdef INET6 + isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) ? 1 : 0; + if (isipv6 && + tp->t_maxopd > V_tcp_v6pmtud_blackhole_mss) { + /* Use the sysctl tuneable blackhole MSS. */ + tp->t_maxopd = V_tcp_v6pmtud_blackhole_mss; + V_tcp_pmtud_blackhole_activated++; + } else if (isipv6) { + /* Use the default MSS. */ + tp->t_maxopd = V_tcp_v6mssdflt; + /* + * Disable Path MTU Discovery when we switch to + * minmss. + */ + tp->t_flags2 &= ~TF2_PLPMTU_PMTUD; + V_tcp_pmtud_blackhole_activated_min_mss++; + } +#endif +#if defined(INET6) && defined(INET) + else +#endif +#ifdef INET + if (tp->t_maxopd > V_tcp_pmtud_blackhole_mss) { + /* Use the sysctl tuneable blackhole MSS. */ + tp->t_maxopd = V_tcp_pmtud_blackhole_mss; + V_tcp_pmtud_blackhole_activated++; + } else { + /* Use the default MSS. */ + tp->t_maxopd = V_tcp_mssdflt; + /* + * Disable Path MTU Discovery when we switch to + * minmss. + */ + tp->t_flags2 &= ~TF2_PLPMTU_PMTUD; + V_tcp_pmtud_blackhole_activated_min_mss++; + } +#endif + tp->t_maxseg = tp->t_maxopd - optlen; + /* + * Reset the slow-start flight size + * as it may depend on the new MSS. + */ + if (CC_ALGO(tp)->conn_init != NULL) + CC_ALGO(tp)->conn_init(tp->ccv); + } else { + /* + * If further retransmissions are still unsuccessful + * with a lowered MTU, maybe this isn't a blackhole and + * we restore the previous MSS and blackhole detection + * flags. + */ + if ((tp->t_flags2 & TF2_PLPMTU_BLACKHOLE) && + (tp->t_rxtshift > 4)) { + tp->t_flags2 |= TF2_PLPMTU_PMTUD; + tp->t_flags2 &= ~TF2_PLPMTU_BLACKHOLE; + optlen = tp->t_maxopd - tp->t_maxseg; + tp->t_maxopd = tp->t_pmtud_saved_maxopd; + tp->t_maxseg = tp->t_maxopd - optlen; + V_tcp_pmtud_blackhole_failed++; + /* + * Reset the slow-start flight size as it + * may depend on the new MSS. + */ + if (CC_ALGO(tp)->conn_init != NULL) + CC_ALGO(tp)->conn_init(tp->ccv); + } + } + } + /* * Disable RFC1323 and SACK if we haven't got any response to * our third SYN to work-around some broken terminal servers diff --git a/sys/netinet/tcp_var.h b/sys/netinet/tcp_var.h index 398df8b..10b1096 100644 --- a/sys/netinet/tcp_var.h +++ b/sys/netinet/tcp_var.h @@ -209,8 +209,10 @@ struct tcpcb { u_int t_keepcnt; /* number of keepalives before close */ u_int t_tsomax; /* tso burst length limit */ + u_int t_pmtud_saved_maxopd; /* pre-blackhole MSS */ + u_int t_flags2; /* More tcpcb flags storage */ - uint32_t t_ispare[8]; /* 5 UTO, 3 TBD */ + uint32_t t_ispare[6]; /* 5 UTO, 1 TBD */ void *t_pspare2[4]; /* 1 TCP_SIGNATURE, 3 TBD */ uint64_t _pad[6]; /* 6 TBD (1-2 CC/RTT?) */ }; @@ -284,6 +286,13 @@ struct tcpcb { #endif /* TCP_SIGNATURE */ /* + * Flags for PLPMTU handling, t_flags2 + */ +#define TF2_PLPMTU_BLACKHOLE 0x00000001 /* Possible PLPMTUD Black Hole. */ +#define TF2_PLPMTU_PMTUD 0x00000002 /* Allowed to attempt PLPMTUD. */ +#define TF2_PLPMTU_MAXSEGSNT 0x00000004 /* Last seg sent was full seg. */ + +/* * Structure to hold TCP options that are only used during segment * processing (in tcp_input), but not held in the tcpcb. * It's basically used to reduce the number of parameters -- cgit v1.1