From 83696408317735d105ad86a5470b39879ad2ec4d Mon Sep 17 00:00:00 2001 From: Xin Long Date: Tue, 22 Jun 2021 14:04:55 -0400 Subject: [PATCH] sctp: do state transition when receiving an icmp TOOBIG packet PLPMTUD will short-circuit the old process for icmp TOOBIG packets. This part is described in rfc8899#section-4.6.2 (PL_PTB_SIZE = PTB_SIZE - other_headers_len). Note that from rfc8899#section-5.2 State Machine, each case below is for some specific states only: a) PL_PTB_SIZE < MIN_PLPMTU || PL_PTB_SIZE >= PROBED_SIZE, discard it, for any state b) MIN_PLPMTU < PL_PTB_SIZE < BASE_PLPMTU, Base -> Error, for Base state c) BASE_PLPMTU <= PL_PTB_SIZE < PLPMTU, Search -> Base or Complete -> Base, for Search and Complete states. d) PLPMTU < PL_PTB_SIZE < PROBED_SIZE, set pl.probe_size to PL_PTB_SIZE then verify it, for Search state. The most important one is case d), which will help find the optimal fast during searching. Like when pathmtu = 1392 for SCTP over IPv4, the search will be (20 is iphdr_len): 1. probe with 1200 - 20 2. probe with 1232 - 20 3. probe with 1264 - 20 ... 7. probe with 1388 - 20 8. probe with 1420 - 20 When sending the probe with 1420 - 20, TOOBIG may come with PL_PTB_SIZE = 1392 - 20. Then it matches case d), and saves some rounds to try with the 1392 - 20 probe. But of course, PLPMTUD doesn't trust TOOBIG packets, and it will go back to the common searching once the probe with the new size can't be verified. Signed-off-by: Xin Long Acked-by: Marcelo Ricardo Leitner Signed-off-by: David S. Miller --- net/sctp/input.c | 4 +++- net/sctp/transport.c | 51 +++++++++++++++++++++++++++++++++++++++++++- 2 files changed, 53 insertions(+), 2 deletions(-) diff --git a/net/sctp/input.c b/net/sctp/input.c index d508f6f3dd08..9ffdbd6526e9 100644 --- a/net/sctp/input.c +++ b/net/sctp/input.c @@ -385,7 +385,9 @@ static int sctp_add_backlog(struct sock *sk, struct sk_buff *skb) void sctp_icmp_frag_needed(struct sock *sk, struct sctp_association *asoc, struct sctp_transport *t, __u32 pmtu) { - if (!t || (t->pathmtu <= pmtu)) + if (!t || + (t->pathmtu <= pmtu && + t->pl.probe_size + sctp_transport_pl_hlen(t) <= pmtu)) return; if (sock_owned_by_user(sk)) { diff --git a/net/sctp/transport.c b/net/sctp/transport.c index 79ff5ca6b472..5cefb4eab8a0 100644 --- a/net/sctp/transport.c +++ b/net/sctp/transport.c @@ -343,10 +343,55 @@ void sctp_transport_pl_recv(struct sctp_transport *t) } } +static bool sctp_transport_pl_toobig(struct sctp_transport *t, u32 pmtu) +{ + pr_debug("%s: PLPMTUD: transport: %p, state: %d, pmtu: %d, size: %d, ptb: %d\n", + __func__, t, t->pl.state, t->pl.pmtu, t->pl.probe_size, pmtu); + + if (pmtu < SCTP_MIN_PLPMTU || pmtu >= t->pl.probe_size) + return false; + + if (t->pl.state == SCTP_PL_BASE) { + if (pmtu >= SCTP_MIN_PLPMTU && pmtu < SCTP_BASE_PLPMTU) { + t->pl.state = SCTP_PL_ERROR; /* Base -> Error */ + + t->pl.pmtu = SCTP_MIN_PLPMTU; + t->pathmtu = t->pl.pmtu + sctp_transport_pl_hlen(t); + } + } else if (t->pl.state == SCTP_PL_SEARCH) { + if (pmtu >= SCTP_BASE_PLPMTU && pmtu < t->pl.pmtu) { + t->pl.state = SCTP_PL_BASE; /* Search -> Base */ + t->pl.probe_size = SCTP_BASE_PLPMTU; + t->pl.probe_count = 0; + + t->pl.probe_high = 0; + t->pl.pmtu = SCTP_BASE_PLPMTU; + t->pathmtu = t->pl.pmtu + sctp_transport_pl_hlen(t); + } else if (pmtu > t->pl.pmtu && pmtu < t->pl.probe_size) { + t->pl.probe_size = pmtu; + t->pl.probe_count = 0; + + return false; + } + } else if (t->pl.state == SCTP_PL_COMPLETE) { + if (pmtu >= SCTP_BASE_PLPMTU && pmtu < t->pl.pmtu) { + t->pl.state = SCTP_PL_BASE; /* Complete -> Base */ + t->pl.probe_size = SCTP_BASE_PLPMTU; + t->pl.probe_count = 0; + + t->pl.probe_high = 0; + t->pl.pmtu = SCTP_BASE_PLPMTU; + t->pathmtu = t->pl.pmtu + sctp_transport_pl_hlen(t); + } + } + + return true; +} + bool sctp_transport_update_pmtu(struct sctp_transport *t, u32 pmtu) { - struct dst_entry *dst = sctp_transport_dst_check(t); struct sock *sk = t->asoc->base.sk; + struct dst_entry *dst; bool change = true; if (unlikely(pmtu < SCTP_DEFAULT_MINSEGMENT)) { @@ -357,6 +402,10 @@ bool sctp_transport_update_pmtu(struct sctp_transport *t, u32 pmtu) } pmtu = SCTP_TRUNC4(pmtu); + if (sctp_transport_pl_enabled(t)) + return sctp_transport_pl_toobig(t, pmtu - sctp_transport_pl_hlen(t)); + + dst = sctp_transport_dst_check(t); if (dst) { struct sctp_pf *pf = sctp_get_pf_specific(dst->ops->family); union sctp_addr addr;