Commit 83696408 authored by Xin Long's avatar Xin Long Committed by David S. Miller
Browse files

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: default avatarXin Long <lucien.xin@gmail.com>
Acked-by: default avatarMarcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent b87641af

net/sctp/input.c

+3 −1
Original line number Diff line number Diff line
@@ -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)) {

net/sctp/transport.c

+50 −1
Original line number Diff line number Diff line
@@ -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;