[PATCH net] sctp: update dst pmtu with the correct daddr

[Xin Long]

When processing pmtu update from an icmp packet, it calls .update_pmtu
with sk instead of skb in sctp_transport_update_pmtu.

However for sctp, the daddr in the transport might be different from
inet_sock->inet_daddr or sk->sk_v6_daddr, which is used to update or
create the route cache. The incorrect daddr will cause a different
route cache created for the path.

So before calling .update_pmtu, inet_sock->inet_daddr/sk->sk_v6_daddr
should be updated with the daddr in the transport, and update it back
after it's done.

The issue has existed since route exceptions introduction.

Fixes: 4895c771c7f0 ("ipv4: Add FIB nexthop exceptions.")
Reported-by: ian.per...@dialogic.com
Signed-off-by: Xin Long <lucien....@gmail.com>
---
 net/sctp/transport.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/net/sctp/transport.c b/net/sctp/transport.c
index 12cac85..033696e 100644
--- a/net/sctp/transport.c
+++ b/net/sctp/transport.c
@@ -260,6 +260,7 @@ void sctp_transport_pmtu(struct sctp_transport *transport, 
struct sock *sk)
 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;
        bool change = true;
 
        if (unlikely(pmtu < SCTP_DEFAULT_MINSEGMENT)) {
@@ -271,12 +272,19 @@ bool sctp_transport_update_pmtu(struct sctp_transport *t, 
u32 pmtu)
        pmtu = SCTP_TRUNC4(pmtu);
 
        if (dst) {
-               dst->ops->update_pmtu(dst, t->asoc->base.sk, NULL, pmtu);
+               struct sctp_pf *pf = sctp_get_pf_specific(dst->ops->family);
+               union sctp_addr addr;
+
+               pf->af->from_sk(&addr, sk);
+               pf->to_sk_daddr(&t->ipaddr, sk);
+               dst->ops->update_pmtu(dst, sk, NULL, pmtu);
+               pf->to_sk_daddr(&addr, sk);
+
                dst = sctp_transport_dst_check(t);
        }
 
        if (!dst) {
-               t->af_specific->get_dst(t, &t->saddr, &t->fl, t->asoc->base.sk);
+               t->af_specific->get_dst(t, &t->saddr, &t->fl, sk);
                dst = t->dst;
        }
 
-- 
2.1.0