3 files changed, 26 insertions, 13 deletions

diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index 2f8f93da5dc2..9a5ccf03a59b 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -966,7 +966,7 @@ void sctp_transport_burst_limited(struct sctp_transport *);
 void sctp_transport_burst_reset(struct sctp_transport *);
 unsigned long sctp_transport_timeout(struct sctp_transport *);
 void sctp_transport_reset(struct sctp_transport *t);
-void sctp_transport_update_pmtu(struct sctp_transport *t, u32 pmtu);
+bool sctp_transport_update_pmtu(struct sctp_transport *t, u32 pmtu);
 void sctp_transport_immediate_rtx(struct sctp_transport *);
 void sctp_transport_dst_release(struct sctp_transport *t);
 void sctp_transport_dst_confirm(struct sctp_transport *t);
diff --git a/net/sctp/input.c b/net/sctp/input.c
index 9320661cc41d..141c9c466ec1 100644
--- a/net/sctp/input.c
+++ b/net/sctp/input.c
@@ -406,8 +406,12 @@ void sctp_icmp_frag_needed(struct sock *sk, struct sctp_association *asoc,
                  */
                 return;
 
-        /* Update transports view of the MTU */
-        sctp_transport_update_pmtu(t, pmtu);
+        /* Update transports view of the MTU. Return if no update was needed.
+         * If an update wasn't needed/possible, it also doesn't make sense to
+         * try to retransmit now.
+         */
+        if (!sctp_transport_update_pmtu(t, pmtu))
+                return;
 
         /* Update association pmtu. */
         sctp_assoc_sync_pmtu(asoc);
diff --git a/net/sctp/transport.c b/net/sctp/transport.c
index 1e5a22430cf5..47f82bd794d9 100644
--- a/net/sctp/transport.c
+++ b/net/sctp/transport.c
@@ -248,28 +248,37 @@ void sctp_transport_pmtu(struct sctp_transport *transport, struct sock *sk)
                 transport->pathmtu = SCTP_DEFAULT_MAXSEGMENT;
 }
 
-void sctp_transport_update_pmtu(struct sctp_transport *t, u32 pmtu)
+bool sctp_transport_update_pmtu(struct sctp_transport *t, u32 pmtu)
 {
         struct dst_entry *dst = sctp_transport_dst_check(t);
+        bool change = true;
 
         if (unlikely(pmtu < SCTP_DEFAULT_MINSEGMENT)) {
-                pr_warn("%s: Reported pmtu %d too low, using default minimum of %d\n",
-                        __func__, pmtu, SCTP_DEFAULT_MINSEGMENT);
-                /* Use default minimum segment size and disable
-                 * pmtu discovery on this transport.
-                 */
-                t->pathmtu = SCTP_DEFAULT_MINSEGMENT;
-        } else {
-                t->pathmtu = pmtu;
+                pr_warn_ratelimited("%s: Reported pmtu %d too low, using default minimum of %d\n",
+                                    __func__, pmtu, SCTP_DEFAULT_MINSEGMENT);
+                /* Use default minimum segment instead */
+                pmtu = SCTP_DEFAULT_MINSEGMENT;
         }
+        pmtu = SCTP_TRUNC4(pmtu);
 
         if (dst) {
                 dst->ops->update_pmtu(dst, t->asoc->base.sk, NULL, pmtu);
                 dst = sctp_transport_dst_check(t);
         }
 
-        if (!dst)
+        if (!dst) {
                 t->af_specific->get_dst(t, &t->saddr, &t->fl, t->asoc->base.sk);
+                dst = t->dst;
+        }
+
+        if (dst) {
+                /* Re-fetch, as under layers may have a higher minimum size */
+                pmtu = SCTP_TRUNC4(dst_mtu(dst));
+                change = t->pathmtu != pmtu;
+        }
+        t->pathmtu = pmtu;
+
+        return change;
 }
 
 /* Caches the dst entry and source address for a transport's destination