1 files changed, 50 insertions, 0 deletions

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index f8c7ec8171a8..b5c3937ca6ec 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -1457,6 +1457,56 @@ static int call_fib_nh_notifiers(struct fib_nh *fib_nh,
         return NOTIFY_DONE;
 }
 
+/* Update the PMTU of exceptions when:
+ * - the new MTU of the first hop becomes smaller than the PMTU
+ * - the old MTU was the same as the PMTU, and it limited discovery of
+ *   larger MTUs on the path. With that limit raised, we can now
+ *   discover larger MTUs
+ * A special case is locked exceptions, for which the PMTU is smaller
+ * than the minimal accepted PMTU:
+ * - if the new MTU is greater than the PMTU, don't make any change
+ * - otherwise, unlock and set PMTU
+ */
+static void nh_update_mtu(struct fib_nh *nh, u32 new, u32 orig)
+{
+        struct fnhe_hash_bucket *bucket;
+        int i;
+
+        bucket = rcu_dereference_protected(nh->nh_exceptions, 1);
+        if (!bucket)
+                return;
+
+        for (i = 0; i < FNHE_HASH_SIZE; i++) {
+                struct fib_nh_exception *fnhe;
+
+                for (fnhe = rcu_dereference_protected(bucket[i].chain, 1);
+                     fnhe;
+                     fnhe = rcu_dereference_protected(fnhe->fnhe_next, 1)) {
+                        if (fnhe->fnhe_mtu_locked) {
+                                if (new <= fnhe->fnhe_pmtu) {
+                                        fnhe->fnhe_pmtu = new;
+                                        fnhe->fnhe_mtu_locked = false;
+                                }
+                        } else if (new < fnhe->fnhe_pmtu ||
+                                   orig == fnhe->fnhe_pmtu) {
+                                fnhe->fnhe_pmtu = new;
+                        }
+                }
+        }
+}
+
+void fib_sync_mtu(struct net_device *dev, u32 orig_mtu)
+{
+        unsigned int hash = fib_devindex_hashfn(dev->ifindex);
+        struct hlist_head *head = &fib_info_devhash[hash];
+        struct fib_nh *nh;
+
+        hlist_for_each_entry(nh, head, nh_hash) {
+                if (nh->nh_dev == dev)
+                        nh_update_mtu(nh, dev->mtu, orig_mtu);
+        }
+}
+
 /* Event              force Flags           Description
  * NETDEV_CHANGE      0     LINKDOWN        Carrier OFF, not for scope host
  * NETDEV_DOWN        0     LINKDOWN|DEAD   Link down, not for scope host