ipv6: Handle PMTU in ICMP error handlers.

One tricky issue on the ipv6 side vs. ipv4 is that the ICMP callouts
to handle the error pass the 32-bit info cookie in network byte order
whereas ipv4 passes it around in host byte order.

Like the ipv4 side, we have two helper functions.  One for when we
have a socket context and one for when we do not.

ip6ip6 tunnels are not handled here, because they handle PMTU events
by essentially relaying another ICMP packet-too-big message back to
the original sender.

This patch allows us to get rid of rt6_do_pmtu_disc().  It handles all
kinds of situations that simply cannot happen when we do the PMTU
update directly using a fully resolved route.

In fact, the "plen == 128" check in ip6_rt_update_pmtu() can very
likely be removed or changed into a BUG_ON() check.  We should never
have a prefixed ipv6 route when we get there.

Another piece of strange history here is that TCP and DCCP, unlike in
ipv4, never invoke the update_pmtu() method from their ICMP error
handlers.  This is incredibly astonishing since this is the context
where we have the most accurate context in which to make a PMTU
update, namely we have a fully connected socket and associated cached
socket route.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 33 insertions, 110 deletions

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 58a3ec23da2..0d41f68daff 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1049,7 +1049,10 @@ static void ip6_rt_update_pmtu(struct dst_entry *dst, u32 mtu)
 {
         struct rt6_info *rt6 = (struct rt6_info*)dst;
 
+        dst_confirm(dst);
         if (mtu < dst_mtu(dst) && rt6->rt6i_dst.plen == 128) {
+                struct net *net = dev_net(dst->dev);
+
                 rt6->rt6i_flags |= RTF_MODIFIED;
                 if (mtu < IPV6_MIN_MTU) {
                         u32 features = dst_metric(dst, RTAX_FEATURES);
@@ -1058,9 +1061,39 @@ static void ip6_rt_update_pmtu(struct dst_entry *dst, u32 mtu)
                         dst_metric_set(dst, RTAX_FEATURES, features);
                 }
                 dst_metric_set(dst, RTAX_MTU, mtu);
+                rt6_update_expires(rt6, net->ipv6.sysctl.ip6_rt_mtu_expires);
         }
 }
 
+void ip6_update_pmtu(struct sk_buff *skb, struct net *net, u32 mtu,
+                     int oif, __be32 mark)
+{
+        const struct ipv6hdr *iph = (struct ipv6hdr *) skb->data;
+        struct dst_entry *dst;
+        struct flowi6 fl6;
+
+        memset(&fl6, 0, sizeof(fl6));
+        fl6.flowi6_oif = oif;
+        fl6.flowi6_mark = mark;
+        fl6.flowi6_flags = FLOWI_FLAG_PRECOW_METRICS;
+        fl6.daddr = iph->daddr;
+        fl6.saddr = iph->saddr;
+        fl6.flowlabel = (*(__be32 *) iph) & IPV6_FLOWINFO_MASK;
+
+        dst = ip6_route_output(net, NULL, &fl6);
+        if (!dst->error)
+                ip6_rt_update_pmtu(dst, ntohl(mtu));
+        dst_release(dst);
+}
+EXPORT_SYMBOL_GPL(ip6_update_pmtu);
+
+void ip6_sk_update_pmtu(struct sk_buff *skb, struct sock *sk, __be32 mtu)
+{
+        ip6_update_pmtu(skb, sock_net(sk), mtu,
+                        sk->sk_bound_dev_if, sk->sk_mark);
+}
+EXPORT_SYMBOL_GPL(ip6_sk_update_pmtu);
+
 static unsigned int ip6_default_advmss(const struct dst_entry *dst)
 {
         struct net_device *dev = dst->dev;
@@ -1704,116 +1737,6 @@ out:
 }
 
 /*
- *      Handle ICMP "packet too big" messages
- *      i.e. Path MTU discovery
- */
-
-static void rt6_do_pmtu_disc(const struct in6_addr *daddr, const struct in6_addr *saddr,
-                             struct net *net, u32 pmtu, int ifindex)
-{
-        struct rt6_info *rt, *nrt;
-        int allfrag = 0;
-again:
-        rt = rt6_lookup(net, daddr, saddr, ifindex, 0);
-        if (!rt)
-                return;
-
-        if (rt6_check_expired(rt)) {
-                ip6_del_rt(rt);
-                goto again;
-        }
-
-        if (pmtu >= dst_mtu(&rt->dst))
-                goto out;
-
-        if (pmtu < IPV6_MIN_MTU) {
-                /*
-                 * According to RFC2460, PMTU is set to the IPv6 Minimum Link
-                 * MTU (1280) and a fragment header should always be included
-                 * after a node receiving Too Big message reporting PMTU is
-                 * less than the IPv6 Minimum Link MTU.
-                 */
-                pmtu = IPV6_MIN_MTU;
-                allfrag = 1;
-        }
-
-        /* New mtu received -> path was valid.
-           They are sent only in response to data packets,
-           so that this nexthop apparently is reachable. --ANK
-         */
-        dst_confirm(&rt->dst);
-
-        /* Host route. If it is static, it would be better
-           not to override it, but add new one, so that
-           when cache entry will expire old pmtu
-           would return automatically.
-         */
-        if (rt->rt6i_flags & RTF_CACHE) {
-                dst_metric_set(&rt->dst, RTAX_MTU, pmtu);
-                if (allfrag) {
-                        u32 features = dst_metric(&rt->dst, RTAX_FEATURES);
-                        features |= RTAX_FEATURE_ALLFRAG;
-                        dst_metric_set(&rt->dst, RTAX_FEATURES, features);
-                }
-                rt6_update_expires(rt, net->ipv6.sysctl.ip6_rt_mtu_expires);
-                rt->rt6i_flags |= RTF_MODIFIED;
-                goto out;
-        }
-
-        /* Network route.
-           Two cases are possible:
-           1. It is connected route. Action: COW
-           2. It is gatewayed route or NONEXTHOP route. Action: clone it.
-         */
-        if (!dst_get_neighbour_noref_raw(&rt->dst) && !(rt->rt6i_flags & RTF_NONEXTHOP))
-                nrt = rt6_alloc_cow(rt, daddr, saddr);
-        else
-                nrt = rt6_alloc_clone(rt, daddr);
-
-        if (nrt) {
-                dst_metric_set(&nrt->dst, RTAX_MTU, pmtu);
-                if (allfrag) {
-                        u32 features = dst_metric(&nrt->dst, RTAX_FEATURES);
-                        features |= RTAX_FEATURE_ALLFRAG;
-                        dst_metric_set(&nrt->dst, RTAX_FEATURES, features);
-                }
-
-                /* According to RFC 1981, detecting PMTU increase shouldn't be
-                 * happened within 5 mins, the recommended timer is 10 mins.
-                 * Here this route expiration time is set to ip6_rt_mtu_expires
-                 * which is 10 mins. After 10 mins the decreased pmtu is expired
-                 * and detecting PMTU increase will be automatically happened.
-                 */
-                rt6_update_expires(nrt, net->ipv6.sysctl.ip6_rt_mtu_expires);
-                nrt->rt6i_flags |= RTF_DYNAMIC;
-                ip6_ins_rt(nrt);
-        }
-out:
-        dst_release(&rt->dst);
-}
-
-void rt6_pmtu_discovery(const struct in6_addr *daddr, const struct in6_addr *saddr,
-                        struct net_device *dev, u32 pmtu)
-{
-        struct net *net = dev_net(dev);
-
-        /*
-         * RFC 1981 states that a node "MUST reduce the size of the packets it
-         * is sending along the path" that caused the Packet Too Big message.
-         * Since it's not possible in the general case to determine which
-         * interface was used to send the original packet, we update the MTU
-         * on the interface that will be used to send future packets. We also
-         * update the MTU on the interface that received the Packet Too Big in
-         * case the original packet was forced out that interface with
-         * SO_BINDTODEVICE or similar. This is the next best thing to the
-         * correct behaviour, which would be to update the MTU on all
-         * interfaces.
-         */
-        rt6_do_pmtu_disc(daddr, saddr, net, pmtu, 0);
-        rt6_do_pmtu_disc(daddr, saddr, net, pmtu, dev->ifindex);
-}
-
-/*
  *      Misc support functions
  */