ipv4: Handle PMTU in all ICMP error handlers.

With ip_rt_frag_needed() removed, we have to explicitly update PMTU
information in every ICMP error handler.

Create two helper functions to facilitate this.

1) ipv4_sk_update_pmtu()

   This updates the PMTU when we have a socket context to
   work with.

2) ipv4_update_pmtu()

   Raw version, used when no socket context is available.  For this
   interface, we essentially just pass in explicit arguments for
   the flow identity information we would have extracted from the
   socket.

   And you'll notice that ipv4_sk_update_pmtu() is simply implemented
   in terms of ipv4_update_pmtu()

Note that __ip_route_output_key() is used, rather than something like
ip_route_output_flow() or ip_route_output_key().  This is because we
absolutely do not want to end up with a route that does IPSEC
encapsulation and the like.  Instead, we only want the route that
would get us to the node described by the outermost IP header.

Reported-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 28 insertions, 0 deletions

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 655506af47ca..41df5297a412 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1711,6 +1711,34 @@ static void ip_rt_update_pmtu(struct dst_entry *dst, u32 mtu)
         }
 }
 
+void ipv4_update_pmtu(struct sk_buff *skb, struct net *net, u32 mtu,
+                      int oif, u32 mark, u8 protocol, int flow_flags)
+{
+        const struct iphdr *iph = (const struct iphdr *)skb->data;
+        struct flowi4 fl4;
+        struct rtable *rt;
+
+        flowi4_init_output(&fl4, oif, mark, RT_TOS(iph->tos), RT_SCOPE_UNIVERSE,
+                           protocol, flow_flags | FLOWI_FLAG_PRECOW_METRICS,
+                           iph->daddr, iph->saddr, 0, 0);
+        rt = __ip_route_output_key(net, &fl4);
+        if (!IS_ERR(rt)) {
+                ip_rt_update_pmtu(&rt->dst, mtu);
+                ip_rt_put(rt);
+        }
+}
+EXPORT_SYMBOL_GPL(ipv4_update_pmtu);
+
+void ipv4_sk_update_pmtu(struct sk_buff *skb, struct sock *sk, u32 mtu)
+{
+        const struct inet_sock *inet = inet_sk(sk);
+
+        return ipv4_update_pmtu(skb, sock_net(sk), mtu,
+                                sk->sk_bound_dev_if, sk->sk_mark,
+                                inet->hdrincl ? IPPROTO_RAW : sk->sk_protocol,
+                                inet_sk_flowi_flags(sk));
+}
+EXPORT_SYMBOL_GPL(ipv4_sk_update_pmtu);
 
 static void ipv4_validate_peer(struct rtable *rt)
 {