Re: [PATCH] ipv6: Fix the pmtu path for connected UDP socket

[Cong Wang]

On Tue, Mar 22, 2016 at 11:03 AM, Wei Wang <tracyw...@gmail.com> wrote:
> Thanks Martin and Cong.
>
> I guess then we are going with the following fix in ip6_sk_update_pmtu():
> 1. call ip6_upate_pmtu() as it is
> 2. do a dst_check()
> 3. re-lookup() if it is invalid
> 4. and then do a ip6_dst_store()/dst_set

Exactly, please try the attached patch. Note I did nothing more than a
compile test.

Does it make sense to you now?

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index ed44663..fcea05e 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1346,18 +1346,20 @@ static bool rt6_cache_allowed_for_pmtu(const struct 
rt6_info *rt)
                (rt->rt6i_flags & RTF_PCPU || rt->rt6i_node);
 }
 
-static void __ip6_rt_update_pmtu(struct dst_entry *dst, const struct sock *sk,
-                                const struct ipv6hdr *iph, u32 mtu)
+static struct dst_entry* __ip6_rt_update_pmtu(struct dst_entry *dst,
+                                             const struct sock *sk,
+                                             const struct ipv6hdr *iph,
+                                             u32 mtu, bool hold)
 {
        struct rt6_info *rt6 = (struct rt6_info *)dst;
 
        if (rt6->rt6i_flags & RTF_LOCAL)
-               return;
+               return dst;
 
        dst_confirm(dst);
        mtu = max_t(u32, mtu, IPV6_MIN_MTU);
        if (mtu >= dst_mtu(dst))
-               return;
+               return dst;
 
        if (!rt6_cache_allowed_for_pmtu(rt6)) {
                rt6_do_update_pmtu(rt6, mtu);
@@ -1372,11 +1374,13 @@ static void __ip6_rt_update_pmtu(struct dst_entry *dst, 
const struct sock *sk,
                        daddr = &sk->sk_v6_daddr;
                        saddr = &inet6_sk(sk)->saddr;
                } else {
-                       return;
+                       return dst;
                }
                nrt6 = ip6_rt_cache_alloc(rt6, daddr, saddr);
                if (nrt6) {
                        rt6_do_update_pmtu(nrt6, mtu);
+                       if (hold)
+                               dst_hold(&nrt6->dst);
 
                        /* ip6_ins_rt(nrt6) will bump the
                         * rt6->rt6i_node->fn_sernum
@@ -1384,14 +1388,17 @@ static void __ip6_rt_update_pmtu(struct dst_entry *dst, 
const struct sock *sk,
                         * invalidate the sk->sk_dst_cache.
                         */
                        ip6_ins_rt(nrt6);
+                       return &nrt6->dst;
                }
        }
+
+       return dst;
 }
 
 static void ip6_rt_update_pmtu(struct dst_entry *dst, struct sock *sk,
                               struct sk_buff *skb, u32 mtu)
 {
-       __ip6_rt_update_pmtu(dst, sk, skb ? ipv6_hdr(skb) : NULL, mtu);
+       __ip6_rt_update_pmtu(dst, sk, skb ? ipv6_hdr(skb) : NULL, mtu, false);
 }
 
 void ip6_update_pmtu(struct sk_buff *skb, struct net *net, __be32 mtu,
@@ -1410,15 +1417,52 @@ void ip6_update_pmtu(struct sk_buff *skb, struct net 
*net, __be32 mtu,
 
        dst = ip6_route_output(net, NULL, &fl6);
        if (!dst->error)
-               __ip6_rt_update_pmtu(dst, NULL, iph, ntohl(mtu));
+               __ip6_rt_update_pmtu(dst, NULL, iph, ntohl(mtu), false);
        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);
+       const struct ipv6hdr *iph = (struct ipv6hdr *) skb->data;
+       struct net *net = sock_net(sk);
+       struct dst_entry *ndst, *dst;
+       struct flowi6 fl6;
+
+       memset(&fl6, 0, sizeof(fl6));
+
+       bh_lock_sock(sk);
+
+       fl6.flowi6_oif = sk->sk_bound_dev_if;
+       fl6.flowi6_mark = sk->sk_mark ? : IP6_REPLY_MARK(net, skb->mark);
+       fl6.daddr = iph->daddr;
+       fl6.saddr = iph->saddr;
+       fl6.flowlabel = ip6_flowinfo(iph);
+
+       dst = sk_dst_get(sk);
+       if (sock_owned_by_user(sk) || !dst) {
+               ip6_update_pmtu(skb, net, mtu, fl6.flowi6_oif, fl6.flowi6_mark);
+               goto out;
+       }
+
+       if (dst->obsolete && !dst->ops->check(dst, 0)) {
+               dst_release(dst);
+               dst = ip6_route_output(net, sk, &fl6);
+               if (dst->error)
+                       goto out;
+       }
+
+       ndst = __ip6_rt_update_pmtu(dst, sk, iph, ntohl(mtu), true);
+       if (ndst != dst) {
+               dst_release(dst);
+               dst = ndst;
+       }
+
+       if (sk->sk_state == TCP_ESTABLISHED)
+               ip6_dst_store(sk, dst, &iph->daddr, &iph->saddr);
+out:
+       bh_unlock_sock(sk);
+       dst_release(dst);
 }
 EXPORT_SYMBOL_GPL(ip6_sk_update_pmtu);