ipv6: Only create RTF_CACHE routes after encountering pmtu exception

This patch creates a RTF_CACHE routes only after encountering a pmtu
exception.

After ip6_rt_update_pmtu() has inserted the RTF_CACHE route to the fib6
tree, the rt->rt6i_node->fn_sernum is bumped which will fail the
ip6_dst_check() and trigger a relookup.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Cc: Julian Anastasov <ja@ssi.bg>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 52 insertions, 49 deletions

diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index bde57b113009..83341b3a248d 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -738,6 +738,7 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct rt6_info *rt,
                                         rt6_clean_expires(iter);
                                 else
                                         rt6_set_expires(iter, rt->dst.expires);
+                                iter->rt6i_pmtu = rt->rt6i_pmtu;
                                 return -EEXIST;
                         }
                         /* If we have the same destination and the same metric,
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index f199d6357b31..e7ae2430dfed 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -873,16 +873,13 @@ static struct rt6_info *ip6_pol_route(struct net *net, struct fib6_table *table,
                                       struct flowi6 *fl6, int flags)
 {
         struct fib6_node *fn, *saved_fn;
-        struct rt6_info *rt, *nrt;
+        struct rt6_info *rt;
         int strict = 0;
-        int attempts = 3;
-        int err;
 
         strict |= flags & RT6_LOOKUP_F_IFACE;
         if (net->ipv6.devconf_all->forwarding == 0)
                 strict |= RT6_LOOKUP_F_REACHABLE;
 
-redo_fib6_lookup_lock:
         read_lock_bh(&table->tb6_lock);
 
         fn = fib6_lookup(&table->tb6_root, &fl6->daddr, &fl6->saddr);
@@ -901,46 +898,12 @@ redo_rt6_select:
                         strict &= ~RT6_LOOKUP_F_REACHABLE;
                         fn = saved_fn;
                         goto redo_rt6_select;
-                } else {
-                        dst_hold(&rt->dst);
-                        read_unlock_bh(&table->tb6_lock);
-                        goto out2;
                 }
         }
 
         dst_hold(&rt->dst);
         read_unlock_bh(&table->tb6_lock);
 
-        if (rt->rt6i_flags & RTF_CACHE)
-                goto out2;
-
-        if (!rt6_is_gw_or_nonexthop(rt) ||
-            !(rt->dst.flags & DST_HOST) || !(rt->rt6i_flags & RTF_LOCAL))
-                nrt = ip6_rt_cache_alloc(rt, &fl6->daddr, &fl6->saddr);
-        else
-                goto out2;
-
-        ip6_rt_put(rt);
-        rt = nrt ? : net->ipv6.ip6_null_entry;
-
-        dst_hold(&rt->dst);
-        if (nrt) {
-                err = ip6_ins_rt(nrt);
-                if (!err)
-                        goto out2;
-        }
-
-        if (--attempts <= 0)
-                goto out2;
-
-        /*
-         * Race condition! In the gap, when table->tb6_lock was
-         * released someone could insert this route.  Relookup.
-         */
-        ip6_rt_put(rt);
-        goto redo_fib6_lookup_lock;
-
-out2:
         rt6_dst_from_metrics_check(rt);
         rt->dst.lastuse = jiffies;
         rt->dst.__use++;
@@ -1113,24 +1076,63 @@ static void ip6_link_failure(struct sk_buff *skb)
         }
 }
 
-static void ip6_rt_update_pmtu(struct dst_entry *dst, struct sock *sk,
-                               struct sk_buff *skb, u32 mtu)
+static void rt6_do_update_pmtu(struct rt6_info *rt, u32 mtu)
+{
+        struct net *net = dev_net(rt->dst.dev);
+
+        rt->rt6i_flags |= RTF_MODIFIED;
+        rt->rt6i_pmtu = mtu;
+        rt6_update_expires(rt, net->ipv6.sysctl.ip6_rt_mtu_expires);
+}
+
+static void __ip6_rt_update_pmtu(struct dst_entry *dst, const struct sock *sk,
+                                 const struct ipv6hdr *iph, u32 mtu)
 {
         struct rt6_info *rt6 = (struct rt6_info *)dst;
 
-        dst_confirm(dst);
-        if (mtu < dst_mtu(dst) && (rt6->rt6i_flags & RTF_CACHE)) {
-                struct net *net = dev_net(dst->dev);
+        if (rt6->rt6i_flags & RTF_LOCAL)
+                return;
 
-                rt6->rt6i_flags |= RTF_MODIFIED;
-                if (mtu < IPV6_MIN_MTU)
-                        mtu = IPV6_MIN_MTU;
+        dst_confirm(dst);
+        mtu = max_t(u32, mtu, IPV6_MIN_MTU);
+        if (mtu >= dst_mtu(dst))
+                return;
 
-                rt6->rt6i_pmtu = mtu;
-                rt6_update_expires(rt6, net->ipv6.sysctl.ip6_rt_mtu_expires);
+        if (rt6->rt6i_flags & RTF_CACHE) {
+                rt6_do_update_pmtu(rt6, mtu);
+        } else {
+                const struct in6_addr *daddr, *saddr;
+                struct rt6_info *nrt6;
+
+                if (iph) {
+                        daddr = &iph->daddr;
+                        saddr = &iph->saddr;
+                } else if (sk) {
+                        daddr = &sk->sk_v6_daddr;
+                        saddr = &inet6_sk(sk)->saddr;
+                } else {
+                        return;
+                }
+                nrt6 = ip6_rt_cache_alloc(rt6, daddr, saddr);
+                if (nrt6) {
+                        rt6_do_update_pmtu(nrt6, mtu);
+
+                        /* ip6_ins_rt(nrt6) will bump the
+                         * rt6->rt6i_node->fn_sernum
+                         * which will fail the next rt6_check() and
+                         * invalidate the sk->sk_dst_cache.
+                         */
+                        ip6_ins_rt(nrt6);
+                }
         }
 }
 
+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);
+}
+
 void ip6_update_pmtu(struct sk_buff *skb, struct net *net, __be32 mtu,
                      int oif, u32 mark)
 {
@@ -1147,7 +1149,7 @@ 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, skb, ntohl(mtu));
+                __ip6_rt_update_pmtu(dst, NULL, iph, ntohl(mtu));
         dst_release(dst);
 }
 EXPORT_SYMBOL_GPL(ip6_update_pmtu);