ipv4: Add FIB nexthop exceptions.

In a regime where we have subnetted route entries, we need a way to
store persistent storage about destination specific learned values
such as redirects and PMTU values.

This is implemented here via nexthop exceptions.

The initial implementation is a 2048 entry hash table with relaiming
starting at chain length 5.  A more sophisticated scheme can be
devised if that proves necessary.

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

3 files changed, 266 insertions, 31 deletions

diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
index 5697acefeba3..e9ee1ca07087 100644
--- a/include/net/ip_fib.h
+++ b/include/net/ip_fib.h
@@ -18,6 +18,7 @@
 
 #include <net/flow.h>
 #include <linux/seq_file.h>
+#include <linux/rcupdate.h>
 #include <net/fib_rules.h>
 #include <net/inetpeer.h>
 
@@ -46,6 +47,22 @@ struct fib_config {
 
 struct fib_info;
 
+struct fib_nh_exception {
+        struct fib_nh_exception __rcu   *fnhe_next;
+        __be32                          fnhe_daddr;
+        u32                             fnhe_pmtu;
+        u32                             fnhe_gw;
+        unsigned long                   fnhe_expires;
+        unsigned long                   fnhe_stamp;
+};
+
+struct fnhe_hash_bucket {
+        struct fib_nh_exception __rcu   *chain;
+};
+
+#define FNHE_HASH_SIZE          2048
+#define FNHE_RECLAIM_DEPTH      5
+
 struct fib_nh {
         struct net_device       *nh_dev;
         struct hlist_node       nh_hash;
@@ -63,6 +80,7 @@ struct fib_nh {
         __be32                  nh_gw;
         __be32                  nh_saddr;
         int                     nh_saddr_genid;
+        struct fnhe_hash_bucket *nh_exceptions;
 };
 
 /*
diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index d71bfbdc0bf4..1e09852df512 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -140,6 +140,27 @@ const struct fib_prop fib_props[RTN_MAX + 1] = {
         },
 };
 
+static void free_nh_exceptions(struct fib_nh *nh)
+{
+        struct fnhe_hash_bucket *hash = nh->nh_exceptions;
+        int i;
+
+        for (i = 0; i < FNHE_HASH_SIZE; i++) {
+                struct fib_nh_exception *fnhe;
+
+                fnhe = rcu_dereference(hash[i].chain);
+                while (fnhe) {
+                        struct fib_nh_exception *next;
+                        
+                        next = rcu_dereference(fnhe->fnhe_next);
+                        kfree(fnhe);
+
+                        fnhe = next;
+                }
+        }
+        kfree(hash);
+}
+
 /* Release a nexthop info record */
 static void free_fib_info_rcu(struct rcu_head *head)
 {
@@ -148,6 +169,8 @@ static void free_fib_info_rcu(struct rcu_head *head)
         change_nexthops(fi) {
                 if (nexthop_nh->nh_dev)
                         dev_put(nexthop_nh->nh_dev);
+                if (nexthop_nh->nh_exceptions)
+                        free_nh_exceptions(nexthop_nh);
         } endfor_nexthops(fi);
 
         release_net(fi->fib_net);
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index b35d3bfc66cd..a5bd0b4acc61 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1275,14 +1275,130 @@ static void rt_del(unsigned int hash, struct rtable *rt)
         spin_unlock_bh(rt_hash_lock_addr(hash));
 }
 
-static void ip_do_redirect(struct dst_entry *dst, struct sock *sk, struct sk_buff *skb)
+static void __build_flow_key(struct flowi4 *fl4, struct sock *sk,
+                             const struct iphdr *iph,
+                             int oif, u8 tos,
+                             u8 prot, u32 mark, int flow_flags)
+{
+        if (sk) {
+                const struct inet_sock *inet = inet_sk(sk);
+
+                oif = sk->sk_bound_dev_if;
+                mark = sk->sk_mark;
+                tos = RT_CONN_FLAGS(sk);
+                prot = inet->hdrincl ? IPPROTO_RAW : sk->sk_protocol;
+        }
+        flowi4_init_output(fl4, oif, mark, tos,
+                           RT_SCOPE_UNIVERSE, prot,
+                           flow_flags,
+                           iph->daddr, iph->saddr, 0, 0);
+}
+
+static void build_skb_flow_key(struct flowi4 *fl4, struct sk_buff *skb, struct sock *sk)
+{
+        const struct iphdr *iph = ip_hdr(skb);
+        int oif = skb->dev->ifindex;
+        u8 tos = RT_TOS(iph->tos);
+        u8 prot = iph->protocol;
+        u32 mark = skb->mark;
+
+        __build_flow_key(fl4, sk, iph, oif, tos, prot, mark, 0);
+}
+
+static void build_sk_flow_key(struct flowi4 *fl4, struct sock *sk)
+{
+        const struct inet_sock *inet = inet_sk(sk);
+        struct ip_options_rcu *inet_opt;
+        __be32 daddr = inet->inet_daddr;
+
+        rcu_read_lock();
+        inet_opt = rcu_dereference(inet->inet_opt);
+        if (inet_opt && inet_opt->opt.srr)
+                daddr = inet_opt->opt.faddr;
+        flowi4_init_output(fl4, sk->sk_bound_dev_if, sk->sk_mark,
+                           RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE,
+                           inet->hdrincl ? IPPROTO_RAW : sk->sk_protocol,
+                           inet_sk_flowi_flags(sk),
+                           daddr, inet->inet_saddr, 0, 0);
+        rcu_read_unlock();
+}
+
+static void ip_rt_build_flow_key(struct flowi4 *fl4, struct sock *sk,
+                                 struct sk_buff *skb)
+{
+        if (skb)
+                build_skb_flow_key(fl4, skb, sk);
+        else
+                build_sk_flow_key(fl4, sk);
+}
+
+static DEFINE_SPINLOCK(fnhe_lock);
+
+static struct fib_nh_exception *fnhe_oldest(struct fnhe_hash_bucket *hash, __be32 daddr)
+{
+        struct fib_nh_exception *fnhe, *oldest;
+
+        oldest = rcu_dereference(hash->chain);
+        for (fnhe = rcu_dereference(oldest->fnhe_next); fnhe;
+             fnhe = rcu_dereference(fnhe->fnhe_next)) {
+                if (time_before(fnhe->fnhe_stamp, oldest->fnhe_stamp))
+                        oldest = fnhe;
+        }
+        return oldest;
+}
+
+static struct fib_nh_exception *find_or_create_fnhe(struct fib_nh *nh, __be32 daddr)
+{
+        struct fnhe_hash_bucket *hash = nh->nh_exceptions;
+        struct fib_nh_exception *fnhe;
+        int depth;
+        u32 hval;
+
+        if (!hash) {
+                hash = nh->nh_exceptions = kzalloc(FNHE_HASH_SIZE * sizeof(*hash),
+                                                   GFP_ATOMIC);
+                if (!hash)
+                        return NULL;
+        }
+
+        hval = (__force u32) daddr;
+        hval ^= (hval >> 11) ^ (hval >> 22);
+        hash += hval;
+
+        depth = 0;
+        for (fnhe = rcu_dereference(hash->chain); fnhe;
+             fnhe = rcu_dereference(fnhe->fnhe_next)) {
+                if (fnhe->fnhe_daddr == daddr)
+                        goto out;
+                depth++;
+        }
+
+        if (depth > FNHE_RECLAIM_DEPTH) {
+                fnhe = fnhe_oldest(hash + hval, daddr);
+                goto out_daddr;
+        }
+        fnhe = kzalloc(sizeof(*fnhe), GFP_ATOMIC);
+        if (!fnhe)
+                return NULL;
+
+        fnhe->fnhe_next = hash->chain;
+        rcu_assign_pointer(hash->chain, fnhe);
+
+out_daddr:
+        fnhe->fnhe_daddr = daddr;
+out:
+        fnhe->fnhe_stamp = jiffies;
+        return fnhe;
+}
+
+static void __ip_do_redirect(struct rtable *rt, struct sk_buff *skb, struct flowi4 *fl4)
 {
         __be32 new_gw = icmp_hdr(skb)->un.gateway;
         __be32 old_gw = ip_hdr(skb)->saddr;
         struct net_device *dev = skb->dev;
         struct in_device *in_dev;
+        struct fib_result res;
         struct neighbour *n;
-        struct rtable *rt;
         struct net *net;
 
         switch (icmp_hdr(skb)->code & 7) {
@@ -1296,7 +1412,6 @@ static void ip_do_redirect(struct dst_entry *dst, struct sock *sk, struct sk_buf
                 return;
         }
 
-        rt = (struct rtable *) dst;
         if (rt->rt_gateway != old_gw)
                 return;
 
@@ -1320,11 +1435,21 @@ static void ip_do_redirect(struct dst_entry *dst, struct sock *sk, struct sk_buf
                         goto reject_redirect;
         }
 
-        n = ipv4_neigh_lookup(dst, NULL, &new_gw);
+        n = ipv4_neigh_lookup(&rt->dst, NULL, &new_gw);
         if (n) {
                 if (!(n->nud_state & NUD_VALID)) {
                         neigh_event_send(n, NULL);
                 } else {
+                        if (fib_lookup(net, fl4, &res) == 0) {
+                                struct fib_nh *nh = &FIB_RES_NH(res);
+                                struct fib_nh_exception *fnhe;
+
+                                spin_lock_bh(&fnhe_lock);
+                                fnhe = find_or_create_fnhe(nh, fl4->daddr);
+                                if (fnhe)
+                                        fnhe->fnhe_gw = new_gw;
+                                spin_unlock_bh(&fnhe_lock);
+                        }
                         rt->rt_gateway = new_gw;
                         rt->rt_flags |= RTCF_REDIRECTED;
                         call_netevent_notifiers(NETEVENT_NEIGH_UPDATE, n);
@@ -1349,6 +1474,17 @@ reject_redirect:
         ;
 }
 
+static void ip_do_redirect(struct dst_entry *dst, struct sock *sk, struct sk_buff *skb)
+{
+        struct rtable *rt;
+        struct flowi4 fl4;
+
+        rt = (struct rtable *) dst;
+
+        ip_rt_build_flow_key(&fl4, sk, skb);
+        __ip_do_redirect(rt, skb, &fl4);
+}
+
 static struct dst_entry *ipv4_negative_advice(struct dst_entry *dst)
 {
         struct rtable *rt = (struct rtable *)dst;
@@ -1508,33 +1644,51 @@ out:	kfree_skb(skb);
         return 0;
 }
 
-static void ip_rt_update_pmtu(struct dst_entry *dst, struct sock *sk,
-                              struct sk_buff *skb, u32 mtu)
+static void __ip_rt_update_pmtu(struct rtable *rt, struct flowi4 *fl4, u32 mtu)
 {
-        struct rtable *rt = (struct rtable *) dst;
-
-        dst_confirm(dst);
+        struct fib_result res;
 
         if (mtu < ip_rt_min_pmtu)
                 mtu = ip_rt_min_pmtu;
 
+        if (fib_lookup(dev_net(rt->dst.dev), fl4, &res) == 0) {
+                struct fib_nh *nh = &FIB_RES_NH(res);
+                struct fib_nh_exception *fnhe;
+
+                spin_lock_bh(&fnhe_lock);
+                fnhe = find_or_create_fnhe(nh, fl4->daddr);
+                if (fnhe) {
+                        fnhe->fnhe_pmtu = mtu;
+                        fnhe->fnhe_expires = jiffies + ip_rt_mtu_expires;
+                }
+                spin_unlock_bh(&fnhe_lock);
+        }
         rt->rt_pmtu = mtu;
         dst_set_expires(&rt->dst, ip_rt_mtu_expires);
 }
 
+static void ip_rt_update_pmtu(struct dst_entry *dst, struct sock *sk,
+                              struct sk_buff *skb, u32 mtu)
+{
+        struct rtable *rt = (struct rtable *) dst;
+        struct flowi4 fl4;
+
+        ip_rt_build_flow_key(&fl4, sk, skb);
+        __ip_rt_update_pmtu(rt, &fl4, 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;
+        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,
-                           iph->daddr, iph->saddr, 0, 0);
+        __build_flow_key(&fl4, NULL, iph, oif,
+                         RT_TOS(iph->tos), protocol, mark, flow_flags);
         rt = __ip_route_output_key(net, &fl4);
         if (!IS_ERR(rt)) {
-                ip_rt_update_pmtu(&rt->dst, NULL, skb, mtu);
+                __ip_rt_update_pmtu(rt, &fl4, mtu);
                 ip_rt_put(rt);
         }
 }
@@ -1542,27 +1696,31 @@ 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);
+        const struct iphdr *iph = (const struct iphdr *) skb->data;
+        struct flowi4 fl4;
+        struct rtable *rt;
 
-        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));
+        __build_flow_key(&fl4, sk, iph, 0, 0, 0, 0, 0);
+        rt = __ip_route_output_key(sock_net(sk), &fl4);
+        if (!IS_ERR(rt)) {
+                __ip_rt_update_pmtu(rt, &fl4, mtu);
+                ip_rt_put(rt);
+        }
 }
 EXPORT_SYMBOL_GPL(ipv4_sk_update_pmtu);
 
 void ipv4_redirect(struct sk_buff *skb, struct net *net,
                    int oif, u32 mark, u8 protocol, int flow_flags)
 {
-        const struct iphdr *iph = (const struct iphdr *)skb->data;
+        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, iph->daddr, iph->saddr, 0, 0);
+        __build_flow_key(&fl4, NULL, iph, oif,
+                         RT_TOS(iph->tos), protocol, mark, flow_flags);
         rt = __ip_route_output_key(net, &fl4);
         if (!IS_ERR(rt)) {
-                ip_do_redirect(&rt->dst, NULL, skb);
+                __ip_do_redirect(rt, skb, &fl4);
                 ip_rt_put(rt);
         }
 }
@@ -1570,12 +1728,16 @@ EXPORT_SYMBOL_GPL(ipv4_redirect);
 
 void ipv4_sk_redirect(struct sk_buff *skb, struct sock *sk)
 {
-        const struct inet_sock *inet = inet_sk(sk);
+        const struct iphdr *iph = (const struct iphdr *) skb->data;
+        struct flowi4 fl4;
+        struct rtable *rt;
 
-        return ipv4_redirect(skb, sock_net(sk), sk->sk_bound_dev_if,
-                             sk->sk_mark,
-                             inet->hdrincl ? IPPROTO_RAW : sk->sk_protocol,
-                             inet_sk_flowi_flags(sk));
+        __build_flow_key(&fl4, sk, iph, 0, 0, 0, 0, 0);
+        rt = __ip_route_output_key(sock_net(sk), &fl4);
+        if (!IS_ERR(rt)) {
+                __ip_do_redirect(rt, skb, &fl4);
+                ip_rt_put(rt);
+        }
 }
 EXPORT_SYMBOL_GPL(ipv4_sk_redirect);
 
@@ -1722,14 +1884,46 @@ static void rt_init_metrics(struct rtable *rt, const struct flowi4 *fl4,
         dst_init_metrics(&rt->dst, fi->fib_metrics, true);
 }
 
+static void rt_bind_exception(struct rtable *rt, struct fib_nh *nh, __be32 daddr)
+{
+        struct fnhe_hash_bucket *hash = nh->nh_exceptions;
+        struct fib_nh_exception *fnhe;
+        u32 hval;
+
+        hval = (__force u32) daddr;
+        hval ^= (hval >> 11) ^ (hval >> 22);
+
+        for (fnhe = rcu_dereference(hash[hval].chain); fnhe;
+             fnhe = rcu_dereference(fnhe->fnhe_next)) {
+                if (fnhe->fnhe_daddr == daddr) {
+                        if (fnhe->fnhe_pmtu) {
+                                unsigned long expires = fnhe->fnhe_expires;
+                                unsigned long diff = jiffies - expires;
+
+                                if (time_before(jiffies, expires)) {
+                                        rt->rt_pmtu = fnhe->fnhe_pmtu;
+                                        dst_set_expires(&rt->dst, diff);
+                                }
+                        }
+                        if (fnhe->fnhe_gw)
+                                rt->rt_gateway = fnhe->fnhe_gw;
+                        fnhe->fnhe_stamp = jiffies;
+                        break;
+                }
+        }
+}
+
 static void rt_set_nexthop(struct rtable *rt, const struct flowi4 *fl4,
                            const struct fib_result *res,
                            struct fib_info *fi, u16 type, u32 itag)
 {
         if (fi) {
-                if (FIB_RES_GW(*res) &&
-                    FIB_RES_NH(*res).nh_scope == RT_SCOPE_LINK)
-                        rt->rt_gateway = FIB_RES_GW(*res);
+                struct fib_nh *nh = &FIB_RES_NH(*res);
+
+                if (nh->nh_gw && nh->nh_scope == RT_SCOPE_LINK)
+                        rt->rt_gateway = nh->nh_gw;
+                if (unlikely(nh->nh_exceptions))
+                        rt_bind_exception(rt, nh, fl4->daddr);
                 rt_init_metrics(rt, fl4, fi);
 #ifdef CONFIG_IP_ROUTE_CLASSID
                 rt->dst.tclassid = FIB_RES_NH(*res).nh_tclassid;