[INET]: Introduce inet_sk_rebuild_header

From tcp_v4_rebuild_header, that already was pretty generic, I only
needed to use sk->sk_protocol instead of the hardcoded IPPROTO_TCP and
establish the requirement that INET transport layer protocols that
want to use this function map TCP_SYN_SENT to its equivalent state.

Signed-off-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 113 insertions, 0 deletions

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 9e83d7773d8f..7137e6420d66 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -951,6 +951,119 @@ void inet_unregister_protosw(struct inet_protosw *p)
         }
 }
 
+/*
+ *      Shall we try to damage output packets if routing dev changes?
+ */
+
+int sysctl_ip_dynaddr;
+
+static int inet_sk_reselect_saddr(struct sock *sk)
+{
+        struct inet_sock *inet = inet_sk(sk);
+        int err;
+        struct rtable *rt;
+        __u32 old_saddr = inet->saddr;
+        __u32 new_saddr;
+        __u32 daddr = inet->daddr;
+
+        if (inet->opt && inet->opt->srr)
+                daddr = inet->opt->faddr;
+
+        /* Query new route. */
+        err = ip_route_connect(&rt, daddr, 0,
+                               RT_CONN_FLAGS(sk),
+                               sk->sk_bound_dev_if,
+                               sk->sk_protocol,
+                               inet->sport, inet->dport, sk);
+        if (err)
+                return err;
+
+        sk_setup_caps(sk, &rt->u.dst);
+
+        new_saddr = rt->rt_src;
+
+        if (new_saddr == old_saddr)
+                return 0;
+
+        if (sysctl_ip_dynaddr > 1) {
+                printk(KERN_INFO "%s(): shifting inet->"
+                                 "saddr from %d.%d.%d.%d to %d.%d.%d.%d\n",
+                       __FUNCTION__,
+                       NIPQUAD(old_saddr),
+                       NIPQUAD(new_saddr));
+        }
+
+        inet->saddr = inet->rcv_saddr = new_saddr;
+
+        /*
+         * XXX The only one ugly spot where we need to
+         * XXX really change the sockets identity after
+         * XXX it has entered the hashes. -DaveM
+         *
+         * Besides that, it does not check for connection
+         * uniqueness. Wait for troubles.
+         */
+        __sk_prot_rehash(sk);
+        return 0;
+}
+
+int inet_sk_rebuild_header(struct sock *sk)
+{
+        struct inet_sock *inet = inet_sk(sk);
+        struct rtable *rt = (struct rtable *)__sk_dst_check(sk, 0);
+        u32 daddr;
+        int err;
+
+        /* Route is OK, nothing to do. */
+        if (rt)
+                return 0;
+
+        /* Reroute. */
+        daddr = inet->daddr;
+        if (inet->opt && inet->opt->srr)
+                daddr = inet->opt->faddr;
+{
+        struct flowi fl = {
+                .oif = sk->sk_bound_dev_if,
+                .nl_u = {
+                        .ip4_u = {
+                                .daddr  = daddr,
+                                .saddr  = inet->saddr,
+                                .tos    = RT_CONN_FLAGS(sk),
+                        },
+                },
+                .proto = sk->sk_protocol,
+                .uli_u = {
+                        .ports = {
+                                .sport = inet->sport,
+                                .dport = inet->dport,
+                        },
+                },
+        };
+                                                
+        err = ip_route_output_flow(&rt, &fl, sk, 0);
+}
+        if (!err)
+                sk_setup_caps(sk, &rt->u.dst);
+        else {
+                /* Routing failed... */
+                sk->sk_route_caps = 0;
+                /*
+                 * Other protocols have to map its equivalent state to TCP_SYN_SENT.
+                 * DCCP maps its DCCP_REQUESTING state to TCP_SYN_SENT. -acme
+                 */
+                if (!sysctl_ip_dynaddr ||
+                    sk->sk_state != TCP_SYN_SENT ||
+                    (sk->sk_userlocks & SOCK_BINDADDR_LOCK) ||
+                    (err = inet_sk_reselect_saddr(sk)) != 0)
+                        sk->sk_err_soft = -err;
+        }
+
+        return err;
+}
+
+EXPORT_SYMBOL(inet_sk_rebuild_header);
+
 #ifdef CONFIG_IP_MULTICAST
 static struct net_protocol igmp_protocol = {
         .handler =      igmp_rcv,