ipv4: Sanitize and simplify ip_route_{connect,newports}()

These functions are used together as a unit for route resolution
during connect().  They address the chicken-and-egg problem that
exists when ports need to be allocated during connect() processing,
yet such port allocations require addressing information from the
routing code.

It's currently more heavy handed than it needs to be, and in
particular we allocate and initialize a flow object twice.

Let the callers provide the on-stack flow object.  That way we only
need to initialize it once in the ip_route_connect() call.

Later, if ip_route_newports() needs to do anything, it re-uses that
flow object as-is except for the ports which it updates before the
route re-lookup.

Also, describe why this set of facilities are needed and how it works
in a big comment.

Signed-off-by: David S. Miller <davem@davemloft.net>
Reviewed-by: Eric Dumazet <eric.dumazet@gmail.com>

3 files changed, 9 insertions, 7 deletions

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index cae75ef21fe..0413af3e228 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1103,6 +1103,7 @@ static int inet_sk_reselect_saddr(struct sock *sk)
 	struct inet_sock *inet = inet_sk(sk);
 	__be32 old_saddr = inet->inet_saddr;
 	__be32 daddr = inet->inet_daddr;
+	struct flowi4 fl4;
 	struct rtable *rt;
 	__be32 new_saddr;
 
@@ -1110,7 +1111,7 @@ static int inet_sk_reselect_saddr(struct sock *sk)
 		daddr = inet->opt->faddr;
 
 	/* Query new route. */
-	rt = ip_route_connect(daddr, 0, RT_CONN_FLAGS(sk),
+	rt = ip_route_connect(&fl4, daddr, 0, RT_CONN_FLAGS(sk),
 			      sk->sk_bound_dev_if, sk->sk_protocol,
 			      inet->inet_sport, inet->inet_dport, sk, false);
 	if (IS_ERR(rt))
diff --git a/net/ipv4/datagram.c b/net/ipv4/datagram.c
index 85bd24ca4f6..216ba2338b6 100644
--- a/net/ipv4/datagram.c
+++ b/net/ipv4/datagram.c
@@ -24,6 +24,7 @@ int ip4_datagram_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 {
 	struct inet_sock *inet = inet_sk(sk);
 	struct sockaddr_in *usin = (struct sockaddr_in *) uaddr;
+	struct flowi4 fl4;
 	struct rtable *rt;
 	__be32 saddr;
 	int oif;
@@ -46,7 +47,7 @@ int ip4_datagram_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 		if (!saddr)
 			saddr = inet->mc_addr;
 	}
-	rt = ip_route_connect(usin->sin_addr.s_addr, saddr,
+	rt = ip_route_connect(&fl4, usin->sin_addr.s_addr, saddr,
 			      RT_CONN_FLAGS(sk), oif,
 			      sk->sk_protocol,
 			      inet->inet_sport, usin->sin_port, sk, true);
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index edf18bd74b8..310454c2f4d 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -146,12 +146,13 @@ EXPORT_SYMBOL_GPL(tcp_twsk_unique);
 /* This will initiate an outgoing connection. */
 int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 {
+	struct sockaddr_in *usin = (struct sockaddr_in *)uaddr;
 	struct inet_sock *inet = inet_sk(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
-	struct sockaddr_in *usin = (struct sockaddr_in *)uaddr;
 	__be16 orig_sport, orig_dport;
-	struct rtable *rt;
 	__be32 daddr, nexthop;
+	struct flowi4 fl4;
+	struct rtable *rt;
 	int err;
 
 	if (addr_len < sizeof(struct sockaddr_in))
@@ -169,7 +170,7 @@ int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 
 	orig_sport = inet->inet_sport;
 	orig_dport = usin->sin_port;
-	rt = ip_route_connect(nexthop, inet->inet_saddr,
+	rt = ip_route_connect(&fl4, nexthop, inet->inet_saddr,
 			      RT_CONN_FLAGS(sk), sk->sk_bound_dev_if,
 			      IPPROTO_TCP,
 			      orig_sport, orig_dport, sk, true);
@@ -236,8 +237,7 @@ int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 	if (err)
 		goto failure;
 
-	rt = ip_route_newports(rt, IPPROTO_TCP,
-			       orig_sport, orig_dport,
+	rt = ip_route_newports(&fl4, rt, orig_sport, orig_dport,
 			       inet->inet_sport, inet->inet_dport, sk);
 	if (IS_ERR(rt)) {
 		err = PTR_ERR(rt);