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>

1 files changed, 4 insertions, 4 deletions

diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
index fce9bd3bd3fe..cc673677c5de 100644
--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -296,12 +296,12 @@ out_in_use:
 
 static int l2tp_ip_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 {
-        int rc;
-        struct inet_sock *inet = inet_sk(sk);
         struct sockaddr_l2tpip *lsa = (struct sockaddr_l2tpip *) uaddr;
+        struct inet_sock *inet = inet_sk(sk);
+        struct flowi4 fl4;
         struct rtable *rt;
         __be32 saddr;
-        int oif;
+        int oif, rc;
 
         rc = -EINVAL;
         if (addr_len < sizeof(*lsa))
@@ -320,7 +320,7 @@ static int l2tp_ip_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len
         if (ipv4_is_multicast(lsa->l2tp_addr.s_addr))
                 goto out;
 
-        rt = ip_route_connect(lsa->l2tp_addr.s_addr, saddr,
+        rt = ip_route_connect(&fl4, lsa->l2tp_addr.s_addr, saddr,
                               RT_CONN_FLAGS(sk), oif,
                               IPPROTO_L2TP,
                               0, 0, sk, true);