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, 5 insertions, 5 deletions

diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index ae451c6d83ba..b92ab655d44e 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -40,12 +40,13 @@
 
 int dccp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 {
+        const struct sockaddr_in *usin = (struct sockaddr_in *)uaddr;
         struct inet_sock *inet = inet_sk(sk);
         struct dccp_sock *dp = dccp_sk(sk);
-        const 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;
 
         dp->dccps_role = DCCP_ROLE_CLIENT;
@@ -65,7 +66,7 @@ int dccp_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_DCCP,
                               orig_sport, orig_dport, sk, true);
@@ -101,8 +102,7 @@ int dccp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
         if (err != 0)
                 goto failure;
 
-        rt = ip_route_newports(rt, IPPROTO_DCCP,
-                               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)) {
                 rt = NULL;