ipv4: tcp: dont cache output dst for syncookies

Don't cache output dst for syncookies, as this adds pressure on IP route
cache and rcu subsystem for no gain.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Hans Schillstrom <hans.schillstrom@ericsson.com>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 17 insertions, 8 deletions

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index f9ee7417f6a0..034ddbe42adf 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -368,17 +368,21 @@ EXPORT_SYMBOL(inet_csk_reset_keepalive_timer);
 
 struct dst_entry *inet_csk_route_req(struct sock *sk,
                                      struct flowi4 *fl4,
-                                     const struct request_sock *req)
+                                     const struct request_sock *req,
+                                     bool nocache)
 {
         struct rtable *rt;
         const struct inet_request_sock *ireq = inet_rsk(req);
         struct ip_options_rcu *opt = inet_rsk(req)->opt;
         struct net *net = sock_net(sk);
+        int flags = inet_sk_flowi_flags(sk) & ~FLOWI_FLAG_PRECOW_METRICS;
 
+        if (nocache)
+                flags |= FLOWI_FLAG_RT_NOCACHE;
         flowi4_init_output(fl4, sk->sk_bound_dev_if, sk->sk_mark,
                            RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE,
                            sk->sk_protocol,
-                           inet_sk_flowi_flags(sk) & ~FLOWI_FLAG_PRECOW_METRICS,
+                           flags,
                            (opt && opt->opt.srr) ? opt->opt.faddr : ireq->rmt_addr,
                            ireq->loc_addr, ireq->rmt_port, inet_sk(sk)->inet_sport);
         security_req_classify_flow(req, flowi4_to_flowi(fl4));
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index a91f6d33804c..8d62d85e68dc 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1156,7 +1156,7 @@ restart:
         candp = NULL;
         now = jiffies;
 
-        if (!rt_caching(dev_net(rt->dst.dev))) {
+        if (!rt_caching(dev_net(rt->dst.dev)) || (rt->dst.flags & DST_NOCACHE)) {
                 /*
                  * If we're not caching, just tell the caller we
                  * were successful and don't touch the route.  The
@@ -2582,6 +2582,9 @@ static struct rtable *__mkroute_output(const struct fib_result *res,
 
         rt_set_nexthop(rth, fl4, res, fi, type, 0);
 
+        if (fl4->flowi4_flags & FLOWI_FLAG_RT_NOCACHE)
+                rth->dst.flags |= DST_NOCACHE;
+
         return rth;
 }
 
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 21e22a00481a..b52934f5334e 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -825,7 +825,8 @@ static void tcp_v4_reqsk_send_ack(struct sock *sk, struct sk_buff *skb,
 static int tcp_v4_send_synack(struct sock *sk, struct dst_entry *dst,
                               struct request_sock *req,
                               struct request_values *rvp,
-                              u16 queue_mapping)
+                              u16 queue_mapping,
+                              bool nocache)
 {
         const struct inet_request_sock *ireq = inet_rsk(req);
         struct flowi4 fl4;
@@ -833,7 +834,7 @@ static int tcp_v4_send_synack(struct sock *sk, struct dst_entry *dst,
         struct sk_buff * skb;
 
         /* First, grab a route. */
-        if (!dst && (dst = inet_csk_route_req(sk, &fl4, req)) == NULL)
+        if (!dst && (dst = inet_csk_route_req(sk, &fl4, req, nocache)) == NULL)
                 return -1;
 
         skb = tcp_make_synack(sk, dst, req, rvp);
@@ -855,7 +856,7 @@ static int tcp_v4_rtx_synack(struct sock *sk, struct request_sock *req,
                               struct request_values *rvp)
 {
         TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
-        return tcp_v4_send_synack(sk, NULL, req, rvp, 0);
+        return tcp_v4_send_synack(sk, NULL, req, rvp, 0, false);
 }
 
 /*
@@ -1388,7 +1389,7 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
                  */
                 if (tmp_opt.saw_tstamp &&
                     tcp_death_row.sysctl_tw_recycle &&
-                    (dst = inet_csk_route_req(sk, &fl4, req)) != NULL &&
+                    (dst = inet_csk_route_req(sk, &fl4, req, want_cookie)) != NULL &&
                     fl4.daddr == saddr &&
                     (peer = rt_get_peer((struct rtable *)dst, fl4.daddr)) != NULL) {
                         inet_peer_refcheck(peer);
@@ -1424,7 +1425,8 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
 
         if (tcp_v4_send_synack(sk, dst, req,
                                (struct request_values *)&tmp_ext,
-                               skb_get_queue_mapping(skb)) ||
+                               skb_get_queue_mapping(skb),
+                               want_cookie) ||
             want_cookie)
                 goto drop_and_free;