tcp: simplify fast open cookie processing

Consolidate various cookie checking and generation code to simplify
the fast open processing. The main goal is to reduce code duplication
in tcp_v4_conn_request() for IPv6 support.

Removes two experimental sysctl flags TFO_SERVER_ALWAYS and
TFO_SERVER_COOKIE_NOT_CHKD used primarily for developmental debugging
purposes.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Daniel Lee <longinus00@gmail.com>
Signed-off-by: Jerry Chu <hkchu@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 32 insertions, 51 deletions

diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
index 0606c91d9d0b..5a98277b9a82 100644
--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c
@@ -228,59 +228,44 @@ static bool tcp_fastopen_queue_check(struct sock *sk)
         return true;
 }
 
+/* Returns true if we should perform Fast Open on the SYN. The cookie (foc)
+ * may be updated and return the client in the SYN-ACK later. E.g., Fast Open
+ * cookie request (foc->len == 0).
+ */
 bool tcp_fastopen_check(struct sock *sk, struct sk_buff *skb,
                         struct request_sock *req,
-                        struct tcp_fastopen_cookie *foc,
-                        struct tcp_fastopen_cookie *valid_foc)
+                        struct tcp_fastopen_cookie *foc)
 {
-        bool skip_cookie = false;
-
-        if (likely(!fastopen_cookie_present(foc))) {
-                /* See include/net/tcp.h for the meaning of these knobs */
-                if ((sysctl_tcp_fastopen & TFO_SERVER_ALWAYS) ||
-                    ((sysctl_tcp_fastopen & TFO_SERVER_COOKIE_NOT_REQD) &&
-                    (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1)))
-                        skip_cookie = true; /* no cookie to validate */
-                else
-                        return false;
-        }
-        /* A FO option is present; bump the counter. */
-        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVE);
+        struct tcp_fastopen_cookie valid_foc = { .len = -1 };
+        bool syn_data = TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1;
 
-        if ((sysctl_tcp_fastopen & TFO_SERVER_ENABLE) == 0 ||
-            !tcp_fastopen_queue_check(sk))
+        if (!((sysctl_tcp_fastopen & TFO_SERVER_ENABLE) &&
+              (syn_data || foc->len >= 0) &&
+              tcp_fastopen_queue_check(sk))) {
+                foc->len = -1;
                 return false;
-
-        if (skip_cookie) {
-                tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
-                return true;
         }
 
-        if (foc->len == TCP_FASTOPEN_COOKIE_SIZE) {
-                if ((sysctl_tcp_fastopen & TFO_SERVER_COOKIE_NOT_CHKED) == 0) {
-                        tcp_fastopen_cookie_gen(ip_hdr(skb)->saddr,
-                                                ip_hdr(skb)->daddr, valid_foc);
-                        if ((valid_foc->len != TCP_FASTOPEN_COOKIE_SIZE) ||
-                            memcmp(&foc->val[0], &valid_foc->val[0],
-                            TCP_FASTOPEN_COOKIE_SIZE) != 0)
-                                return false;
-                        valid_foc->len = -1;
-                }
-                /* Acknowledge the data received from the peer. */
+        if (syn_data && (sysctl_tcp_fastopen & TFO_SERVER_COOKIE_NOT_REQD))
+                goto fastopen;
+
+        tcp_fastopen_cookie_gen(ip_hdr(skb)->saddr,
+                                ip_hdr(skb)->daddr, &valid_foc);
+
+        if (foc->len == TCP_FASTOPEN_COOKIE_SIZE &&
+            foc->len == valid_foc.len &&
+            !memcmp(foc->val, valid_foc.val, foc->len)) {
+fastopen:
                 tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
+                foc->len = -1;
+                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVE);
                 return true;
-        } else if (foc->len == 0) { /* Client requesting a cookie */
-                tcp_fastopen_cookie_gen(ip_hdr(skb)->saddr,
-                                        ip_hdr(skb)->daddr, valid_foc);
-                NET_INC_STATS_BH(sock_net(sk),
-                    LINUX_MIB_TCPFASTOPENCOOKIEREQD);
-        } else {
-                /* Client sent a cookie with wrong size. Treat it
-                 * the same as invalid and return a valid one.
-                 */
-                tcp_fastopen_cookie_gen(ip_hdr(skb)->saddr,
-                                        ip_hdr(skb)->daddr, valid_foc);
         }
+
+        NET_INC_STATS_BH(sock_net(sk), foc->len ?
+                         LINUX_MIB_TCPFASTOPENPASSIVEFAIL :
+                         LINUX_MIB_TCPFASTOPENCOOKIEREQD);
+        *foc = valid_foc;
         return false;
 }
 EXPORT_SYMBOL(tcp_fastopen_check);
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 032fcaee164a..5ea0949dadfd 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1273,7 +1273,6 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
         bool want_cookie = false;
         struct flowi4 fl4;
         struct tcp_fastopen_cookie foc = { .len = -1 };
-        struct tcp_fastopen_cookie valid_foc = { .len = -1 };
         struct sk_buff *skb_synack;
         int do_fastopen;
 
@@ -1381,7 +1380,8 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
                 if (dst == NULL)
                         goto drop_and_free;
         }
-        do_fastopen = tcp_fastopen_check(sk, skb, req, &foc, &valid_foc);
+        do_fastopen = !want_cookie &&
+                      tcp_fastopen_check(sk, skb, req, &foc);
 
         /* We don't call tcp_v4_send_synack() directly because we need
          * to make sure a child socket can be created successfully before
@@ -1394,8 +1394,7 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
          * latter to remove its dependency on the current implementation
          * of tcp_v4_send_synack()->tcp_select_initial_window().
          */
-        skb_synack = tcp_make_synack(sk, dst, req,
-            fastopen_cookie_present(&valid_foc) ? &valid_foc : NULL);
+        skb_synack = tcp_make_synack(sk, dst, req, &foc);
 
         if (skb_synack) {
                 __tcp_v4_send_check(skb_synack, ireq->ir_loc_addr, ireq->ir_rmt_addr);
@@ -1415,9 +1414,6 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
                 tcp_rsk(req)->listener = NULL;
                 /* Add the request_sock to the SYN table */
                 inet_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
-                if (fastopen_cookie_present(&foc) && foc.len != 0)
-                        NET_INC_STATS_BH(sock_net(sk),
-                            LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
         } else if (tcp_fastopen_create_child(sk, skb, skb_synack, req))
                 goto drop_and_release;
 
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 694711a140d4..b20fc02920f9 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -627,7 +627,7 @@ static unsigned int tcp_synack_options(struct sock *sk,
                 if (unlikely(!ireq->tstamp_ok))
                         remaining -= TCPOLEN_SACKPERM_ALIGNED;
         }
-        if (foc != NULL) {
+        if (foc != NULL && foc->len >= 0) {
                 u32 need = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
                 need = (need + 3) & ~3U;  /* Align to 32 bits */
                 if (remaining >= need) {