4 files changed, 36 insertions, 14 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 24f1630b2afb..031cf72cd05c 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5378,8 +5378,8 @@ static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
 {
         struct tcp_sock *tp = tcp_sk(sk);
         struct sk_buff *data = tp->syn_data ? tcp_write_queue_head(sk) : NULL;
-        u16 mss = tp->rx_opt.mss_clamp;
-        bool syn_drop;
+        u16 mss = tp->rx_opt.mss_clamp, try_exp = 0;
+        bool syn_drop = false;
 
         if (mss == tp->rx_opt.user_mss) {
                 struct tcp_options_received opt;
@@ -5391,16 +5391,25 @@ static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
                 mss = opt.mss_clamp;
         }
 
-        if (!tp->syn_fastopen)  /* Ignore an unsolicited cookie */
+        if (!tp->syn_fastopen) {
+                /* Ignore an unsolicited cookie */
                 cookie->len = -1;
+        } else if (tp->total_retrans) {
+                /* SYN timed out and the SYN-ACK neither has a cookie nor
+                 * acknowledges data. Presumably the remote received only
+                 * the retransmitted (regular) SYNs: either the original
+                 * SYN-data or the corresponding SYN-ACK was dropped.
+                 */
+                syn_drop = (cookie->len < 0 && data);
+        } else if (cookie->len < 0 && !tp->syn_data) {
+                /* We requested a cookie but didn't get it. If we did not use
+                 * the (old) exp opt format then try so next time (try_exp=1).
+                 * Otherwise we go back to use the RFC7413 opt (try_exp=2).
+                 */
+                try_exp = tp->syn_fastopen_exp ? 2 : 1;
+        }
 
-        /* The SYN-ACK neither has cookie nor acknowledges the data. Presumably
-         * the remote receives only the retransmitted (regular) SYNs: either
-         * the original SYN-data or the corresponding SYN-ACK is lost.
-         */
-        syn_drop = (cookie->len <= 0 && data && tp->total_retrans);
-
-        tcp_fastopen_cache_set(sk, mss, cookie, syn_drop);
+        tcp_fastopen_cache_set(sk, mss, cookie, syn_drop, try_exp);
 
         if (data) { /* Retransmit unacked data in SYN */
                 tcp_for_write_queue_from(data, sk) {
diff --git a/net/ipv4/tcp_metrics.c b/net/ipv4/tcp_metrics.c
index 78ecc4a01712..a51d63a43e33 100644
--- a/net/ipv4/tcp_metrics.c
+++ b/net/ipv4/tcp_metrics.c
@@ -28,7 +28,8 @@ static struct tcp_metrics_block *__tcp_get_metrics(const struct inetpeer_addr *s
 
 struct tcp_fastopen_metrics {
         u16     mss;
-        u16     syn_loss:10;            /* Recurring Fast Open SYN losses */
+        u16     syn_loss:10,            /* Recurring Fast Open SYN losses */
+                try_exp:2;              /* Request w/ exp. option (once) */
         unsigned long   last_syn_loss;  /* Last Fast Open SYN loss */
         struct  tcp_fastopen_cookie     cookie;
 };
@@ -131,6 +132,8 @@ static void tcpm_suck_dst(struct tcp_metrics_block *tm,
         if (fastopen_clear) {
                 tm->tcpm_fastopen.mss = 0;
                 tm->tcpm_fastopen.syn_loss = 0;
+                tm->tcpm_fastopen.try_exp = 0;
+                tm->tcpm_fastopen.cookie.exp = false;
                 tm->tcpm_fastopen.cookie.len = 0;
         }
 }
@@ -713,6 +716,8 @@ void tcp_fastopen_cache_get(struct sock *sk, u16 *mss,
                         if (tfom->mss)
                                 *mss = tfom->mss;
                         *cookie = tfom->cookie;
+                        if (cookie->len <= 0 && tfom->try_exp == 1)
+                                cookie->exp = true;
                         *syn_loss = tfom->syn_loss;
                         *last_syn_loss = *syn_loss ? tfom->last_syn_loss : 0;
                 } while (read_seqretry(&fastopen_seqlock, seq));
@@ -721,7 +726,8 @@ void tcp_fastopen_cache_get(struct sock *sk, u16 *mss,
 }
 
 void tcp_fastopen_cache_set(struct sock *sk, u16 mss,
-                            struct tcp_fastopen_cookie *cookie, bool syn_lost)
+                            struct tcp_fastopen_cookie *cookie, bool syn_lost,
+                            u16 try_exp)
 {
         struct dst_entry *dst = __sk_dst_get(sk);
         struct tcp_metrics_block *tm;
@@ -738,6 +744,9 @@ void tcp_fastopen_cache_set(struct sock *sk, u16 mss,
                         tfom->mss = mss;
                 if (cookie && cookie->len > 0)
                         tfom->cookie = *cookie;
+                else if (try_exp > tfom->try_exp &&
+                         tfom->cookie.len <= 0 && !tfom->cookie.exp)
+                        tfom->try_exp = try_exp;
                 if (syn_lost) {
                         ++tfom->syn_loss;
                         tfom->last_syn_loss = jiffies;
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 464bd8c5de69..e662d85d1635 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -592,13 +592,17 @@ static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
         }
 
         if (fastopen && fastopen->cookie.len >= 0) {
-                u32 need = TCPOLEN_EXP_FASTOPEN_BASE + fastopen->cookie.len;
+                u32 need = fastopen->cookie.len;
+
+                need += fastopen->cookie.exp ? TCPOLEN_EXP_FASTOPEN_BASE :
+                                               TCPOLEN_FASTOPEN_BASE;
                 need = (need + 3) & ~3U;  /* Align to 32 bits */
                 if (remaining >= need) {
                         opts->options |= OPTION_FAST_OPEN_COOKIE;
                         opts->fastopen_cookie = &fastopen->cookie;
                         remaining -= need;
                         tp->syn_fastopen = 1;
+                        tp->syn_fastopen_exp = fastopen->cookie.exp ? 1 : 0;
                 }
         }
 
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 2568fd282873..8c65dc147d8b 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -167,7 +167,7 @@ static int tcp_write_timeout(struct sock *sk)
                 if (icsk->icsk_retransmits) {
                         dst_negative_advice(sk);
                         if (tp->syn_fastopen || tp->syn_data)
-                                tcp_fastopen_cache_set(sk, 0, NULL, true);
+                                tcp_fastopen_cache_set(sk, 0, NULL, true, 0);
                         if (tp->syn_data)
                                 NET_INC_STATS_BH(sock_net(sk),
                                                  LINUX_MIB_TCPFASTOPENACTIVEFAIL);