diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index a0e134d..d47c000 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -164,6 +164,14 @@ tcp_congestion_control - STRING
 	additional choices may be available based on kernel configuration.
 	Default is set as part of kernel configuration.
 
+tcp_cookie_size - INTEGER
+	Default size of TCP Cookie Transactions (TCPCT) option, that may be
+	overridden on a per socket basis by the TCPCT socket option.
+	Values greater than the maximum (16) are interpreted as the maximum.
+	Values greater than zero and less than the minimum (8) are interpreted
+	as the minimum.
+	Default: 0 (off).
+
 tcp_dsack - BOOLEAN
 	Allows TCP to send "duplicate" SACKs.
 
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 61723a7..6fd59d1 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -96,6 +96,7 @@ enum {
 #define TCP_QUICKACK		12	/* Block/reenable quick acks */
 #define TCP_CONGESTION		13	/* Congestion control algorithm */
 #define TCP_MD5SIG		14	/* TCP MD5 Signature (RFC2385) */
+#define TCP_COOKIE_TRANSACTIONS	15	/* TCP Cookie Transactions */
 
 #define TCPI_OPT_TIMESTAMPS	1
 #define TCPI_OPT_SACK		2
@@ -170,6 +171,34 @@ struct tcp_md5sig {
 	__u8	tcpm_key[TCP_MD5SIG_MAXKEYLEN];		/* key (binary) */
 };
 
+/* for TCP_COOKIE_TRANSACTIONS (TCPCT) socket option */
+#define TCP_COOKIE_MAX		16		/* 128-bits */
+#define TCP_COOKIE_MIN		 8		/*  64-bits */
+#define TCP_COOKIE_PAIR_SIZE	(2*TCP_COOKIE_MAX)
+
+#define TCP_S_DATA_MAX		64U		/* after TCP+IP options */
+#define TCP_S_DATA_MSS_DEFAULT	536U		/* default MSS (RFC1122) */
+
+/* Flags for both getsockopt and setsockopt */
+#define TCP_COOKIE_IN_ALWAYS	(1 << 0)	/* Discard SYN without cookie */
+#define TCP_COOKIE_OUT_NEVER	(1 << 1)	/* Prohibit outgoing cookies,
+						 * supercedes everything else. */
+#define TCP_EXTEND_TIMESTAMP	(1 << 4)	/* Initiate 64-bit timestamps */
+
+/* Flags for getsockopt */
+#define TCP_S_DATA_IN		(1 << 2)	/* Was data received? */
+#define TCP_S_DATA_OUT		(1 << 3)	/* Was data sent? */
+
+/* TCP_COOKIE_TRANSACTIONS data */
+struct tcp_cookie_transactions {
+	__u16	tcpct_flags;			/* see above */
+	__u8	__tcpct_pad1;			/* zero */
+	__u8	tcpct_cookie_desired;		/* bytes */
+	__u16	tcpct_s_data_desired;		/* bytes of variable data */
+	__u16	tcpct_used;			/* bytes in value */
+	__u8	tcpct_value[TCP_S_DATA_MSS_DEFAULT];
+};
+
 #ifdef __KERNEL__
 
 #include <linux/skbuff.h>
@@ -193,6 +222,17 @@ static inline unsigned int tcp_optlen(const struct sk_buff *skb)
 	return (tcp_hdr(skb)->doff - 5) * 4;
 }
 
+static inline unsigned int tcp_header_len_th(const struct tcphdr *th)
+{
+	return th->doff * 4;
+}
+
+/* When doff is bad, this could be negative. */
+static inline int tcp_option_len_th(const struct tcphdr *th)
+{
+	return (int)(th->doff * 4) - sizeof(*th);
+}
+
 /* This defines a selective acknowledgement block. */
 struct tcp_sack_block_wire {
 	__be32	start_seq;
@@ -223,6 +263,11 @@ struct tcp_options_received {
 	u16	mss_clamp;	/* Maximal mss, negotiated at connection setup */
 };
 
+static inline void tcp_clear_options(struct tcp_options_received *rx_opt)
+{
+	rx_opt->tstamp_ok = rx_opt->sack_ok = rx_opt->wscale_ok = rx_opt->snd_wscale = 0;
+}
+
 /* This is the max number of SACKS that we'll generate and process. It's safe
  * to increse this, although since:
  *   size = TCPOLEN_SACK_BASE_ALIGNED (4) + n * TCPOLEN_SACK_PERBLOCK (8)
@@ -431,6 +476,6 @@ static inline struct tcp_timewait_sock *tcp_twsk(const struct sock *sk)
 	return (struct tcp_timewait_sock *)sk;
 }
 
-#endif
+#endif	/* __KERNEL__ */
 
 #endif	/* _LINUX_TCP_H */
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 4abdb4d..142f32e 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -237,6 +237,7 @@ extern int sysctl_tcp_base_mss;
 extern int sysctl_tcp_workaround_signed_windows;
 extern int sysctl_tcp_slow_start_after_idle;
 extern int sysctl_tcp_max_ssthresh;
+extern int sysctl_tcp_cookie_size;
 
 extern atomic_t tcp_memory_allocated;
 extern struct percpu_counter tcp_sockets_allocated;
@@ -343,11 +344,6 @@ static inline void tcp_dec_quickack_mode(struct sock *sk,
 
 extern void tcp_enter_quickack_mode(struct sock *sk);
 
-static inline void tcp_clear_options(struct tcp_options_received *rx_opt)
-{
- 	rx_opt->tstamp_ok = rx_opt->sack_ok = rx_opt->wscale_ok = rx_opt->snd_wscale = 0;
-}
-
 #define	TCP_ECN_OK		1
 #define	TCP_ECN_QUEUE_CWR	2
 #define	TCP_ECN_DEMAND_CWR	4
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 2dcf04d..3422c54 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -714,6 +714,14 @@ static struct ctl_table ipv4_table[] = {
 	},
 	{
 		.ctl_name	= CTL_UNNUMBERED,
+		.procname	= "tcp_cookie_size",
+		.data		= &sysctl_tcp_cookie_size,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec
+	},
+	{
+		.ctl_name	= CTL_UNNUMBERED,
 		.procname	= "udp_mem",
 		.data		= &sysctl_udp_mem,
 		.maxlen		= sizeof(sysctl_udp_mem),
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 79042f4..bcfbe41 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -59,6 +59,14 @@ int sysctl_tcp_base_mss __read_mostly = 512;
 /* By default, RFC2861 behavior.  */
 int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
 
+#ifdef CONFIG_SYSCTL
+/* By default, let the user enable it. */
+int sysctl_tcp_cookie_size __read_mostly = 0;
+#else
+int sysctl_tcp_cookie_size __read_mostly = TCP_COOKIE_MAX;
+#endif
+
+
 /* Account for new data that has been sent to the network. */
 static void tcp_event_new_data_sent(struct sock *sk, struct sk_buff *skb)
 {
-- 
1.6.0.4