TCPCT part 1c: sysctl_tcp_cookie_size, socket option TCP_COOKIE_TRANSACTIONS

Define sysctl (tcp_cookie_size) to turn on and off the cookie option
default globally, instead of a compiled configuration option.

Define per socket option (TCP_COOKIE_TRANSACTIONS) for setting constant
data values, retrieving variable cookie values, and other facilities.

Move inline tcp_clear_options() unchanged from net/tcp.h to linux/tcp.h,
near its corresponding struct tcp_options_received (prior to changes).

This is a straightforward re-implementation of an earlier (year-old)
patch that no longer applies cleanly, with permission of the original
author (Adam Langley):

    http://thread.gmane.org/gmane.linux.network/102586

These functions will also be used in subsequent patches that implement
additional features.

Requires:
   net: TCP_MSS_DEFAULT, TCP_MSS_DESIRED

Signed-off-by: William.Allen.Simpson@gmail.com
Signed-off-by: David S. Miller <davem@davemloft.net>

5 files changed, 52 insertions, 6 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 554440af675c..989f5538b8dd 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.  Odd values are interpreted as the next even value.
+        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 32d7d77b4a01..eaa3113b3786 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -102,7 +102,9 @@ 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 */
 
+/* for TCP_INFO socket option */
 #define TCPI_OPT_TIMESTAMPS     1
 #define TCPI_OPT_SACK           2
 #define TCPI_OPT_WSCALE         4
@@ -174,6 +176,30 @@ struct tcp_md5sig {
         __u8    tcpm_key[TCP_MD5SIG_MAXKEYLEN];         /* key (binary) */
 };
 
+/* for TCP_COOKIE_TRANSACTIONS (TCPCT) socket option */
+#define TCP_COOKIE_MIN           8              /*  64-bits */
+#define TCP_COOKIE_MAX          16              /* 128-bits */
+#define TCP_COOKIE_PAIR_SIZE    (2*TCP_COOKIE_MAX)
+
+/* 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. */
+
+/* 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_MSS_DEFAULT];
+};
+
 #ifdef __KERNEL__
 
 #include <linux/skbuff.h>
@@ -227,6 +253,11 @@ 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)
@@ -435,6 +466,6 @@ 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 4a99a8e39121..738b65f01e26 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -234,6 +234,7 @@ 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;
@@ -340,11 +341,6 @@ 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 c00323bae044..13f7ab6ad6a0 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 b8b25049f257..307f318fe931 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -59,6 +59,9 @@ int sysctl_tcp_base_mss __read_mostly = 512;
 /* By default, RFC2861 behavior.  */
 int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
 
+int sysctl_tcp_cookie_size __read_mostly = 0; /* TCP_COOKIE_MAX */
+
+
 /* 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)
 {