TCPCT part 1g: Responder Cookie => Initiator

Parse incoming TCP_COOKIE option(s).

Calculate <SYN,ACK> TCP_COOKIE option.

Send optional <SYN,ACK> data.

This is a significantly revised 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

Requires:
   TCPCT part 1a: add request_values parameter for sending SYNACK
   TCPCT part 1b: generate Responder Cookie secret
   TCPCT part 1c: sysctl_tcp_cookie_size, socket option TCP_COOKIE_TRANSACTIONS
   TCPCT part 1d: define TCP cookie option, extend existing struct's
   TCPCT part 1e: implement socket option TCP_COOKIE_TRANSACTIONS
   TCPCT part 1f: Initiator Cookie => Responder

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

2 files changed, 53 insertions, 4 deletions

diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index 612fc53e0bb9..5b9af508b8f2 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -159,6 +159,8 @@ static inline int cookie_check(struct sk_buff *skb, __u32 cookie)
 
 struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 {
+        struct tcp_options_received tcp_opt;
+        u8 *hash_location;
         struct inet_request_sock *ireq;
         struct inet6_request_sock *ireq6;
         struct tcp_request_sock *treq;
@@ -171,7 +173,6 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
         int mss;
         struct dst_entry *dst;
         __u8 rcv_wscale;
-        struct tcp_options_received tcp_opt;
 
         if (!sysctl_tcp_syncookies || !th->ack)
                 goto out;
@@ -254,7 +255,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 
         /* check for timestamp cookie support */
         memset(&tcp_opt, 0, sizeof(tcp_opt));
-        tcp_parse_options(skb, &tcp_opt, 0, dst);
+        tcp_parse_options(skb, &tcp_opt, &hash_location, 0, dst);
 
         if (tcp_opt.saw_tstamp)
                 cookie_check_timestamp(&tcp_opt);
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index f2ec38289a4a..fc0a4e5895ee 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1162,7 +1162,9 @@ static struct sock *tcp_v6_hnd_req(struct sock *sk,struct sk_buff *skb)
  */
 static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
 {
+        struct tcp_extend_values tmp_ext;
         struct tcp_options_received tmp_opt;
+        u8 *hash_location;
         struct request_sock *req;
         struct inet6_request_sock *treq;
         struct ipv6_pinfo *np = inet6_sk(sk);
@@ -1206,8 +1208,52 @@ static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
         tcp_clear_options(&tmp_opt);
         tmp_opt.mss_clamp = IPV6_MIN_MTU - sizeof(struct tcphdr) - sizeof(struct ipv6hdr);
         tmp_opt.user_mss = tp->rx_opt.user_mss;
+        tcp_parse_options(skb, &tmp_opt, &hash_location, 0, dst);
+
+        if (tmp_opt.cookie_plus > 0 &&
+            tmp_opt.saw_tstamp &&
+            !tp->rx_opt.cookie_out_never &&
+            (sysctl_tcp_cookie_size > 0 ||
+             (tp->cookie_values != NULL &&
+              tp->cookie_values->cookie_desired > 0))) {
+                u8 *c;
+                u32 *d;
+                u32 *mess = &tmp_ext.cookie_bakery[COOKIE_DIGEST_WORDS];
+                int l = tmp_opt.cookie_plus - TCPOLEN_COOKIE_BASE;
+
+                if (tcp_cookie_generator(&tmp_ext.cookie_bakery[0]) != 0)
+                        goto drop_and_free;
+
+                /* Secret recipe starts with IP addresses */
+                d = &ipv6_hdr(skb)->daddr.s6_addr32[0];
+                *mess++ ^= *d++;
+                *mess++ ^= *d++;
+                *mess++ ^= *d++;
+                *mess++ ^= *d++;
+                d = &ipv6_hdr(skb)->saddr.s6_addr32[0];
+                *mess++ ^= *d++;
+                *mess++ ^= *d++;
+                *mess++ ^= *d++;
+                *mess++ ^= *d++;
+
+                /* plus variable length Initiator Cookie */
+                c = (u8 *)mess;
+                while (l-- > 0)
+                        *c++ ^= *hash_location++;
 
-        tcp_parse_options(skb, &tmp_opt, 0, dst);
+#ifdef CONFIG_SYN_COOKIES
+                want_cookie = 0;        /* not our kind of cookie */
+#endif
+                tmp_ext.cookie_out_never = 0; /* false */
+                tmp_ext.cookie_plus = tmp_opt.cookie_plus;
+        } else if (!tp->rx_opt.cookie_in_always) {
+                /* redundant indications, but ensure initialization. */
+                tmp_ext.cookie_out_never = 1; /* true */
+                tmp_ext.cookie_plus = 0;
+        } else {
+                goto drop_and_free;
+        }
+        tmp_ext.cookie_in_always = tp->rx_opt.cookie_in_always;
 
         if (want_cookie && !tmp_opt.saw_tstamp)
                 tcp_clear_options(&tmp_opt);
@@ -1244,7 +1290,9 @@ static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
 
         security_inet_conn_request(sk, skb, req);
 
-        if (tcp_v6_send_synack(sk, req, NULL) || want_cookie)
+        if (tcp_v6_send_synack(sk, req,
+                               (struct request_values *)&tmp_ext) ||
+            want_cookie)
                 goto drop_and_free;
 
         inet6_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);