syncookies: add support for ECN

Allows use of ECN when syncookies are in effect by encoding ecn_ok
into the syn-ack tcp timestamp.

While at it, remove a uneeded #ifdef CONFIG_SYN_COOKIES.
With CONFIG_SYN_COOKIES=nm want_cookie is ifdef'd to 0 and gcc
removes the "if (0)".

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 12 insertions, 9 deletions

diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 8896329aebd0..650cace2180d 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -19,7 +19,7 @@
 #include <net/route.h>
 
 /* Timestamps: lowest bits store TCP options */
-#define TSBITS 5
+#define TSBITS 6
 #define TSMASK (((__u32)1 << TSBITS) - 1)
 
 extern int sysctl_tcp_syncookies;
@@ -73,6 +73,7 @@ __u32 cookie_init_timestamp(struct request_sock *req)
 
         options = ireq->wscale_ok ? ireq->snd_wscale : 0xf;
         options |= ireq->sack_ok << 4;
+        options |= ireq->ecn_ok << 5;
 
         ts = ts_now & ~TSMASK;
         ts |= options;
@@ -226,11 +227,11 @@ static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
  * This extracts these options from the timestamp echo.
  *
  * The lowest 4 bits store snd_wscale.
- * The next lsb is for sack_ok
+ * next 2 bits indicate SACK and ECN support.
  *
  * return false if we decode an option that should not be.
  */
-bool cookie_check_timestamp(struct tcp_options_received *tcp_opt)
+bool cookie_check_timestamp(struct tcp_options_received *tcp_opt, bool *ecn_ok)
 {
         /* echoed timestamp, lowest bits contain options */
         u32 options = tcp_opt->rcv_tsecr & TSMASK;
@@ -244,6 +245,9 @@ bool cookie_check_timestamp(struct tcp_options_received *tcp_opt)
                 return false;
 
         tcp_opt->sack_ok = (options >> 4) & 0x1;
+        *ecn_ok = (options >> 5) & 1;
+        if (*ecn_ok && !sysctl_tcp_ecn)
+                return false;
 
         if (tcp_opt->sack_ok && !sysctl_tcp_sack)
                 return false;
@@ -272,6 +276,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
         int mss;
         struct rtable *rt;
         __u8 rcv_wscale;
+        bool ecn_ok;
 
         if (!sysctl_tcp_syncookies || !th->ack || th->rst)
                 goto out;
@@ -288,7 +293,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
         memset(&tcp_opt, 0, sizeof(tcp_opt));
         tcp_parse_options(skb, &tcp_opt, &hash_location, 0);
 
-        if (!cookie_check_timestamp(&tcp_opt))
+        if (!cookie_check_timestamp(&tcp_opt, &ecn_ok))
                 goto out;
 
         ret = NULL;
@@ -305,7 +310,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
         ireq->rmt_port          = th->source;
         ireq->loc_addr          = ip_hdr(skb)->daddr;
         ireq->rmt_addr          = ip_hdr(skb)->saddr;
-        ireq->ecn_ok            = 0;
+        ireq->ecn_ok            = ecn_ok;
         ireq->snd_wscale        = tcp_opt.snd_wscale;
         ireq->sack_ok           = tcp_opt.sack_ok;
         ireq->wscale_ok         = tcp_opt.wscale_ok;
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 2e41e6f92968..8fa32f5ae2ce 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1328,14 +1328,12 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
         if (security_inet_conn_request(sk, skb, req))
                 goto drop_and_free;
 
-        if (!want_cookie)
+        if (!want_cookie || tmp_opt.tstamp_ok)
                 TCP_ECN_create_request(req, tcp_hdr(skb));
 
         if (want_cookie) {
-#ifdef CONFIG_SYN_COOKIES
-                req->cookie_ts = tmp_opt.tstamp_ok;
-#endif
                 isn = cookie_v4_init_sequence(sk, skb, &req->mss);
+                req->cookie_ts = tmp_opt.tstamp_ok;
         } else if (!isn) {
                 struct inet_peer *peer = NULL;