[PATCH v1 bpf-next 09/11] tcp: Split cookie_ecn_ok().

[Kuniyuki Iwashima <kuniyu@amazon.com>]

This patch is a prerequisite for the following change.

For non-BPF SYN Cookie, inet_rsk(req)->ecn_ok is initialised with
tcp_opt->rcv_tsecr & TS_OPT_ECN.  OTOH, we will initialise it
differently for BPF SYN Cookie.

Then, inet_rsk(req)->ecn_ok is updated with net->ipv4.sysctl_tcp_ecn
or dst_feature(dst, RTAX_FEATURE_ECN).

Now cookie_ecn_ok() is just oneliner, but TS_OPT_ECN is only available
in net/ipv4/syncookies.c.  Instead of exporting the function, we move
it and TS_OPT_XXX to tcp.h.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 include/net/tcp.h     | 31 +++++++++++++++++++++++++++++--
 net/ipv4/syncookies.c | 43 +++----------------------------------------
 net/ipv6/syncookies.c |  4 +++-
 3 files changed, 35 insertions(+), 43 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 4fe19917db6c..143f47c28312 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -569,8 +569,35 @@ __u32 cookie_v4_init_sequence(const struct sk_buff *skb, __u16 *mss);
 u64 cookie_init_timestamp(struct request_sock *req, u64 now);
 bool cookie_timestamp_decode(const struct net *net,
 			     struct tcp_options_received *opt);
-bool cookie_ecn_ok(const struct tcp_options_received *opt,
-		   const struct net *net, const struct dst_entry *dst);
+
+/* TCP Timestamp: 6 lowest bits of timestamp sent in the cookie SYN-ACK
+ * stores TCP options:
+ *
+ * MSB                               LSB
+ * | 31 ...   6 |  5  |  4   | 3 2 1 0 |
+ * |  Timestamp | ECN | SACK | WScale  |
+ *
+ * When we receive a valid cookie-ACK, we look at the echoed tsval (if
+ * any) to figure out which TCP options we should use for the rebuilt
+ * connection.
+ *
+ * A WScale setting of '0xf' (which is an invalid scaling value)
+ * means that original syn did not include the TCP window scaling option.
+ */
+#define TS_OPT_WSCALE_MASK	0xf
+#define TS_OPT_SACK		BIT(4)
+#define TS_OPT_ECN		BIT(5)
+/* There is no TS_OPT_TIMESTAMP:
+ * if ACK contains timestamp option, we already know it was
+ * requested/supported by the syn/synack exchange.
+ */
+#define TSBITS	6
+#define TSMASK	(((__u32)1 << TSBITS) - 1)
+
+static inline bool cookie_ecn_ok(const struct tcp_options_received *tcp_opt)
+{
+	return tcp_opt->rcv_tsecr & TS_OPT_ECN;
+}
 
 /* From net/ipv6/syncookies.c */
 int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th,
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index f78566991e08..ff979cc314da 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -19,30 +19,6 @@ static siphash_aligned_key_t syncookie_secret[2];
 #define COOKIEBITS 24	/* Upper bits store count */
 #define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
 
-/* TCP Timestamp: 6 lowest bits of timestamp sent in the cookie SYN-ACK
- * stores TCP options:
- *
- * MSB                               LSB
- * | 31 ...   6 |  5  |  4   | 3 2 1 0 |
- * |  Timestamp | ECN | SACK | WScale  |
- *
- * When we receive a valid cookie-ACK, we look at the echoed tsval (if
- * any) to figure out which TCP options we should use for the rebuilt
- * connection.
- *
- * A WScale setting of '0xf' (which is an invalid scaling value)
- * means that original syn did not include the TCP window scaling option.
- */
-#define TS_OPT_WSCALE_MASK	0xf
-#define TS_OPT_SACK		BIT(4)
-#define TS_OPT_ECN		BIT(5)
-/* There is no TS_OPT_TIMESTAMP:
- * if ACK contains timestamp option, we already know it was
- * requested/supported by the syn/synack exchange.
- */
-#define TSBITS	6
-#define TSMASK	(((__u32)1 << TSBITS) - 1)
-
 static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport,
 		       u32 count, int c)
 {
@@ -266,21 +242,6 @@ bool cookie_timestamp_decode(const struct net *net,
 }
 EXPORT_SYMBOL(cookie_timestamp_decode);
 
-bool cookie_ecn_ok(const struct tcp_options_received *tcp_opt,
-		   const struct net *net, const struct dst_entry *dst)
-{
-	bool ecn_ok = tcp_opt->rcv_tsecr & TS_OPT_ECN;
-
-	if (!ecn_ok)
-		return false;
-
-	if (READ_ONCE(net->ipv4.sysctl_tcp_ecn))
-		return true;
-
-	return dst_feature(dst, RTAX_FEATURE_ECN);
-}
-EXPORT_SYMBOL(cookie_ecn_ok);
-
 struct request_sock *cookie_tcp_reqsk_alloc(const struct request_sock_ops *ops,
 					    const struct tcp_request_sock_ops *af_ops,
 					    struct sock *sk,
@@ -438,6 +399,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 			goto out;
 		}
 	} else {
+		ireq->ecn_ok = cookie_ecn_ok(&tcp_opt);
 		treq->ts_off = tsoff;
 	}
 
@@ -498,7 +460,8 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 				  dst_metric(&rt->dst, RTAX_INITRWND));
 
 	ireq->rcv_wscale  = rcv_wscale;
-	ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, net, &rt->dst);
+	ireq->ecn_ok &= READ_ONCE(net->ipv4.sysctl_tcp_ecn) ||
+		dst_feature(&rt->dst, RTAX_FEATURE_ECN);
 
 	ret = tcp_get_cookie_sock(sk, skb, req, &rt->dst);
 	/* ip_queue_xmit() depends on our flow being setup
diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index b0a7ea75a504..f4c0cb463e02 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -198,6 +198,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 			goto out;
 		}
 	} else {
+		ireq->ecn_ok = cookie_ecn_ok(&tcp_opt);
 		treq->ts_off = tsoff;
 	}
 
@@ -272,7 +273,8 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 				  dst_metric(dst, RTAX_INITRWND));
 
 	ireq->rcv_wscale = rcv_wscale;
-	ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, net, dst);
+	ireq->ecn_ok &= READ_ONCE(net->ipv4.sysctl_tcp_ecn) ||
+		dst_feature(dst, RTAX_FEATURE_ECN);
 
 	ret = tcp_get_cookie_sock(sk, skb, req, dst);
 out:
-- 
2.30.2