[PATCH v1 bpf-next 10/11] bpf: tcp: Make WS, SACK, ECN configurable from BPF SYN Cookie.

[Kuniyuki Iwashima <kuniyu@amazon.com>]

This patch allows BPF_SOCK_OPS_CHECK_SYNCOOKIE_CB hook to enable WScale,
SACK, and ECN by passing corresponding flags to bpf_sock_ops.replylong[1].

The same flags are passed to BPF_SOCK_OPS_GEN_SYNCOOKIE_CB hook as
bpf_sock_ops.args[1] so that the BPF prog need not parse the TCP header to
check if WScale, SACK, ECN, and TS are available in SYN.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 include/uapi/linux/bpf.h       | 18 ++++++++++++++++++
 net/ipv4/syncookies.c          | 20 ++++++++++++++++++++
 net/ipv4/tcp_input.c           | 11 +++++++++++
 tools/include/uapi/linux/bpf.h | 18 ++++++++++++++++++
 4 files changed, 67 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 24f673d88c0d..cdae4dd5d797 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -6869,6 +6869,7 @@ enum {
 					 * option.
 					 *
 					 * args[0]: MSS
+					 * args[1]: BPF_SYNCOOKIE_XXX
 					 *
 					 * replylong[0]: ISN
 					 * replylong[1]: TS
@@ -6883,6 +6884,7 @@ enum {
 					 * args[1]: TS
 					 *
 					 * replylong[0]: MSS
+					 * replylong[1]: BPF_SYNCOOKIE_XXX
 					 */
 };
 
@@ -6970,6 +6972,22 @@ enum {
 						 */
 };
 
+/* arg[1] value for BPF_SOCK_OPS_GEN_SYNCOOKIE_CB and
+ * replylong[1] for BPF_SOCK_OPS_CHECK_SYNCOOKIE_CB.
+ *
+ * MSB                                LSB
+ * | 31 ... | 6  | 5   | 4    | 3 2 1 0 |
+ * |    ... | TS | ECN | SACK | WScale  |
+ */
+enum {
+	/* 0xf is invalid thus means that SYN did not have WScale. */
+	BPF_SYNCOOKIE_WSCALE_MASK	= (1 << 4) - 1,
+	BPF_SYNCOOKIE_SACK		= (1 << 4),
+	BPF_SYNCOOKIE_ECN		= (1 << 5),
+	/* Only available for BPF_SOCK_OPS_GEN_SYNCOOKIE_CB to check if SYN has TS */
+	BPF_SYNCOOKIE_TS		= (1 << 6),
+};
+
 struct bpf_perf_event_value {
 	__u64 counter;
 	__u64 enabled;
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index ff979cc314da..22353a9af52d 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -286,6 +286,7 @@ int bpf_skops_cookie_check(struct sock *sk, struct request_sock *req, struct sk_
 {
 	struct bpf_sock_ops_kern sock_ops;
 	struct net *net = sock_net(sk);
+	u32 options;
 
 	if (tcp_opt->saw_tstamp) {
 		if (!READ_ONCE(net->ipv4.sysctl_tcp_timestamps))
@@ -309,6 +310,25 @@ int bpf_skops_cookie_check(struct sock *sk, struct request_sock *req, struct sk_
 	if (!sock_ops.replylong[0])
 		goto err;
 
+	options = sock_ops.replylong[1];
+
+	if ((options & BPF_SYNCOOKIE_WSCALE_MASK) != BPF_SYNCOOKIE_WSCALE_MASK) {
+		if (!READ_ONCE(net->ipv4.sysctl_tcp_window_scaling))
+			goto err;
+
+		tcp_opt->wscale_ok = 1;
+		tcp_opt->snd_wscale = options & BPF_SYNCOOKIE_WSCALE_MASK;
+	}
+
+	if (options & BPF_SYNCOOKIE_SACK) {
+		if (!READ_ONCE(net->ipv4.sysctl_tcp_sack))
+			goto err;
+
+		tcp_opt->sack_ok = 1;
+	}
+
+	inet_rsk(req)->ecn_ok = options & BPF_SYNCOOKIE_ECN;
+
 	__NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
 
 	return sock_ops.replylong[0];
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index feb44bff29ef..483e2f36afe5 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6970,14 +6970,25 @@ EXPORT_SYMBOL_GPL(tcp_get_syncookie_mss);
 static int bpf_skops_cookie_init_sequence(struct sock *sk, struct request_sock *req,
 					  struct sk_buff *skb, __u32 *isn)
 {
+	struct inet_request_sock *ireq = inet_rsk(req);
 	struct bpf_sock_ops_kern sock_ops;
+	u32 options;
 	int ret;
 
+	options = ireq->wscale_ok ? ireq->snd_wscale : BPF_SYNCOOKIE_WSCALE_MASK;
+	if (ireq->sack_ok)
+		options |= BPF_SYNCOOKIE_SACK;
+	if (ireq->ecn_ok)
+		options |= BPF_SYNCOOKIE_ECN;
+	if (ireq->tstamp_ok)
+		options |= BPF_SYNCOOKIE_TS;
+
 	memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
 
 	sock_ops.op = BPF_SOCK_OPS_GEN_SYNCOOKIE_CB;
 	sock_ops.sk = req_to_sk(req);
 	sock_ops.args[0] = req->mss;
+	sock_ops.args[1] = options;
 
 	bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb));
 
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 24f673d88c0d..cdae4dd5d797 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -6869,6 +6869,7 @@ enum {
 					 * option.
 					 *
 					 * args[0]: MSS
+					 * args[1]: BPF_SYNCOOKIE_XXX
 					 *
 					 * replylong[0]: ISN
 					 * replylong[1]: TS
@@ -6883,6 +6884,7 @@ enum {
 					 * args[1]: TS
 					 *
 					 * replylong[0]: MSS
+					 * replylong[1]: BPF_SYNCOOKIE_XXX
 					 */
 };
 
@@ -6970,6 +6972,22 @@ enum {
 						 */
 };
 
+/* arg[1] value for BPF_SOCK_OPS_GEN_SYNCOOKIE_CB and
+ * replylong[1] for BPF_SOCK_OPS_CHECK_SYNCOOKIE_CB.
+ *
+ * MSB                                LSB
+ * | 31 ... | 6  | 5   | 4    | 3 2 1 0 |
+ * |    ... | TS | ECN | SACK | WScale  |
+ */
+enum {
+	/* 0xf is invalid thus means that SYN did not have WScale. */
+	BPF_SYNCOOKIE_WSCALE_MASK	= (1 << 4) - 1,
+	BPF_SYNCOOKIE_SACK		= (1 << 4),
+	BPF_SYNCOOKIE_ECN		= (1 << 5),
+	/* Only available for BPF_SOCK_OPS_GEN_SYNCOOKIE_CB to check if SYN has TS */
+	BPF_SYNCOOKIE_TS		= (1 << 6),
+};
+
 struct bpf_perf_event_value {
 	__u64 counter;
 	__u64 enabled;
-- 
2.30.2