tcp: Factorise cookie-independent fields initialisation in cookie_v[46]_check().

We will support arbitrary SYN Cookie with BPF, and then some reqsk fields
are initialised in kfunc, and others are done in cookie_v[46]_check().

This patch factorises the common part as cookie_tcp_reqsk_init() and
calls it in cookie_tcp_reqsk_alloc() to minimise the discrepancy between
cookie_v[46]_check().

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20231129022924.96156-8-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/syncookies.c

@@ -285,10 +285,43 @@ bool cookie_ecn_ok(const struct tcp_options_received *tcp_opt,
 }
 EXPORT_SYMBOL(cookie_ecn_ok);
 
+static int cookie_tcp_reqsk_init(struct sock *sk, struct sk_buff *skb,
+				 struct request_sock *req)
+{
+	struct inet_request_sock *ireq = inet_rsk(req);
+	struct tcp_request_sock *treq = tcp_rsk(req);
+	const struct tcphdr *th = tcp_hdr(skb);
+
+	req->num_retrans = 0;
+
+	ireq->ir_num = ntohs(th->dest);
+	ireq->ir_rmt_port = th->source;
+	ireq->ir_iif = inet_request_bound_dev_if(sk, skb);
+	ireq->ir_mark = inet_request_mark(sk, skb);
+
+	if (IS_ENABLED(CONFIG_SMC))
+		ireq->smc_ok = 0;
+
+	treq->snt_synack = 0;
+	treq->tfo_listener = false;
+	treq->txhash = net_tx_rndhash();
+	treq->rcv_isn = ntohl(th->seq) - 1;
+	treq->snt_isn = ntohl(th->ack_seq) - 1;
+	treq->syn_tos = TCP_SKB_CB(skb)->ip_dsfield;
+	treq->req_usec_ts = false;
+
+#if IS_ENABLED(CONFIG_MPTCP)
+	treq->is_mptcp = sk_is_mptcp(sk);
+	if (treq->is_mptcp)
+		return mptcp_subflow_init_cookie_req(req, sk, skb);
+#endif
+
+	return 0;
+}
+
 struct request_sock *cookie_tcp_reqsk_alloc(const struct request_sock_ops *ops,
 					    struct sock *sk, struct sk_buff *skb)
 {
-	struct tcp_request_sock *treq;
 	struct request_sock *req;
 
 	if (sk_is_mptcp(sk))
@@ -299,22 +332,10 @@ struct request_sock *cookie_tcp_reqsk_alloc(const struct request_sock_ops *ops,
 	if (!req)
 		return NULL;
 
-	treq = tcp_rsk(req);
+	if (cookie_tcp_reqsk_init(sk, skb, req)) {
-
+		reqsk_free(req);
-	treq->syn_tos = TCP_SKB_CB(skb)->ip_dsfield;
+		return NULL;
-	treq->req_usec_ts = false;
-
-#if IS_ENABLED(CONFIG_MPTCP)
-	treq->is_mptcp = sk_is_mptcp(sk);
-	if (treq->is_mptcp) {
-		int err = mptcp_subflow_init_cookie_req(req, sk, skb);
-
-		if (err) {
-			reqsk_free(req);
-			return NULL;
-		}
 	}
-#endif
 
 	return req;
 }
@@ -376,28 +397,15 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 
 	ireq = inet_rsk(req);
 	treq = tcp_rsk(req);
-	treq->rcv_isn		= ntohl(th->seq) - 1;
-	treq->snt_isn		= ntohl(th->ack_seq) - 1;
 	treq->ts_off		= tsoff;
-	treq->txhash		= net_tx_rndhash();
 	req->mss		= mss;
-	ireq->ir_num		= ntohs(th->dest);
-	ireq->ir_rmt_port	= th->source;
 	sk_rcv_saddr_set(req_to_sk(req), ip_hdr(skb)->daddr);
 	sk_daddr_set(req_to_sk(req), ip_hdr(skb)->saddr);
-	ireq->ir_mark		= inet_request_mark(sk, skb);
 	ireq->snd_wscale	= tcp_opt.snd_wscale;
 	ireq->sack_ok		= tcp_opt.sack_ok;
 	ireq->wscale_ok		= tcp_opt.wscale_ok;
 	ireq->tstamp_ok		= tcp_opt.saw_tstamp;
 	req->ts_recent		= tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
-	treq->snt_synack	= 0;
-	treq->tfo_listener	= false;
-
-	if (IS_ENABLED(CONFIG_SMC))
-		ireq->smc_ok = 0;
-
-	ireq->ir_iif = inet_request_bound_dev_if(sk, skb);
 
 	/* We throwed the options of the initial SYN away, so we hope
 	 * the ACK carries the same options again (see RFC1122 4.2.3.8)
@@ -409,8 +417,6 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 
 	tcp_ao_syncookie(sk, skb, req, AF_INET);
 
-	req->num_retrans = 0;
-
 	/*
 	 * We need to lookup the route here to get at the correct
 	 * window size. We should better make sure that the window size

net/ipv6/syncookies.c

@@ -178,11 +178,8 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 
 	ireq = inet_rsk(req);
 	treq = tcp_rsk(req);
-	treq->tfo_listener = false;
 
 	req->mss = mss;
-	ireq->ir_rmt_port = th->source;
-	ireq->ir_num = ntohs(th->dest);
 	ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr;
 	ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr;
 
@@ -196,31 +193,20 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 		ireq->pktopts = skb;
 	}
 
-	ireq->ir_iif = inet_request_bound_dev_if(sk, skb);
 	/* So that link locals have meaning */
 	if (!sk->sk_bound_dev_if &&
 	    ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL)
 		ireq->ir_iif = tcp_v6_iif(skb);
 
-	ireq->ir_mark = inet_request_mark(sk, skb);
-
-	req->num_retrans = 0;
 	ireq->snd_wscale	= tcp_opt.snd_wscale;
 	ireq->sack_ok		= tcp_opt.sack_ok;
 	ireq->wscale_ok		= tcp_opt.wscale_ok;
 	ireq->tstamp_ok		= tcp_opt.saw_tstamp;
 	req->ts_recent		= tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
-	treq->snt_synack	= 0;
-	treq->rcv_isn = ntohl(th->seq) - 1;
-	treq->snt_isn = ntohl(th->ack_seq) - 1;
 	treq->ts_off = tsoff;
-	treq->txhash = net_tx_rndhash();
 
 	tcp_ao_syncookie(sk, skb, req, AF_INET6);
 
-	if (IS_ENABLED(CONFIG_SMC))
-		ireq->smc_ok = 0;
-
 	/*
 	 * We need to lookup the dst_entry to get the correct window size.
 	 * This is taken from tcp_v6_syn_recv_sock.  Somebody please enlighten