tcp: secure_seq: add back ports to TS offset

[ Upstream commit 165573e41f2f66ef98940cf65f838b2cb575d9d1 ]

This reverts 28ee1b746f49 ("secure_seq: downgrade to per-host timestamp offsets")

tcp_tw_recycle went away in 2017.

Zhouyan Deng reported off-path TCP source port leakage via
SYN cookie side-channel that can be fixed in multiple ways.

One of them is to bring back TCP ports in TS offset randomization.

As a bonus, we perform a single siphash() computation
to provide both an ISN and a TS offset.

Fixes: 28ee1b746f49 ("secure_seq: downgrade to per-host timestamp offsets")
Reported-by: Zhouyan Deng <dengzhouyan_nwpu@163.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Acked-by: Florian Westphal <fw@strlen.de>
Link: https://patch.msgid.link/20260302205527.1982836-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

3 files changed, 31 insertions, 25 deletions

diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 061751aabc8e..fc3affd9c801 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -378,9 +378,14 @@ static struct request_sock *cookie_tcp_check(struct net *net, struct sock *sk,
 	tcp_parse_options(net, skb, &tcp_opt, 0, NULL);
 
 	if (tcp_opt.saw_tstamp && tcp_opt.rcv_tsecr) {
-		tsoff = secure_tcp_ts_off(net,
-					  ip_hdr(skb)->daddr,
-					  ip_hdr(skb)->saddr);
+		union tcp_seq_and_ts_off st;
+
+		st = secure_tcp_seq_and_ts_off(net,
+					       ip_hdr(skb)->daddr,
+					       ip_hdr(skb)->saddr,
+					       tcp_hdr(skb)->dest,
+					       tcp_hdr(skb)->source);
+		tsoff = st.ts_off;
 		tcp_opt.rcv_tsecr -= tsoff;
 	}
 
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 1c9db9a246f7..3e95b36fa273 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -7411,6 +7411,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 	const struct tcp_sock *tp = tcp_sk(sk);
 	struct net *net = sock_net(sk);
 	struct sock *fastopen_sk = NULL;
+	union tcp_seq_and_ts_off st;
 	struct request_sock *req;
 	bool want_cookie = false;
 	struct dst_entry *dst;
@@ -7480,9 +7481,12 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 	if (!dst)
 		goto drop_and_free;
 
+	if (tmp_opt.tstamp_ok || (!want_cookie && !isn))
+		st = af_ops->init_seq_and_ts_off(net, skb);
+
 	if (tmp_opt.tstamp_ok) {
 		tcp_rsk(req)->req_usec_ts = dst_tcp_usec_ts(dst);
-		tcp_rsk(req)->ts_off = af_ops->init_ts_off(net, skb);
+		tcp_rsk(req)->ts_off = st.ts_off;
 	}
 	if (!want_cookie && !isn) {
 		int max_syn_backlog = READ_ONCE(net->ipv4.sysctl_max_syn_backlog);
@@ -7504,7 +7508,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 			goto drop_and_release;
 		}
 
-		isn = af_ops->init_seq(skb);
+		isn = st.seq;
 	}
 
 	tcp_ecn_create_request(req, skb, sk, dst);
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index e4e7bc8782ab..d27965294aef 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -104,17 +104,14 @@ static DEFINE_PER_CPU(struct sock_bh_locked, ipv4_tcp_sk) = {
 
 static DEFINE_MUTEX(tcp_exit_batch_mutex);
 
-static u32 tcp_v4_init_seq(const struct sk_buff *skb)
+static union tcp_seq_and_ts_off
+tcp_v4_init_seq_and_ts_off(const struct net *net, const struct sk_buff *skb)
 {
-	return secure_tcp_seq(ip_hdr(skb)->daddr,
-			      ip_hdr(skb)->saddr,
-			      tcp_hdr(skb)->dest,
-			      tcp_hdr(skb)->source);
-}
-
-static u32 tcp_v4_init_ts_off(const struct net *net, const struct sk_buff *skb)
-{
-	return secure_tcp_ts_off(net, ip_hdr(skb)->daddr, ip_hdr(skb)->saddr);
+	return secure_tcp_seq_and_ts_off(net,
+					 ip_hdr(skb)->daddr,
+					 ip_hdr(skb)->saddr,
+					 tcp_hdr(skb)->dest,
+					 tcp_hdr(skb)->source);
 }
 
 int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp)
@@ -326,15 +323,16 @@ int tcp_v4_connect(struct sock *sk, struct sockaddr_unsized *uaddr, int addr_len
 	rt = NULL;
 
 	if (likely(!tp->repair)) {
+		union tcp_seq_and_ts_off st;
+
+		st = secure_tcp_seq_and_ts_off(net,
+					       inet->inet_saddr,
+					       inet->inet_daddr,
+					       inet->inet_sport,
+					       usin->sin_port);
 		if (!tp->write_seq)
-			WRITE_ONCE(tp->write_seq,
-				   secure_tcp_seq(inet->inet_saddr,
-						  inet->inet_daddr,
-						  inet->inet_sport,
-						  usin->sin_port));
-		WRITE_ONCE(tp->tsoffset,
-			   secure_tcp_ts_off(net, inet->inet_saddr,
-					     inet->inet_daddr));
+			WRITE_ONCE(tp->write_seq, st.seq);
+		WRITE_ONCE(tp->tsoffset, st.ts_off);
 	}
 
 	atomic_set(&inet->inet_id, get_random_u16());
@@ -1677,8 +1675,7 @@ const struct tcp_request_sock_ops tcp_request_sock_ipv4_ops = {
 	.cookie_init_seq =	cookie_v4_init_sequence,
 #endif
 	.route_req	=	tcp_v4_route_req,
-	.init_seq	=	tcp_v4_init_seq,
-	.init_ts_off	=	tcp_v4_init_ts_off,
+	.init_seq_and_ts_off	=	tcp_v4_init_seq_and_ts_off,
 	.send_synack	=	tcp_v4_send_synack,
 };