[PATCH 6.18 280/314] tcp: secure_seq: add back ports to TS offset

Sasha Levin
2026-03-10T11:29:51Z

From: Eric Dumazet <edumazet@google.com>

[ 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>
---
include/net/secure_seq.h | 45 ++++++++++++++++++----
include/net/tcp.h | 6 ++-
net/core/secure_seq.c | 80 +++++++++++++++-------------------------
net/ipv4/syncookies.c | 11 ++++--
net/ipv4/tcp_input.c | 8 +++-
net/ipv4/tcp_ipv4.c | 37 +++++++++----------
net/ipv6/syncookies.c | 11 ++++--
net/ipv6/tcp_ipv6.c | 37 +++++++++----------
8 files changed, 127 insertions(+), 108 deletions(-)

diff --git a/include/net/secure_seq.h b/include/net/secure_seq.h
index cddebafb9f779..6f996229167b3 100644
--- a/include/net/secure_seq.h
+++ b/include/net/secure_seq.h
@@ -5,16 +5,47 @@
#include <linux/types.h>

struct net;
+extern struct net init_net;
+
+union tcp_seq_and_ts_off {
+ struct {
+ u32 seq;
+ u32 ts_off;
+ };
+ u64 hash64;
+};

u64 secure_ipv4_port_ephemeral(__be32 saddr, __be32 daddr, __be16 dport);
u64 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,
__be16 dport);
-u32 secure_tcp_seq(__be32 saddr, __be32 daddr,
- __be16 sport, __be16 dport);
-u32 secure_tcp_ts_off(const struct net *net, __be32 saddr, __be32 daddr);
-u32 secure_tcpv6_seq(const __be32 *saddr, const __be32 *daddr,
- __be16 sport, __be16 dport);
-u32 secure_tcpv6_ts_off(const struct net *net,
- const __be32 *saddr, const __be32 *daddr);
+union tcp_seq_and_ts_off
+secure_tcp_seq_and_ts_off(const struct net *net, __be32 saddr, __be32 daddr,
+ __be16 sport, __be16 dport);
+
+static inline u32 secure_tcp_seq(__be32 saddr, __be32 daddr,
+ __be16 sport, __be16 dport)
+{
+ union tcp_seq_and_ts_off ts;
+
+ ts = secure_tcp_seq_and_ts_off(&init_net, saddr, daddr,
+ sport, dport);
+
+ return ts.seq;
+}
+
+union tcp_seq_and_ts_off
+secure_tcpv6_seq_and_ts_off(const struct net *net, const __be32 *saddr,
+ const __be32 *daddr,
+ __be16 sport, __be16 dport);
+
+static inline u32 secure_tcpv6_seq(const __be32 *saddr, const __be32 *daddr,
+ __be16 sport, __be16 dport)
+{
+ union tcp_seq_and_ts_off ts;
+
+ ts = secure_tcpv6_seq_and_ts_off(&init_net, saddr, daddr,
+ sport, dport);

+ return ts.seq;
+}
#endif /* _NET_SECURE_SEQ */
diff --git a/include/net/tcp.h b/include/net/tcp.h
index aa4d24c42a270..7647ed5c732c1 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -43,6 +43,7 @@
#include <net/dst.h>
#include <net/mptcp.h>
#include <net/xfrm.h>
+#include <net/secure_seq.h>

#include <linux/seq_file.h>
#include <linux/memcontrol.h>
@@ -2435,8 +2436,9 @@ struct tcp_request_sock_ops {
struct flowi *fl,
struct request_sock *req,
u32 tw_isn);
- u32 (*init_seq)(const struct sk_buff *skb);
- u32 (*init_ts_off)(const struct net *net, const struct sk_buff *skb);
+ union tcp_seq_and_ts_off (*init_seq_and_ts_off)(
+ const struct net *net,
+ const struct sk_buff *skb);
int (*send_synack)(const struct sock *sk, struct dst_entry *dst,
struct flowi *fl, struct request_sock *req,
struct tcp_fastopen_cookie *foc,
diff --git a/net/core/secure_seq.c b/net/core/secure_seq.c
index 9a39656804513..6a6f2cda5aaef 100644
--- a/net/core/secure_seq.c
+++ b/net/core/secure_seq.c
@@ -20,7 +20,6 @@
#include <net/tcp.h>

static siphash_aligned_key_t net_secret;
-static siphash_aligned_key_t ts_secret;

#define EPHEMERAL_PORT_SHUFFLE_PERIOD (10 * HZ)

@@ -28,11 +27,6 @@ static __always_inline void net_secret_init(void)
{
net_get_random_once(&net_secret, sizeof(net_secret));
}
-
-static __always_inline void ts_secret_init(void)
-{
- net_get_random_once(&ts_secret, sizeof(ts_secret));
-}
#endif

#ifdef CONFIG_INET
@@ -53,28 +47,9 @@ static u32 seq_scale(u32 seq)
#endif

#if IS_ENABLED(CONFIG_IPV6)
-u32 secure_tcpv6_ts_off(const struct net *net,
- const __be32 *saddr, const __be32 *daddr)
-{
- const struct {
- struct in6_addr saddr;
- struct in6_addr daddr;
- } __aligned(SIPHASH_ALIGNMENT) combined = {
- .saddr = *(struct in6_addr *)saddr,
- .daddr = *(struct in6_addr *)daddr,
- };
-
- if (READ_ONCE(net->ipv4.sysctl_tcp_timestamps) != 1)
- return 0;
-
- ts_secret_init();
- return siphash(&combined, offsetofend(typeof(combined), daddr),
- &ts_secret);
-}
-EXPORT_IPV6_MOD(secure_tcpv6_ts_off);
-
-u32 secure_tcpv6_seq(const __be32 *saddr, const __be32 *daddr,
- __be16 sport, __be16 dport)
+union tcp_seq_and_ts_off
+secure_tcpv6_seq_and_ts_off(const struct net *net, const __be32 *saddr,
+ const __be32 *daddr, __be16 sport, __be16 dport)
{
const struct {
struct in6_addr saddr;
@@ -87,14 +62,20 @@ u32 secure_tcpv6_seq(const __be32 *saddr, const __be32 *daddr,
.sport = sport,
.dport = dport
};
- u32 hash;
+ union tcp_seq_and_ts_off st;

net_secret_init();
- hash = siphash(&combined, offsetofend(typeof(combined), dport),
- &net_secret);
- return seq_scale(hash);
+
+ st.hash64 = siphash(&combined, offsetofend(typeof(combined), dport),
+ &net_secret);
+
+ if (READ_ONCE(net->ipv4.sysctl_tcp_timestamps) != 1)
+ st.ts_off = 0;
+
+ st.seq = seq_scale(st.seq);
+ return st;
}
-EXPORT_SYMBOL(secure_tcpv6_seq);
+EXPORT_SYMBOL(secure_tcpv6_seq_and_ts_off);

u64 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,
__be16 dport)
@@ -118,33 +99,30 @@ EXPORT_SYMBOL(secure_ipv6_port_ephemeral);
#endif

#ifdef CONFIG_INET
-u32 secure_tcp_ts_off(const struct net *net, __be32 saddr, __be32 daddr)
-{
- if (READ_ONCE(net->ipv4.sysctl_tcp_timestamps) != 1)
- return 0;
-
- ts_secret_init();
- return siphash_2u32((__force u32)saddr, (__force u32)daddr,
- &ts_secret);
-}
-
/* secure_tcp_seq_and_tsoff(a, b, 0, d) == secure_ipv4_port_ephemeral(a, b, d),
* but fortunately, `sport' cannot be 0 in any circumstances. If this changes,
* it would be easy enough to have the former function use siphash_4u32, passing
* the arguments as separate u32.
*/
-u32 secure_tcp_seq(__be32 saddr, __be32 daddr,
- __be16 sport, __be16 dport)
+union tcp_seq_and_ts_off
+secure_tcp_seq_and_ts_off(const struct net *net, __be32 saddr, __be32 daddr,
+ __be16 sport, __be16 dport)
{
- u32 hash;
+ u32 ports = (__force u32)sport << 16 | (__force u32)dport;
+ union tcp_seq_and_ts_off st;

net_secret_init();
- hash = siphash_3u32((__force u32)saddr, (__force u32)daddr,
- (__force u32)sport << 16 | (__force u32)dport,
- &net_secret);
- return seq_scale(hash);
+
+ st.hash64 = siphash_3u32((__force u32)saddr, (__force u32)daddr,
+ ports, &net_secret);
+
+ if (READ_ONCE(net->ipv4.sysctl_tcp_timestamps) != 1)
+ st.ts_off = 0;
+
+ st.seq = seq_scale(st.seq);
+ return st;
}
-EXPORT_SYMBOL_GPL(secure_tcp_seq);
+EXPORT_SYMBOL_GPL(secure_tcp_seq_and_ts_off);

u64 secure_ipv4_port_ephemeral(__be32 saddr, __be32 daddr, __be16 dport)
{
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 061751aabc8e1..fc3affd9c8014 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 87e678903b977..96486eea26724 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -7385,6 +7385,7 @@ 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;
@@ -7454,9 +7455,12 @@ 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);
@@ -7478,7 +7482,7 @@ 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 0fbf13dcf3c2b..75a11d7feb260 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 *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());
@@ -1727,8 +1725,7 @@ 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,
};

diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index 7e007f013ec82..4f6f0d751d6c5 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -151,9 +151,14 @@ 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_tcpv6_ts_off(net,
- ipv6_hdr(skb)->daddr.s6_addr32,
- ipv6_hdr(skb)->saddr.s6_addr32);
+ union tcp_seq_and_ts_off st;
+
+ st = secure_tcpv6_seq_and_ts_off(net,
+ ipv6_hdr(skb)->daddr.s6_addr32,
+ ipv6_hdr(skb)->saddr.s6_addr32,
+ tcp_hdr(skb)->dest,
+ tcp_hdr(skb)->source);
+ tsoff = st.ts_off;
tcp_opt.rcv_tsecr -= tsoff;
}

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 5faa46f4cf9a2..90afe81bc8e5d 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -105,18 +105,14 @@ static void inet6_sk_rx_dst_set(struct sock *sk, const struct sk_buff *skb)
}
}

-static u32 tcp_v6_init_seq(const struct sk_buff *skb)
+static union tcp_seq_and_ts_off
+tcp_v6_init_seq_and_ts_off(const struct net *net, const struct sk_buff *skb)
{
- return secure_tcpv6_seq(ipv6_hdr(skb)->daddr.s6_addr32,
- ipv6_hdr(skb)->saddr.s6_addr32,
- tcp_hdr(skb)->dest,
- tcp_hdr(skb)->source);
-}
-
-static u32 tcp_v6_init_ts_off(const struct net *net, const struct sk_buff *skb)
-{
- return secure_tcpv6_ts_off(net, ipv6_hdr(skb)->daddr.s6_addr32,
- ipv6_hdr(skb)->saddr.s6_addr32);
+ return secure_tcpv6_seq_and_ts_off(net,
+ ipv6_hdr(skb)->daddr.s6_addr32,
+ ipv6_hdr(skb)->saddr.s6_addr32,
+ tcp_hdr(skb)->dest,
+ tcp_hdr(skb)->source);
}

static int tcp_v6_pre_connect(struct sock *sk, struct sockaddr *uaddr,
@@ -319,14 +315,16 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
sk_set_txhash(sk);

if (likely(!tp->repair)) {
+ union tcp_seq_and_ts_off st;
+
+ st = secure_tcpv6_seq_and_ts_off(net,
+ np->saddr.s6_addr32,
+ sk->sk_v6_daddr.s6_addr32,
+ inet->inet_sport,
+ inet->inet_dport);
if (!tp->write_seq)
- WRITE_ONCE(tp->write_seq,
- secure_tcpv6_seq(np->saddr.s6_addr32,
- sk->sk_v6_daddr.s6_addr32,
- inet->inet_sport,
- inet->inet_dport));
- tp->tsoffset = secure_tcpv6_ts_off(net, np->saddr.s6_addr32,
- sk->sk_v6_daddr.s6_addr32);
+ WRITE_ONCE(tp->write_seq, st.seq);
+ tp->tsoffset = st.ts_off;
}

if (tcp_fastopen_defer_connect(sk, &err))
@@ -859,8 +857,7 @@ const struct tcp_request_sock_ops tcp_request_sock_ipv6_ops = {
.cookie_init_seq = cookie_v6_init_sequence,
#endif
.route_req = tcp_v6_route_req,
- .init_seq = tcp_v6_init_seq,
- .init_ts_off = tcp_v6_init_ts_off,
+ .init_seq_and_ts_off = tcp_v6_init_seq_and_ts_off,
.send_synack = tcp_v6_send_synack,
};

--
2.51.0