[PATCH v2 07/17] net: tcp: allow tcp_timewait_sock to validate skbs before handing to device

Daniel Zahka
2025-06-25T13:52:20Z

Provide a callback to validate skb's originating from tcp timewait
socks before passing to the device layer. Full socks have a
sk_validate_xmit_skb member for checking that a device is capable of
performing offloads required for transmitting an skb. With psp, tcp
timewait socks will inherit the crypto state from their corresponding
full socks. Any ACKs or RSTs that originate from a tcp timewait sock
carrying psp state should be psp encapsulated.

Signed-off-by: Daniel Zahka <daniel.zahka@gmail.com>
---

Notes:
v2:
- patch introduced in v2

include/net/inet_timewait_sock.h | 5 +++++
net/core/dev.c | 14 ++++++++++++--
net/ipv4/inet_timewait_sock.c | 3 +++
3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/include/net/inet_timewait_sock.h b/include/net/inet_timewait_sock.h
index c1295246216c..3a31c74c9e15 100644
--- a/include/net/inet_timewait_sock.h
+++ b/include/net/inet_timewait_sock.h
@@ -84,6 +84,11 @@ struct inet_timewait_sock {
#if IS_ENABLED(CONFIG_INET_PSP)
struct psp_assoc __rcu *psp_assoc;
#endif
+#ifdef CONFIG_SOCK_VALIDATE_XMIT
+ struct sk_buff* (*tw_validate_xmit_skb)(struct sock *sk,
+ struct net_device *dev,
+ struct sk_buff *skb);
+#endif
};
#define tw_tclass tw_tos

diff --git a/net/core/dev.c b/net/core/dev.c
index b825b3f5b7db..bf013436a57b 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3904,10 +3904,20 @@ static struct sk_buff *sk_validate_xmit_skb(struct sk_buff *skb,
struct net_device *dev)
{
#ifdef CONFIG_SOCK_VALIDATE_XMIT
+ struct sk_buff *(*sk_validate)(struct sock *sk, struct net_device *dev,
+ struct sk_buff *skb);
struct sock *sk = skb->sk;

- if (sk && sk_fullsock(sk) && sk->sk_validate_xmit_skb) {
- skb = sk->sk_validate_xmit_skb(sk, dev, skb);
+ sk_validate = NULL;
+ if (sk) {
+ if (sk_fullsock(sk))
+ sk_validate = sk->sk_validate_xmit_skb;
+ else if (sk->sk_state == TCP_TIME_WAIT)
+ sk_validate = inet_twsk(sk)->tw_validate_xmit_skb;
+ }
+
+ if (sk_validate) {
+ skb = sk_validate(sk, dev, skb);
} else if (unlikely(skb_is_decrypted(skb))) {
pr_warn_ratelimited("unencrypted skb with no associated socket - dropping\n");
kfree_skb(skb);
diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c
index dfde7895d8f2..859c03e07466 100644
--- a/net/ipv4/inet_timewait_sock.c
+++ b/net/ipv4/inet_timewait_sock.c
@@ -210,6 +210,9 @@ struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk,
atomic64_set(&tw->tw_cookie, atomic64_read(&sk->sk_cookie));
twsk_net_set(tw, sock_net(sk));
timer_setup(&tw->tw_timer, tw_timer_handler, 0);
+#ifdef CONFIG_SOCK_VALIDATE_XMIT
+ tw->tw_validate_xmit_skb = NULL;
+#endif
/*
* Because we use RCU lookups, we should not set tw_refcnt
* to a non null value before everything is setup for this
--
2.47.1