[PATCH net 1/1] net: xfrm: reject unrepresentable espintcp transport headers

[Ren Wei <weir@nebusec.ai>]

From: Wyatt Feng <wf.kernel.dev@gmail.com>

ESP-in-TCP can hand xfrm packets whose transport header offset no longer
fits after the stream parser trims the TCP envelope. The plain transport
header reset truncates that offset and triggers the skb warning path.

Use the careful transport-header helper and drop the skb through the
existing XFRM error path when the offset cannot be represented.

Fixes: e27cca96cd68 ("xfrm: add espintcp (RFC 8229)")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Assisted-by: Codex:GPT-5.4
Signed-off-by: Wyatt Feng <wf.kernel.dev@gmail.com>
Signed-off-by: Ren Wei <weir@nebusec.ai>
---
 net/xfrm/espintcp.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/xfrm/espintcp.c b/net/xfrm/espintcp.c
index 674aedc5af5a..3e72b9f067b9 100644
--- a/net/xfrm/espintcp.c
+++ b/net/xfrm/espintcp.c
@@ -30,7 +30,11 @@ static void handle_esp(struct sk_buff *skb, struct sock *sk)
 {
 	struct tcp_skb_cb *tcp_cb = (struct tcp_skb_cb *)skb->cb;
 
-	skb_reset_transport_header(skb);
+	if (!skb_reset_transport_header_careful(skb)) {
+		XFRM_INC_STATS(sock_net(sk), LINUX_MIB_XFRMINERROR);
+		kfree_skb(skb);
+		return;
+	}
 
 	/* restore IP CB, we need at least IP6CB->nhoff */
 	memmove(skb->cb, &tcp_cb->header, sizeof(tcp_cb->header));
-- 
2.47.3