[PATCH net 1/1] xfrm: drop ESP-in-TCP packets with no ingress device

[PATCH net 1/1] xfrm: drop ESP-in-TCP packets with no ingress device

[Ren Wei]

From: Zhiling Zou <roxy520tt@gmail.com>

ESP-in-TCP receives records through the TCP strparser. handle_esp()
restores skb->dev from the saved skb_iif before passing the packet into
the XFRM input path.

Queued TCP data can be processed after the original ingress device has
been removed, for example during veth or net namespace teardown. In that
case dev_get_by_index_rcu() returns NULL. The XFRM IPv4 and IPv6 input
paths both expect skb->dev to be valid while building the route lookup,
so queued ESP-in-TCP data can dereference a NULL device.

Drop the packet if the saved ingress device can no longer be resolved.
Such a packet can no longer be routed through the normal XFRM receive
path, and this preserves the existing behaviour for packets whose ingress
device still exists.

Fixes: e27cca96cd68 ("xfrm: add espintcp (RFC 8229)")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Signed-off-by: Zhiling Zou <roxy520tt@gmail.com>
Assisted-by: Codex:gpt-5.4
Reviewed-by: Ren Wei <enjou1224z@gmail.com>
---
 net/xfrm/espintcp.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/xfrm/espintcp.c b/net/xfrm/espintcp.c
index 374e1b964438..fc01ce89492a 100644
--- a/net/xfrm/espintcp.c
+++ b/net/xfrm/espintcp.c
@@ -37,6 +37,11 @@ static void handle_esp(struct sk_buff *skb, struct sock *sk)
 
 	rcu_read_lock();
 	skb->dev = dev_get_by_index_rcu(sock_net(sk), skb->skb_iif);
+	if (!skb->dev) {
+		XFRM_INC_STATS(sock_net(sk), LINUX_MIB_XFRMINERROR);
+		kfree_skb(skb);
+		goto out;
+	}
 	local_bh_disable();
 #if IS_ENABLED(CONFIG_IPV6)
 	if (sk->sk_family == AF_INET6)
@@ -45,6 +50,7 @@ static void handle_esp(struct sk_buff *skb, struct sock *sk)
 #endif
 		xfrm4_rcv_encap(skb, IPPROTO_ESP, 0, TCP_ENCAP_ESPINTCP);
 	local_bh_enable();
+out:
 	rcu_read_unlock();
 }
 
-- 
2.43.0

Re: [PATCH net 1/1] xfrm: drop ESP-in-TCP packets with no ingress device

[Steffen Klassert]

On Sat, Jul 18, 2026 at 03:12:50PM +0800, Ren Wei wrote:
> From: Zhiling Zou <roxy520tt@gmail.com>
> 
> ESP-in-TCP receives records through the TCP strparser. handle_esp()
> restores skb->dev from the saved skb_iif before passing the packet into
> the XFRM input path.
> 
> Queued TCP data can be processed after the original ingress device has
> been removed, for example during veth or net namespace teardown. In that
> case dev_get_by_index_rcu() returns NULL. The XFRM IPv4 and IPv6 input
> paths both expect skb->dev to be valid while building the route lookup,
> so queued ESP-in-TCP data can dereference a NULL device.
> 
> Drop the packet if the saved ingress device can no longer be resolved.
> Such a packet can no longer be routed through the normal XFRM receive
> path, and this preserves the existing behaviour for packets whose ingress
> device still exists.
> 
> Fixes: e27cca96cd68 ("xfrm: add espintcp (RFC 8229)")
> Cc: stable@vger.kernel.org
> Reported-by: Vega <vega@nebusec.ai>
> Signed-off-by: Zhiling Zou <roxy520tt@gmail.com>
> Assisted-by: Codex:gpt-5.4
> Reviewed-by: Ren Wei <enjou1224z@gmail.com>

Applied, thanks a lot!