netdev - [PATCH ipsec] xfrm: Prevent locally generated packets from direct output in tunnel mode

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Message-ID: <20251029095213.3108-1-jianbol@nvidia.com>
Date: Wed, 29 Oct 2025 11:50:25 +0200
From: Jianbo Liu <jianbol@...dia.com>
To: <netdev@...r.kernel.org>, <davem@...emloft.net>, <kuba@...nel.org>,
	<steffen.klassert@...unet.com>, <acassen@...p.free.fr>
CC: Jianbo Liu <jianbol@...dia.com>, Leon Romanovsky <leonro@...dia.com>,
	Herbert Xu <herbert@...dor.apana.org.au>, Eric Dumazet <edumazet@...gle.com>,
	Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, "Leon
 Romanovsky" <leon@...nel.org>
Subject: [PATCH ipsec] xfrm: Prevent locally generated packets from direct output in tunnel mode

Add a check to ensure locally generated packets (skb->sk != NULL) do
not use direct output in tunnel mode, as these packets require proper
L2 header setup that is handled by the normal XFRM processing path.

Fixes: 5eddd76ec2fd ("xfrm: fix tunnel mode TX datapath in packet offload mode")
Signed-off-by: Jianbo Liu <jianbol@...dia.com>
Reviewed-by: Leon Romanovsky <leonro@...dia.com>
---
 net/xfrm/xfrm_output.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/xfrm/xfrm_output.c b/net/xfrm/xfrm_output.c
index 9077730ff7d0..c8fd506ca5cf 100644
--- a/net/xfrm/xfrm_output.c
+++ b/net/xfrm/xfrm_output.c
@@ -772,8 +772,12 @@ int xfrm_output(struct sock *sk, struct sk_buff *skb)
 		/* Exclusive direct xmit for tunnel mode, as
 		 * some filtering or matching rules may apply
 		 * in transport mode.
+		 * Locally generated packets also require
+		 * the normal XFRM path for L2 header setup,
+		 * as the hardware needs the L2 header to match
+		 * for encryption, so skip direct output as well.
 		 */
-		if (x->props.mode == XFRM_MODE_TUNNEL)
+		if (x->props.mode == XFRM_MODE_TUNNEL && !skb->sk)
 			return xfrm_dev_direct_output(sk, x, skb);
 
 		return xfrm_output_resume(sk, skb, 0);
-- 
2.49.0