netdev - [PATCH ipsec v2] xfrm: Preserve xfrm interface secpath for packets forwarded

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Date:   Wed, 12 Apr 2023 10:56:15 +0200
From:   Martin Willi <martin@...ongswan.org>
To:     Steffen Klassert <steffen.klassert@...unet.com>,
        Benedict Wong <benedictwong@...gle.com>,
        Eyal Birger <eyal.birger@...il.com>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Subject: [PATCH ipsec v2] xfrm: Preserve xfrm interface secpath for packets forwarded

The commit referenced below clears the secpath on packets received via
xfrm interfaces to support nested IPsec tunnels. This breaks Netfilter
policy matching using xt_policy in the FORWARD chain, as the secpath
is missing during forwarding. INPUT matching is not affected, as it is
done before secpath reset.

A work-around could use XFRM input interface matching for such rules,
but this does not work if the XFRM interface is part of a VRF; the
Netfilter input interface is replaced by the VRF interface, making a
sufficient match for IPsec-protected packets difficult.

So instead, limit the secpath reset to packets that are not using a
XFRM forward policy. This should allow nested tunnels, but keeps the
secpath intact on packets that are passed to Netfilter chains with
potential IPsec policy matches.

Fixes: b0355dbbf13c ("Fix XFRM-I support for nested ESP tunnels")
Suggested-by: Eyal Birger <eyal.birger@...il.com>
Signed-off-by: Martin Willi <martin@...ongswan.org>
---
v1 -> v2: Use policy dir instead of flowi outif to check for forwarding

 net/xfrm/xfrm_policy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 5c61ec04b839..669c3c0880a6 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -3745,7 +3745,7 @@ int __xfrm_policy_check(struct sock *sk, int dir, struct sk_buff *skb,
 			goto reject;
 		}

-		if (if_id)
+		if (if_id && dir != XFRM_POLICY_FWD)
 			secpath_reset(skb);

 		xfrm_pols_put(pols, npols);
-- 
2.34.1