netdev - [PATCH ipsec-rc] xfrm: fix tunnel mode TX datapath in packet offload mode

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Message-ID: <dd53723e4ba4dcb4efa9f731b54ebfb9ca24e049.1739959873.git.leon@kernel.org>
Date: Wed, 19 Feb 2025 12:20:37 +0200
From: Leon Romanovsky <leon@...nel.org>
To: Steffen Klassert <steffen.klassert@...unet.com>
Cc: Alexandre Cassen <acassen@...p.free.fr>,
	netdev@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>
Subject: [PATCH ipsec-rc] xfrm: fix tunnel mode TX datapath in packet offload mode

From: Alexandre Cassen <acassen@...p.free.fr>

Packets that match the output xfrm policy are delivered to the netstack.
In IPsec packet mode for tunnel mode, the HW is responsible for building
the hard header and outer IP header. In such a situation, the inner
header may refer to a network that is not directly reachable by the host,
resulting in a failed neighbor resolution. The packet is then dropped.
xfrm policy defines the netdevice to use for xmit so we can send packets
directly to it.

Makes direct xmit exclusive to tunnel mode, since some rules may apply
in transport mode.

Fixes: f8a70afafc17 ("xfrm: add TX datapath support for IPsec packet offload mode")
Signed-off-by: Alexandre Cassen <acassen@...p.free.fr>
Signed-off-by: Leon Romanovsky <leonro@...dia.com>
---
Steffen,

Fixes line is not accurate as at that point, I didn't implement tunnel
mode yet. However it is still useful SHA-1 as it points to the commit
which changed these lines.

Changelog:
v0:
 * Added more comments
 * Make sure that we are calling to new function in tunnel mode only
RFC: https://lore.kernel.org/all/af1b9df0b22d7a9f208e093356412f8976cc1bc2.1738780166.git.leon@kernel.org
---
 net/xfrm/xfrm_output.c | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/net/xfrm/xfrm_output.c b/net/xfrm/xfrm_output.c
index 34c8e266641c..8b4e044162b8 100644
--- a/net/xfrm/xfrm_output.c
+++ b/net/xfrm/xfrm_output.c
@@ -612,6 +612,40 @@ int xfrm_output_resume(struct sock *sk, struct sk_buff *skb, int err)
 }
 EXPORT_SYMBOL_GPL(xfrm_output_resume);
 
+static int xfrm_dev_direct_output(struct sock *sk, struct xfrm_state *x,
+				  struct sk_buff *skb)
+{
+	struct dst_entry *dst = skb_dst(skb);
+	struct net *net = xs_net(x);
+	int err;
+
+	dst = skb_dst_pop(skb);
+	if (!dst) {
+		XFRM_INC_STATS(net, LINUX_MIB_XFRMOUTERROR);
+		kfree_skb(skb);
+		return -EHOSTUNREACH;
+	}
+	skb_dst_set(skb, dst);
+	nf_reset_ct(skb);
+
+	err = skb_dst(skb)->ops->local_out(net, sk, skb);
+	if (unlikely(err != 1)) {
+		kfree_skb(skb);
+		return err;
+	}
+
+	/* In transport mode, network destination is
+	 * directly reachable, while in tunnel mode,
+	 * inner packet network may not be. In packet
+	 * offload type, HW is responsible for hard
+	 * header packet mangling so directly xmit skb
+	 * to netdevice.
+	 */
+	skb->dev = x->xso.dev;
+	__skb_push(skb, skb->dev->hard_header_len);
+	return dev_queue_xmit(skb);
+}
+
 static int xfrm_output2(struct net *net, struct sock *sk, struct sk_buff *skb)
 {
 	return xfrm_output_resume(sk, skb, 1);
@@ -735,6 +769,13 @@ int xfrm_output(struct sock *sk, struct sk_buff *skb)
 			return -EHOSTUNREACH;
 		}
 
+		/* Exclusive direct xmit for tunnel mode, as
+		 * some filtering or matching rules may apply
+		 * in transport mode.
+		 */
+		if (x->props.mode == XFRM_MODE_TUNNEL)
+			return xfrm_dev_direct_output(sk, x, skb);
+
 		return xfrm_output_resume(sk, skb, 0);
 	}
 
-- 
2.48.1