netdev - [PATCH ipsec 3/3] udp: also consider secpath when evaluating ipsec use for checksumming

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Message-ID: <0e8fbdd7e0086f4cc73a46f010a79638d4910498.1753631391.git.sd@queasysnail.net>
Date: Mon, 28 Jul 2025 17:17:20 +0200
From: Sabrina Dubroca <sd@...asysnail.net>
To: netdev@...r.kernel.org
Cc: Sabrina Dubroca <sd@...asysnail.net>,
	David Ahern <dsahern@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Ansis Atteka <aatteka@....org>,
	Steffen Klassert <steffen.klassert@...unet.com>
Subject: [PATCH ipsec 3/3] udp: also consider secpath when evaluating ipsec use for checksumming

Commit b40c5f4fde22 ("udp: disable inner UDP checksum offloads in
IPsec case") tried to fix checksumming in UFO when the packets are
going through IPsec, so that we can't rely on offloads because the UDP
header and payload will be encrypted.

But when doing a TCP test over VXLAN going through IPsec transport
mode with GSO enabled (esp4_offload module loaded), I'm seeing broken
UDP checksums on the encap after successful decryption.

The skbs get to udp4_ufo_fragment/__skb_udp_tunnel_segment via
__dev_queue_xmit -> validate_xmit_skb -> skb_gso_segment and at this
point we've already dropped the dst (unless the device sets
IFF_XMIT_DST_RELEASE, which is not common), so need_ipsec is false and
we proceed with checksum offload.

Make need_ipsec also check the secpath, which is not dropped on this
callpath.

Fixes: b40c5f4fde22 ("udp: disable inner UDP checksum offloads in IPsec case")
Signed-off-by: Sabrina Dubroca <sd@...asysnail.net>
---
Since the issue is related to IPsec and currently not visible since
GSO is currently broken for SW crypto, I'm including this patch in the
same series for the ipsec tree. I can split it out if that's prefered,
just let me know.

 net/ipv4/udp_offload.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index 85b5aa82d7d7..8758701c67d0 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -224,7 +224,7 @@ static struct sk_buff *__skb_udp_tunnel_segment(struct sk_buff *skb,
 	remcsum = !!(skb_shinfo(skb)->gso_type & SKB_GSO_TUNNEL_REMCSUM);
 	skb->remcsum_offload = remcsum;

-	need_ipsec = skb_dst(skb) && dst_xfrm(skb_dst(skb));
+	need_ipsec = (skb_dst(skb) && dst_xfrm(skb_dst(skb))) || skb_sec_path(skb);
 	/* Try to offload checksum if possible */
 	offload_csum = !!(need_csum &&
 			  !need_ipsec &&
-- 
2.50.0