netdev - [PATCH ipsec] xfrm: Set transport header to fix UDP GRO handling

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Message-ID: <d14acb9a-bc2b-4459-a8e7-a9017d9d75fc@strongswan.org>
Date: Tue, 24 Jun 2025 14:47:20 +0200
From: Tobias Brunner <tobias@...ongswan.org>
To: Steffen Klassert <steffen.klassert@...unet.com>,
 Herbert Xu <herbert@...dor.apana.org.au>,
 "David S. Miller" <davem@...emloft.net>
Cc: netdev@...r.kernel.org, devel@...ux-ipsec.org
Subject: [PATCH ipsec] xfrm: Set transport header to fix UDP GRO handling

The referenced commit replaced a call to __xfrm4|6_udp_encap_rcv() with
a custom check for non-ESP markers.  But what the called function also
did was setting the transport header to the ESP header.  The function
that follows, esp4|6_gro_receive(), relies on that being set when it calls
xfrm_parse_spi().  We have to set the full offset as the skb's head was
not moved yet so adding just the UDP header length won't work.

Fixes: e3fd05777685 ("xfrm: Fix UDP GRO handling for some corner cases")
Signed-off-by: Tobias Brunner <tobias@...ongswan.org>
---
 net/ipv4/xfrm4_input.c | 3 +++
 net/ipv6/xfrm6_input.c | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/net/ipv4/xfrm4_input.c b/net/ipv4/xfrm4_input.c
index 0d31a8c108d4..f28cfd88eaf5 100644
--- a/net/ipv4/xfrm4_input.c
+++ b/net/ipv4/xfrm4_input.c
@@ -202,6 +202,9 @@ struct sk_buff *xfrm4_gro_udp_encap_rcv(struct sock *sk, struct list_head *head,
 	if (len <= sizeof(struct ip_esp_hdr) || udpdata32[0] == 0)
 		goto out;

+	/* set the transport header to ESP */
+	skb_set_transport_header(skb, offset);
+
 	NAPI_GRO_CB(skb)->proto = IPPROTO_UDP;

 	pp = call_gro_receive(ops->callbacks.gro_receive, head, skb);
diff --git a/net/ipv6/xfrm6_input.c b/net/ipv6/xfrm6_input.c
index 841c81abaaf4..9005fc156a20 100644
--- a/net/ipv6/xfrm6_input.c
+++ b/net/ipv6/xfrm6_input.c
@@ -202,6 +202,9 @@ struct sk_buff *xfrm6_gro_udp_encap_rcv(struct sock *sk, struct list_head *head,
 	if (len <= sizeof(struct ip_esp_hdr) || udpdata32[0] == 0)
 		goto out;

+	/* set the transport header to ESP */
+	skb_set_transport_header(skb, offset);
+
 	NAPI_GRO_CB(skb)->proto = IPPROTO_UDP;

 	pp = call_gro_receive(ops->callbacks.gro_receive, head, skb);
-- 
2.43.0