[PATCH 6.6 005/254] xfrm: Fix inner mode lookup in tunnel mode GSO segmentation

Greg Kroah-Hartman
2026-01-28T15:28:22Z

From: Jianbo Liu <jianbol@nvidia.com>

[ Upstream commit 3d5221af9c7711b7aec8da1298c8fc393ef6183d ]

Commit 61fafbee6cfe ("xfrm: Determine inner GSO type from packet inner
protocol") attempted to fix GSO segmentation by reading the inner
protocol from XFRM_MODE_SKB_CB(skb)->protocol. This was incorrect
because the field holds the inner L4 protocol (TCP/UDP) instead of the
required tunnel protocol. Also, the memory location (shared by
XFRM_SKB_CB(skb) which could be overwritten by xfrm_replay_overflow())
is prone to corruption. This combination caused the kernel to select
the wrong inner mode and get the wrong address family.

The correct value is in xfrm_offload(skb)->proto, which is set from
the outer tunnel header's protocol field by esp[4|6]_gso_encap(). It
is initialized by xfrm[4|6]_tunnel_encap_add() to either IPPROTO_IPIP
or IPPROTO_IPV6, using xfrm_af2proto() and correctly reflects the
inner packet's address family.

Fixes: 61fafbee6cfe ("xfrm: Determine inner GSO type from packet inner protocol")
Signed-off-by: Jianbo Liu <jianbol@nvidia.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ipv4/esp4_offload.c | 4 ++--
net/ipv6/esp6_offload.c | 4 ++--
2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/esp4_offload.c b/net/ipv4/esp4_offload.c
index 11e33a4312674..028d2d3477d13 100644
--- a/net/ipv4/esp4_offload.c
+++ b/net/ipv4/esp4_offload.c
@@ -111,8 +111,8 @@ static struct sk_buff *xfrm4_tunnel_gso_segment(struct xfrm_state *x,
struct sk_buff *skb,
netdev_features_t features)
{
- const struct xfrm_mode *inner_mode = xfrm_ip2inner_mode(x,
- XFRM_MODE_SKB_CB(skb)->protocol);
+ struct xfrm_offload *xo = xfrm_offload(skb);
+ const struct xfrm_mode *inner_mode = xfrm_ip2inner_mode(x, xo->proto);
__be16 type = inner_mode->family == AF_INET6 ? htons(ETH_P_IPV6)
: htons(ETH_P_IP);

diff --git a/net/ipv6/esp6_offload.c b/net/ipv6/esp6_offload.c
index 438f9cbdca299..333d87557bf32 100644
--- a/net/ipv6/esp6_offload.c
+++ b/net/ipv6/esp6_offload.c
@@ -145,8 +145,8 @@ static struct sk_buff *xfrm6_tunnel_gso_segment(struct xfrm_state *x,
struct sk_buff *skb,
netdev_features_t features)
{
- const struct xfrm_mode *inner_mode = xfrm_ip2inner_mode(x,
- XFRM_MODE_SKB_CB(skb)->protocol);
+ struct xfrm_offload *xo = xfrm_offload(skb);
+ const struct xfrm_mode *inner_mode = xfrm_ip2inner_mode(x, xo->proto);
__be16 type = inner_mode->family == AF_INET ? htons(ETH_P_IP)
: htons(ETH_P_IPV6);

--
2.51.0