netdev - [PATCH net-next 2/3] xfrm: Check inner packet family directly from skb

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Message-ID: <20251024023931.65002-3-jianbol@nvidia.com>
Date: Fri, 24 Oct 2025 05:31:36 +0300
From: Jianbo Liu <jianbol@...dia.com>
To: <netdev@...r.kernel.org>, <davem@...emloft.net>, <kuba@...nel.org>,
	<steffen.klassert@...unet.com>
CC: Jianbo Liu <jianbol@...dia.com>, Cosmin Ratiu <cratiu@...dia.com>,
	"Herbert Xu" <herbert@...dor.apana.org.au>, Eric Dumazet
	<edumazet@...gle.com>, "Paolo Abeni" <pabeni@...hat.com>, Simon Horman
	<horms@...nel.org>
Subject: [PATCH net-next 2/3] xfrm: Check inner packet family directly from skb_dst

In the output path, xfrm_dev_offload_ok and xfrm_get_inner_ipproto
need to determine the protocol family of the inner packet (skb) before
it gets encapsulated.

In xfrm_dev_offload_ok, the code checked x->inner_mode.family. This is
incorrect because the state's true inner family might be specified in
x->inner_mode_iaf.family (e.g., for tunnel mode).

In xfrm_get_inner_ipproto, the code checked x->outer_mode.family. This
is also incorrect for tunnel mode, as the inner packet's family can be
different from the outer header's family.

At both of these call sites, the skb variable holds the original inner
packet. The most direct and reliable source of truth for its protocol
family is its destination entry. This patch fixes the issue by using
skb_dst(skb)->ops->family to ensure protocol-specific headers are only
accessed for the correct packet type.

Signed-off-by: Jianbo Liu <jianbol@...dia.com>
Reviewed-by: Cosmin Ratiu <cratiu@...dia.com>
---
 net/xfrm/xfrm_device.c | 2 +-
 net/xfrm/xfrm_output.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/xfrm/xfrm_device.c b/net/xfrm/xfrm_device.c
index 44b9de6e4e77..52ae0e034d29 100644
--- a/net/xfrm/xfrm_device.c
+++ b/net/xfrm/xfrm_device.c
@@ -438,7 +438,7 @@ bool xfrm_dev_offload_ok(struct sk_buff *skb, struct xfrm_state *x)

 	check_tunnel_size = x->xso.type == XFRM_DEV_OFFLOAD_PACKET &&
 			    x->props.mode == XFRM_MODE_TUNNEL;
-	switch (x->inner_mode.family) {
+	switch (skb_dst(skb)->ops->family) {
 	case AF_INET:
 		/* Check for IPv4 options */
 		if (ip_hdr(skb)->ihl != 5)
diff --git a/net/xfrm/xfrm_output.c b/net/xfrm/xfrm_output.c
index 9077730ff7d0..a98b5bf55ac3 100644
--- a/net/xfrm/xfrm_output.c
+++ b/net/xfrm/xfrm_output.c
@@ -698,7 +698,7 @@ static void xfrm_get_inner_ipproto(struct sk_buff *skb, struct xfrm_state *x)
 		return;

 	if (x->outer_mode.encap == XFRM_MODE_TUNNEL) {
-		switch (x->outer_mode.family) {
+		switch (skb_dst(skb)->ops->family) {
 		case AF_INET:
 			xo->inner_ipproto = ip_hdr(skb)->protocol;
 			break;
-- 
2.49.0