[PATCH 6.18 070/198] net: sched: act_csum: validate nested VLAN headers

Greg Kroah-Hartman
2026-04-20T16:02:03Z

From: Ruide Cao <caoruide123@gmail.com>

[ Upstream commit c842743d073bdd683606cb414eb0ca84465dd834 ]

tcf_csum_act() walks nested VLAN headers directly from skb->data when an
skb still carries in-payload VLAN tags. The current code reads
vlan->h_vlan_encapsulated_proto and then pulls VLAN_HLEN bytes without
first ensuring that the full VLAN header is present in the linear area.

If only part of an inner VLAN header is linearized, accessing
h_vlan_encapsulated_proto reads past the linear area, and the following
skb_pull(VLAN_HLEN) may violate skb invariants.

Fix this by requiring pskb_may_pull(skb, VLAN_HLEN) before accessing and
pulling each nested VLAN header. If the header still is not fully
available, drop the packet through the existing error path.

Fixes: 2ecba2d1e45b ("net: sched: act_csum: Fix csum calc for tagged packets")
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Co-developed-by: Yuan Tan <yuantan098@gmail.com>
Signed-off-by: Yuan Tan <yuantan098@gmail.com>
Suggested-by: Xin Liu <bird@lzu.edu.cn>
Tested-by: Ren Wei <enjou1224z@gmail.com>
Signed-off-by: Ruide Cao <caoruide123@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/22df2fcb49f410203eafa5d97963dd36089f4ecf.1774892775.git.caoruide123@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/sched/act_csum.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/sched/act_csum.c b/net/sched/act_csum.c
index 0939e6b2ba4d1..3a377604ad343 100644
--- a/net/sched/act_csum.c
+++ b/net/sched/act_csum.c
@@ -604,8 +604,12 @@ TC_INDIRECT_SCOPE int tcf_csum_act(struct sk_buff *skb,
protocol = skb->protocol;
orig_vlan_tag_present = true;
} else {
- struct vlan_hdr *vlan = (struct vlan_hdr *)skb->data;
+ struct vlan_hdr *vlan;

+ if (!pskb_may_pull(skb, VLAN_HLEN))
+ goto drop;
+
+ vlan = (struct vlan_hdr *)skb->data;
protocol = vlan->h_vlan_encapsulated_proto;
skb_pull(skb, VLAN_HLEN);
skb_reset_network_header(skb);
--
2.53.0