CVE-2026-31684

In the Linux kernel, the following vulnerability has been resolved:

net: sched: act_csum: validate nested VLAN headers

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.