CVE-2026-81000

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

net: tun: bound receive headroom

tun get user() uses tun->align both as skb headroom and when choosing how much packet data to keep linear. OVS can propagate an oversized headroom request from another port to TUN or TAP.

When align is larger than the usable space in a one-page skb head, SKB MAX HEAD(align) underflows and the result becomes negative when stored in good linear. That value later wraps when assigned to the size t linear variable, and tun alloc skb() can place skb->data outside the allocated head.

Bound the headroom stored by TUN to the one-page skb-head budget and the largest non-sentinel 16-bit skb header offset. Leave one linear byte for raw TUN and a complete Ethernet header for TAP, including NET IP ALIGN.

Also pull the raw-TUN protocol byte and the TAP Ethernet header before accessing them, so these checks remain safe for nonlinear skbs supplied by other allocation paths.