CVE-2026-80978

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

net: cap advertised IP tunnel headroom

IP tunnel devices derive their advertised needed headroom from lower output devices. A stack of user-created devices can make the derived value larger than the 16-bit skb header offsets can represent. Once IP output reserves it, skb head expansion can wrap those offsets.

The runtime transmit path already caps a growing needed headroom at 512. Apply the same cap when tunnel configuration publishes needed headroom derived from a lower output device.

Capping the advertised value is safe: IP tunnel transmit still expands the skb when a packet needs more headroom. A nonsensical stacked configuration can therefore incur an extra reallocation, but it cannot publish an unbounded reservation to upper layers.