CVE-2026-80978

Summary

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.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/fb889a619723032140f5d983a3a34d25a5a2bed4
• https://git.kernel.org/stable/c/b160422f8103574425e2834130e169d84c94fa1d
• https://git.kernel.org/stable/c/d36e75f5669140b66515ad3a176ca6337bd80a5e
• https://git.kernel.org/stable/c/84783961cb8bdb36b4f41a02ce43aafc6d52b176
• https://git.kernel.org/stable/c/bc4e05ae66c9797a0972ac44326e69c5305e0020
• https://git.kernel.org/stable/c/af0ee8f04bea22cdb331fa3509e17f81b48938ad
• https://git.kernel.org/stable/c/9144f2c53a04465a6878172b523f640313c5559e
• https://git.kernel.org/stable/c/6b222adeb9340306e2ff97127c76117abb9b3df8

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