In the Linux kernel, the following vulnerability has been resolved: eth: fbnic: Avoid rounding zero ring sizes roundup_pow_of_two() is undefined for… (CVE-2026-98585)

The Linux kernel fbnic Ethernet driver had a vulnerability where the ethtool interface permitted a zero ring size to be passed to the driver. The rounding function roundup_pow_of_two() is undefined for zero, which could cause unexpected behavior. The fix involved leaving zero ring sizes unchanged during rounding and relying on the minimum-size check to reject zero values deterministically, preserving expected behavior for other ring sizes.

The vulnerability could allow invalid zero ring sizes to be processed by the driver, potentially leading to undefined behavior or instability in the network driver. No known exploits are reported in the wild. The impact is limited to the fbnic Ethernet driver within the Linux kernel.

A fix has been implemented in the Linux kernel to address this issue by modifying the rounding behavior and enforcing the minimum-size check for zero ring sizes. Users should update to the fixed kernel version once available. No additional mitigation is required beyond applying the official fix.