CVE-2026-90074

/// Technical description

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

net/sched: fq_pie: clamp default quantum to avoid signed overflow

fq_pie_init() sets q->quantum = psched_mtu(qdisc_dev(sch)) without

clamping. A device with a huge MTU (e.g. dummy with max_mtu == 0

accepting MTU 2147483634) makes psched_mtu() return 0x80000000, which

overflows the signed flow->deficit to INT_MIN in fq_pie_qdisc_dequeue(),

causing an infinite loop and soft lockup. Emulate fq_pie_policy which

is already bounded to [1, 1 << 20]; clamp the default to [256, 1 << 20].

256 matches fq_codel's floor and is a sane minimum for a DRR quantum.

Conditions to recreate the bug: a device whose MTU (plus

hard_header_len) wraps psched_mtu() into the sign bit (e.g. a dummy

device with max_mtu == 0 accepting MTU 2147483634). Requires

CAP_NET_ADMIN in a user namespace.

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References