CVE-2026-90072

/// Technical description

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

net/sched: sfq: clamp quantum to avoid signed overflow soft lockup

sfq_init() sets q->quantum = psched_mtu(qdisc_dev(sch)) (unsigned). A

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

2147483634) makes psched_mtu() return 0x80000000, so slot->allot = INT_MIN

and INT_MIN + INT_MIN toggles between INT_MIN and 0 forever, spinning

sfq_dequeue() under the qdisc lock.

Clamp the quantum to [256, 1 << 20] so the refill loop terminates. The

lower bound also covers q->quantum == 0 (psched_mtu() returning 0),

which spins sfq_dequeue() identically. sfq_change() already rejects a

negative quantum, so only the init path was exposed.

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