CVE-2026-90073net/sched: hhf: clamp quantum before hhf_change() to avoid overflow

Official description

In the Linux kernel, the following vulnerability has been resolved: net/sched: hhf: clamp quantum before hhf_change() to avoid overflow hhf_init() sets q->quantum = psched_mtu(qdisc_dev(sch)) with no overflow check. A device with a huge MTU (e.g. dummy with max_mtu == 0 accepting MTU 2147483634) makes weight * quantum overflow the signed deficit in hhf_dequeue(), spinning forever. Clamp q->quantum before hhf_change() so both the opt and !opt paths see a sane quantum. Without this, bare "tc qdisc add ... hhf" succeeds with a clamped quantum but "tc qdisc add ... hhf limit 1000" (any option present) fails with -EINVAL because hhf_change() re-validates the unclamped default (sch_hhf.c:559). 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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/2e0f0729f922c8de13801004e2131b57646c7c5f
• https://git.kernel.org/stable/c/0c66223e90ddb4fd3700965a9241f2fde7bd6bc7
• https://git.kernel.org/stable/c/20b65bf7ca06e48ec1d62ed8012f71205328dbe4
• https://git.kernel.org/stable/c/dea2789a9d5ff38bdd77f2e64d550430899e2839
• https://git.kernel.org/stable/c/fa9c2055f0a60f801ccf286af53d387dc6202c3f
• https://git.kernel.org/stable/c/99770b5d8e0e1c69b996f74a19d71afd2c4a9aa4
• https://git.kernel.org/stable/c/2446644b0f6d045b01db6acbaf55552dbec8a59a
• https://git.kernel.org/stable/c/2164b512b97bb053e8ce4d6e95576f11bed6a005