CVE-2026-90050

Summary

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

net/sched: fq: clamp quantum and initial_quantum in change path

The fq change path accepts TCA_FQ_QUANTUM in [1, INT_MAX] and TCA_FQ_INITIAL_QUANTUM up to INT_MAX, while fq_init() already clamps to [1, 1<<20]. A user can override the init clamp via tc qdisc change, restoring the small-quantum deficit spin that the init clamp prevents.

Narrow iq_range.max to 1<<20 so TCA_FQ_INITIAL_QUANTUM is rejected at parse time. Clamp TCA_FQ_QUANTUM to [256, 1<<20] in fq_change() and fq_init() quantum to [256, 1<<20] for tiny-MTU devices.

Conditions to recreate the bug: CONFIG_NET_SCH_FQ=y. Requires CAP_NET_ADMIN (namespace-local via unshare -Urn suffices).

tc qdisc add dev dummy0 root fq tc qdisc change dev dummy0 root fq quantum 1 stab data 32768 size_log 15 cell_log 0

Affected Software

VendorProductVersion RangeStatus
LinuxLinuxd16dac3925be95ad46e986d4b139c9898b6e227f < a27498d34c3f429fb6db3aa609569f8154afa175affected
LinuxLinuxf6b3e3848a5fca63438984acd6d9eceac80814c1 < 798283cd0fe7ba997f67e5a917f14ab40afa8d9faffected
LinuxLinuxe35acd56f244d94355f9ab237c2ecc8fba5e6f04 < 72e9387884554f47b03bfd40fb8b2bf52789c68daffected
LinuxLinux709f34f7c28dc4dd6c40343d101850f11e172312 < 094cc07f98dfe70a34e2a1923af17fd29b8cf622affected
LinuxLinux7.3-rc1affected
LinuxLinux0 < 7.3-rc1unaffected
LinuxLinux7.3-rc3 <= *unaffected

Weaknesses

References