GHSA-6J38-2PG6-M9MV
Vulnerability from github – Published: 2026-09-17 18:31 – Updated: 2026-10-30 15:33In the Linux kernel, the following vulnerability has been resolved:
net/sched: fq: add overflow bounds to quantum and initial quantum
fq_init() computes quantum = 2 * psched_mtu() and initial_quantum = 10 * psched_mtu() with no overflow check. A device with a huge MTU (e.g. dummy with max_mtu == 0 accepting MTU 2147483634) makes psched_mtu() return 0x80000000; the 2 * and 10 * multiplications wrap to 0 in 32-bit arithmetic, so q->quantum == 0. Then in fq_dequeue() the credit-refill loop adds 0 to f->credit (which stays <= 0) and goto begin loops forever under the qdisc lock, creating a soft lockup.
Clamp psched_mtu() to [1, 1 << 20] before multiplying so the product cannot wrap, then cap the result at 1 << 20, matching the bound already enforced on TCA_FQ_QUANTUM in fq_change().
Conditions to recreate the bug: a device whose MTU (plus hard_header_len) is large enough that 2 * psched_mtu() wraps (e.g. a dummy device with max_mtu == 0 accepting MTU 2147483634). Requires CAP_NET_ADMIN in a user namespace.
{
"affected": [],
"aliases": [
"CVE-2026-90076"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-17T17:16:56Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: fq: add overflow bounds to quantum and initial quantum\n\nfq_init() computes quantum = 2 * psched_mtu() and initial_quantum = 10 *\npsched_mtu() with no overflow check. A device with a huge MTU (e.g. dummy\nwith max_mtu == 0 accepting MTU 2147483634) makes psched_mtu() return\n0x80000000; the 2 * and 10 * multiplications wrap to 0 in 32-bit\narithmetic, so q-\u003equantum == 0. Then in fq_dequeue() the credit-refill\nloop adds 0 to f-\u003ecredit (which stays \u003c= 0) and goto begin loops\nforever under the qdisc lock, creating a soft lockup.\n\nClamp psched_mtu() to [1, 1 \u003c\u003c 20] before multiplying so the product\ncannot wrap, then cap the result at 1 \u003c\u003c 20, matching the bound already\nenforced on TCA_FQ_QUANTUM in fq_change().\n\nConditions to recreate the bug: a device whose MTU (plus\nhard_header_len) is large enough that 2 * psched_mtu() wraps (e.g. a\ndummy device with max_mtu == 0 accepting MTU 2147483634). Requires\nCAP_NET_ADMIN in a user namespace.",
"id": "GHSA-6j38-2pg6-m9mv",
"modified": "2026-10-30T15:33:30Z",
"published": "2026-09-17T18:31:49Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-90076"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/709f34f7c28dc4dd6c40343d101850f11e172312"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/cf398f67d9caa71af3b9fb9319058b22fe6b524e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/d16dac3925be95ad46e986d4b139c9898b6e227f"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e35acd56f244d94355f9ab237c2ecc8fba5e6f04"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f6b3e3848a5fca63438984acd6d9eceac80814c1"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/fd63409b669f9951f1cc6b02486a5254103800d1"
}
],
"schema_version": "1.4.0",
"severity": []
}
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