CVE-2026-90076 (GCVE-0-2026-90076)
Vulnerability from cvelistv5
Published
2026-09-17 16:05
Modified
2026-10-30 12:34
Severity ?
Summary
In 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.
References
Impacted products
Vendor Product Version
Linux Linux Version: afe4fd062416b158a8a8538b23adc1930a9b88dc
Version: afe4fd062416b158a8a8538b23adc1930a9b88dc
Version: afe4fd062416b158a8a8538b23adc1930a9b88dc
Version: afe4fd062416b158a8a8538b23adc1930a9b88dc
Version: afe4fd062416b158a8a8538b23adc1930a9b88dc
Version: afe4fd062416b158a8a8538b23adc1930a9b88dc
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      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-30T12:34:01.376Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/cf398f67d9caa71af3b9fb9319058b22fe6b524e"
        },
        {
          "url": "https://git.kernel.org/stable/c/fd63409b669f9951f1cc6b02486a5254103800d1"
        },
        {
          "url": "https://git.kernel.org/stable/c/d16dac3925be95ad46e986d4b139c9898b6e227f"
        },
        {
          "url": "https://git.kernel.org/stable/c/f6b3e3848a5fca63438984acd6d9eceac80814c1"
        },
        {
          "url": "https://git.kernel.org/stable/c/e35acd56f244d94355f9ab237c2ecc8fba5e6f04"
        },
        {
          "url": "https://git.kernel.org/stable/c/709f34f7c28dc4dd6c40343d101850f11e172312"
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      ],
      "title": "net/sched: fq: add overflow bounds to quantum and initial quantum",
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  "cveMetadata": {
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-90076",
    "datePublished": "2026-09-17T16:05:55.517Z",
    "dateReserved": "2026-09-11T19:38:34.785Z",
    "dateUpdated": "2026-10-30T12:34:01.376Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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