CVE-2026-90075 (GCVE-0-2026-90075)
Vulnerability from cvelistv5
Published
2026-09-17 16:05
Modified
2026-10-19 08:57
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: net/sched: fq_codel: clamp default quantum and mtu fq_codel_init() sets q->quantum = psched_mtu(qdisc_dev(sch)) without clamping. A device with a huge MTU (e.g. dummy with max_mtu == 0 accepting MTU 2147483634) makes psched_mtu() return 0x80000000, which overflows the signed flow->deficit to INT_MIN in fq_codel_dequeue(), causing an infinite loop and soft lockup. Emulate fq_codel_change() and constrain to [256, FQ_CODEL_QUANTUM_MAX]. The same unclamped psched_mtu() is assigned to q->cparams.mtu a bit below, and fq_codel_change() never updates it. codel_should_drop() tests "*backlog <= params->mtu"; with mtu == 0x80000000 (~2 GiB) and the default 32 MiB memory_limit, the test is always true, so CoDel is silently and completely disabled (no drops, no ECN). Declare a single clamped mtu and assign both q->quantum and q->cparams.mtu from it, which also removes the double psched_mtu() call. 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.
References
Impacted products
Vendor Product Version
Linux Linux Version: 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe
Version: 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe
Version: 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe
Version: 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe
Version: 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe
Version: 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe
Version: 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe
Version: 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe
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{
  "containers": {
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        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/sched/sch_fq_codel.c"
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          "versions": [
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              "version": "0",
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              "version": "5.10.270",
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              "version": "5.15.221",
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              "version": "7.2.6",
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              "version": "7.3",
              "versionType": "original_commit_for_fix"
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      ],
      "cpeApplicability": [
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          "nodes": [
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              "operator": "OR"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: fq_codel: clamp default quantum and mtu\n\nfq_codel_init() sets q-\u003equantum = psched_mtu(qdisc_dev(sch)) without\nclamping. A device with a huge MTU (e.g. dummy with max_mtu == 0\naccepting MTU 2147483634) makes psched_mtu() return 0x80000000, which\noverflows the signed flow-\u003edeficit to INT_MIN in fq_codel_dequeue(),\ncausing an infinite loop and soft lockup. Emulate fq_codel_change()\nand constrain to [256, FQ_CODEL_QUANTUM_MAX].\n\nThe same unclamped psched_mtu() is assigned to q-\u003ecparams.mtu a bit\nbelow, and fq_codel_change() never updates it. codel_should_drop()\ntests \"*backlog \u003c= params-\u003emtu\"; with mtu == 0x80000000 (~2 GiB) and\nthe default 32 MiB memory_limit, the test is always true, so CoDel is\nsilently and completely disabled (no drops, no ECN). Declare a single\nclamped mtu and assign both q-\u003equantum and q-\u003ecparams.mtu from it,\nwhich also removes the double psched_mtu() call.\n\nConditions to recreate the bug: a device whose MTU (plus\nhard_header_len) wraps psched_mtu() into the sign bit (e.g. a dummy\ndevice with max_mtu == 0 accepting MTU 2147483634). Requires\nCAP_NET_ADMIN in a user namespace."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T08:57:32.110Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/d315ee8a07fd1810880227319cf60e6cd925ef22"
        },
        {
          "url": "https://git.kernel.org/stable/c/a9a5b2943a00df2ab81a2209f31dd9e87016f120"
        },
        {
          "url": "https://git.kernel.org/stable/c/3782067ec0d485628b6f1f9ede3eeeb4f611fcf2"
        },
        {
          "url": "https://git.kernel.org/stable/c/397e2b1f71d9f15b8b4e47d24eb620e4dff8878d"
        },
        {
          "url": "https://git.kernel.org/stable/c/324f86806673ae4a55f66d28db84577f46f615e1"
        },
        {
          "url": "https://git.kernel.org/stable/c/dfb4b61db886917244284b18b44b23d2254b82c2"
        },
        {
          "url": "https://git.kernel.org/stable/c/9f499e5827fdb6d7fdb46a7ce731852f6b1a1bb9"
        },
        {
          "url": "https://git.kernel.org/stable/c/d9ebd8f9aa8b2773235889cb903fafd61f2d8585"
        }
      ],
      "title": "net/sched: fq_codel: clamp default quantum and mtu",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-90075",
    "datePublished": "2026-09-17T16:05:54.851Z",
    "dateReserved": "2026-09-11T19:38:34.785Z",
    "dateUpdated": "2026-10-19T08:57:32.110Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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