FKIE_CVE-2026-90075

Vulnerability from fkie_nvd - Published: 2026-09-17 17:16 - Updated: 2026-09-17 17:16
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
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/324f86806673ae4a55f66d28db84577f46f615e1
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/3782067ec0d485628b6f1f9ede3eeeb4f611fcf2
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/397e2b1f71d9f15b8b4e47d24eb620e4dff8878d
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/9f499e5827fdb6d7fdb46a7ce731852f6b1a1bb9
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/a9a5b2943a00df2ab81a2209f31dd9e87016f120
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/d315ee8a07fd1810880227319cf60e6cd925ef22
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/d9ebd8f9aa8b2773235889cb903fafd61f2d8585
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/dfb4b61db886917244284b18b44b23d2254b82c2
Impacted products
Vendor Product Version
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{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/sched/sch_fq_codel.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "d315ee8a07fd1810880227319cf60e6cd925ef22",
              "status": "affected",
              "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
              "versionType": "git"
            },
            {
              "lessThan": "a9a5b2943a00df2ab81a2209f31dd9e87016f120",
              "status": "affected",
              "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
              "versionType": "git"
            },
            {
              "lessThan": "3782067ec0d485628b6f1f9ede3eeeb4f611fcf2",
              "status": "affected",
              "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
              "versionType": "git"
            },
            {
              "lessThan": "397e2b1f71d9f15b8b4e47d24eb620e4dff8878d",
              "status": "affected",
              "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
              "versionType": "git"
            },
            {
              "lessThan": "324f86806673ae4a55f66d28db84577f46f615e1",
              "status": "affected",
              "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
              "versionType": "git"
            },
            {
              "lessThan": "dfb4b61db886917244284b18b44b23d2254b82c2",
              "status": "affected",
              "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
              "versionType": "git"
            },
            {
              "lessThan": "9f499e5827fdb6d7fdb46a7ce731852f6b1a1bb9",
              "status": "affected",
              "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
              "versionType": "git"
            },
            {
              "lessThan": "d9ebd8f9aa8b2773235889cb903fafd61f2d8585",
              "status": "affected",
              "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "net/sched/sch_fq_codel.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "3.5"
            },
            {
              "lessThan": "3.5",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.10.*",
              "status": "unaffected",
              "version": "5.10.270",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.221",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.188",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.157",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.110",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.52",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.6",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3-rc1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "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."
    }
  ],
  "id": "CVE-2026-90075",
  "lastModified": "2026-09-17T17:16:56.670",
  "metrics": {},
  "published": "2026-09-17T17:16:56.670",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/324f86806673ae4a55f66d28db84577f46f615e1"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/3782067ec0d485628b6f1f9ede3eeeb4f611fcf2"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/397e2b1f71d9f15b8b4e47d24eb620e4dff8878d"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/9f499e5827fdb6d7fdb46a7ce731852f6b1a1bb9"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/a9a5b2943a00df2ab81a2209f31dd9e87016f120"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/d315ee8a07fd1810880227319cf60e6cd925ef22"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/d9ebd8f9aa8b2773235889cb903fafd61f2d8585"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/dfb4b61db886917244284b18b44b23d2254b82c2"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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