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net/sched: fq_codel: clamp default quantum and mtu

Type: advisorySource: Official CVE List1 source record

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.

Announced Source revision 1
Original source ↗

CVE-2026-90075

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: cve:CVE-2026-90075

Linux

Source reference: /containers/cna/affected/0/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
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Linux

Source reference: /containers/cna/affected/1/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
        "lessThan": "d315ee8a07fd1810880227319cf60e6cd925ef22",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
        "lessThan": "a9a5b2943a00df2ab81a2209f31dd9e87016f120",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
        "lessThan": "3782067ec0d485628b6f1f9ede3eeeb4f611fcf2",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
        "lessThan": "397e2b1f71d9f15b8b4e47d24eb620e4dff8878d",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
        "lessThan": "324f86806673ae4a55f66d28db84577f46f615e1",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
        "lessThan": "dfb4b61db886917244284b18b44b23d2254b82c2",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
        "lessThan": "9f499e5827fdb6d7fdb46a7ce731852f6b1a1bb9",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
        "lessThan": "d9ebd8f9aa8b2773235889cb903fafd61f2d8585",
        "versionType": "git"
      }
    ],
    "programFiles": [
      "net/sched/sch_fq_codel.c"
    ],
    "defaultStatus": "unaffected"
  },
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "3.5"
      },
      {
        "status": "unaffected",
        "version": "0",
        "lessThan": "3.5",
        "versionType": "semver"
      },
      {
        "status": "unaffected",
        "version": "5.10.270",
        "versionType": "semver",
        "lessThanOrEqual": "5.10.*"
      },
      {
        "status": "unaffected",
        "version": "5.15.221",
        "versionType": "semver",
        "lessThanOrEqual": "5.15.*"
      },
      {
        "status": "unaffected",
        "version": "6.1.188",
        "versionType": "semver",
        "lessThanOrEqual": "6.1.*"
      },
      {
        "status": "unaffected",
        "version": "6.6.157",
        "versionType": "semver",
        "lessThanOrEqual": "6.6.*"
      },
      {
        "status": "unaffected",
        "version": "6.12.110",
        "versionType": "semver",
        "lessThanOrEqual": "6.12.*"
      },
      {
        "status": "unaffected",
        "version": "6.18.52",
        "versionType": "semver",
        "lessThanOrEqual": "6.18.*"
      },
      {
        "status": "unaffected",
        "version": "7.2.6",
        "versionType": "semver",
        "lessThanOrEqual": "7.2.*"
      },
      {
        "status": "unaffected",
        "version": "7.3",
        "versionType": "original_commit_for_fix",
        "lessThanOrEqual": "*"
      }
    ],
    "programFiles": [
      "net/sched/sch_fq_codel.c"
    ],
    "defaultStatus": "affected"
  }
]
Related CVEs
CVE-2026-90075

Source reference: /cveMetadata/cveId

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Event
#36494 · Revision 1
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