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CVE-2026-89521 (GCVE-0-2026-89521)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:44 – Updated: 2026-09-13 06:30
VLAI
Title
sched/core: Handle pick_task() releasing the rq lock
Summary
In the Linux kernel, the following vulnerability has been resolved: sched/core: Handle pick_task() releasing the rq lock Core scheduling's pick_next_task() breaks when a ->pick_task() implementation can release the rq lock. The selection state derived on entry is only valid while the lock is held continuously. Once a pick can drop the lock, an interleaving selection can invalidate all of it: the single-CPU fast path can commit an uncookied pick although the core went cookied during the release, and forceidle committed by the interleaving selection skews the restarted pass's accounting. Fix it by restarting the whole selection when a pick returns RETRY_TASK after releasing the lock: a single restart point above the state derivation replaces the per-loop restart labels, so a retry picks up state committed by interleaving selections and accounts and resets forceidle like a fresh selection would. need_sync and fi_before latch across retries. Clock validity can't be re-derived - there is no program-ordered way to tell whether the own and core rq clocks are still updated after the lock was released, as other lockers' pin cycles may or may not have invalidated them. When restarting, clear core_clock_updated so that the sibling loop re-updates the core rq, and update the own rq clock if invalidated.
Severity
7.3 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 4c95380701f58b8112f0b891de8d160e4199e19d , < 88ed5a66467ca2a5148b9997af9c71d8c43060ad (git)
Affected: 4c95380701f58b8112f0b891de8d160e4199e19d , < c10b216a072ff5c57bc880a05f87eb519aecc529 (git)
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Linux Linux Affected: 6.19
Unaffected: 0 , < 6.19 (semver)
Unaffected: 7.2.4 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)
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{
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          "product": "Linux",
          "programFiles": [
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsched/core: Handle pick_task() releasing the rq lock\n\nCore scheduling\u0027s pick_next_task() breaks when a -\u003epick_task()\nimplementation can release the rq lock. The selection state derived on entry\nis only valid while the lock is held continuously. Once a pick can drop the\nlock, an interleaving selection can invalidate all of it: the single-CPU\nfast path can commit an uncookied pick although the core went cookied during\nthe release, and forceidle committed by the interleaving selection skews the\nrestarted pass\u0027s accounting.\n\nFix it by restarting the whole selection when a pick returns RETRY_TASK\nafter releasing the lock: a single restart point above the state derivation\nreplaces the per-loop restart labels, so a retry picks up state committed by\ninterleaving selections and accounts and resets forceidle like a fresh\nselection would.\n\nneed_sync and fi_before latch across retries. Clock validity can\u0027t be\nre-derived - there is no program-ordered way to tell whether the own and\ncore rq clocks are still updated after the lock was released, as other\nlockers\u0027 pin cycles may or may not have invalidated them. When restarting,\nclear core_clock_updated so that the sibling loop re-updates the core rq,\nand update the own rq clock if invalidated."
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            "baseSeverity": "HIGH",
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            "version": "3.1"
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              "value": "AV:L - The flaw is in pick_next_task() in kernel/sched/core.c, reached only from the local __schedule() hotpath. An attacker triggers it with prctl(PR_SCHED_CORE) and their own threads; it is not reachable from network packet processing, ksmbd/nfsd, or other remote handlers.\nAC:L - The attacker controls both sides of the race: they create cookied and uncookied tasks, pin them on both SMT siblings, and generate concurrent scheduling so pick_task_scx() drops the rq lock during core-wide selection. Success does not depend on an uncontrollable victim state or memory layout.\nPR:L - prctl(PR_SCHED_CORE) is available to an unprivileged process (only ptrace_may_access on its own tasks). The lock-dropping pick_task() is sched_ext, which an attacker can load with CAP_BPF/CAP_PERFMON via a user namespace or BPF token, or which may already be loaded on the host.\nUI:N - The attacker enables core scheduling, runs their own threads on SMT siblings, and drives context switches themselves. No victim action such as mounting a filesystem or opening a file is required.\nS:U - Impact is confined to the host kernel scheduler (SMT cookie selection and forceidle/vruntime accounting). This is a same-host isolation failure, not a VM/guest-to-host escape or IOMMU/DMA boundary bypass.\nC:H - After pick_task() drops the rq lock, the single-CPU fast path can commit an uncookied pick while an interleaving selection made the core cookied, so SMT siblings run mismatched cookies and bypass core scheduling\u0027s L1TF/MDS isolation, enabling cross-domain memory disclosure via SMT side channels.\nI:L - The misplaced RETRY_TASK restart skips forceidle reset and can apply invalidated rq clocks to vruntime and forceidle accounting, which is limited corruption of scheduler metadata rather than an arbitrary kernel write or control-flow hijack.\nA:H - Invalidated rq clocks and skewed forceidle accounting after a lock-dropping pick can apply a huge bogus vruntime delta or incorrectly force-idle SMT siblings, stranding runnable tasks in a hang-class scheduling DoS on the core."
            }
          ]
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      "providerMetadata": {
        "dateUpdated": "2026-09-13T06:30:19.786Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/88ed5a66467ca2a5148b9997af9c71d8c43060ad"
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          "url": "https://git.kernel.org/stable/c/c10b216a072ff5c57bc880a05f87eb519aecc529"
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89521",
    "datePublished": "2026-09-11T19:44:03.257Z",
    "dateReserved": "2026-09-11T19:38:34.718Z",
    "dateUpdated": "2026-09-13T06:30:19.786Z",
    "state": "PUBLISHED"
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    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-09-13T06:56:52+00:00",
      "cve": "CVE-2026-89521",
      "id": "CVE-2026-89521",
      "initial_release_date": "2026-09-11T19:44:03.257000+00:00",
      "product_status:known_affected": "2",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: Linux kernel: Denial of Service due to inconsistent core scheduling state",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89521.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-09-13T16:59:06Z",
      "cve": "CVE-2026-89521",
      "id": "CVE-2026-89521",
      "initial_release_date": "2026-09-12T16:26:57Z",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-89521",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-89521.json",
      "version": "3"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.