Vulnerability-Lookup

GHSA-32G6-M5FV-FHV6

Vulnerability from github – Published: 2025-04-01 18:30 – Updated: 2025-10-31 21:30

Details

In the Linux kernel, the following vulnerability has been resolved:

sched_ext: Fix pick_task_scx() picking non-queued tasks when it's called without balance()

a6250aa251ea ("sched_ext: Handle cases where pick_task_scx() is called without preceding balance_scx()") added a workaround to handle the cases where pick_task_scx() is called without prececing balance_scx() which is due to a fair class bug where pick_taks_fair() may return NULL after a true return from balance_fair().

The workaround detects when pick_task_scx() is called without preceding balance_scx() and emulates SCX_RQ_BAL_KEEP and triggers kicking to avoid stalling. Unfortunately, the workaround code was testing whether @prev was on SCX to decide whether to keep the task running. This is incorrect as the task may be on SCX but no longer runnable.

This could lead to a non-runnable task to be returned from pick_task_scx() which cause interesting confusions and failures. e.g. A common failure mode is the task ending up with (!on_rq && on_cpu) state which can cause potential wakers to busy loop, which can easily lead to deadlocks.

Fix it by testing whether @prev has SCX_TASK_QUEUED set. This makes @prev_on_scx only used in one place. Open code the usage and improve the comment while at it.

Severity

5.5 (Medium)


                  
                    CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

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{
  "affected": [],
  "aliases": [
    "CVE-2025-21897"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-667"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2025-04-01T16:15:20Z",
    "severity": "MODERATE"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nsched_ext: Fix pick_task_scx() picking non-queued tasks when it\u0027s called without balance()\n\na6250aa251ea (\"sched_ext: Handle cases where pick_task_scx() is called\nwithout preceding balance_scx()\") added a workaround to handle the cases\nwhere pick_task_scx() is called without prececing balance_scx() which is due\nto a fair class bug where pick_taks_fair() may return NULL after a true\nreturn from balance_fair().\n\nThe workaround detects when pick_task_scx() is called without preceding\nbalance_scx() and emulates SCX_RQ_BAL_KEEP and triggers kicking to avoid\nstalling. Unfortunately, the workaround code was testing whether @prev was\non SCX to decide whether to keep the task running. This is incorrect as the\ntask may be on SCX but no longer runnable.\n\nThis could lead to a non-runnable task to be returned from pick_task_scx()\nwhich cause interesting confusions and failures. e.g. A common failure mode\nis the task ending up with (!on_rq \u0026\u0026 on_cpu) state which can cause\npotential wakers to busy loop, which can easily lead to deadlocks.\n\nFix it by testing whether @prev has SCX_TASK_QUEUED set. This makes\n@prev_on_scx only used in one place. Open code the usage and improve the\ncomment while at it.",
  "id": "GHSA-32g6-m5fv-fhv6",
  "modified": "2025-10-31T21:30:53Z",
  "published": "2025-04-01T18:30:50Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-21897"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/5324c459f90d16b0c43a78b494c598915d782b7a"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/8fef0a3b17bb258130a4fcbcb5addf94b25e9ec5"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/de60a31cb0bcacfaf9487546eac5e70e0a9c66d7"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}

CVE-2025-21897 (GCVE-0-2025-21897)

Vulnerability from cvelistv5 – Published: 2025-04-01 15:26 – Updated: 2026-05-11 21:08

Title

sched_ext: Fix pick_task_scx() picking non-queued tasks when it's called without balance()

Summary

In the Linux kernel, the following vulnerability has been resolved: sched_ext: Fix pick_task_scx() picking non-queued tasks when it's called without balance() a6250aa251ea ("sched_ext: Handle cases where pick_task_scx() is called without preceding balance_scx()") added a workaround to handle the cases where pick_task_scx() is called without prececing balance_scx() which is due to a fair class bug where pick_taks_fair() may return NULL after a true return from balance_fair(). The workaround detects when pick_task_scx() is called without preceding balance_scx() and emulates SCX_RQ_BAL_KEEP and triggers kicking to avoid stalling. Unfortunately, the workaround code was testing whether @prev was on SCX to decide whether to keep the task running. This is incorrect as the task may be on SCX but no longer runnable. This could lead to a non-runnable task to be returned from pick_task_scx() which cause interesting confusions and failures. e.g. A common failure mode is the task ending up with (!on_rq && on_cpu) state which can cause potential wakers to busy loop, which can easily lead to deadlocks. Fix it by testing whether @prev has SCX_TASK_QUEUED set. This makes @prev_on_scx only used in one place. Open code the usage and improve the comment while at it.

Severity

No CVSS data available.

Assigner

Linux CNA under the mitre root

CNA scorecard D 53/100 over 6996 records in the last 180 days details

References

3 references

URL	Tags
https://git.kernel.org/stable/c/5324c459f90d16b0c…
https://git.kernel.org/stable/c/de60a31cb0bcacfaf…
https://git.kernel.org/stable/c/8fef0a3b17bb25813…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: a6250aa251eacaf3ebfcfe152a96a727fd483ecd , < 5324c459f90d16b0c43a78b494c598915d782b7a (git) Affected: a6250aa251eacaf3ebfcfe152a96a727fd483ecd , < de60a31cb0bcacfaf9487546eac5e70e0a9c66d7 (git) Affected: a6250aa251eacaf3ebfcfe152a96a727fd483ecd , < 8fef0a3b17bb258130a4fcbcb5addf94b25e9ec5 (git)
Linux	Linux	Affected: 6.12 Unaffected: 0 , < 6.12 (semver) Unaffected: 6.12.18 , ≤ 6.12.* (semver) Unaffected: 6.13.6 , ≤ 6.13.* (semver) Unaffected: 6.14 , ≤ * (original_commit_for_fix)

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JSON

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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "kernel/sched/ext.c"
          ],
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          "vendor": "Linux",
          "versions": [
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              "status": "affected",
              "version": "a6250aa251eacaf3ebfcfe152a96a727fd483ecd",
              "versionType": "git"
            },
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              "versionType": "git"
            },
            {
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              "versionType": "git"
            }
          ]
        },
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          "versions": [
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              "version": "6.12"
            },
            {
              "lessThan": "6.12",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.18",
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            },
            {
              "lessThanOrEqual": "6.13.*",
              "status": "unaffected",
              "version": "6.13.6",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "6.14",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
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          "nodes": [
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsched_ext: Fix pick_task_scx() picking non-queued tasks when it\u0027s called without balance()\n\na6250aa251ea (\"sched_ext: Handle cases where pick_task_scx() is called\nwithout preceding balance_scx()\") added a workaround to handle the cases\nwhere pick_task_scx() is called without prececing balance_scx() which is due\nto a fair class bug where pick_taks_fair() may return NULL after a true\nreturn from balance_fair().\n\nThe workaround detects when pick_task_scx() is called without preceding\nbalance_scx() and emulates SCX_RQ_BAL_KEEP and triggers kicking to avoid\nstalling. Unfortunately, the workaround code was testing whether @prev was\non SCX to decide whether to keep the task running. This is incorrect as the\ntask may be on SCX but no longer runnable.\n\nThis could lead to a non-runnable task to be returned from pick_task_scx()\nwhich cause interesting confusions and failures. e.g. A common failure mode\nis the task ending up with (!on_rq \u0026\u0026 on_cpu) state which can cause\npotential wakers to busy loop, which can easily lead to deadlocks.\n\nFix it by testing whether @prev has SCX_TASK_QUEUED set. This makes\n@prev_on_scx only used in one place. Open code the usage and improve the\ncomment while at it."
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    "dateReserved": "2024-12-29T08:45:45.783Z",
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}

Sightings

Author	Source	Type	Date	Other

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.

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