CVE-2025-21897 (GCVE-0-2025-21897)
Vulnerability from cvelistv5
Published
2025-04-01 15:26
Modified
2025-05-04 07:23
Severity ?
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.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/5324c459f90d16b0c43a78b494c598915d782b7a
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/8fef0a3b17bb258130a4fcbcb5addf94b25e9ec5
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/de60a31cb0bcacfaf9487546eac5e70e0a9c66d7
Impacted products
Vendor Product Version
Linux Linux Version: a6250aa251eacaf3ebfcfe152a96a727fd483ecd
Version: a6250aa251eacaf3ebfcfe152a96a727fd483ecd
Version: a6250aa251eacaf3ebfcfe152a96a727fd483ecd
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   Linux Linux Version: 6.12
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{
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          "programFiles": [
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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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      "providerMetadata": {
        "dateUpdated": "2025-05-04T07:23:45.349Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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        {
          "url": "https://git.kernel.org/stable/c/8fef0a3b17bb258130a4fcbcb5addf94b25e9ec5"
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      ],
      "title": "sched_ext: Fix pick_task_scx() picking non-queued tasks when it\u0027s called without balance()",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2025-21897",
    "datePublished": "2025-04-01T15:26:49.705Z",
    "dateReserved": "2024-12-29T08:45:45.783Z",
    "dateUpdated": "2025-05-04T07:23:45.349Z",
    "state": "PUBLISHED"
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    "nvd": "{\"cve\":{\"id\":\"CVE-2025-21897\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2025-04-01T16:15:20.083\",\"lastModified\":\"2025-04-01T20:26:01.990\",\"vulnStatus\":\"Awaiting Analysis\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"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.\"}],\"metrics\":{},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/5324c459f90d16b0c43a78b494c598915d782b7a\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/8fef0a3b17bb258130a4fcbcb5addf94b25e9ec5\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/de60a31cb0bcacfaf9487546eac5e70e0a9c66d7\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}"
  }
}


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