ghsa-32g6-m5fv-fhv6
Vulnerability from github
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.
{
"affected": [],
"aliases": [
"CVE-2025-21897"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-04-01T16:15:20Z",
"severity": null
},
"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": "2025-04-01T18:30:50Z",
"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": []
}
Sightings
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