GHSA-748M-JM5V-3475

Vulnerability from github – Published: 2026-06-24 18:32 – Updated: 2026-06-24 18:32
VLAI
Details

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

sched/fair: Clear rel_deadline when initializing forked entities

A yield-triggered crash can happen when a newly forked sched_entity enters the fair class with se->rel_deadline unexpectedly set.

The failing sequence is:

  1. A task is forked while se->rel_deadline is still set.
  2. __sched_fork() initializes vruntime, vlag and other sched_entity state, but does not clear rel_deadline.
  3. On the first enqueue, enqueue_entity() calls place_entity().
  4. Because se->rel_deadline is set, place_entity() treats se->deadline as a relative deadline and converts it to an absolute deadline by adding the current vruntime.
  5. However, the forked entity's deadline is not a valid inherited relative deadline for this new scheduling instance, so the conversion produces an abnormally large deadline.
  6. If the task later calls sched_yield(), yield_task_fair() advances se->vruntime to se->deadline.
  7. The inflated vruntime is then used by the following enqueue path, where the vruntime-derived key can overflow when multiplied by the entity weight.
  8. This corrupts cfs_rq->sum_w_vruntime, breaks EEVDF eligibility calculation, and can eventually make all entities appear ineligible. pick_next_entity() may then return NULL unexpectedly, leading to a later NULL dereference.

A captured trace shows the effect clearly. Before yield, the entity's vruntime was around:

9834017729983308

After yield_task_fair() executed:

se->vruntime = se->deadline

the vruntime jumped to:

19668035460670230

and the deadline was later advanced further to:

19668035463470230

This shows that the deadline had already become abnormally large before yield_task_fair() copied it into vruntime.

rel_deadline is only meaningful when se->deadline really carries a relative deadline that still needs to be placed against vruntime. A freshly forked sched_entity should not inherit or retain this state. Clear se->rel_deadline in __sched_fork(), together with the other sched_entity runtime state, so that the first enqueue does not interpret the new entity's deadline as a stale relative deadline.

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{
  "affected": [],
  "aliases": [
    "CVE-2026-52980"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-06-24T17:17:08Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nsched/fair: Clear rel_deadline when initializing forked entities\n\nA yield-triggered crash can happen when a newly forked sched_entity\nenters the fair class with se-\u003erel_deadline unexpectedly set.\n\nThe failing sequence is:\n\n  1. A task is forked while se-\u003erel_deadline is still set.\n  2. __sched_fork() initializes vruntime, vlag and other sched_entity\n     state, but does not clear rel_deadline.\n  3. On the first enqueue, enqueue_entity() calls place_entity().\n  4. Because se-\u003erel_deadline is set, place_entity() treats se-\u003edeadline\n     as a relative deadline and converts it to an absolute deadline by\n     adding the current vruntime.\n  5. However, the forked entity\u0027s deadline is not a valid inherited\n     relative deadline for this new scheduling instance, so the conversion\n     produces an abnormally large deadline.\n  6. If the task later calls sched_yield(), yield_task_fair() advances\n     se-\u003evruntime to se-\u003edeadline.\n  7. The inflated vruntime is then used by the following enqueue path,\n     where the vruntime-derived key can overflow when multiplied by the\n     entity weight.\n  8. This corrupts cfs_rq-\u003esum_w_vruntime, breaks EEVDF eligibility\n     calculation, and can eventually make all entities appear ineligible.\n     pick_next_entity() may then return NULL unexpectedly, leading to a\n     later NULL dereference.\n\nA captured trace shows the effect clearly. Before yield, the entity\u0027s\nvruntime was around:\n\n  9834017729983308\n\nAfter yield_task_fair() executed:\n\n  se-\u003evruntime = se-\u003edeadline\n\nthe vruntime jumped to:\n\n  19668035460670230\n\nand the deadline was later advanced further to:\n\n  19668035463470230\n\nThis shows that the deadline had already become abnormally large before\nyield_task_fair() copied it into vruntime.\n\nrel_deadline is only meaningful when se-\u003edeadline really carries a\nrelative deadline that still needs to be placed against vruntime. A\nfreshly forked sched_entity should not inherit or retain this state.\nClear se-\u003erel_deadline in __sched_fork(), together with the other\nsched_entity runtime state, so that the first enqueue does not interpret\nthe new entity\u0027s deadline as a stale relative deadline.",
  "id": "GHSA-748m-jm5v-3475",
  "modified": "2026-06-24T18:32:42Z",
  "published": "2026-06-24T18:32:42Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-52980"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/3da56dc063cd77b9c0b40add930767fab4e389f3"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/8f4a16200785f49cf02c5b71bdfe7a9dab63f23a"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/c71bf35caba12bfd9bc23e32b0bcd9e02d1cf1ac"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f3c16e1f4a314a20717ab90a41885f8111a242ab"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}


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