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CVE-2026-52980

Estado: AnalizadaMedia (5.5)—

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:

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

After yield_task_fair() executed:

the vruntime jumped to:

and the deadline was later advanced further to:

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.

Leer descripción completaMostrar menos

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.

Detalles técnicos trazas, registros y código del informe original
  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.

  9834017729983308

  se->vruntime = se->deadline

  19668035460670230

  19668035463470230

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

Tecnologías afectadas (1)

Linux — Linux Kernel

CWE

Referencias

JSON original (NVD)

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          "attackVector": "LOCAL",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
          "integrityImpact": "NONE",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
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      "value": "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->rel_deadline unexpectedly set.\n\nThe failing sequence is:\n\n  1. A task is forked while se->rel_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->rel_deadline is set, place_entity() treats se->deadline\n     as a relative deadline and converts it to an absolute deadline by\n     adding the current vruntime.\n  5. However, the forked entity's 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->vruntime to se->deadline.\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->sum_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's\nvruntime was around:\n\n  9834017729983308\n\nAfter yield_task_fair() executed:\n\n  se->vruntime = se->deadline\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->deadline 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->rel_deadline in __sched_fork(), together with the other\nsched_entity runtime state, so that the first enqueue does not interpret\nthe new entity's deadline as a stale relative deadline."
    }
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  "lastModified": "2026-07-14T16:51:26.420",
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