CVE-2026-31733
Estado: AnalizadaMedia (5.5)—
In the Linux kernel, the following vulnerability has been resolved:
sched_ext: Fix stale direct dispatch state in ddsp_dsq_id
@p->scx.ddsp_dsq_id can be left set (non-SCX_DSQ_INVALID) triggering a spurious warning in mark_direct_dispatch() when the next wakeup's ops.select_cpu() calls scx_bpf_dsq_insert(), such as:
The root cause is that ddsp_dsq_id was only cleared in dispatch_enqueue(), which is not reached in all paths that consume or cancel a direct dispatch verdict.
Fix it by clearing it at the right places:
Detalles técnicos trazas, registros y código del informe original
WARNING: kernel/sched/ext.c:1273 at scx_dsq_insert_commit+0xcd/0x140 - direct_dispatch(): cache the direct dispatch state in local variables and clear it before dispatch_enqueue() on the synchronous path. For the deferred path, the direct dispatch state must remain set until process_ddsp_deferred_locals() consumes them. - process_ddsp_deferred_locals(): cache the dispatch state in local variables and clear it before calling dispatch_to_local_dsq(), which may migrate the task to another rq. - do_enqueue_task(): clear the dispatch state on the enqueue path (local/global/bypass fallbacks), where the direct dispatch verdict is ignored. - dequeue_task_scx(): clear the dispatch state after dispatch_dequeue() to handle both the deferred dispatch cancellation and the holding_cpu race, covering all cases where a pending direct dispatch is cancelled. - scx_disable_task(): clear the direct dispatch state when transitioning a task out of the current scheduler. Waking tasks may have had the direct dispatch state set by the outgoing scheduler's ops.select_cpu() and then been queued on a wake_list via ttwu_queue_wakelist(), when SCX_OPS_ALLOW_QUEUED_WAKEUP is set. Such tasks are not on the runqueue and are not iterated by scx_bypass(), so their direct dispatch state won't be cleared. Without this clear, any subsequent SCX scheduler that tries to direct dispatch the task will trigger the WARN_ON_ONCE() in mark_direct_dispatch().
CVSS
- Versión: 3.1
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- Puntuación base: 5.5
Probabilidad de explotación (EPSS)
- Probabilidad de explotación en los próximos 30 días: 0.17%
- Percentil entre todas las CVEs puntuadas: 6
- Fecha de la puntuación: 5/10/2026
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)
CWE
- NVD-CWE-noinfo
Referencias
JSON original (NVD)
Mostrar
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsched_ext: Fix stale direct dispatch state in ddsp_dsq_id\n\n@p->scx.ddsp_dsq_id can be left set (non-SCX_DSQ_INVALID) triggering a\nspurious warning in mark_direct_dispatch() when the next wakeup's\nops.select_cpu() calls scx_bpf_dsq_insert(), such as:\n\n WARNING: kernel/sched/ext.c:1273 at scx_dsq_insert_commit+0xcd/0x140\n\nThe root cause is that ddsp_dsq_id was only cleared in dispatch_enqueue(),\nwhich is not reached in all paths that consume or cancel a direct dispatch\nverdict.\n\nFix it by clearing it at the right places:\n\n - direct_dispatch(): cache the direct dispatch state in local variables\n and clear it before dispatch_enqueue() on the synchronous path. For\n the deferred path, the direct dispatch state must remain set until\n process_ddsp_deferred_locals() consumes them.\n\n - process_ddsp_deferred_locals(): cache the dispatch state in local\n variables and clear it before calling dispatch_to_local_dsq(), which\n may migrate the task to another rq.\n\n - do_enqueue_task(): clear the dispatch state on the enqueue path\n (local/global/bypass fallbacks), where the direct dispatch verdict is\n ignored.\n\n - dequeue_task_scx(): clear the dispatch state after dispatch_dequeue()\n to handle both the deferred dispatch cancellation and the holding_cpu\n race, covering all cases where a pending direct dispatch is\n cancelled.\n\n - scx_disable_task(): clear the direct dispatch state when\n transitioning a task out of the current scheduler. Waking tasks may\n have had the direct dispatch state set by the outgoing scheduler's\n ops.select_cpu() and then been queued on a wake_list via\n ttwu_queue_wakelist(), when SCX_OPS_ALLOW_QUEUED_WAKEUP is set. Such\n tasks are not on the runqueue and are not iterated by scx_bypass(),\n so their direct dispatch state won't be cleared. Without this clear,\n any subsequent SCX scheduler that tries to direct dispatch the task\n will trigger the WARN_ON_ONCE() in mark_direct_dispatch()."
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