CVE-2025-39749
Estado: ModificadaAlta (7)—
In the Linux kernel, the following vulnerability has been resolved:
rcu: Protect ->defer_qs_iw_pending from data race
On kernels built with CONFIG_IRQ_WORK=y, when rcu_read_unlock() is invoked within an interrupts-disabled region of code [1], it will invoke rcu_read_unlock_special(), which uses an irq-work handler to force the system to notice when the RCU read-side critical section actually ends. That end won't happen until interrupts are enabled at the soonest.
In some kernels, such as those booted with rcutree.use_softirq=y, the irq-work handler is used unconditionally.
The per-CPU rcu_data structure's ->defer_qs_iw_pending field is updated by the irq-work handler and is both read and updated by rcu_read_unlock_special(). This resulted in the following KCSAN splat:
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------------------------------------------------------------------------
------------------------------------------------------------------------
The problem is that irq-work handlers run with interrupts enabled, which means that rcu_preempt_deferred_qs_handler() could be interrupted, and that interrupt handler might contain an RCU read-side critical section, which might invoke rcu_read_unlock_special(). In the strict KCSAN mode of operation used by RCU, this constitutes a data race on the ->defer_qs_iw_pending field.
This commit therefore disables interrupts across the portion of the rcu_preempt_deferred_qs_handler() that updates the ->defer_qs_iw_pending field. This suffices because this handler is not a fast path.
Detalles técnicos trazas, registros y código del informe original
BUG: KCSAN: data-race in rcu_preempt_deferred_qs_handler / rcu_read_unlock_special read to 0xffff96b95f42d8d8 of 1 bytes by task 90 on cpu 8: rcu_read_unlock_special+0x175/0x260 __rcu_read_unlock+0x92/0xa0 rt_spin_unlock+0x9b/0xc0 __local_bh_enable+0x10d/0x170 __local_bh_enable_ip+0xfb/0x150 rcu_do_batch+0x595/0xc40 rcu_cpu_kthread+0x4e9/0x830 smpboot_thread_fn+0x24d/0x3b0 kthread+0x3bd/0x410 ret_from_fork+0x35/0x40 ret_from_fork_asm+0x1a/0x30 write to 0xffff96b95f42d8d8 of 1 bytes by task 88 on cpu 8: rcu_preempt_deferred_qs_handler+0x1e/0x30 irq_work_single+0xaf/0x160 run_irq_workd+0x91/0xc0 smpboot_thread_fn+0x24d/0x3b0 kthread+0x3bd/0x410 ret_from_fork+0x35/0x40 ret_from_fork_asm+0x1a/0x30 no locks held by irq_work/8/88. irq event stamp: 200272 hardirqs last enabled at (200272): [<ffffffffb0f56121>] finish_task_switch+0x131/0x320 hardirqs last disabled at (200271): [<ffffffffb25c7859>] __schedule+0x129/0xd70 softirqs last enabled at (0): [<ffffffffb0ee093f>] copy_process+0x4df/0x1cc0 softirqs last disabled at (0): [<0000000000000000>] 0x0
CVSS
- Versión: 3.1
- Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
- Puntuación base: 7
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).
🎯 Técnicas ATT&CK
Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.
- Explotación
T1068Exploitation for Privilege Escalationprivilege escalation45 % - Impacto principal
T1499.004Application or System Exploitationimpact35 %
Vulnerabilidad local de race condition en kernel RCU sin interacción requerida (UI:N). Acceso local (AV:L) con privilegios limitados (PR:L). La raza de datos podría causar negación de servicio o corrupción de memoria, pero sin evidencia explícita de escalada o ejecución remota.
Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.
🛡️ Mitigaciones ATT&CK que cubren estas técnicas
Tecnologías afectadas (2)
CWE
- NVD-CWE-noinfo
Referencias
- https://git.kernel.org/stable/c/0ad84d62217488e679ecc90e8628980dcc003de3
- https://git.kernel.org/stable/c/55e11f6776798b27cf09a7aa0d718415d4fc9cf5
- https://git.kernel.org/stable/c/74f58f382a7c8333f8d09701aefaa25913bdbe0e
- https://git.kernel.org/stable/c/90c09d57caeca94e6f3f87c49e96a91edd40cbfd
- https://git.kernel.org/stable/c/90de9c94ea72327cfa9c2c9f6113c23a513af60b
- https://git.kernel.org/stable/c/b55947b725f190396f475d5d0c59aa855a4d8895
- https://git.kernel.org/stable/c/b5de8d80b5d049f051b95d9b1ee50ae4ab656124
- https://git.kernel.org/stable/c/e35e711c78c8a4c43330c0dcb1c4d507a19c20f4
- https://git.kernel.org/stable/c/f937759c7432d6151b73e1393b6517661813d506
- https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html
- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
- https://cert-portal.siemens.com/productcert/html/ssa-032379.html
JSON original (NVD)
Mostrar
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nrcu: Protect ->defer_qs_iw_pending from data race\n\nOn kernels built with CONFIG_IRQ_WORK=y, when rcu_read_unlock() is\ninvoked within an interrupts-disabled region of code [1], it will invoke\nrcu_read_unlock_special(), which uses an irq-work handler to force the\nsystem to notice when the RCU read-side critical section actually ends.\nThat end won't happen until interrupts are enabled at the soonest.\n\nIn some kernels, such as those booted with rcutree.use_softirq=y, the\nirq-work handler is used unconditionally.\n\nThe per-CPU rcu_data structure's ->defer_qs_iw_pending field is\nupdated by the irq-work handler and is both read and updated by\nrcu_read_unlock_special(). This resulted in the following KCSAN splat:\n\n------------------------------------------------------------------------\n\nBUG: KCSAN: data-race in rcu_preempt_deferred_qs_handler / rcu_read_unlock_special\n\nread to 0xffff96b95f42d8d8 of 1 bytes by task 90 on cpu 8:\n rcu_read_unlock_special+0x175/0x260\n __rcu_read_unlock+0x92/0xa0\n rt_spin_unlock+0x9b/0xc0\n __local_bh_enable+0x10d/0x170\n __local_bh_enable_ip+0xfb/0x150\n rcu_do_batch+0x595/0xc40\n rcu_cpu_kthread+0x4e9/0x830\n smpboot_thread_fn+0x24d/0x3b0\n kthread+0x3bd/0x410\n ret_from_fork+0x35/0x40\n ret_from_fork_asm+0x1a/0x30\n\nwrite to 0xffff96b95f42d8d8 of 1 bytes by task 88 on cpu 8:\n rcu_preempt_deferred_qs_handler+0x1e/0x30\n irq_work_single+0xaf/0x160\n run_irq_workd+0x91/0xc0\n smpboot_thread_fn+0x24d/0x3b0\n kthread+0x3bd/0x410\n ret_from_fork+0x35/0x40\n ret_from_fork_asm+0x1a/0x30\n\nno locks held by irq_work/8/88.\nirq event stamp: 200272\nhardirqs last enabled at (200272): [<ffffffffb0f56121>] finish_task_switch+0x131/0x320\nhardirqs last disabled at (200271): [<ffffffffb25c7859>] __schedule+0x129/0xd70\nsoftirqs last enabled at (0): [<ffffffffb0ee093f>] copy_process+0x4df/0x1cc0\nsoftirqs last disabled at (0): [<0000000000000000>] 0x0\n\n------------------------------------------------------------------------\n\nThe problem is that irq-work handlers run with interrupts enabled, which\nmeans that rcu_preempt_deferred_qs_handler() could be interrupted,\nand that interrupt handler might contain an RCU read-side critical\nsection, which might invoke rcu_read_unlock_special(). In the strict\nKCSAN mode of operation used by RCU, this constitutes a data race on\nthe ->defer_qs_iw_pending field.\n\nThis commit therefore disables interrupts across the portion of the\nrcu_preempt_deferred_qs_handler() that updates the ->defer_qs_iw_pending\nfield. This suffices because this handler is not a fast path."
}
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