CVE-2026-64248
Full vulnerability record from the local CVENow database.
Description
In the Linux kernel, the following vulnerability has been resolved: MIPS: smp: report dying CPU to RCU in stop_this_cpu() smp_send_stop() parks all secondary CPUs in stop_this_cpu(). The function marks the CPU offline for the scheduler via set_cpu_online(false) but never informs RCU, so RCU keeps expecting a quiescent state from CPUs that are now spinning forever with interrupts disabled. As long as nothing waits for an RCU grace period after smp_send_stop() this is harmless, which is why it went unnoticed. Since commit 91840be8f710 ("irq_work: Fix use-after-free in irq_work_single() on PREEMPT_RT") however, irq_work_sync() calls synchronize_rcu() on architectures without an irq_work self-IPI, i.e. where arch_irq_work_has_interrupt() returns false. That is the asm-generic default used by MIPS. Any irq_work_sync() issued in the reboot/shutdown path after smp_send_stop() then blocks on a grace period that can never complete, hanging the reboot: WARNING: CPU: 0 PID: 15 at kernel/irq_work.c:144 irq_work_queue_on ... rcu: INFO: rcu_sched detected stalls on CPUs/tasks: rcu: Offline CPU 1 blocking current GP. rcu: Offline CPU 2 blocking current GP. rcu: Offline CPU 3 blocking current GP. This issue was noticed on several Realtek MIPS switch SoCs (MIPS interAptiv) and came up during kernel bump downstream in OpenWrt from 6.18.33 to 6.18.34, after the backport of the patch to the 6.18 stable branch. The patch also has been backported all the way back to 6.1. Call rcutree_report_cpu_dead() once interrupts are disabled, mirroring the generic CPU-hotplug offline path, so RCU stops waiting on the parked CPUs and grace periods can still complete. MIPS shuts down all CPUs here without going through the CPU-hotplug mechanism, so this report is not otherwise issued. Reporting a dying CPU to RCU outside the regular hotplug offline path is not unprecedented: arm64 does the same in cpu_die_early(). There it is an exception for a CPU that was coming online and is aborting bringup, rather than the default shutdown action as on MIPS.
Severity
MEDIUM
CVSS score
5.5
(v3.1)
Vulnerability status
Analyzed
Source identifier
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Published
2026-07-24 16:16:54.280000
Last modified
2026-11-08 16:10:00.183000
View original CVE JSON
{
"id": "CVE-2026-64248",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"published": "2026-07-24T16:16:54.280",
"lastModified": "2026-11-08T16:10:00.183",
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{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nMIPS: smp: report dying CPU to RCU in stop_this_cpu()\n\nsmp_send_stop() parks all secondary CPUs in stop_this_cpu(). The function\nmarks the CPU offline for the scheduler via set_cpu_online(false) but\nnever informs RCU, so RCU keeps expecting a quiescent state from CPUs\nthat are now spinning forever with interrupts disabled.\n\nAs long as nothing waits for an RCU grace period after smp_send_stop()\nthis is harmless, which is why it went unnoticed. Since commit\n91840be8f710 (\"irq_work: Fix use-after-free in irq_work_single() on PREEMPT_RT\")\nhowever, irq_work_sync() calls synchronize_rcu() on architectures without\nan irq_work self-IPI, i.e. where arch_irq_work_has_interrupt() returns\nfalse. That is the asm-generic default used by MIPS. Any irq_work_sync()\nissued in the reboot/shutdown path after smp_send_stop() then blocks on\na grace period that can never complete, hanging the reboot:\n\n WARNING: CPU: 0 PID: 15 at kernel/irq_work.c:144 irq_work_queue_on\n ...\n rcu: INFO: rcu_sched detected stalls on CPUs/tasks:\n rcu: Offline CPU 1 blocking current GP.\n rcu: Offline CPU 2 blocking current GP.\n rcu: Offline CPU 3 blocking current GP.\n\nThis issue was noticed on several Realtek MIPS switch SoCs (MIPS\ninterAptiv) and came up during kernel bump downstream in OpenWrt from\n6.18.33 to 6.18.34, after the backport of the patch to the 6.18 stable\nbranch. The patch also has been backported all the way back to 6.1.\n\nCall rcutree_report_cpu_dead() once interrupts are disabled, mirroring the\ngeneric CPU-hotplug offline path, so RCU stops waiting on the parked CPUs\nand grace periods can still complete. MIPS shuts down all CPUs here\nwithout going through the CPU-hotplug mechanism, so this report is not\notherwise issued. Reporting a dying CPU to RCU outside the regular hotplug\noffline path is not unprecedented: arm64 does the same in cpu_die_early().\nThere it is an exception for a CPU that was coming online and is aborting\nbringup, rather than the default shutdown action as on MIPS."
},
{
"lang": "es",
"value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nMIPS: smp: informar CPU moribunda a RCU en stop_this_cpu()\n\nsmp_send_stop() estaciona todas las CPUs secundarias en stop_this_cpu(). La función marca la CPU como fuera de línea para el planificador a través de set_cpu_online(false) pero nunca informa a RCU, por lo que RCU sigue esperando un estado de reposo de las CPUs que ahora están girando indefinidamente con las interrupciones deshabilitadas.\n\nMientras nada espere un período de gracia de RCU después de smp_send_stop(), esto es inofensivo, razón por la cual pasó desapercibido. Sin embargo, desde el commit 91840be8f710 (’irq_work: Fix use-after-free in irq_work_single() on PREEMPT_RT’), irq_work_sync() llama a synchronize_rcu() en arquitecturas sin un auto-IPI de irq_work, es decir, donde arch_irq_work_has_interrupt() devuelve falso. Ese es el valor predeterminado asm-generic utilizado por MIPS. Cualquier irq_work_sync() emitido en la ruta de reinicio/apagado después de smp_send_stop() se bloquea entonces en un período de gracia que nunca puede completarse, colgando el reinicio:\n\n ADVERTENCIA: CPU: 0 PID: 15 en kernel/irq_work.c:144 irq_work_queue_on\n ...\n rcu: INFO: rcu_sched detectó bloqueos en CPUs/tareas:\n rcu: CPU 1 fuera de línea bloqueando GP actual.\n rcu: CPU 2 fuera de línea bloqueando GP actual.\n rcu: CPU 3 fuera de línea bloqueando GP actual.\n\nEste problema fue notado en varios SoCs de switch MIPS de Realtek (MIPS interAptiv) y surgió durante la actualización del kernel en OpenWrt de 6.18.33 a 6.18.34, después del backport del parche a la rama estable 6.18. El parche también ha sido backporteado hasta la versión 6.1.\n\nLlamar a rcutree_report_cpu_dead() una vez que las interrupciones estén deshabilitadas, reflejando la ruta genérica de desconexión de CPU-hotplug, para que RCU deje de esperar en las CPUs estacionadas y los períodos de gracia aún puedan completarse. MIPS apaga todas las CPUs aquí sin pasar por el mecanismo de CPU-hotplug, por lo que este informe no se emite de otra manera. Informar una CPU moribunda a RCU fuera de la ruta regular de desconexión de hotplug no tiene precedentes: arm64 hace lo mismo en cpu_die_early(). Allí es una excepción para una CPU que estaba entrando en línea y está abortando el inicio, en lugar de la acción de apagado predeterminada como en MIPS."
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