PT-2026-64363 · Linux · Linux
CVE-2026-64248
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Published
2026-07-24
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Updated
2026-07-24
None
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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.
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Related Identifiers
Affected Products
Linux