Padata CPU Dead Callback Failure in Linux Kernel

Executive Summary

This vulnerability in the Linux kernel involves the handling of CPU offline callbacks within the padata subsystem. Specifically, a CPU offline callback was placed in a section where failure was not allowed, causing errors during CPU hotplug operations. The fix involved moving the CPU offline callback to a section where failure is permitted, preventing the kernel from encountering a DEAD callback error when taking a CPU offline.

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Detection Guidance

This vulnerability relates to a CPU offline callback issue in the Linux kernel, which can cause a DEAD callback error and kernel warnings related to CPU hotplug states.

Detection would involve monitoring kernel logs for specific warning messages such as:

• DEAD callback error for CPU1
• WARNING: kernel/cpu.c:1463 at _cpu_down+0x759/0x1020

You can use commands like `dmesg | grep -i 'DEAD callback error'` or `journalctl -k | grep -i 'cpu.c:1463'` to search for these warnings in kernel logs.

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Impact Analysis

This vulnerability can cause kernel errors or warnings related to CPU hotplug operations, such as the DEAD callback error. This may lead to instability or unexpected behavior when CPUs are taken offline, potentially affecting system reliability and uptime.

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Mitigation Strategies

The vulnerability has been resolved by moving the CPU offline callback to the ONLINE section where failure is allowed.

Immediate mitigation steps include updating your Linux kernel to a version that contains the fix (commit 4ae12d8bd9a8 or later).

Until the update is applied, monitor for the described kernel warnings and avoid CPU hotplug operations that may trigger the issue.

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