Executive Summary

This vulnerability exists in the Linux kernel's netconsole feature. The issue arises because the message (msg) passed to netconsole from the console subsystem is not guaranteed to be null-terminated. This can lead to out-of-bounds (OOB) reads when the kernel attempts to process the message as a string.

Previously, the message was placed in a static global buffer, which made it harder for the Kernel Address Sanitizer (KASAN) to detect OOB accesses. After a recent commit converting netconsole to the NBCON console infrastructure, KASAN can now detect these out-of-bounds reads more easily, revealing a bug where the kernel reads beyond the allocated buffer size.

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Impact Analysis

This vulnerability can cause the Linux kernel to perform out-of-bounds memory reads when handling netconsole messages. Such behavior can lead to system instability, crashes, or kernel bugs detected by KASAN.

While the description does not explicitly mention exploitation scenarios, out-of-bounds reads in kernel space can potentially be leveraged to leak sensitive information or cause denial of service, impacting system reliability and security.

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Detection Guidance

This vulnerability can be detected by monitoring kernel logs for KASAN (Kernel Address Sanitizer) slab-out-of-bounds errors related to netconsole. Specifically, look for messages indicating out-of-bounds reads in the netconsole subsystem, such as errors mentioning "BUG: KASAN: slab-out-of-bounds" and traces involving netconsole functions like netconsole_write or nbcon_kthread_func.

You can check the kernel log using commands like:

• dmesg | grep -i kasan
• journalctl -k | grep -i netconsole
• journalctl -k | grep -i kasan

These commands help identify if the kernel has reported any out-of-bounds memory access errors related to netconsole, which would indicate the presence of this vulnerability.

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Mitigation Strategies

To mitigate this vulnerability immediately, you should disable the netconsole kernel console if it is enabled, as the vulnerability involves out-of-bounds reads in the netconsole subsystem.

Additionally, update your Linux kernel to a version that includes the fix for this issue, specifically one that contains the commit 7eab73b18630 which converts netconsole to the NBCON console infrastructure and avoids out-of-bounds reads.

Disabling netconsole can typically be done by removing or commenting out any netconsole related kernel boot parameters or unloading the netconsole kernel module if it is loaded.

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