Impact Analysis

This vulnerability can lead to leaking of internal kernel memory pointers (percpu counter pointers) to userspace. Such information leaks can potentially be used by attackers to gain insights into kernel memory layout, which may aid in further exploitation such as privilege escalation or bypassing security mechanisms. Although the vulnerability does not directly allow code execution or data modification, leaking kernel pointers can weaken system security by providing attackers with sensitive information about kernel internals.

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Mitigation Strategies

The vulnerability has been resolved in the Linux kernel by changing the way the netfilter x_tables get-entries paths copy rule entries to userspace, preventing leaking of percpu counter pointers.

To mitigate this vulnerability immediately, you should update your Linux kernel to a version that includes this fix.

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Executive Summary

This vulnerability exists in the Linux kernel's netfilter x_tables component. It involves the way rule entries and their counters are copied from kernel space to userspace. Specifically, on SMP (Symmetric Multi-Processing) kernels, a pointer to a per-CPU counter allocation (percpu pointer) can be leaked to userspace if a userspace buffer faults during the copying process. This happens because the kernel copies the fixed rule entry header, including the percpu pointer, before overwriting the counter fields with sanitized data. If a fault occurs after the pointer is copied but before the sanitized counters are copied, the raw percpu pointer remains exposed in userspace. The fix involves changing the copy order to ensure only the fixed entry prefix is copied before counters, and then the sanitized counter snapshot is copied, preventing exposure of internal kernel pointers.

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