Linux Kernel Vulnerability in zswap Resource Management

CVE-2025-21693

Summary

A resource management flaw exists in the Linux kernel's zswap mechanism. This vulnerability arises during CPU hotunplug operations, where a situation can occur that leads to the use-after-free (UAF) condition. Specifically, when utilizing the crypto_acomp API in zswap_compress() and zswap_decompress(), the per-CPU acomp_ctx can lead to complications if the original CPU is removed while resources are in use. If the acomp_ctx's resources are freed during the hotunplug process, it results in critical failures. The vulnerability necessitated refinements in the synchronization process to ensure safe management of resources across CPU hotplug events.

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