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CVE-2025-21693 is a use-after-free vulnerability in the Linux kernel zswap compression and decompression paths. The zswap_compress() and zswap_decompress() functions retain the initial CPU's per-CPU asynchronous compression context while execution can migrate to another CPU. If the original CPU is hot-unplugged during the operation, zswap_cpu_comp_dead() can free the context's buffer, request, or compression resources while they remain in use. The flaw was introduced by the transition to the crypto_acomp API, which requires a sleepable context and prevents the previous preemption-disabling approach. Insufficient synchronization between resource cleanup and ongoing operations permits access to freed kernel resources.
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A use-after-free vulnerability in the Linux kernel's zswap compression and decompression paths. An operation can migrate between CPUs while retaining the original CPU's compression context; hot-unplugging that CPU can free resources still in use. The fix synchronizes resource allocation and freeing with compression/decompression using a mutex and retries when a CPU has been offlined. The advisory assigns a CVSS v3 score of 7.8 and recommends updating Echo's linux package and related packages to version 6.12.12-1 or later.
Linux kernel zswap resource-freeing synchronization flaw during CPU hot-unplug.
Linux kernel zswap resource-free synchronization flaw.
A Linux kernel zswap use-after-free vulnerability caused by insufficient synchronization between compression/decompression operations and CPU hot-unplug resource cleanup for per-CPU crypto_acomp contexts.
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Cross-references every affected SKU, including bundled OEM variants.
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