CVE-2025-22030

Summary

In the Linux kernel, the following vulnerability has been resolved:

mm: zswap: fix crypto_free_acomp() deadlock in zswap_cpu_comp_dead()

Currently, zswap_cpu_comp_dead() calls crypto_free_acomp() while holding the per-CPU acomp_ctx mutex. crypto_free_acomp() then holds scomp_lock (through crypto_exit_scomp_ops_async()).

On the other hand, crypto_alloc_acomp_node() holds the scomp_lock (through crypto_scomp_init_tfm()), and then allocates memory. If the allocation results in reclaim, we may attempt to hold the per-CPU acomp_ctx mutex.

The above dependencies can cause an ABBA deadlock. For example in the following scenario:

(1) Task A running on CPU #1: crypto_alloc_acomp_node() Holds scomp_lock Enters reclaim Reads per_cpu_ptr(pool->acomp_ctx, 1)

(2) Task A is descheduled

(3) CPU #1 goes offline zswap_cpu_comp_dead(CPU #1) Holds per_cpu_ptr(pool->acomp_ctx, 1)) Calls crypto_free_acomp() Waits for scomp_lock

(4) Task A running on CPU #2: Waits for per_cpu_ptr(pool->acomp_ctx, 1) // Read on CPU #1 DEADLOCK

Since there is no requirement to call crypto_free_acomp() with the per-CPU acomp_ctx mutex held in zswap_cpu_comp_dead(), move it after the mutex is unlocked. Also move the acomp_request_free() and kfree() calls for consistency and to avoid any potential sublte locking dependencies in the future.

With this, only setting acomp_ctx fields to NULL occurs with the mutex held. This is similar to how zswap_cpu_comp_prepare() only initializes acomp_ctx fields with the mutex held, after performing all allocations before holding the mutex.

Opportunistically, move the NULL check on acomp_ctx so that it takes place before the mutex dereference.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/747e3eec1d7d124ea90ed3d7b85369df8b4e36d2
• https://git.kernel.org/stable/c/a8d18000e9d2d97aaf105f5f9b3b0e8a6fbf8b96
• https://git.kernel.org/stable/c/717d9c35deff6c33235693171bacbb03e9643fa4
• https://git.kernel.org/stable/c/c11bcbc0a517acf69282c8225059b2a8ac5fe628

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