CVE-2022-49554: zsmalloc: fix races between asynchronous zspage free and page migration

Severity: medium (CVSS 4.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-02-26 · updated 2026-10-15
Weakness: CWE-362

Description

In the Linux kernel, the following vulnerability has been resolved: zsmalloc: fix races between asynchronous zspage free and page migration The asynchronous zspage free worker tries to lock a zspage's entire page list without defending against page migration. Since pages which haven't yet been locked can concurrently migrate off the zspage page list while lock_zspage() churns away, lock_zspage() can suffer from a few different lethal races. It can lock a page which no longer belongs to the zspage and unsafely dereference page_private(), it can unsafely dereference a torn pointer to the next page (since there's a data race), and it can observe a spurious NULL pointer to the next page and thus not lock all of the zspage's pages (since a single page migration will reconstruct the entire page list, and create_page_chain() unconditionally zeroes out each list pointer in the process). Fix the races by using migrate_read_lock() in lock_zspage() to synchronize with page migration.

Affected products

Linux kernel: from 4.14 before 4.14.282; from 4.15 before 4.19.246; from 4.20 before 5.4.197; from 5.5 before 5.10.120; from 5.11 before 5.15.45; from 5.16 before 5.17.13 — fixed in 4.14.282, 4.19.246, 5.10.120, 5.15.45, 5.17.13, 5.18.2

How to fix

Upgrade to a fixed version: Linux kernel 4.14.282, 4.19.246, 5.10.120, 5.15.45. Check the vendor advisory for mitigations.

References

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