CVE-2025-22015
MediumCVSS 5.5Exploitation Probability (EPSS)
Low risk8th percentile - higher than 8% of all known CVEs
Summary
A vulnerability was found in the Linux kernel's memory migration mechanism (mm/migrate). The bug incorrectly determines the number of xarray entries to update during shmem folio migration, causing multi-index entry corruption. The issue occurs when __folio_migrate_mapping() uses folio_test_swapbacked() instead of folio_test_swapcache() to distinguish between page cache and swap cache folios.
Risk Assessment
The vulnerability can corrupt xarray data structures, leading to system instability, potential data loss, or kernel crashes. Organizations using Linux systems with memory migration enabled (e.g., in virtualization or HPC environments) are at risk of service disruption.
Recommendation
Immediately update the Linux kernel to a version containing the fix (commit in Linus Torvalds' repository). Monitor official security advisories from your Linux distribution and apply the patch as soon as it is available.
Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: mm/migrate: fix shmem xarray update during migration A shmem folio can be either in page cache or in swap cache, but not at the same time. Namely, once it is in swap cache, folio->mapping should be NULL, and the folio is no longer in a shmem mapping. In __folio_migrate_mapping(), to determine the number of xarray entries to update, folio_test_swapbacked() is used, but that conflates shmem in page cache case and shmem in swap cache case. It leads to xarray multi-index entry corruption, since it turns a sibling entry to a normal entry during xas_store() (see [1] for a userspace reproduction). Fix it by only using folio_test_swapcache() to determine whether xarray is storing swap cache entries or not to choose the right number of xarray entries to update. [1] https://lore.kernel.org/linux-mm/[email protected]/ Note: In __split_huge_page(), folio_test_anon() && folio_test_swapcache() is used to get swap_cache address space, but that ignores the shmem folio in swap cache case. It could lead to NULL pointer dereferencing when a in-swap-cache shmem folio is split at __xa_store(), since !folio_test_anon() is true and folio->mapping is NULL. But fortunately, its caller split_huge_page_to_list_to_order() bails out early with EBUSY when folio->mapping is NULL. So no need to take care of it here.