CVE-2026-89755mm/migrate_device: clear stale mapping after freeing swapcache

Official description

In the Linux kernel, the following vulnerability has been resolved: mm/migrate_device: clear stale mapping after freeing swapcache __migrate_device_pages() reads the folio mapping before calling folio_free_swap(). When folio_free_swap() succeeds, the folio is removed from the swap cache, but the saved mapping still points to swap_space. Passing the stale mapping to folio_migrate_mapping() makes it use the mapped-folio path for a folio that is no longer in swapcache. It can then operate on swap_space.i_pages with invalid reference accounting, eventually triggering a folio reference count BUG. After a successful split, nr still contains the number of pages in the original large folio, although each resulting page is now a separate order-0 folio. Reset nr to 1 so each split folio is processed separately, including its own swapcache removal and mapping lookup. Refresh the saved mapping after folio_free_swap() so the current folio state is used during migration.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/92db780dd644590c751246187e1229d5ac2e5544
• https://git.kernel.org/stable/c/4fa91f7bbc4135240b67daac03fc17d9e180a331
• https://git.kernel.org/stable/c/8ffedc6573a665cdc31ebe47eae7b32b78d0df83
• https://git.kernel.org/stable/c/34a00895d032a414830d41106a09329ae6c251b6