Affected: Linux

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

mm: turn folio_test_hugetlb into a PageType

The current folio_test_hugetlb() can be fooled by a concurrent folio split into returning true for a folio which has never belonged to hugetlbfs. This can't happen if the caller holds a refcount on it, but we have a few places (memory-failure, compaction, procfs) which do not and should not take a speculative reference.

Since hugetlb pages do not use individual page mapcounts (they are always fully mapped and use the entire_mapcount field to record the number of mappings), the PageType field is available now that page_mapcount() ignores the value in this field.

In compaction and with CONFIG_DEBUG_VM enabled, the current implementation can result in an oops, as reported by Luis. This happens since 9c5ccf2db04b ("mm: remove HUGETLB_PAGE_DTOR") effectively added some VM_BUG_ON() checks in the PageHuge() testing path.

[willy@infradead.org: update vmcoreinfo]