CVE-2026-64295

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

mm: page_ext: add count limit to page_ext_iter_next to prevent invalid PFN access

The page_ext iteration API does not validate if the PFN still belongs to a

valid section while advancing the iterator. When dynamically adding

memory in the hotplug path, it can lead to a NULL pointer dereference

during page_ext_lookup at the boundary of the last valid section when

iterator count equals __pgcount.

The for_each_page_ext() macro calls page_ext_iter_next() as its loop

increment. for_each_page_ext() does a "__page_ext =

page_ext_iter_next(&__iter)" at the end. This causes page_ext_iter_next()

to increment iter->index past __pgcount and call page_ext_lookup(start_pfn

+ __pgcount). During memory hotplug (online), the PFN at start_pfn +

__pgcount may belong to a section that has not yet been initialized,

causing page_ext_lookup() to trigger a NULL pointer dereference.

[ 14.555124][ T846] Call trace:

[ 14.555125][ T846] lookup_page_ext+0x6c/0x108 (P)

[ 14.555127][ T846] page_ext_lookup+0x30/0x3c

[ 14.555129][ T846] __reset_page_owner+0x11c/0x260

[ 14.571201][ T846] __free_pages_ok+0x5e8/0x8e0

[ 14.571204][ T846] __free_pages_core+0x78/0xf0

[ 14.571206][ T846] generic_online_page+0x14/0x24

[ 14.597782][ T846] online_pages+0x178/0x30c

[ 14.597784][ T846] memory_block_change_state+0x284/0x32c

[ 14.597787][ T846] memory_subsys_online+0x4c/0x64

[ 14.597789][ T846] device_online+0x88/0xb0

[ 14.597791][ T846] online_memory_block+0x30/0x40

[ 14.597793][ T846] walk_memory_blocks+0xac/0xe8

[ 14.597794][ T846] add_memory_resource+0x280/0x298

[ 14.656161][ T846] add_memory+0x60/0x98

Move the iteration boundary enforcement inside the iterator functions, so

callers cannot inadvertently access beyond the requested range.