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.

Quoted source text, attributed separately from HOL analysis.

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.

Quoted source text, attributed separately from HOL analysis.