{"id":"CVE-2026-64295","summary":"mm: page_ext: add count limit to page_ext_iter_next to prevent invalid PFN access","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nmm: page_ext: add count limit to page_ext_iter_next to prevent invalid PFN access\n\nThe page_ext iteration API does not validate if the PFN still belongs to a\nvalid section while advancing the iterator.  When dynamically adding\nmemory in the hotplug path, it can lead to a NULL pointer dereference\nduring page_ext_lookup at the boundary of the last valid section when\niterator count equals __pgcount.\n\nThe for_each_page_ext() macro calls page_ext_iter_next() as its loop\nincrement.  for_each_page_ext() does a \"__page_ext =\npage_ext_iter_next(&__iter)\" at the end.  This causes page_ext_iter_next()\nto increment iter-\u003eindex past __pgcount and call page_ext_lookup(start_pfn\n+ __pgcount).  During memory hotplug (online), the PFN at start_pfn +\n__pgcount may belong to a section that has not yet been initialized,\ncausing page_ext_lookup() to trigger a NULL pointer dereference.\n\n[   14.555124][  T846] Call trace:\n[   14.555125][  T846]  lookup_page_ext+0x6c/0x108 (P)\n[   14.555127][  T846]  page_ext_lookup+0x30/0x3c\n[   14.555129][  T846]  __reset_page_owner+0x11c/0x260\n[   14.571201][  T846]  __free_pages_ok+0x5e8/0x8e0\n[   14.571204][  T846]  __free_pages_core+0x78/0xf0\n[   14.571206][  T846]  generic_online_page+0x14/0x24\n[   14.597782][  T846]  online_pages+0x178/0x30c\n[   14.597784][  T846]  memory_block_change_state+0x284/0x32c\n[   14.597787][  T846]  memory_subsys_online+0x4c/0x64\n[   14.597789][  T846]  device_online+0x88/0xb0\n[   14.597791][  T846]  online_memory_block+0x30/0x40\n[   14.597793][  T846]  walk_memory_blocks+0xac/0xe8\n[   14.597794][  T846]  add_memory_resource+0x280/0x298\n[   14.656161][  T846]  add_memory+0x60/0x98\n\nMove the iteration boundary enforcement inside the iterator functions, so\ncallers cannot inadvertently access beyond the requested range.","modified":"2026-07-27T04:03:21.382533887Z","published":"2026-07-25T08:49:33.194Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64295.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/377b1cd6bbcf327338cd951cc2fd74bc75540235"},{"type":"WEB","url":"https://git.kernel.org/stable/c/8dcaa0f87a88d720d13106f3a306c6b61d189d86"},{"type":"WEB","url":"https://git.kernel.org/stable/c/ffd017237cfe99e6e5602ab14179b0e6878a0840"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64295.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-64295"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"9039b9096ea27a20f0349d1537537663c935c8ed"},{"fixed":"8dcaa0f87a88d720d13106f3a306c6b61d189d86"},{"fixed":"377b1cd6bbcf327338cd951cc2fd74bc75540235"},{"fixed":"ffd017237cfe99e6e5602ab14179b0e6878a0840"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-64295.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.15.0"},{"fixed":"6.18.39"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.1.4"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-64295.json"}}],"schema_version":"1.7.5"}