{"id":"CVE-2026-72174","summary":"fs/proc/task_mmu: fix hugetlb self-deadlock in pagemap_scan_pte_hole()","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nfs/proc/task_mmu: fix hugetlb self-deadlock in pagemap_scan_pte_hole()\n\nA PAGEMAP_SCAN ioctl requesting PM_SCAN_WP_MATCHING on a hugetlb VMA hangs\nthe calling thread, unkillably, as soon as the scan reaches an unpopulated\npart of the range:\n\n  do_pagemap_scan()\n    walk_page_range()\n      walk_hugetlb_range()\n        hugetlb_vma_lock_read()           # take the vma lock for read ...\n        pagemap_scan_pte_hole()           # ... -\u003epte_hole() for a hole\n          uffd_wp_range()\n            change_protection()\n              hugetlb_change_protection()\n                hugetlb_vma_lock_write()  # ... and block taking it for write\n\nwalk_hugetlb_range() holds the hugetlb vma lock for read across the whole\nwalk.  A present entry goes to -\u003ehugetlb_entry(); an unpopulated one goes\nto -\u003epte_hole(), i.e.  pagemap_scan_pte_hole().  To write-protect the hole\nthat handler calls uffd_wp_range(), which on a hugetlb VMA reaches\nhugetlb_change_protection() and takes the same vma lock for write.  The\nthread then blocks in down_write() waiting for the read lock it is itself\nholding.\n\nThe populated path avoids this: pagemap_scan_hugetlb_entry()\nwrite-protects the entry inline under the page-table lock and never enters\nhugetlb_change_protection().\n\nDo the same for holes.  Fault in the page table and install the uffd-wp\nmarker directly with make_uffd_wp_huge_pte() under the page-table lock,\nrather than routing through uffd_wp_range().  That is the same sequence\nhugetlb_change_protection() runs for an unpopulated entry, minus the vma\nwrite lock -- which is safe to skip because PMD sharing is disabled on\nuffd-wp VMAs (hugetlb_unshare_all_pmds() runs at registration), leaving\nnothing for that lock to serialise against.","modified":"2026-08-18T03:31:08.613428073Z","published":"2026-08-15T05:53:39.276Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/72xxx/CVE-2026-72174.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/18b8a9700610299819d21fd0ea85d24726d17f65"},{"type":"WEB","url":"https://git.kernel.org/stable/c/43b987ed35be9be21a303d1036d4241fec9943df"},{"type":"WEB","url":"https://git.kernel.org/stable/c/a6ac03652d9edc30c2912037ac83beb42cc67f8e"},{"type":"WEB","url":"https://git.kernel.org/stable/c/e92d92bbafb264dc0518d52b846a3c07ed8d523f"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/72xxx/CVE-2026-72174.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-72174"},{"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":"52526ca7fdb905a768a93f8faa418e9b988fc34b"},{"fixed":"a6ac03652d9edc30c2912037ac83beb42cc67f8e"},{"fixed":"43b987ed35be9be21a303d1036d4241fec9943df"},{"fixed":"18b8a9700610299819d21fd0ea85d24726d17f65"},{"fixed":"e92d92bbafb264dc0518d52b846a3c07ed8d523f"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-72174.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.97"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.40"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.1.5"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-72174.json"}}],"schema_version":"1.9.0"}