{"id":"CVE-2026-72175","state":"PUBLISHED","title":"fs/proc/task_mmu: fix make_uffd_wp_huge_pte() prot-update race","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nfs/proc/task_mmu: fix make_uffd_wp_huge_pte() prot-update race\n\nPatch series \"userfaultfd/pagemap: pre-existing fixes\".\n\nThese are pre-existing bug fixes that were carried at the front of the\nuserfaultfd RWP working-set-tracking series up to v5 [1].  Per review\nfeedback that fixes should not sit in the middle of a feature series, they\nare split out and sent on their own; the RWP series is reposted rebased on\ntop of this.\n\nAll six were flagged by the Sashiko AI review of the RWP series and carry\nindependent of RWP, apply to mm-new directly, and carry Cc: stable@.\n\n  1: fs/proc/task_mmu: a missing huge_ptep_modify_prot_start() in\n     make_uffd_wp_huge_pte() can lose hardware Dirty/Accessed updates\n     when PAGEMAP_SCAN write-protects a hugetlb PTE.\n\n  2: fs/proc/task_mmu: pagemap_scan_hugetlb_entry() compares the range\n     against HPAGE_SIZE rather than the hstate page size, so it never\n     write-protects gigantic hugetlb pages.\n\n  3: fs/proc/task_mmu: PAGEMAP_SCAN with PM_SCAN_WP_MATCHING over an\n     unpopulated hugetlb range self-deadlocks -- pagemap_scan_pte_hole()\n     calls uffd_wp_range() while walk_hugetlb_range() holds the hugetlb\n     vma lock for read, and hugetlb_change_protection() then takes it\n     for write. Install the marker inline instead.\n\n  4: mm/huge_memory: change_non_present_huge_pmd() drops pmd_swp_uffd_wp\n     on a device-private PMD permission downgrade, silently losing the\n     uffd-wp marker.\n\n  5: userfaultfd: must_wait() applies pte_write() to a locklessly read\n     PTE without checking pte_present(), so swap/migration entries\n     decode random offset bits and a thread can stay parked on a stale\n     fault.\n\n  6: userfaultfd: __VMA_UFFD_FLAGS feeds VMA_UFFD_MINOR_BIT (41) to\n     mk_vma_flags() unconditionally, an out-of-bounds write into the\n     single-word vma_flags_t on 32-bit. Build the mask from config-gated\n     per-mode masks so an unavailable bit is never materialised.\n\n\nThis patch (of 6):\n\nmake_uffd_wp_huge_pte() arms the UFFD_WP bit on a present HugeTLB PTE by\ncalling huge_ptep_modify_prot_commit() with a ptent snapshot that was\nfetched without the corresponding huge_ptep_modify_prot_start().  The\nstart helper is what atomically clears the entry so the kernel-owned\nsnapshot stays consistent until the commit; without it, the hardware may\nset Dirty or Accessed in the live PTE between the original read and the\ncommit, and huge_ptep_modify_prot_commit() (whose generic implementation\njust calls set_huge_pte_at()) then writes the stale snapshot back over the\nlive hardware bits, losing the update.\n\nThe non-hugetlb sibling make_uffd_wp_pte() does this correctly via\nptep_modify_prot_start() / ptep_modify_prot_commit().  Mirror that pattern\nfor the present-PTE branch.  The migration case stays as-is -- migration\nentries are non-present, so there's no hardware update to race against.","publishedAt":"2026-08-15T05:53:40.011Z","updatedAt":"2026-10-16T18:45:00.474Z","severity":{"score":7.1,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"52526ca7fdb905a768a93f8faa418e9b988fc34b","status":"affected","lessThan":"50a25249a6355db74c2c1b6be541b4caab9f3655","versionType":"git"},{"version":"52526ca7fdb905a768a93f8faa418e9b988fc34b","status":"affected","lessThan":"8e39ed92d7c5c6bfc08dc45153916f49a4e98bab","versionType":"git"},{"version":"52526ca7fdb905a768a93f8faa418e9b988fc34b","status":"affected","lessThan":"6b7f774b8882445d9174681747d37c42548686a4","versionType":"git"},{"version":"52526ca7fdb905a768a93f8faa418e9b988fc34b","status":"affected","lessThan":"04718f7c9290f95385f0dd328758753dc1c36dec","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/proc/task_mmu.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.7","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.7","versionType":"semver"},{"version":"6.12.101","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.42","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.5","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/proc/task_mmu.c"]}],"references":["https://git.kernel.org/stable/c/50a25249a6355db74c2c1b6be541b4caab9f3655","https://git.kernel.org/stable/c/8e39ed92d7c5c6bfc08dc45153916f49a4e98bab","https://git.kernel.org/stable/c/6b7f774b8882445d9174681747d37c42548686a4","https://git.kernel.org/stable/c/04718f7c9290f95385f0dd328758753dc1c36dec"],"weaknesses":[],"ingestedAt":"2026-10-29T20:12:58.252Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/72xxx/CVE-2026-72175.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-72175","state":"PUBLISHED","datePublished":"2026-08-15T05:53:40.011Z","dateUpdated":"2026-10-16T18:45:00.474Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-08-09T03:40:39.910Z"},"containers":{"cna":{"title":"fs/proc/task_mmu: fix make_uffd_wp_huge_pte() prot-update race","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nfs/proc/task_mmu: fix make_uffd_wp_huge_pte() prot-update race\n\nPatch series \"userfaultfd/pagemap: pre-existing fixes\".\n\nThese are pre-existing bug fixes that were carried at the front of the\nuserfaultfd RWP working-set-tracking series up to v5 [1].  Per review\nfeedback that fixes should not sit in the middle of a feature series, they\nare split out and sent on their own; the RWP series is reposted rebased on\ntop of this.\n\nAll six were flagged by the Sashiko AI review of the RWP series and carry\nindependent of RWP, apply to mm-new directly, and carry Cc: stable@.\n\n  1: fs/proc/task_mmu: a missing huge_ptep_modify_prot_start() in\n     make_uffd_wp_huge_pte() can lose hardware Dirty/Accessed updates\n     when PAGEMAP_SCAN write-protects a hugetlb PTE.\n\n  2: fs/proc/task_mmu: pagemap_scan_hugetlb_entry() compares the range\n     against HPAGE_SIZE rather than the hstate page size, so it never\n     write-protects gigantic hugetlb pages.\n\n  3: fs/proc/task_mmu: PAGEMAP_SCAN with PM_SCAN_WP_MATCHING over an\n     unpopulated hugetlb range self-deadlocks -- pagemap_scan_pte_hole()\n     calls uffd_wp_range() while walk_hugetlb_range() holds the hugetlb\n     vma lock for read, and hugetlb_change_protection() then takes it\n     for write. Install the marker inline instead.\n\n  4: mm/huge_memory: change_non_present_huge_pmd() drops pmd_swp_uffd_wp\n     on a device-private PMD permission downgrade, silently losing the\n     uffd-wp marker.\n\n  5: userfaultfd: must_wait() applies pte_write() to a locklessly read\n     PTE without checking pte_present(), so swap/migration entries\n     decode random offset bits and a thread can stay parked on a stale\n     fault.\n\n  6: userfaultfd: __VMA_UFFD_FLAGS feeds VMA_UFFD_MINOR_BIT (41) to\n     mk_vma_flags() unconditionally, an out-of-bounds write into the\n     single-word vma_flags_t on 32-bit. Build the mask from config-gated\n     per-mode masks so an unavailable bit is never materialised.\n\n\nThis patch (of 6):\n\nmake_uffd_wp_huge_pte() arms the UFFD_WP bit on a present HugeTLB PTE by\ncalling huge_ptep_modify_prot_commit() with a ptent snapshot that was\nfetched without the corresponding huge_ptep_modify_prot_start().  The\nstart helper is what atomically clears the entry so the kernel-owned\nsnapshot stays consistent until the commit; without it, the hardware may\nset Dirty or Accessed in the live PTE between the original read and the\ncommit, and huge_ptep_modify_prot_commit() (whose generic implementation\njust calls set_huge_pte_at()) then writes the stale snapshot back over the\nlive hardware bits, losing the update.\n\nThe non-hugetlb sibling make_uffd_wp_pte() does this correctly via\nptep_modify_prot_start() / ptep_modify_prot_commit().  Mirror that pattern\nfor the present-PTE branch.  The migration case stays as-is -- migration\nentries are non-present, so there's no hardware update to race against."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"52526ca7fdb905a768a93f8faa418e9b988fc34b","status":"affected","lessThan":"50a25249a6355db74c2c1b6be541b4caab9f3655","versionType":"git"},{"version":"52526ca7fdb905a768a93f8faa418e9b988fc34b","status":"affected","lessThan":"8e39ed92d7c5c6bfc08dc45153916f49a4e98bab","versionType":"git"},{"version":"52526ca7fdb905a768a93f8faa418e9b988fc34b","status":"affected","lessThan":"6b7f774b8882445d9174681747d37c42548686a4","versionType":"git"},{"version":"52526ca7fdb905a768a93f8faa418e9b988fc34b","status":"affected","lessThan":"04718f7c9290f95385f0dd328758753dc1c36dec","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/proc/task_mmu.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.7","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.7","versionType":"semver"},{"version":"6.12.101","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.42","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.5","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/proc/task_mmu.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/50a25249a6355db74c2c1b6be541b4caab9f3655"},{"url":"https://git.kernel.org/stable/c/8e39ed92d7c5c6bfc08dc45153916f49a4e98bab"},{"url":"https://git.kernel.org/stable/c/6b7f774b8882445d9174681747d37c42548686a4"},{"url":"https://git.kernel.org/stable/c/04718f7c9290f95385f0dd328758753dc1c36dec"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N","baseScore":7.1,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - The bug is reached only through the PAGEMAP_SCAN ioctl on /proc/<pid>/pagemap, which requires local access to a process address space and cannot be triggered remotely.\nAC:L - The attacker controls both sides of the race by issuing PAGEMAP_SCAN with PM_SCAN_WP_MATCHING while concurrently writing the same present HugeTLB page from another thread in the target process.\nPR:L - Any unprivileged local user can open /proc/self/pagemap and trigger the ioctl; ptrace read checks also allow same-UID access to another process's pagemap without real root privileges.\nUI:N - No victim user action is required; exploitation is performed entirely by the attacker ioctl-ing pagemap and racing writes against their own or same-UID process mappings.\nS:U - The vulnerability corrupts PTE metadata within the target mm only and does not cross VM, container, or kernel/user security boundaries.\nC:H - Stale HugeTLB PTE commits can clear hardware Dirty/Accessed bits; this PTE corruption can expose stale file-backed data to other mappers or userfaultfd migration consumers instead of current memory contents.\nI:H - Lost Dirty bits break folio dirty tracking and writeback for HugeTLB mappings, allowing silent loss or corruption of in-memory modifications that should have been persisted or migrated.\nA:N - The race corrupts PTE metadata without causing kernel oops, panic, or hang; availability impact is limited to incorrect page state rather than system crash."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-17T05:41:11.530Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.7","versionEndExcluding":"6.12.101"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.7","versionEndExcluding":"6.18.42"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.7","versionEndExcluding":"7.1.5"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.7","versionEndExcluding":"7.2"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-72175","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T18:43:23.910702Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-16T18:45:00.474Z"}}]}}}