{"id":"CVE-2026-72175","title":"fs/proc/task_mmu: fix make_uffd_wp_huge_pte() prot-update race","summary":"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 carr…","severity":"high","cvss":7.1,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N","cvssSource":"cna","vendor":"Linux","product":"Linux","affected":["Linux >= 52526ca7fdb905a768a93f8faa418e9b988fc34b < 50a25249a6355db74c2c1b6be541b4caab9f3655","Linux >= 52526ca7fdb905a768a93f8faa418e9b988fc34b < 8e39ed92d7c5c6bfc08dc45153916f49a4e98bab","Linux >= 52526ca7fdb905a768a93f8faa418e9b988fc34b < 6b7f774b8882445d9174681747d37c42548686a4","Linux >= 52526ca7fdb905a768a93f8faa418e9b988fc34b < 04718f7c9290f95385f0dd328758753dc1c36dec","Linux 6.7"],"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"total","timestamp":"2026-10-16T18:43:23.910702Z"},"published":"2026-08-15","updated":"2026-10-16","sourceUpdated":"2026-10-16T18:45:00.474Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-72175","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"}],"tags":["cve.org"],"epss":0.00172,"epssPercentile":0.06108,"ingestedAt":"2026-10-16T19:46:24.424Z","slug":"CVE-2026-72175","body":"## Overview\n\nIn 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.\n\n## Affected\n\n- `Linux >= 52526ca7fdb905a768a93f8faa418e9b988fc34b < 50a25249a6355db74c2c1b6be541b4caab9f3655`\n- `Linux >= 52526ca7fdb905a768a93f8faa418e9b988fc34b < 8e39ed92d7c5c6bfc08dc45153916f49a4e98bab`\n- `Linux >= 52526ca7fdb905a768a93f8faa418e9b988fc34b < 6b7f774b8882445d9174681747d37c42548686a4`\n- `Linux >= 52526ca7fdb905a768a93f8faa418e9b988fc34b < 04718f7c9290f95385f0dd328758753dc1c36dec`\n- `Linux 6.7`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":39,"depthScoreParts":{"impact":39.1,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}