CVE-2026-72174

Summary

In the Linux kernel, the following vulnerability has been resolved:

fs/proc/task_mmu: fix hugetlb self-deadlock in pagemap_scan_pte_hole()

A PAGEMAP_SCAN ioctl requesting PM_SCAN_WP_MATCHING on a hugetlb VMA hangs the calling thread, unkillably, as soon as the scan reaches an unpopulated part of the range:

do_pagemap_scan() walk_page_range() walk_hugetlb_range() hugetlb_vma_lock_read() # take the vma lock for read … pagemap_scan_pte_hole() # … ->pte_hole() for a hole uffd_wp_range() change_protection() hugetlb_change_protection() hugetlb_vma_lock_write() # … and block taking it for write

walk_hugetlb_range() holds the hugetlb vma lock for read across the whole walk. A present entry goes to ->hugetlb_entry(); an unpopulated one goes to ->pte_hole(), i.e. pagemap_scan_pte_hole(). To write-protect the hole that handler calls uffd_wp_range(), which on a hugetlb VMA reaches hugetlb_change_protection() and takes the same vma lock for write. The thread then blocks in down_write() waiting for the read lock it is itself holding.

The populated path avoids this: pagemap_scan_hugetlb_entry() write-protects the entry inline under the page-table lock and never enters hugetlb_change_protection().

Do the same for holes. Fault in the page table and install the uffd-wp marker directly with make_uffd_wp_huge_pte() under the page-table lock, rather than routing through uffd_wp_range(). That is the same sequence hugetlb_change_protection() runs for an unpopulated entry, minus the vma write lock – which is safe to skip because PMD sharing is disabled on uffd-wp VMAs (hugetlb_unshare_all_pmds() runs at registration), leaving nothing for that lock to serialise against.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/a6ac03652d9edc30c2912037ac83beb42cc67f8e
• https://git.kernel.org/stable/c/43b987ed35be9be21a303d1036d4241fec9943df
• https://git.kernel.org/stable/c/18b8a9700610299819d21fd0ea85d24726d17f65
• https://git.kernel.org/stable/c/e92d92bbafb264dc0518d52b846a3c07ed8d523f

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