CVE-2026-72203: ntfs: skip extent mft records in writeback to prevent deadlock

CVE-2026-72203: ntfs: skip extent mft records in writeback to prevent deadlock

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

ntfs: skip extent mft records in writeback to prevent deadlock

This patch fixes the ABBA deadlock between extent_lock and extent
mrec_lock triggered by xfstests generic/113, that occurs since the commit
6994acf33bae ("ntfs: use base mft_no when looking up base inode for
		extent record").

Path A (inode writeback):
  VFS writeback
    -> ntfs_write_inode()
      -> __ntfs_write_inode()
        -> mutex_lock(&ni->extent_lock)
        -> mutex_lock(&tni->mrec_lock)

Path B (MFT folio writeback):
  VFS writeback of $MFT dirty folios
    -> ntfs_mft_writepages()
      -> ntfs_write_mft_block()
        -> ntfs_may_write_mft_record()
          -> holds one extent mrec_lock from a previous iteration
          -> tries to acquire another base inode extent_lock

By removing all extent_lock and extent mrec_lock acquisition from the MFT
folio writeback path, the ABBA lock ordering is eliminated:

Path A: __ntfs_write_inode(): extent_lock -> mrec_lock
Path B (removed): ntfs_write_mft_block(): mrec_lock -> extent_lock

Path B is always redundant for extent records because:

1. mark_mft_record_dirty(ext_ni) does NOT dirty the MFT folio.
   It only sets NInoDirty(ext_ni) and marks the base VFS inode dirty
   via __mark_inode_dirty(I_DIRTY_DATASYNC), which triggers Path A.
   Therefore, normal extent modifications never create a situation where
   the MFT folio is dirty and Path B is not scheduled.

2. The MFT folio only gets dirtied via ntfs_mft_mark_dirty() inside
   ntfs_mft_record_alloc(). But all identified callers in attrib.c
   (ntfs_attr_add, ntfs_attr_record_move_away,
   ntfs_attr_make_non_resident, ntfs_attr_record_resize) follow through
   with mark_mft_record_dirty(), which triggers Path A to write the
   complete record.

3. ntfs_evict_big_inode() calls ntfs_commit_inode() before freeing extent
   inodes, ensuring all dirty extents are flushed via Path A before the
   base inode leaves the icache.

The Linux kernel CVE team has assigned CVE-2026-72203 to this issue.


Affected and fixed versions
===========================

	Fixed in 7.1.5 with commit f831ab09d521898bf1dd99bf5adfd630ea1428e3
	Fixed in 7.2-rc1 with commit 76bc14c7097ff678b2b5dbfd4fa33b46897d87ce

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-72203
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/ntfs/mft.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/f831ab09d521898bf1dd99bf5adfd630ea1428e3
	https://git.kernel.org/stable/c/76bc14c7097ff678b2b5dbfd4fa33b46897d87ce