CVE-2026-72186: ntfs: make system files immutable to prevent corruption

CVE-2026-72186: ntfs: make system files immutable to prevent corruption

[Greg Kroah-Hartman]

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

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

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

ntfs: make system files immutable to prevent corruption

When a system file such as $Bitmap is exposed via show_sys_files and
written from userspace, the volume is corrupted and, because the cluster
allocator scans $Bitmap through the same inode's page cache, a write to
$Bitmap also deadlocks writeback against the folio it already holds locked.

These files are maintained by the driver itself and have no valid reason
to be written through the file interface. Mark base metadata files
(mft_no < FILE_first_user) as immutable during inode read so the VFS
rejects write, mmap, truncate and unlink with -EPERM. Directories are
skipped so the root and $Extend remain usable. Internal metadata updates
do not go through the VFS write path and are unaffected.

The Linux kernel CVE team has assigned CVE-2026-72186 to this issue.


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

	Issue introduced in 7.1 with commit af0db57d4293cc9fe6ce99fb5592dc2652228c9d and fixed in 7.1.5 with commit 8f313e92522ac41d273ea137db13ea8a8df2beed
	Issue introduced in 7.1 with commit af0db57d4293cc9fe6ce99fb5592dc2652228c9d and fixed in 7.2-rc3 with commit f72df3a4c33b64de3418ec74d1ad4f028e09d161

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-2026-72186
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/inode.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/8f313e92522ac41d273ea137db13ea8a8df2beed
	https://git.kernel.org/stable/c/f72df3a4c33b64de3418ec74d1ad4f028e09d161