CVE-2026-72025: s390/monwriter: Reject buffer reuse with different data length

CVE-2026-72025: s390/monwriter: Reject buffer reuse with different data length

[Greg Kroah-Hartman]

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

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

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

s390/monwriter: Reject buffer reuse with different data length

When data buffers are reused, e.g. for interval sample records, the
first record determines the data length, and the size of the buffer for
user copy. Current monwriter code does not check if the data length was
changed for subsequent records, which also would never happen for valid
user programs.

However, a malicious user could change the data length, resulting in out
of bounds user copy to the kernel buffer, and memory corruption. By
default, the monwriter misc device is created with root-only permissions,
so practical impact is typically low.

Fix this by checking for changed data length and rejecting such records.

The Linux kernel CVE team has assigned CVE-2026-72025 to this issue.


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

	Fixed in 5.10.261 with commit 096dff1247037d329c04b3a5be0ecdfb1c5c7ac6
	Fixed in 5.15.212 with commit d39cf4a6d721b1ae21eb53bbf3e8cd984253d7ab
	Fixed in 6.1.178 with commit 759d91378203ea35fa9bca6726dcf0010de081fb
	Fixed in 6.6.145 with commit 036bc5661060702e798d215e81bb46da530965b3
	Fixed in 6.12.97 with commit 01f3ce411711c2c919598ea25320a5a48f71edbc
	Fixed in 6.18.40 with commit f0745496f7c171271cafd9457df3b914a483ddeb
	Fixed in 7.1.5 with commit ae5347f3db1782c6118f6cc0d9fd8b1d43397db3
	Fixed in 7.2-rc2 with commit 2995ccec260caa9e85b3301a4aba1e66ed80ad74

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-2026-72025
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:
	drivers/s390/char/monwriter.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/096dff1247037d329c04b3a5be0ecdfb1c5c7ac6
	https://git.kernel.org/stable/c/d39cf4a6d721b1ae21eb53bbf3e8cd984253d7ab
	https://git.kernel.org/stable/c/759d91378203ea35fa9bca6726dcf0010de081fb
	https://git.kernel.org/stable/c/036bc5661060702e798d215e81bb46da530965b3
	https://git.kernel.org/stable/c/01f3ce411711c2c919598ea25320a5a48f71edbc
	https://git.kernel.org/stable/c/f0745496f7c171271cafd9457df3b914a483ddeb
	https://git.kernel.org/stable/c/ae5347f3db1782c6118f6cc0d9fd8b1d43397db3
	https://git.kernel.org/stable/c/2995ccec260caa9e85b3301a4aba1e66ed80ad74