CVE-2026-89726: lib/ucs2_string.c: fix out-of-bounds read in ucs2_strnlen()

CVE-2026-89726: lib/ucs2_string.c: fix out-of-bounds read in ucs2_strnlen()

[Greg Kroah-Hartman]

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

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

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

lib/ucs2_string.c: fix out-of-bounds read in ucs2_strnlen()

Patch series "lib/ucs2_string.c: fix out-of-bounds read in
ucs2_strnlen()", v2.

This series fixes an off-by-one out-of-bounds read in ucs2_strnlen().

The first patch is the real fix, the second patch comes as a bonus and
fixes the code indentation.


This patch (of 2):

ucs2_strnlen() checks the current character before checking whether the
caller-provided maximum length has been reached.  If the input is not
NUL-terminated within that bound, the loop can read one ucs2_char_t past
the limit.

Test the length before dereferencing to prevent an off-by-one
out-of-bounds read.

The Linux kernel CVE team has assigned CVE-2026-89726 to this issue.


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

	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.12.109 with commit 709eb41adaf78d59d4579a13a898125919b69bcc
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.18.50 with commit 7d658da725ea81c91f73087547b97e7ced82d62b
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 7.2.4 with commit 1b0dc3cbb8630f0b5cb34d848628225920a904be
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 7.3-rc1 with commit cec0d03fe785380540dc1b4d07c80f67ae2ffc78

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-2026-89726
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:
	lib/ucs2_string.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/709eb41adaf78d59d4579a13a898125919b69bcc
	https://git.kernel.org/stable/c/7d658da725ea81c91f73087547b97e7ced82d62b
	https://git.kernel.org/stable/c/1b0dc3cbb8630f0b5cb34d848628225920a904be
	https://git.kernel.org/stable/c/cec0d03fe785380540dc1b4d07c80f67ae2ffc78