CVE-2026-68385: s390/checksum: Fix csum_partial() without vector facility

From: Greg Kroah-Hartman <[email protected]>

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

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

s390/checksum: Fix csum_partial() without vector facility

Currently csum_partial() calls csum_copy() with copy=false and dst=NULL.
On machines without the vector facility, csum_copy() falls back to
cksm(dst, ...), causing the checksum to be calculated from address zero
instead of the source buffer.

The VX implementation already checksums data loaded from src. Make the
fallback do the same by passing src to cksm().

The Linux kernel CVE team has assigned CVE-2026-68385 to this issue.


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

	Issue introduced in 6.9 with commit dcd3e1de9d17dc43dfed87a9fc814b9dec508043 and fixed in 6.12.101 with commit 5fc0a2a6eeb99cac991242bb48796c7749ce3261
	Issue introduced in 6.9 with commit dcd3e1de9d17dc43dfed87a9fc814b9dec508043 and fixed in 6.18.42 with commit 1d9a2f01b3c4e5c88e06b2db4b5460c2ec884722
	Issue introduced in 6.9 with commit dcd3e1de9d17dc43dfed87a9fc814b9dec508043 and fixed in 7.1.6 with commit 898bb2814f38399108bdd2113f38d97383a7036a
	Issue introduced in 6.9 with commit dcd3e1de9d17dc43dfed87a9fc814b9dec508043 and fixed in 7.2-rc4 with commit 4bb06b60d982355e22647b3d12d6619419f8c1fa

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-2026-68385
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:
	arch/s390/lib/csum-partial.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/5fc0a2a6eeb99cac991242bb48796c7749ce3261
	https://git.kernel.org/stable/c/1d9a2f01b3c4e5c88e06b2db4b5460c2ec884722
	https://git.kernel.org/stable/c/898bb2814f38399108bdd2113f38d97383a7036a
	https://git.kernel.org/stable/c/4bb06b60d982355e22647b3d12d6619419f8c1fa