CVE-2026-74514: KVM: s390: pci: Fix memory accounting for pinned/unpinned pages

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

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

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

KVM: s390: pci: Fix memory accounting for pinned/unpinned pages

The account_mem() and unaccount_mem() functions call get_uid() which
increments the reference count of struct user_struct on every invocation.
But we don't decrement the count by calling free_uid(). It also
accounted/unaccounted the pages against the current->mm. But its possible
the unaccount_mem() can be called from a different process context than the
one that originally pinned the pages.

Let's fix this by storing the pinning process user_struct and mm_struct
when accounting for pinned pages, and subsequently free these resources
when the pages are unpinned.

[[email protected]: Fixed whitespace]

The Linux kernel CVE team has assigned CVE-2026-74514 to this issue.


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

	Issue introduced in 6.0 with commit 3c5a1b6f0a18520a0edd0600fef6f1a8553b8fdc and fixed in 6.18.44 with commit 70871b121f81d08879363cb1238a4c85c5c2800c
	Issue introduced in 6.0 with commit 3c5a1b6f0a18520a0edd0600fef6f1a8553b8fdc and fixed in 7.1.8 with commit e3f732e086e438c52c7400bd2734bb166aa4752c
	Issue introduced in 6.0 with commit 3c5a1b6f0a18520a0edd0600fef6f1a8553b8fdc and fixed in 7.2-rc6 with commit 36f6999ecde3976731a8bfc0b8e667da6f593069

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-2026-74514
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/kvm/pci.c
	arch/s390/kvm/pci.h


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/70871b121f81d08879363cb1238a4c85c5c2800c
	https://git.kernel.org/stable/c/e3f732e086e438c52c7400bd2734bb166aa4752c
	https://git.kernel.org/stable/c/36f6999ecde3976731a8bfc0b8e667da6f593069