CVE-2026-74515: KVM: s390: pci: Reject adapter interrupt forwarding if already enabled

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

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

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

KVM: s390: pci: Reject adapter interrupt forwarding if already enabled

The MPCIFC instruction doesn't allow registering adapter interrupts without
first unregistering. So reject any request to enable interrupt forwarding
if its already enabled for the zPCI device. This also fixes overwriting and
thus leaking resources when the ioctl is called multiple times for the same
device.

The Linux kernel CVE team has assigned CVE-2026-74515 to this issue.


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

	Issue introduced in 6.0 with commit 3c5a1b6f0a18520a0edd0600fef6f1a8553b8fdc and fixed in 6.6.151 with commit 78d9648e7e960546d5b72504a0b0358cd8bb1e9d
	Issue introduced in 6.0 with commit 3c5a1b6f0a18520a0edd0600fef6f1a8553b8fdc and fixed in 6.12.103 with commit 6be1ff49ba81f96a6fa55915e6d920be43ac57cc
	Issue introduced in 6.0 with commit 3c5a1b6f0a18520a0edd0600fef6f1a8553b8fdc and fixed in 6.18.44 with commit 6837f0ae85fd54cf64c8a0c7c530bba2fae0a207
	Issue introduced in 6.0 with commit 3c5a1b6f0a18520a0edd0600fef6f1a8553b8fdc and fixed in 7.1.8 with commit 591952b63a9f976da7d49f719f36ec826ee2a575
	Issue introduced in 6.0 with commit 3c5a1b6f0a18520a0edd0600fef6f1a8553b8fdc and fixed in 7.2-rc6 with commit 8fa01be5a6149404adb82c0979a78f6347edd3ef

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-2026-74515
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


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/78d9648e7e960546d5b72504a0b0358cd8bb1e9d
	https://git.kernel.org/stable/c/6be1ff49ba81f96a6fa55915e6d920be43ac57cc
	https://git.kernel.org/stable/c/6837f0ae85fd54cf64c8a0c7c530bba2fae0a207
	https://git.kernel.org/stable/c/591952b63a9f976da7d49f719f36ec826ee2a575
	https://git.kernel.org/stable/c/8fa01be5a6149404adb82c0979a78f6347edd3ef