Subject: CVE-2022-48700: vfio/type1: Unpin zero pages

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

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

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

vfio/type1: Unpin zero pages

There's currently a reference count leak on the zero page.  We increment
the reference via pin_user_pages_remote(), but the page is later handled
as an invalid/reserved page, therefore it's not accounted against the
user and not unpinned by our put_pfn().

Introducing special zero page handling in put_pfn() would resolve the
leak, but without accounting of the zero page, a single user could
still create enough mappings to generate a reference count overflow.

The zero page is always resident, so for our purposes there's no reason
to keep it pinned.  Therefore, add a loop to walk pages returned from
pin_user_pages_remote() and unpin any zero pages.

The Linux kernel CVE team has assigned CVE-2022-48700 to this issue.

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

	Fixed in 5.10.146 with commit 578d644edc7d
	Fixed in 5.15.68 with commit 5321908ef74f
	Fixed in 5.19.9 with commit 5d721bf22293
	Fixed in 6.0 with commit 873aefb376bb

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-2022-48700
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/vfio/vfio_iommu_type1.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/578d644edc7d2c1ff53f7e4d0a25da473deb4a03
	https://git.kernel.org/stable/c/5321908ef74fb593e0dbc8737d25038fc86c9986
	https://git.kernel.org/stable/c/5d721bf222936f5cf3ee15ced53cc483ecef7e46
	https://git.kernel.org/stable/c/873aefb376bbc0ed1dd2381ea1d6ec88106fdbd4