Subject: CVE-2024-36881: mm/userfaultfd: reset ptes when close() for wr-protected ones

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

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

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

mm/userfaultfd: reset ptes when close() for wr-protected ones

Userfaultfd unregister includes a step to remove wr-protect bits from all
the relevant pgtable entries, but that only covered an explicit
UFFDIO_UNREGISTER ioctl, not a close() on the userfaultfd itself.  Cover
that too.  This fixes a WARN trace.

The only user visible side effect is the user can observe leftover
wr-protect bits even if the user close()ed on an userfaultfd when
releasing the last reference of it.  However hopefully that should be
harmless, and nothing bad should happen even if so.

This change is now more important after the recent page-table-check
patch we merged in mm-unstable (446dd9ad37d0 ("mm/page_table_check:
support userfault wr-protect entries")), as we'll do sanity check on
uffd-wp bits without vma context.  So it's better if we can 100%
guarantee no uffd-wp bit leftovers, to make sure each report will be
valid.

The Linux kernel CVE team has assigned CVE-2024-36881 to this issue.

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

	Issue introduced in 6.0 with commit f369b07c8614 and fixed in 6.6.31 with commit 377f3a9a3d03
	Issue introduced in 6.0 with commit f369b07c8614 and fixed in 6.8.10 with commit 8d8b68a5b0c9
	Issue introduced in 6.0 with commit f369b07c8614 and fixed in 6.9 with commit c88033efe9a3
	Issue introduced in 5.19.6 with commit 3e2747c3ddfa

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-2024-36881
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:
	fs/userfaultfd.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/377f3a9a3d032a52325a5b110379a25dd1ab1931
	https://git.kernel.org/stable/c/8d8b68a5b0c9fb23d37df06bb273ead38fd5a29d
	https://git.kernel.org/stable/c/c88033efe9a391e72ba6b5df4b01d6e628f4e734