Subject: CVE-2021-47214: hugetlb, userfaultfd: fix reservation restore on userfaultfd error

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

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

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

hugetlb, userfaultfd: fix reservation restore on userfaultfd error

Currently in the is_continue case in hugetlb_mcopy_atomic_pte(), if we
bail out using "goto out_release_unlock;" in the cases where idx >=
size, or !huge_pte_none(), the code will detect that new_pagecache_page
== false, and so call restore_reserve_on_error().  In this case I see
restore_reserve_on_error() delete the reservation, and the following
call to remove_inode_hugepages() will increment h->resv_hugepages
causing a 100% reproducible leak.

We should treat the is_continue case similar to adding a page into the
pagecache and set new_pagecache_page to true, to indicate that there is
no reservation to restore on the error path, and we need not call
restore_reserve_on_error().  Rename new_pagecache_page to
page_in_pagecache to make that clear.

The Linux kernel CVE team has assigned CVE-2021-47214 to this issue.

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

	Issue introduced in 5.14 with commit c7b1850dfb41 and fixed in 5.15.5 with commit b5069d44e2fb
	Issue introduced in 5.14 with commit c7b1850dfb41 and fixed in 5.16 with commit cc30042df6fc
	Issue introduced in 5.13.13 with commit 515b6124df6a

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-2021-47214
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:
	mm/hugetlb.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/b5069d44e2fbc4a9093d005b3ef0949add3dd27e
	https://git.kernel.org/stable/c/cc30042df6fcc82ea18acf0dace831503e60a0b7