CVE-2021-46923: fs/mount_setattr: always cleanup mount_kattr

CVE-2021-46923: fs/mount_setattr: always cleanup mount_kattr

[Greg Kroah-Hartman]

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

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

fs/mount_setattr: always cleanup mount_kattr

Make sure that finish_mount_kattr() is called after mount_kattr was
succesfully built in both the success and failure case to prevent
leaking any references we took when we built it.  We returned early if
path lookup failed thereby risking to leak an additional reference we
took when building mount_kattr when an idmapped mount was requested.

The Linux kernel CVE team has assigned CVE-2021-46923 to this issue.


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

	Issue introduced in 5.12 with commit 9caccd41541a and fixed in 5.15.13 with commit 47b5d0a7532d
	Issue introduced in 5.12 with commit 9caccd41541a and fixed in 5.16 with commit 012e332286e2

Please see https://www.kernel.org or 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-2021-46923
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/namespace.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/47b5d0a7532d39e42a938f81e3904268145c341d
	https://git.kernel.org/stable/c/012e332286e2bb9f6ac77d195f17e74b2963d663