Subject: CVE-2021-46971: perf/core: Fix unconditional security_locked_down() call

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

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

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

perf/core: Fix unconditional security_locked_down() call

Currently, the lockdown state is queried unconditionally, even though
its result is used only if the PERF_SAMPLE_REGS_INTR bit is set in
attr.sample_type. While that doesn't matter in case of the Lockdown LSM,
it causes trouble with the SELinux's lockdown hook implementation.

SELinux implements the locked_down hook with a check whether the current
task's type has the corresponding "lockdown" class permission
("integrity" or "confidentiality") allowed in the policy. This means
that calling the hook when the access control decision would be ignored
generates a bogus permission check and audit record.

Fix this by checking sample_type first and only calling the hook when
its result would be honored.

The Linux kernel CVE team has assigned CVE-2021-46971 to this issue.

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

	Issue introduced in 5.4 with commit b0c8fdc7fdb7 and fixed in 5.4.117 with commit b246759284d6
	Issue introduced in 5.4 with commit b0c8fdc7fdb7 and fixed in 5.10.35 with commit 4348d3b5027b
	Issue introduced in 5.4 with commit b0c8fdc7fdb7 and fixed in 5.11.19 with commit f5809ca4c311
	Issue introduced in 5.4 with commit b0c8fdc7fdb7 and fixed in 5.12.2 with commit c7b0208ee370
	Issue introduced in 5.4 with commit b0c8fdc7fdb7 and fixed in 5.13 with commit 08ef1af4de5f

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-2021-46971
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:
	kernel/events/core.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/b246759284d6a2bc5b6f1009caeeb3abce2ec9ff
	https://git.kernel.org/stable/c/4348d3b5027bc3ff6336368b6c60605d4ef8e1ce
	https://git.kernel.org/stable/c/f5809ca4c311b71bfaba6d13f4e39eab0557895e
	https://git.kernel.org/stable/c/c7b0208ee370b89d20486fae71cd9abb759819c1
	https://git.kernel.org/stable/c/08ef1af4de5fe7de9c6d69f1e22e51b66e385d9b