Subject: CVE-2021-47276: ftrace: Do not blindly read the ip address in ftrace_bug()

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

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

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

ftrace: Do not blindly read the ip address in ftrace_bug()

It was reported that a bug on arm64 caused a bad ip address to be used for
updating into a nop in ftrace_init(), but the error path (rightfully)
returned -EINVAL and not -EFAULT, as the bug caused more than one error to
occur. But because -EINVAL was returned, the ftrace_bug() tried to report
what was at the location of the ip address, and read it directly. This
caused the machine to panic, as the ip was not pointing to a valid memory
address.

Instead, read the ip address with copy_from_kernel_nofault() to safely
access the memory, and if it faults, report that the address faulted,
otherwise report what was in that location.

The Linux kernel CVE team has assigned CVE-2021-47276 to this issue.

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

	Issue introduced in 2.6.28 with commit 05736a427f7e and fixed in 4.4.273 with commit 0bc62e398bbd
	Issue introduced in 2.6.28 with commit 05736a427f7e and fixed in 4.9.273 with commit 4aedc2bc2b32
	Issue introduced in 2.6.28 with commit 05736a427f7e and fixed in 4.14.237 with commit acf671ba79c1
	Issue introduced in 2.6.28 with commit 05736a427f7e and fixed in 4.19.195 with commit 862dcc14f280
	Issue introduced in 2.6.28 with commit 05736a427f7e and fixed in 5.4.126 with commit 7e4e824b109f
	Issue introduced in 2.6.28 with commit 05736a427f7e and fixed in 5.10.44 with commit 97524384762c
	Issue introduced in 2.6.28 with commit 05736a427f7e and fixed in 5.12.11 with commit 3e4ddeb68751
	Issue introduced in 2.6.28 with commit 05736a427f7e and fixed in 5.13 with commit 6c14133d2d3f

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-2021-47276
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/trace/ftrace.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/0bc62e398bbd9e600959e610def5109957437b28
	https://git.kernel.org/stable/c/4aedc2bc2b32c93555f47c95610efb89cc1ec09b
	https://git.kernel.org/stable/c/acf671ba79c1feccc3ec7cfdcffead4efcec49e7
	https://git.kernel.org/stable/c/862dcc14f2803c556bdd73b43c27b023fafce2fb
	https://git.kernel.org/stable/c/7e4e824b109f1d41ccf223fbb0565d877d6223a2
	https://git.kernel.org/stable/c/97524384762c1fb9b3ded931498dd2047bd0de81
	https://git.kernel.org/stable/c/3e4ddeb68751fb4fb657199aed9cfd5d02796875
	https://git.kernel.org/stable/c/6c14133d2d3f768e0a35128faac8aa6ed4815051