Subject: CVE-2021-46945: ext4: always panic when errors=panic is specified

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

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

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

ext4: always panic when errors=panic is specified

Before commit 014c9caa29d3 ("ext4: make ext4_abort() use
__ext4_error()"), the following series of commands would trigger a
panic:

1. mount /dev/sda -o ro,errors=panic test
2. mount /dev/sda -o remount,abort test

After commit 014c9caa29d3, remounting a file system using the test
mount option "abort" will no longer trigger a panic.  This commit will
restore the behaviour immediately before commit 014c9caa29d3.
(However, note that the Linux kernel's behavior has not been
consistent; some previous kernel versions, including 5.4 and 4.19
similarly did not panic after using the mount option "abort".)

This also makes a change to long-standing behaviour; namely, the
following series commands will now cause a panic, when previously it
did not:

1. mount /dev/sda -o ro,errors=panic test
2. echo test > /sys/fs/ext4/sda/trigger_fs_error

However, this makes ext4's behaviour much more consistent, so this is
a good thing.

The Linux kernel CVE team has assigned CVE-2021-46945 to this issue.

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

	Issue introduced in 5.11 with commit 014c9caa29d3 and fixed in 5.11.20 with commit 64e1eebe2131
	Issue introduced in 5.11 with commit 014c9caa29d3 and fixed in 5.12.3 with commit 1e9ea8f46370
	Issue introduced in 5.11 with commit 014c9caa29d3 and fixed in 5.13 with commit ac2f7ca51b09

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-2021-46945
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/ext4/super.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/64e1eebe2131183174f4fbb6b1491355f96c6cde
	https://git.kernel.org/stable/c/1e9ea8f4637026b8e965128953f2da061ccae9c4
	https://git.kernel.org/stable/c/ac2f7ca51b0929461ea49918f27c11b680f28995