Subject: CVE-2021-47439: net: dsa: microchip: Added the condition for scheduling ksz_mib_read_work

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

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

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

net: dsa: microchip: Added the condition for scheduling ksz_mib_read_work

When the ksz module is installed and removed using rmmod, kernel crashes
with null pointer dereferrence error. During rmmod, ksz_switch_remove
function tries to cancel the mib_read_workqueue using
cancel_delayed_work_sync routine and unregister switch from dsa.

During dsa_unregister_switch it calls ksz_mac_link_down, which in turn
reschedules the workqueue since mib_interval is non-zero.
Due to which queue executed after mib_interval and it tries to access
dp->slave. But the slave is unregistered in the ksz_switch_remove
function. Hence kernel crashes.

To avoid this crash, before canceling the workqueue, resetted the
mib_interval to 0.

v1 -> v2:
-Removed the if condition in ksz_mib_read_work

The Linux kernel CVE team has assigned CVE-2021-47439 to this issue.

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

	Issue introduced in 5.7 with commit 469b390e1ba3 and fixed in 5.10.75 with commit f2e1de075018
	Issue introduced in 5.7 with commit 469b390e1ba3 and fixed in 5.14.14 with commit 383239a33cf2
	Issue introduced in 5.7 with commit 469b390e1ba3 and fixed in 5.15 with commit ef1100ef20f2

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-2021-47439
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:
	drivers/net/dsa/microchip/ksz_common.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/f2e1de075018cf71bcd7d628e9f759cb8540b0c3
	https://git.kernel.org/stable/c/383239a33cf29ebee9ce0d4e0e5c900b77a16148
	https://git.kernel.org/stable/c/ef1100ef20f29aec4e62abeccdb5bdbebba1e378