Subject: CVE-2022-48815: net: dsa: bcm_sf2: don't use devres for mdiobus

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

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

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

net: dsa: bcm_sf2: don't use devres for mdiobus

As explained in commits:
74b6d7d13307 ("net: dsa: realtek: register the MDIO bus under devres")
5135e96a3dd2 ("net: dsa: don't allocate the slave_mii_bus using devres")

mdiobus_free() will panic when called from devm_mdiobus_free() <-
devres_release_all() <- __device_release_driver(), and that mdiobus was
not previously unregistered.

The Starfighter 2 is a platform device, so the initial set of
constraints that I thought would cause this (I2C or SPI buses which call
->remove on ->shutdown) do not apply. But there is one more which
applies here.

If the DSA master itself is on a bus that calls ->remove from ->shutdown
(like dpaa2-eth, which is on the fsl-mc bus), there is a device link
between the switch and the DSA master, and device_links_unbind_consumers()
will unbind the bcm_sf2 switch driver on shutdown.

So the same treatment must be applied to all DSA switch drivers, which
is: either use devres for both the mdiobus allocation and registration,
or don't use devres at all.

The bcm_sf2 driver has the code structure in place for orderly mdiobus
removal, so just replace devm_mdiobus_alloc() with the non-devres
variant, and add manual free where necessary, to ensure that we don't
let devres free a still-registered bus.

The Linux kernel CVE team has assigned CVE-2022-48815 to this issue.

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

	Issue introduced in 5.9 with commit ac3a68d56651 and fixed in 5.10.101 with commit 2770b795294e
	Issue introduced in 5.9 with commit ac3a68d56651 and fixed in 5.15.24 with commit caabb5f64f5c
	Issue introduced in 5.9 with commit ac3a68d56651 and fixed in 5.16.10 with commit 08e1a3554e99
	Issue introduced in 5.9 with commit ac3a68d56651 and fixed in 5.17 with commit 08f1a2082234

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-2022-48815
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/bcm_sf2.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/2770b795294ed312375c11ef1d0b810499c66b83
	https://git.kernel.org/stable/c/caabb5f64f5c32fceed93356bb688ef1ec6c5783
	https://git.kernel.org/stable/c/08e1a3554e99a1a5bd2835907381e2383ee85cae
	https://git.kernel.org/stable/c/08f1a20822349004bb9cc1b153ecb516e9f2889d