CVE-2021-46969: bus: mhi: core: Fix invalid error returning in mhi_queue

CVE-2021-46969: bus: mhi: core: Fix invalid error returning in mhi_queue

[Greg Kroah-Hartman]

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

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

bus: mhi: core: Fix invalid error returning in mhi_queue

mhi_queue returns an error when the doorbell is not accessible in
the current state. This can happen when the device is in non M0
state, like M3, and needs to be waken-up prior ringing the DB. This
case is managed earlier by triggering an asynchronous M3 exit via
controller resume/suspend callbacks, that in turn will cause M0
transition and DB update.

So, since it's not an error but just delaying of doorbell update, there
is no reason to return an error.

This also fixes a use after free error for skb case, indeed a caller
queuing skb will try to free the skb if the queueing fails, but in
that case queueing has been done.

The Linux kernel CVE team has assigned CVE-2021-46969 to this issue.


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

	Issue introduced in 5.12 with commit a8f75cb348fd and fixed in 5.12.3 with commit a99b661c3187
	Issue introduced in 5.12 with commit a8f75cb348fd and fixed in 5.13 with commit 0ecc1c70dcd3

Please see https://www.kernel.org or 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-2021-46969
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/bus/mhi/core/main.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/a99b661c3187365f81026d89b1133a76cd2652b3
	https://git.kernel.org/stable/c/0ecc1c70dcd32c0f081b173a1a5d89952686f271