Subject: CVE-2021-47060: KVM: Stop looking for coalesced MMIO zones if the bus is destroyed

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

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

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

KVM: Stop looking for coalesced MMIO zones if the bus is destroyed

Abort the walk of coalesced MMIO zones if kvm_io_bus_unregister_dev()
fails to allocate memory for the new instance of the bus.  If it can't
instantiate a new bus, unregister_dev() destroys all devices _except_ the
target device.   But, it doesn't tell the caller that it obliterated the
bus and invoked the destructor for all devices that were on the bus.  In
the coalesced MMIO case, this can result in a deleted list entry
dereference due to attempting to continue iterating on coalesced_zones
after future entries (in the walk) have been deleted.

Opportunistically add curly braces to the for-loop, which encompasses
many lines but sneaks by without braces due to the guts being a single
if statement.

The Linux kernel CVE team has assigned CVE-2021-47060 to this issue.

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

	Issue introduced in 5.4.66 with commit 41b2ea7a6a11 and fixed in 5.4.119 with commit 7d1bc32d6477
	Issue introduced in 5.9 with commit f65886606c2d and fixed in 5.10.37 with commit 2a20592baff5
	Issue introduced in 5.9 with commit f65886606c2d and fixed in 5.11.21 with commit 168e82f640ed
	Issue introduced in 5.9 with commit f65886606c2d and fixed in 5.12.4 with commit 50cbad42bfea
	Issue introduced in 5.9 with commit f65886606c2d and fixed in 5.13 with commit 5d3c4c79384a
	Issue introduced in 4.4.238 with commit f0dfffce3f4f
	Issue introduced in 4.9.238 with commit 840e124f89a5
	Issue introduced in 4.14.200 with commit 40a023f681be
	Issue introduced in 4.19.148 with commit 19184bd06f48
	Issue introduced in 5.8.10 with commit 68c125324b5e

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-2021-47060
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:
	include/linux/kvm_host.h
	virt/kvm/coalesced_mmio.c
	virt/kvm/kvm_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/7d1bc32d6477ff96a32695ea4be8144e4513ab2d
	https://git.kernel.org/stable/c/2a20592baff59c5351c5200ec667e1a2aa22af85
	https://git.kernel.org/stable/c/168e82f640ed1891a700bdb43e37da354b2ab63c
	https://git.kernel.org/stable/c/50cbad42bfea8c052b7ca590bd4126cdc898713c
	https://git.kernel.org/stable/c/5d3c4c79384af06e3c8e25b7770b6247496b4417