CVE-2021-47520: can: pch_can: pch_can_rx_normal: fix use after free

CVE-2021-47520: can: pch_can: pch_can_rx_normal: fix use after free

[Greg Kroah-Hartman]

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

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

can: pch_can: pch_can_rx_normal: fix use after free

After calling netif_receive_skb(skb), dereferencing skb is unsafe.
Especially, the can_frame cf which aliases skb memory is dereferenced
just after the call netif_receive_skb(skb).

Reordering the lines solves the issue.

The Linux kernel CVE team has assigned CVE-2021-47520 to this issue.


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

	Issue introduced in 2.6.37 with commit b21d18b51b31 and fixed in 4.4.295 with commit bafe343a885c
	Issue introduced in 2.6.37 with commit b21d18b51b31 and fixed in 4.9.293 with commit 3a3c46e2eff0
	Issue introduced in 2.6.37 with commit b21d18b51b31 and fixed in 4.14.258 with commit affbad02bf80
	Issue introduced in 2.6.37 with commit b21d18b51b31 and fixed in 4.19.221 with commit 3e193ef4e0a3
	Issue introduced in 2.6.37 with commit b21d18b51b31 and fixed in 5.4.165 with commit abb4eff3dcd2
	Issue introduced in 2.6.37 with commit b21d18b51b31 and fixed in 5.10.85 with commit 703dde112021
	Issue introduced in 2.6.37 with commit b21d18b51b31 and fixed in 5.15.8 with commit 6c73fc931658
	Issue introduced in 2.6.37 with commit b21d18b51b31 and fixed in 5.16 with commit 94cddf1e9227

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-2021-47520
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/can/pch_can.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/bafe343a885c70dddf358379cf0b2a1c07355d8d
	https://git.kernel.org/stable/c/3a3c46e2eff0577454860a203be1a8295f4acb76
	https://git.kernel.org/stable/c/affbad02bf80380a7403885b9fe4a1587d1bb4f3
	https://git.kernel.org/stable/c/3e193ef4e0a3f5bf92ede83ef214cb09d01b00aa
	https://git.kernel.org/stable/c/abb4eff3dcd2e583060082a18a8dbf31f02689d4
	https://git.kernel.org/stable/c/703dde112021c93d6e89443c070e7dbd4dea612e
	https://git.kernel.org/stable/c/6c73fc931658d8cbc8a1714b326cb31eb71d16a7
	https://git.kernel.org/stable/c/94cddf1e9227a171b27292509d59691819c458db