Subject: CVE-2021-47559: net/smc: Fix NULL pointer dereferencing in smc_vlan_by_tcpsk()

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

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

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

net/smc: Fix NULL pointer dereferencing in smc_vlan_by_tcpsk()

Coverity reports a possible NULL dereferencing problem:

in smc_vlan_by_tcpsk():
6. returned_null: netdev_lower_get_next returns NULL (checked 29 out of 30 times).
7. var_assigned: Assigning: ndev = NULL return value from netdev_lower_get_next.
1623                ndev = (struct net_device *)netdev_lower_get_next(ndev, &lower);
CID 1468509 (#1 of 1): Dereference null return value (NULL_RETURNS)
8. dereference: Dereferencing a pointer that might be NULL ndev when calling is_vlan_dev.
1624                if (is_vlan_dev(ndev)) {

Remove the manual implementation and use netdev_walk_all_lower_dev() to
iterate over the lower devices. While on it remove an obsolete function
parameter comment.

The Linux kernel CVE team has assigned CVE-2021-47559 to this issue.

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

	Issue introduced in 4.18 with commit cb9d43f67754 and fixed in 5.10.83 with commit c94cbd262b6a
	Issue introduced in 4.18 with commit cb9d43f67754 and fixed in 5.15.6 with commit bb851d0fb025
	Issue introduced in 4.18 with commit cb9d43f67754 and fixed in 5.16 with commit 587acad41f1b

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-2021-47559
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:
	net/smc/smc_core.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/c94cbd262b6aa3b54d73a1ed1f9c0d19df57f4ff
	https://git.kernel.org/stable/c/bb851d0fb02547d03cd40106b5f2391c4fed6ed1
	https://git.kernel.org/stable/c/587acad41f1bc48e16f42bb2aca63bf323380be8