Subject: CVE-2021-47241: ethtool: strset: fix message length calculation

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

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

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

ethtool: strset: fix message length calculation

Outer nest for ETHTOOL_A_STRSET_STRINGSETS is not accounted for.
This may result in ETHTOOL_MSG_STRSET_GET producing a warning like:

    calculated message payload length (684) not sufficient
    WARNING: CPU: 0 PID: 30967 at net/ethtool/netlink.c:369 ethnl_default_doit+0x87a/0xa20

and a splat.

As usually with such warnings three conditions must be met for the warning
to trigger:
 - there must be no skb size rounding up (e.g. reply_size of 684);
 - string set must be per-device (so that the header gets populated);
 - the device name must be at least 12 characters long.

all in all with current user space it looks like reading priv flags
is the only place this could potentially happen. Or with syzbot :)

The Linux kernel CVE team has assigned CVE-2021-47241 to this issue.

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

	Issue introduced in 5.6 with commit 71921690f974 and fixed in 5.10.46 with commit fb3a94814368
	Issue introduced in 5.6 with commit 71921690f974 and fixed in 5.12.13 with commit cfc7f0e70d64
	Issue introduced in 5.6 with commit 71921690f974 and fixed in 5.13 with commit e175aef90269

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-2021-47241
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/ethtool/strset.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/fb3a948143688e14e2cfd2a2812877923d0e5e92
	https://git.kernel.org/stable/c/cfc7f0e70d649e6d2233fba0d9390b525677d971
	https://git.kernel.org/stable/c/e175aef902697826d344ce3a12189329848fe898