Subject: CVE-2024-42108: net: rswitch: Avoid use-after-free in rswitch_poll()

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

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

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

net: rswitch: Avoid use-after-free in rswitch_poll()

The use-after-free is actually in rswitch_tx_free(), which is inlined in
rswitch_poll(). Since `skb` and `gq->skbs[gq->dirty]` are in fact the
same pointer, the skb is first freed using dev_kfree_skb_any(), then the
value in skb->len is used to update the interface statistics.

Let's move around the instructions to use skb->len before the skb is
freed.

This bug is trivial to reproduce using KFENCE. It will trigger a splat
every few packets. A simple ARP request or ICMP echo request is enough.

The Linux kernel CVE team has assigned CVE-2024-42108 to this issue.

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

	Issue introduced in 6.8 with commit 271e015b9153 and fixed in 6.9.9 with commit 92cbbe775919
	Issue introduced in 6.8 with commit 271e015b9153 and fixed in 6.10 with commit 9a0c28efeec6

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-2024-42108
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/ethernet/renesas/rswitch.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/92cbbe7759193e3418f38d0d73f8fe125312c58b
	https://git.kernel.org/stable/c/9a0c28efeec6383ef22e97437616b920e7320b67