Subject: CVE-2024-44951: serial: sc16is7xx: fix TX fifo corruption

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

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

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

serial: sc16is7xx: fix TX fifo corruption

Sometimes, when a packet is received on channel A at almost the same time
as a packet is about to be transmitted on channel B, we observe with a
logic analyzer that the received packet on channel A is transmitted on
channel B. In other words, the Tx buffer data on channel B is corrupted
with data from channel A.

The problem appeared since commit 4409df5866b7 ("serial: sc16is7xx: change
EFR lock to operate on each channels"), which changed the EFR locking to
operate on each channel instead of chip-wise.

This commit has introduced a regression, because the EFR lock is used not
only to protect the EFR registers access, but also, in a very obscure and
undocumented way, to protect access to the data buffer, which is shared by
the Tx and Rx handlers, but also by each channel of the IC.

Fix this regression first by switching to kfifo_out_linear_ptr() in
sc16is7xx_handle_tx() to eliminate the need for a shared Rx/Tx buffer.

Secondly, replace the chip-wise Rx buffer with a separate Rx buffer for
each channel.

The Linux kernel CVE team has assigned CVE-2024-44951 to this issue.

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

	Issue introduced in 6.8 with commit 4409df5866b7 and fixed in 6.10.5 with commit 09cfe05e9907
	Issue introduced in 6.8 with commit 4409df5866b7 and fixed in 6.11 with commit 133f4c00b8b2
	Issue introduced in 6.1.76 with commit 4b068e55bf5e
	Issue introduced in 6.6.15 with commit 9879e1bec3c0
	Issue introduced in 6.7.3 with commit dbe196ca489f

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-2024-44951
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/tty/serial/sc16is7xx.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/09cfe05e9907f3276887a20e267cc40e202f4fdd
	https://git.kernel.org/stable/c/133f4c00b8b2bfcacead9b81e7e8edfceb4b06c4