Subject: CVE-2021-47339: media: v4l2-core: explicitly clear ioctl input data

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

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

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

media: v4l2-core: explicitly clear ioctl input data

As seen from a recent syzbot bug report, mistakes in the compat ioctl
implementation can lead to uninitialized kernel stack data getting used
as input for driver ioctl handlers.

The reported bug is now fixed, but it's possible that other related
bugs are still present or get added in the future. As the drivers need
to check user input already, the possible impact is fairly low, but it
might still cause an information leak.

To be on the safe side, always clear the entire ioctl buffer before
calling the conversion handler functions that are meant to initialize
them.

The Linux kernel CVE team has assigned CVE-2021-47339 to this issue.

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

	Fixed in 5.12.18 with commit dc02c0b2bd60
	Fixed in 5.13.3 with commit bfb48b54db25
	Fixed in 5.14 with commit 7b53cca764f9

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-2021-47339
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/media/v4l2-core/v4l2-ioctl.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/dc02c0b2bd6096f2f3ce63e1fc317aeda05f74d8
	https://git.kernel.org/stable/c/bfb48b54db25c3b4ef4bef5e0691464ebc4aa335
	https://git.kernel.org/stable/c/7b53cca764f9b291b7907fcd39d9e66ad728ee0b