Subject: CVE-2024-38605: ALSA: core: Fix NULL module pointer assignment at card init

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

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

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

ALSA: core: Fix NULL module pointer assignment at card init

The commit 81033c6b584b ("ALSA: core: Warn on empty module")
introduced a WARN_ON() for a NULL module pointer passed at snd_card
object creation, and it also wraps the code around it with '#ifdef
MODULE'.  This works in most cases, but the devils are always in
details.  "MODULE" is defined when the target code (i.e. the sound
core) is built as a module; but this doesn't mean that the caller is
also built-in or not.  Namely, when only the sound core is built-in
(CONFIG_SND=y) while the driver is a module (CONFIG_SND_USB_AUDIO=m),
the passed module pointer is ignored even if it's non-NULL, and
card->module remains as NULL.  This would result in the missing module
reference up/down at the device open/close, leading to a race with the
code execution after the module removal.

For addressing the bug, move the assignment of card->module again out
of ifdef.  The WARN_ON() is still wrapped with ifdef because the
module can be really NULL when all sound drivers are built-in.

Note that we keep 'ifdef MODULE' for WARN_ON(), otherwise it would
lead to a false-positive NULL module check.  Admittedly it won't catch
perfectly, i.e. no check is performed when CONFIG_SND=y.  But, it's no
real problem as it's only for debugging, and the condition is pretty
rare.

The Linux kernel CVE team has assigned CVE-2024-38605 to this issue.

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

	Issue introduced in 5.9 with commit 81033c6b584b and fixed in 5.10.219 with commit d7ff29a429b5
	Issue introduced in 5.9 with commit 81033c6b584b and fixed in 5.15.161 with commit e7e0ca200772
	Issue introduced in 5.9 with commit 81033c6b584b and fixed in 6.1.93 with commit e00747672573
	Issue introduced in 5.9 with commit 81033c6b584b and fixed in 6.6.33 with commit e644036a3e2b
	Issue introduced in 5.9 with commit 81033c6b584b and fixed in 6.8.12 with commit c935e72139e6
	Issue introduced in 5.9 with commit 81033c6b584b and fixed in 6.9.3 with commit 6b8374ee2cab
	Issue introduced in 5.9 with commit 81033c6b584b and fixed in 6.10 with commit 39381fe7394e

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-2024-38605
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:
	sound/core/init.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/d7ff29a429b56f04783152ad7bbd7233b740e434
	https://git.kernel.org/stable/c/e7e0ca200772bdb2fdc6d43d32d341e87a36f811
	https://git.kernel.org/stable/c/e007476725730c1a68387b54b7629486d8a8301e
	https://git.kernel.org/stable/c/e644036a3e2b2c9b3eee3c61b5d31c2ca8b5ba92
	https://git.kernel.org/stable/c/c935e72139e6d523defd60fe875c01eb1f9ea5c5
	https://git.kernel.org/stable/c/6b8374ee2cabcf034faa34e69a855dc496a9ec12
	https://git.kernel.org/stable/c/39381fe7394e5eafac76e7e9367e7351138a29c1