CVE-2024-38605

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.