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 doesnt 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 its 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 wont catch perfectly, i.e. no check is performed when CONFIG_SND=y. But, its no real problem as its only for debugging, and the condition is pretty rare.

Weakness

A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/39381fe7394e5eafac76e7e9367e7351138a29c1
• https://git.kernel.org/stable/c/6b8374ee2cabcf034faa34e69a855dc496a9ec12
• https://git.kernel.org/stable/c/c935e72139e6d523defd60fe875c01eb1f9ea5c5
• https://git.kernel.org/stable/c/d7ff29a429b56f04783152ad7bbd7233b740e434
• https://git.kernel.org/stable/c/e007476725730c1a68387b54b7629486d8a8301e
• https://git.kernel.org/stable/c/e644036a3e2b2c9b3eee3c61b5d31c2ca8b5ba92
• https://git.kernel.org/stable/c/e7e0ca200772bdb2fdc6d43d32d341e87a36f811