CVE-2026-53193

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

ALSA: timer: Forcibly close timer instances at closing

When snd_timer object is freed via snd_timer_free() and still pending snd_timer_instance objects are assigned to the timer object, it tries to unlink all instances and just set NULL to each ti->timer, then releases the resources immediately. The problem is, however, when there are slave timer instances that are associated with a master instance linked to this timer: namely, those slave instances still point to the freed timer object although the master instance is unlinked, which may lead to user-after-free. The bug can be easily triggered particularly when a new userspace-driven timers (CONFIG_SND_UTIMER) is involved, since it can create and delete the timer object via a simple file open/close, while the other applications may keep accessing to that timer.

This patch is an attempt to paper over the problem above: now instead of just unlinking, call snd_timer_close_locked forcibly for each pending timer instance, so that all assigned slave timer instances are properly detached, too. Since snd_timer_close() might be called later by the driver that created that instance, the check of SNDRV_TIMER_IFLG_DEAD is added at the beginning, too.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/586b219a22b1032b28b8bd356b963276c5e5bf53
• https://git.kernel.org/stable/c/60e73ab87b84bbd6bd7ddd1d16019a3a3705ab8f
• https://git.kernel.org/stable/c/da3039e91d1f835874ed6e9a33ea19ee80c2cb92
• https://git.kernel.org/stable/c/f46093dd22969037beb1fce2e043f3236be41c92