CVE-2024-26654 Information

Description

In the Linux kernel the following vulnerability has been resolved:

ALSA: sh: aica: reorder cleanup operations to avoid UAF bugs

The dreamcastcard->timer could schedule the spu_dma_work and the spu_dma_work could also arm the dreamcastcard->timer.

When the snd_pcm_substream is closing the aica_channel will be deallocated. But it could still be dereferenced in the worker thread. The reason is that del_timer() will return directly regardless of whether the timer handler is running or not and the worker could be rescheduled in the timer handler. As a result the UAF bug will happen. The racy situation is shown below:

  (Thread 1)                 |      (Thread 2)

snd_aicapcm_pcm_close() | … | run_spu_dma() //worker | mod_timer() flush_work() | del_timer() | aica_period_elapsed() //timer kfree(dreamcastcard->channel) | schedule_work() | run_spu_dma() //worker … | dreamcastcard->channel-> //USE

In order to mitigate this bug and other possible corner cases call mod_timer() conditionally in run_spu_dma() then implement PCM sync_stop op to cancel both the timer and worker. The sync_stop op will be called from PCM core appropriately when needed.

Reference

https://git.kernel.org/stable/c/051e0840ffa8ab25554d6b14b62c9ab9e4901457