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

Vulnerability 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.

References

• https://git.kernel.org/stable/c/eeb2a2ca0b8de7e1c66afaf719529154e7dc60b2
• https://git.kernel.org/stable/c/4206ad65a0ee76920041a755bd3c17c6ba59bba2
• https://git.kernel.org/stable/c/aa39e6878f61f50892ee2dd9d2176f72020be845
• https://git.kernel.org/stable/c/8c990221681688da34295d6d76cc2f5b963e83f5
• https://git.kernel.org/stable/c/9d66ae0e7bb78b54e1e0525456c6b54e1d132046
• https://git.kernel.org/stable/c/61d4787692c1fccdc268ffa7a891f9c149f50901
• https://git.kernel.org/stable/c/e955e8a7f38a856fc6534ba4e6bffd4d5cc80ac3
• https://git.kernel.org/stable/c/3c907bf56905de7d27b329afaf59c2fb35d17b04
• https://git.kernel.org/stable/c/051e0840ffa8ab25554d6b14b62c9ab9e4901457