CVE-2024-26654

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.