| 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.
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