[PATCH] ASoC: soc-pcm: fix fe and be race when accessing substream->runtime

[Amadeusz Sławiński]

On 9/26/2022 6:35 PM, Eugeniu Rosca wrote:
> From: xiao jin <jin.xiao at intel.com>
> 
> After start of fe and be, fe might go to close without triggering
> STOP, and substream->runtime is freed. However, be is still at
> START state and its substream->runtime still points to the
> freed runtime.
> 

Well if it is being freed, maybe pointer should be set to NULL instead 
in place that happens?

> Later on, FE is opened/started again, and triggers STOP.
> snd_pcm_do_stop => dpcm_fe_dai_trigger
>                  => dpcm_fe_dai_do_trigger
>                  => dpcm_be_dai_trigger
>                  => dpcm_do_trigger
>                  => soc_pcm_trigger
>                  => skl_platform_pcm_trigger
> skl_platform_pcm_trigger accesses the freed old runtime data and
> kernel panic.
> 
> The patch fixes it by assigning be_substream->runtime in
> dpcm_be_dai_startup when be's state is START.
> 
> Signed-off-by: xiao jin <jin.xiao at intel.com>
> Signed-off-by: Zhang Yanmin <yanmin.zhang at intel.com>
> Signed-off-by: Eugeniu Rosca <erosca at de.adit-jv.com>
> ---
>   sound/soc/soc-pcm.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/sound/soc/soc-pcm.c b/sound/soc/soc-pcm.c
> index 4f60c0a83311..6ca1d02065ce 100644
> --- a/sound/soc/soc-pcm.c
> +++ b/sound/soc/soc-pcm.c
> @@ -1608,6 +1608,8 @@ int dpcm_be_dai_startup(struct snd_soc_pcm_runtime *fe, int stream)
>   		if (be->dpcm[stream].users++ != 0)
>   			continue;
>   
> +		be_substream->runtime = be->dpcm[stream].runtime;
> +
>   		if ((be->dpcm[stream].state != SND_SOC_DPCM_STATE_NEW) &&
>   		    (be->dpcm[stream].state != SND_SOC_DPCM_STATE_CLOSE))
>   			continue;
> @@ -1615,7 +1617,6 @@ int dpcm_be_dai_startup(struct snd_soc_pcm_runtime *fe, int stream)
>   		dev_dbg(be->dev, "ASoC: open %s BE %s\n",
>   			stream ? "capture" : "playback", be->dai_link->name);
>   
> -		be_substream->runtime = be->dpcm[stream].runtime;
>   		err = __soc_pcm_open(be, be_substream);
>   		if (err < 0) {
>   			be->dpcm[stream].users--;