linux-kernel - Re: [PATCH] ALSA: pcm: Remove VLA usage

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Date:   Tue, 13 Mar 2018 22:59:10 +0900
From:   Takashi Sakamoto <o-takashi@...amocchi.jp>
To:     Takashi Iwai <tiwai@...e.de>, alsa-devel@...a-project.org
Cc:     Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ALSA: pcm: Remove VLA usage

Hi,

On Mar 13 2018 20:37, Takashi Iwai wrote:
> A helper function used by snd_pcm_hw_refine() still keeps using VLA
> for timestamps of hw constraint rules that are non-fixed size.
> 
> Let's replace the VLA with a simple kmalloc() array.
> 
> Reference: https://lkml.org/lkml/2018/3/7/621
> Signed-off-by: Takashi Iwai <tiwai@...e.de>
> ---
>   sound/core/pcm_native.c | 19 ++++++++++++-------
>   1 file changed, 12 insertions(+), 7 deletions(-)

Yeah. I have concerned about it for a long time but kept it as is 
because it had no issue. Now, let's obsolete it.

Reviewed-by: Takashi Sakamoto <o-takashi@...amocchi.jp>

> diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
> index 77ba50ddcf9e..756a9a3884a5 100644
> --- a/sound/core/pcm_native.c
> +++ b/sound/core/pcm_native.c
> @@ -323,7 +323,7 @@ static int constrain_params_by_rules(struct snd_pcm_substream *substream,
>   	struct snd_pcm_hw_constraints *constrs =
>   					&substream->runtime->hw_constraints;
>   	unsigned int k;
> -	unsigned int rstamps[constrs->rules_num];
> +	unsigned int *rstamps;
>   	unsigned int vstamps[SNDRV_PCM_HW_PARAM_LAST_INTERVAL + 1];
>   	unsigned int stamp;
>   	struct snd_pcm_hw_rule *r;
> @@ -331,7 +331,7 @@ static int constrain_params_by_rules(struct snd_pcm_substream *substream,
>   	struct snd_mask old_mask;
>   	struct snd_interval old_interval;
>   	bool again;
> -	int changed;
> +	int changed, err = 0;
>   
>   	/*
>   	 * Each application of rule has own sequence number.
> @@ -339,8 +339,9 @@ static int constrain_params_by_rules(struct snd_pcm_substream *substream,
>   	 * Each member of 'rstamps' array represents the sequence number of
>   	 * recent application of corresponding rule.
>   	 */
> -	for (k = 0; k < constrs->rules_num; k++)
> -		rstamps[k] = 0;
> +	rstamps = kcalloc(constrs->rules_num, sizeof(unsigned int), GFP_KERNEL);
> +	if (!rstamps)
> +		return -ENOMEM;
>   
>   	/*
>   	 * Each member of 'vstamps' array represents the sequence number of
> @@ -398,8 +399,10 @@ static int constrain_params_by_rules(struct snd_pcm_substream *substream,
>   		}
>   
>   		changed = r->func(params, r);
> -		if (changed < 0)
> -			return changed;
> +		if (changed < 0) {
> +			err = changed;
> +			goto out;
> +		}
>   
>   		/*
>   		 * When the parameter is changed, notify it to the caller
> @@ -430,7 +433,9 @@ static int constrain_params_by_rules(struct snd_pcm_substream *substream,
>   	if (again)
>   		goto retry;
>   
> -	return 0;
> + out:
> +	kfree(rstamps);
> +	return err;
>   }
>   
>   static int fixup_unreferenced_params(struct snd_pcm_substream *substream,


Thanks

Takashi Sakamoto