Re: [PATCH] ASoC: dapm: Fix NULL pointer dereference in snd_soc_dapm_new_dai

[Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>]

On 3/21/19 7:31 AM, Mark Brown wrote:

> On Thu, Mar 21, 2019 at 03:41:25PM +0530, Pankaj Bharadiya wrote:
>
>>   outfree_kcontrol_news:
>>   	devm_kfree(card->dev, (void *)template.kcontrol_news);
>> -	snd_soc_dapm_free_kcontrol(card, &private_value,
>> -				   rtd->dai_link->num_params, w_param_text);
>> +	if (w_param_text)
>> +		snd_soc_dapm_free_kcontrol(card, &private_value,
>> +				rtd->dai_link->num_params, w_param_text);
> This is very non-obvious - it's not at all clear why we'd need the text
> to free controls.  If there is an issue here it seems like it'd be
> better to make sure that snd_soc_dapm_free_kcontrol() can cope with that
> being NULL, that will be clearer and also avoid potential issues with
> other callers.

I believe the issue is real, but you need to look at the entire code to figure it out

     /* allocate memory for control, only in case of multiple configs */
     if (rtd->dai_link->num_params > 1) {
         w_param_text = devm_kcalloc(card->dev,
                         rtd->dai_link->num_params,
                         sizeof(char *), GFP_KERNEL);
         if (!w_param_text) {
             ret = -ENOMEM;
             goto param_fail;
         }

         template.num_kcontrols = 1;
         template.kcontrol_news =
                     snd_soc_dapm_alloc_kcontrol(card,
                         link_name,
                         rtd->dai_link->params,
                         rtd->dai_link->num_params,
                         w_param_text, &private_value);
         if (!template.kcontrol_news) {
             ret = -ENOMEM;
             goto param_fail;
         }
     } else {
         w_param_text = NULL; <<<< this is set when there is a single config
     }
     dev_dbg(card->dev, "ASoC: adding %s widget\n", link_name);

     w = snd_soc_dapm_new_control_unlocked(&card->dapm, &template);
     if (IS_ERR(w)) {
         ret = PTR_ERR(w);
         goto outfree_kcontrol_news; <<< the control creation failed
     }

     w->priv = rtd;

     return w;

outfree_kcontrol_news:
     devm_kfree(card->dev, (void *)template.kcontrol_news);

<<< and in the function below we try to access w_param_text and private_value which haven't been allocated.

     snd_soc_dapm_free_kcontrol(card, &private_value,
                    rtd->dai_link->num_params, w_param_text);

That said I agree with Mark that it's better to change snd_soc_dapm_free_kcontrol directly.