linux-kernel - Re: [PATCH 1/3] ASoC: Intel: catpt: remove check of list iterator against head past the loop body

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Message-ID: <c69ee5e5-213f-389c-9d22-69addddf2aca@intel.com>
Date:   Fri, 1 Apr 2022 09:00:09 +0200
From:   Cezary Rojewski <cezary.rojewski@...el.com>
To:     Jakob Koschel <jakobkoschel@...il.com>
CC:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Liam Girdwood <liam.r.girdwood@...ux.intel.com>,
        Jie Yang <yang.jie@...ux.intel.com>,
        "Mark Brown" <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Orson Zhai <orsonzhai@...il.com>,
        Baolin Wang <baolin.wang7@...il.com>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        "Yang Yingliang" <yangyingliang@...wei.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <alsa-devel@...a-project.org>,
        Mike Rapoport <rppt@...nel.org>,
        Brian Johannesmeyer <bjohannesmeyer@...il.com>,
        "Cristiano Giuffrida" <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>,
        Codrin Ciubotariu <codrin.ciubotariu@...rochip.com>
Subject: Re: [PATCH 1/3] ASoC: Intel: catpt: remove check of list iterator
 against head past the loop body

On 2022-03-31 11:50 PM, Jakob Koschel wrote:
> When list_for_each_entry() completes the iteration over the whole list
> without breaking the loop, the iterator value will be a bogus pointer
> computed based on the head element.
> 
> While it is safe to use the pointer to determine if it was computed
> based on the head element, either with list_entry_is_head() or
> &pos->member == head, using the iterator variable after the loop should
> be avoided.
> 
> In preparation to limiting the scope of a list iterator to the list
> traversal loop, use a dedicated pointer to point to the found element [1].
> 
> Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/ [1]
> Signed-off-by: Jakob Koschel <jakobkoschel@...il.com>

Thank you for taking time and updating catpt-driver along the way.

Acked-by: Cezary Rojewski <cezary.rojewski@...el.com>

> ---
>   sound/soc/intel/catpt/pcm.c | 13 ++++++++-----
>   1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/sound/soc/intel/catpt/pcm.c b/sound/soc/intel/catpt/pcm.c
> index a26000cd5ceb..b103b2d4026e 100644
> --- a/sound/soc/intel/catpt/pcm.c
> +++ b/sound/soc/intel/catpt/pcm.c
> @@ -330,7 +330,8 @@ static int catpt_dai_apply_usettings(struct snd_soc_dai *dai,
>   				     struct catpt_stream_runtime *stream)
>   {
>   	struct snd_soc_component *component = dai->component;
> -	struct snd_kcontrol *pos;
> +	struct snd_kcontrol *pos = NULL;
> +	struct snd_kcontrol *iter;
>   	struct catpt_dev *cdev = dev_get_drvdata(dai->dev);
>   	const char *name;
>   	int ret;
> @@ -354,12 +355,14 @@ static int catpt_dai_apply_usettings(struct snd_soc_dai *dai,
>   		return 0;
>   	}
>   
> -	list_for_each_entry(pos, &component->card->snd_card->controls, list) {
> -		if (pos->private_data == component &&
> -		    !strncmp(name, pos->id.name, sizeof(pos->id.name)))
> +	list_for_each_entry(iter, &component->card->snd_card->controls, list) {
> +		if (iter->private_data == component &&
> +		    !strncmp(name, iter->id.name, sizeof(iter->id.name))) {
> +			pos = iter;
>   			break;
> +		}
>   	}
> -	if (list_entry_is_head(pos, &component->card->snd_card->controls, list))
> +	if (!pos)
>   		return -ENOENT;
>   
>   	if (stream->template->type != CATPT_STRM_TYPE_LOOPBACK)
> 
> base-commit: f82da161ea75dc4db21b2499e4b1facd36dab275