linux-kernel - Re: [PATCH v2] media: camss: Intepret OF graph connections more sensibly

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Message-ID: <ZLUcaQN6hCjjulTv@hovoldconsulting.com>
Date:   Mon, 17 Jul 2023 12:48:09 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     Robert Foss <rfoss@...nel.org>, Todor Tomov <todor.too@...il.com>,
        Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        Yassine Oudjana <y.oudjana@...tonmail.com>,
        linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] media: camss: Intepret OF graph connections more
 sensibly

On Sat, Jul 15, 2023 at 05:37:52PM +0200, Konrad Dybcio wrote:
> Not all endpoints of camss have to be populated. In fact, most of the
> time they shouldn't be as n-th auxilliary cameras are usually ewaste.
> 
> Don't fail probing the entire camss even even one endpoint is not
> linked and throw an error when none is found.
> 
> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
> ---
> Changes in v2:
> - Use if-else instead of the ternary operator (Bryan)
> - Drop "RFC"
> - Link to v1: https://lore.kernel.org/r/20230614-topic-camss_grpah-v1-1-5f4b516310fa@linaro.org
> ---
>  drivers/media/platform/qcom/camss/camss.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/media/platform/qcom/camss/camss.c b/drivers/media/platform/qcom/camss/camss.c
> index 1ef26aea3eae..8b75197fa5d7 100644
> --- a/drivers/media/platform/qcom/camss/camss.c
> +++ b/drivers/media/platform/qcom/camss/camss.c
> @@ -1084,9 +1084,8 @@ static int camss_of_parse_ports(struct camss *camss)
>  
>  		remote = of_graph_get_remote_port_parent(node);
>  		if (!remote) {
> -			dev_err(dev, "Cannot get remote parent\n");
> -			ret = -EINVAL;
> -			goto err_cleanup;
> +			of_node_put(node);

This is broken and could potentially lead to a use after free.

Specifically, the iteration macro already takes care of putting this
reference.

> +			continue;
>  		}
>  
>  		csd = v4l2_async_nf_add_fwnode(&camss->notifier,
> @@ -1105,7 +1104,10 @@ static int camss_of_parse_ports(struct camss *camss)
>  		num_subdevs++;
>  	}
>  
> -	return num_subdevs;
> +	if (num_subdevs)
> +		return num_subdevs;
> +
> +	return -EINVAL;

Please change this so that you test for the error condition rather than
its inverse for symmetry. That is

	if (!num_subdevs)
		return -EINVAL;

	return num_subdevs;

Returning EINVAL (invalid argument) is perhaps not the best choice, but
the driver already does so here and in other places so keeping it for
now should be fine.

>  err_cleanup:
>  	of_node_put(node);

Johan