linux-kernel - Re: [PATCH 3/3] input: misc: pm8941-pwrkey: avoid potential null pointer dereference

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Message-ID: <YenpwnE3WrIEAOlm@ripper>
Date:   Thu, 20 Jan 2022 15:01:22 -0800
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Anjelique Melendez <quic_amelende@...cinc.com>
Cc:     dmitry.torokhov@...il.com, linux-input@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        collinsd@...eaurora.org, swboyd@...omium.org, skakit@...eaurora.org
Subject: Re: [PATCH 3/3] input: misc: pm8941-pwrkey: avoid potential null
 pointer dereference

On Thu 20 Jan 12:41 PST 2022, Anjelique Melendez wrote:

> From: David Collins <collinsd@...eaurora.org>
> 
> Add a null check for the pwrkey->data pointer after it is assigned
> in pm8941_pwrkey_probe().  This avoids a potential null pointer
> dereference when pwrkey->data->has_pon_pbs is accessed later in
> the probe function.
> 
> Change-Id: I589c4851e544d79a1863fd110b32a0b45ac03caf
> Signed-off-by: David Collins <collinsd@...eaurora.org>
> Signed-off-by: Anjelique Melendez <quic_amelende@...cinc.com>
> ---
>  drivers/input/misc/pm8941-pwrkey.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/input/misc/pm8941-pwrkey.c b/drivers/input/misc/pm8941-pwrkey.c
> index 0ce00736e695..ac08ed025802 100644
> --- a/drivers/input/misc/pm8941-pwrkey.c
> +++ b/drivers/input/misc/pm8941-pwrkey.c
> @@ -263,6 +263,10 @@ static int pm8941_pwrkey_probe(struct platform_device *pdev)
>  
>  	pwrkey->dev = &pdev->dev;
>  	pwrkey->data = of_device_get_match_data(&pdev->dev);
> +	if (!pwrkey->data) {

The only way this can happen is if you add a new compatible and forget
to specify data and when that happens you will get a print in the log
somewhere, which once you realize that you don't have your pwrkey you
might be able to find among all the other prints.

If you instead don't NULL check this pointer you will get a large splat
in the log, with callstack and all, immediately hinting you that
pwrkey->data is NULL.


In other words, there's already a print, a much larger print and I don't
think there's value in handling this mistake gracefully.

Regards,
Bjorn

> +		dev_err(&pdev->dev, "match data not found\n");
> +		return -ENODEV;
> +	}
>  
>  	parent = pdev->dev.parent;
>  	regmap_node = pdev->dev.of_node;
> -- 
> 2.34.1
>