linux-kernel - Re: [PATCH v2 7/9] mfd: mfd-core: Protect against NULL call-back function pointer

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Message-ID: <20191021123012.qpk7tgyjtwp3wtxv@holly.lan>
Date:   Mon, 21 Oct 2019 13:30:12 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     arnd@...db.de, broonie@...nel.org, linus.walleij@...aro.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        baohua@...nel.org, stephan@...hold.net
Subject: Re: [PATCH v2 7/9] mfd: mfd-core: Protect against NULL call-back
 function pointer

On Mon, Oct 21, 2019 at 11:58:20AM +0100, Lee Jones wrote:
> If a child device calls mfd_cell_{en,dis}able() without an appropriate
> call-back being set, we are likely to encounter a panic.  Avoid this
> by adding suitable checking.
> 
> Signed-off-by: Lee Jones <lee.jones@...aro.org>

Reviewed-by: Daniel Thompson <daniel.thompson@...aro.org>

> ---
>  drivers/mfd/mfd-core.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/mfd/mfd-core.c b/drivers/mfd/mfd-core.c
> index 8126665bb2d8..90b43b44a15a 100644
> --- a/drivers/mfd/mfd-core.c
> +++ b/drivers/mfd/mfd-core.c
> @@ -28,6 +28,11 @@ int mfd_cell_enable(struct platform_device *pdev)
>  	const struct mfd_cell *cell = mfd_get_cell(pdev);
>  	int err = 0;
>  
> +	if (!cell->enable) {
> +		dev_dbg(&pdev->dev, "No .enable() call-back registered\n");
> +		return 0;
> +	}
> +
>  	/* only call enable hook if the cell wasn't previously enabled */
>  	if (atomic_inc_return(cell->usage_count) == 1)
>  		err = cell->enable(pdev);
> @@ -45,6 +50,11 @@ int mfd_cell_disable(struct platform_device *pdev)
>  	const struct mfd_cell *cell = mfd_get_cell(pdev);
>  	int err = 0;
>  
> +	if (!cell->enable) {
> +		dev_dbg(&pdev->dev, "No .disable() call-back registered\n");
> +		return 0;
> +	}
> +
>  	/* only disable if no other clients are using it */
>  	if (atomic_dec_return(cell->usage_count) == 0)
>  		err = cell->disable(pdev);
> -- 
> 2.17.1
>