linux-kernel - Re: [PATCH] reset: Fix potential use-after-free in __of_reset_control

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Date:   Mon, 08 Oct 2018 14:56:15 +0200
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH] reset: Fix potential use-after-free in
 __of_reset_control_get()

Hi Geert,

On Mon, 2018-10-08 at 13:14 +0200, Geert Uytterhoeven wrote:
> Calling of_node_put() decreases the reference count of a device tree
> object, and may free some data.
> 
> However, the of_phandle_args structure embedding it is passed to
> reset_controller_dev.of_xlate() after that, so it may still be accessed.
> 
> Move the call to of_node_put() down to fix this.
> 
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
>  drivers/reset/core.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/reset/core.c b/drivers/reset/core.c
> index 225e34c56b94a2e3..bc9df10d31b4bae1 100644
> --- a/drivers/reset/core.c
> +++ b/drivers/reset/core.c
> @@ -496,27 +496,28 @@ struct reset_control *__of_reset_control_get(struct device_node *node,
>  			break;
>  		}
>  	}
> -	of_node_put(args.np);
>  
>  	if (!rcdev) {
> -		mutex_unlock(&reset_list_mutex);
> -		return ERR_PTR(-EPROBE_DEFER);
> +		rstc = ERR_PTR(-EPROBE_DEFER);
> +		goto out;
>  	}
>  
>  	if (WARN_ON(args.args_count != rcdev->of_reset_n_cells)) {
> -		mutex_unlock(&reset_list_mutex);
> -		return ERR_PTR(-EINVAL);
> +		rstc = ERR_PTR(-EINVAL);
> +		goto out;
>  	}
>  
>  	rstc_id = rcdev->of_xlate(rcdev, &args);
>  	if (rstc_id < 0) {
> -		mutex_unlock(&reset_list_mutex);
> -		return ERR_PTR(rstc_id);
> +		rstc = ERR_PTR(rstc_id);
> +		goto out;
>  	}
>  
>  	/* reset_list_mutex also protects the rcdev's reset_control list */
>  	rstc = __reset_control_get_internal(rcdev, rstc_id, shared);
>  
> +out:
> +	of_node_put(args.np);
>  	mutex_unlock(&reset_list_mutex);

Thank you for the patch. I'd like to move of_node_put after mutex_unlock
for symmetry. If you agree, I can switch the two when applying.

regards
Philipp