linux-kernel - Re: [patch v2] mfd: vexpress: fix error handling vexpress_syscfg_regmap

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Date:	Wed, 11 Jun 2014 11:33:20 +0100
From:	Pawel Moll <pawel.moll@....com>
To:	Dan Carpenter <dan.carpenter@...cle.com>,
	Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Lee Jones <lee.jones@...aro.org>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>
Subject: Re: [patch v2] mfd: vexpress: fix error handling
 vexpress_syscfg_regmap_init()

On Wed, 2014-06-11 at 11:17 +0100, Dan Carpenter wrote:
> This function should be returning an ERR_PTR() on failure instead of
> NULL.  Also there is a use after free bug if regmap_init() fails because
> we free "func" and then dereference doing the return.
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> 
> diff --git a/drivers/misc/vexpress-syscfg.c b/drivers/misc/vexpress-syscfg.c
> index 73068e5..3250fc1 100644
> --- a/drivers/misc/vexpress-syscfg.c
> +++ b/drivers/misc/vexpress-syscfg.c
> @@ -199,7 +199,7 @@ static struct regmap *vexpress_syscfg_regmap_init(struct device *dev,
>  	func = kzalloc(sizeof(*func) + sizeof(*func->template) * num,
>  			GFP_KERNEL);
>  	if (!func)
> -		return NULL;
> +		return ERR_PTR(-ENOMEM);
>  
>  	func->syscfg = syscfg;
>  	func->num_templates = num;
> @@ -231,10 +231,14 @@ static struct regmap *vexpress_syscfg_regmap_init(struct device *dev,
>  	func->regmap = regmap_init(dev, NULL, func,
>  			&vexpress_syscfg_regmap_config);
>  
> -	if (IS_ERR(func->regmap))
> +	if (IS_ERR(func->regmap)) {
> +		void *err = func->regmap;
> +
>  		kfree(func);
> -	else
> -		list_add(&func->list, &syscfg->funcs);
> +		return err;
> +	}
> +
> +	list_add(&func->list, &syscfg->funcs);
>  
>  	return func->regmap;
>  }

Uh, right. Dereferencing a freed structure. My bad. Thanks for spotting
this!

Acked-by: Pawel Moll <pawel.moll@....com>

(nit: the subject should be "misc: vexpress:" rather then "mfd:")

Arnd, Olof, can you pick this one as an early fix or do you want me to
queue it for rc1-based fixes branch?

Paweł

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