Re: [PATCH master v2] nv: fix use-after-free when clearing from shell

[Sascha Hauer <s.hauer@pengutronix.de>]

On Thu, Nov 12, 2020 at 06:25:24PM +0100, Ahmad Fatoum wrote:
> When we use hush to set the same nv.var twice to the empty string:
> 
>   $ nv.user=
>   $ nv.user=
> 
> nv_set is called twice with a NULL val argument leading
> to a double free and accompanied memory corruption.
> 
> Reorder the code, so p->value is freed just once.
> 
> Fixes: fa4c41ba60af ("nvvar: when setting a nvvar to NULL just free the content")
> Cc: Holger Assmann <has@pengutronix.de>
> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
> ---
> v1 -> v2:
>   Use correct author email in DCO
> ---
>  common/globalvar.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)

Took this one instead of v1

Sascha

> 
> diff --git a/common/globalvar.c b/common/globalvar.c
> index 60793d7a30c6..a55b38b00fd5 100644
> --- a/common/globalvar.c
> +++ b/common/globalvar.c
> @@ -179,16 +179,12 @@ static int nv_set(struct device_d *dev, struct param_d *p, const char *name, con
>  {
>  	int ret;
>  
> -	if (!val) {
> -		if (p)
> -			free(p->value);
> -		return 0;
> +	if (val) {
> +		ret = dev_set_param(&global_device, name, val);
> +		if (ret)
> +			return ret;
>  	}
>  
> -	ret = dev_set_param(&global_device, name, val);
> -	if (ret)
> -		return ret;
> -
>  	if (p) {
>  		free(p->value);
>  		p->value = xstrdup(val);
> -- 
> 2.28.0
> 
> 
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