Re: [PATCH v2] s390/chsc: Switch over to memdup_user()

[Alexander Gordeev]

On Wed, Jan 18, 2023 at 05:58:23PM +0800, Jiapeng Chong wrote:
> Use memdup_user rather than duplicating its implementation, this is a
> little bit restricted to reduce false positives.
> 
> ./drivers/s390/cio/chsc_sch.c:703:7-14: WARNING opportunity for
> memdup_user.
> 
> Link: https://bugzilla.openanolis.cn/show_bug.cgi?id=3785
> Reported-by: Abaci Robot <abaci@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Jiapeng Chong <jiapeng.chong@xxxxxxxxxxxxxxxxx>
> ---
> Changes in v2:
>   -Add free_page((unsigned long)sccl_area); 
> 
>  drivers/s390/cio/chsc_sch.c | 14 ++++++--------
>  1 file changed, 6 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/s390/cio/chsc_sch.c b/drivers/s390/cio/chsc_sch.c
> index 180ab899289c..09dcce7ff24b 100644
> --- a/drivers/s390/cio/chsc_sch.c
> +++ b/drivers/s390/cio/chsc_sch.c
> @@ -700,15 +700,13 @@ static int chsc_ioctl_conf_comp_list(void __user *user_ccl)
>  	sccl_area = (void *)get_zeroed_page(GFP_KERNEL | GFP_DMA);
>  	if (!sccl_area)
>  		return -ENOMEM;
> -	ccl = kzalloc(sizeof(*ccl), GFP_KERNEL);
> -	if (!ccl) {
> -		ret = -ENOMEM;
> -		goto out_free;
> -	}
> -	if (copy_from_user(ccl, user_ccl, sizeof(*ccl))) {
> -		ret = -EFAULT;
> -		goto out_free;
> +
> +	ccl = memdup_user(user_ccl, sizeof(*ccl));
> +	if (IS_ERR(ccl)) {
> +		free_page((unsigned long)sccl_area);
> +		return PTR_ERR(ccl);
>  	}
> +
>  	sccl_area->request.length = 0x0020;
>  	sccl_area->request.code = 0x0030;
>  	sccl_area->fmt = ccl->req.fmt;

Such a change would have to address other similar patterns in this source.
Besides, it is not that obvious that swapping GFP_KERNEL for GFP_USER
(memdup_user() is called with) is issue-free.