Re: [PATCH] sys: don't hold uts_sem while accessing userspace memory

[Al Viro]

On Mon, Jun 25, 2018 at 06:34:10PM +0200, Jann Horn wrote:

> +	char tmp[32];
>  
> -	if (namelen > 32)
> +	if (namelen < 0 || namelen > 32)
>  		namelen = 32;
>  
>  	down_read(&uts_sem);
>  	kname = utsname()->domainname;
>  	len = strnlen(kname, namelen);
> -	if (copy_to_user(name, kname, min(len + 1, namelen)))
> -		err = -EFAULT;
> +	len = min(len + 1, namelen);
> +	memcpy(tmp, kname, len);
>  	up_read(&uts_sem);
>  
> -	return err;
> +	if (copy_to_user(name, tmp, len))
> +		return -EFAULT;

Infoleak, and similar in a lot of other places.