Re: [PATCH] cpumask: fix double string traverse in cpumask_parse

[Andrew Morton]

On Tue,  9 Apr 2019 13:42:08 -0700 Yury Norov <yury.norov@xxxxxxxxx> wrote:

> From: Yury Norov <ynorov@xxxxxxxxxxx>
> 
> cpumask_parse() finds first occurrence of either \n or \0 by calling
> strchr() and strlen(). We can do it better with a single call of
> strchrnul().

Fair enough.

> --- a/include/linux/cpumask.h
> +++ b/include/linux/cpumask.h
> @@ -633,8 +633,7 @@ static inline int cpumask_parselist_user(const char __user *buf, int len,
>   */
>  static inline int cpumask_parse(const char *buf, struct cpumask *dstp)
>  {
> -	char *nl = strchr(buf, '\n');
> -	unsigned int len = nl ? (unsigned int)(nl - buf) : strlen(buf);
> +	unsigned int len = (unsigned int)(strchrnul(buf, '\n') - buf);

Does the cast do anything useful?  The compiler will convert a
ptrdiff_t to uint without issues, I think?

>  	return bitmap_parse(buf, len, cpumask_bits(dstp), nr_cpumask_bits);
>  }