linux-kernel - Re: [PATCH] cpumask: fix double string traverse in cpumask

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Message-ID: <b3ce41ca-6a20-a53d-7db2-451e3e700040@rasmusvillemoes.dk>
Date:   Tue, 9 Apr 2019 23:31:50 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Yury Norov <yury.norov@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Amritha Nambiar <amritha.nambiar@...el.com>,
        "David S. Miller" <davem@...emloft.net>, Tejun Heo <tj@...nel.org>,
        Willem de Bruijn <willemb@...gle.com>
Cc:     Yury Norov <ynorov@...vell.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpumask: fix double string traverse in cpumask_parse

On 09/04/2019 22.42, Yury Norov wrote:
> From: Yury Norov <ynorov@...vell.com>
> 
> 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().
> 
> Signed-off-by: Yury Norov <ynorov@...vell.com>
> ---
>  include/linux/cpumask.h | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
> index 147bdec42215..2b87f35c586c 100644
> --- 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);

ack, but please drop the cast. "len = strchrnul(buf, '\n') - buf;"

Rasmus