[PATCH] cpumask: fix double string traverse in cpumask_parse

[PATCH] cpumask: fix double string traverse in cpumask_parse

[Yury Norov]

From: Yury Norov <ynorov@marvell.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@marvell.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);
 
 	return bitmap_parse(buf, len, cpumask_bits(dstp), nr_cpumask_bits);
 }
-- 
2.17.1

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

[Rasmus Villemoes]

On 09/04/2019 22.42, Yury Norov wrote:
> From: Yury Norov <ynorov@marvell.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@marvell.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

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@gmail.com> wrote:

> From: Yury Norov <ynorov@marvell.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().

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);
>  }

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

[Yury Norov]

On Tue, Apr 09, 2019 at 11:31:50PM +0200, Rasmus Villemoes wrote:
> On 09/04/2019 22.42, Yury Norov wrote:
> > From: Yury Norov <ynorov@marvell.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@marvell.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;"

Indeed. See below.

Thanks,
Yury

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

From: Yury Norov <ynorov@marvell.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@marvell.com>
Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
 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 = strchrnul(buf, '\n') - buf;
 
 	return bitmap_parse(buf, len, cpumask_bits(dstp), nr_cpumask_bits);
 }
-- 
2.17.1