[PATCH 0/2][next] Use flexible_array_size() helper in memcpy()

[PATCH 0/2][next] Use flexible_array_size() helper in memcpy()

[Gustavo A. R. Silva]

Hi,

This small series aims to:

1. Make use of the flexible_array_size() helper in a call to memcpy()
2. While there, use the preferred form for passing the size of a structure type

Thanks

Gustavo A. R. Silva (2):
  mm: memcontrol: Use flex_array_size() helper in memcpy()
  mm: memcontrol: Use the preferred form for passing the size of a
    structure type

 mm/memcontrol.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

-- 
2.27.0

[PATCH 1/2][next] mm: memcontrol: Use flex_array_size() helper in memcpy()

[Gustavo A. R. Silva]

Make use of the flex_array_size() helper to calculate the size of a
flexible array member within an enclosing structure.

This helper offers defense-in-depth against potential integer
overflows, while at the same time makes it explicitly clear that
we are dealing with a flexible array member.

Also, remove unnecessary braces.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 mm/memcontrol.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e84c2b5596f2..bd7f972ceea4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4246,10 +4246,9 @@ static int __mem_cgroup_usage_register_event(struct mem_cgroup *memcg,
 	new->size = size;
 
 	/* Copy thresholds (if any) to new array */
-	if (thresholds->primary) {
-		memcpy(new->entries, thresholds->primary->entries, (size - 1) *
-				sizeof(struct mem_cgroup_threshold));
-	}
+	if (thresholds->primary)
+		memcpy(new->entries, thresholds->primary->entries,
+		       flex_array_size(new, entries, size - 1));
 
 	/* Add new threshold */
 	new->entries[size - 1].eventfd = eventfd;
-- 
2.27.0

[PATCH 2/2][next] mm: memcontrol: Use the preferred form for passing the size of a structure type

[Gustavo A. R. Silva]

Use the preferred form for passing the size of a structure type. The
alternative form where the structure type is spelled out hurts
readability and introduces an opportunity for a bug when the object
type is changed but the corresponding object identifier to which the
sizeof operator is applied is not.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 mm/memcontrol.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index bd7f972ceea4..bd0f56785841 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4255,7 +4255,7 @@ static int __mem_cgroup_usage_register_event(struct mem_cgroup *memcg,
 	new->entries[size - 1].threshold = threshold;
 
 	/* Sort thresholds. Registering of new threshold isn't time-critical */
-	sort(new->entries, size, sizeof(struct mem_cgroup_threshold),
+	sort(new->entries, size, sizeof(*new->entries),
 			compare_thresholds, NULL);
 
 	/* Find current threshold */
-- 
2.27.0

Re: [PATCH 1/2][next] mm: memcontrol: Use flex_array_size() helper in memcpy()

[Michal Hocko]

On Fri 31-07-20 12:12:53, Gustavo A. R. Silva wrote:
> Make use of the flex_array_size() helper to calculate the size of a
> flexible array member within an enclosing structure.
> 
> This helper offers defense-in-depth against potential integer
> overflows, while at the same time makes it explicitly clear that
> we are dealing with a flexible array member.
> 
> Also, remove unnecessary braces.

I was not aware of this helper. The code looks slightly better.
 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Acked-by: Michal Hocko <mhocko@suse.com>
> ---
>  mm/memcontrol.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index e84c2b5596f2..bd7f972ceea4 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4246,10 +4246,9 @@ static int __mem_cgroup_usage_register_event(struct mem_cgroup *memcg,
>  	new->size = size;
>  
>  	/* Copy thresholds (if any) to new array */
> -	if (thresholds->primary) {
> -		memcpy(new->entries, thresholds->primary->entries, (size - 1) *
> -				sizeof(struct mem_cgroup_threshold));
> -	}
> +	if (thresholds->primary)
> +		memcpy(new->entries, thresholds->primary->entries,
> +		       flex_array_size(new, entries, size - 1));
>  
>  	/* Add new threshold */
>  	new->entries[size - 1].eventfd = eventfd;
> -- 
> 2.27.0

-- 
Michal Hocko
SUSE Labs

Re: [PATCH 2/2][next] mm: memcontrol: Use the preferred form for passing the size of a structure type

[Michal Hocko]

On Fri 31-07-20 12:13:14, Gustavo A. R. Silva wrote:
> Use the preferred form for passing the size of a structure type. The
> alternative form where the structure type is spelled out hurts
> readability and introduces an opportunity for a bug when the object
> type is changed but the corresponding object identifier to which the
> sizeof operator is applied is not.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  mm/memcontrol.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index bd7f972ceea4..bd0f56785841 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4255,7 +4255,7 @@ static int __mem_cgroup_usage_register_event(struct mem_cgroup *memcg,
>  	new->entries[size - 1].threshold = threshold;
>  
>  	/* Sort thresholds. Registering of new threshold isn't time-critical */
> -	sort(new->entries, size, sizeof(struct mem_cgroup_threshold),
> +	sort(new->entries, size, sizeof(*new->entries),
>  			compare_thresholds, NULL);
>  
>  	/* Find current threshold */
> -- 
> 2.27.0

-- 
Michal Hocko
SUSE Labs