Re: [PATCH] libnvdimm, region: Use struct_size() in kzalloc()

[Verma, Vishal L]

On Mon, 2019-06-10 at 16:06 -0500, Gustavo A. R. Silva wrote:
> One of the more common cases of allocation size calculations is
> finding
> the size of a structure that has a zero-sized array at the end, along
> with memory for some number of elements for that array. For example:
> 
> struct nd_region {
> 	...
>         struct nd_mapping mapping[0];
> };
> 
> instance = kzalloc(sizeof(struct nd_region) + sizeof(struct
> nd_mapping) *
>                           count, GFP_KERNEL);
> 
> Instead of leaving these open-coded and prone to type mistakes, we can
> now use the new struct_size() helper:
> 
> instance = kzalloc(struct_size(instance, mapping, count), GFP_KERNEL);
> 
> This code was detected with the help of Coccinelle.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
> ---
>  drivers/nvdimm/region_devs.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/nvdimm/region_devs.c
> b/drivers/nvdimm/region_devs.c
> index b4ef7d9ff22e..88becc87e234 100644
> --- a/drivers/nvdimm/region_devs.c
> +++ b/drivers/nvdimm/region_devs.c
> @@ -1027,10 +1027,9 @@ static struct nd_region
> *nd_region_create(struct nvdimm_bus *nvdimm_bus,
>  		}
>  		region_buf = ndbr;
>  	} else {
> -		nd_region = kzalloc(sizeof(struct nd_region)
> -				+ sizeof(struct nd_mapping)
> -				* ndr_desc->num_mappings,
> -				GFP_KERNEL);
> +		nd_region = kzalloc(struct_size(nd_region, mapping,
> +						ndr_desc->num_mappings),
> +				    GFP_KERNEL);
>  		region_buf = nd_region;
>  	}
>  

Hi Gustavo,

The patch looks good to me, however it looks like it might've missed
some instances where this replacement can be performed?

One is just a few lines below from the above, in the 'else' block[1].
Additionally, maybe the Coccinelle script can be augmented to catch
devm_kzalloc instances as well - there is one of those in this file[2].

Thanks,
	-Vishal

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm.git/tree/drivers/nvdimm/region_devs.c#n1030
[2]: https://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm.git/tree/drivers/nvdimm/region_devs.c#n96