linux-kernel - Re: [PATCH] libnvdimm, region: Use struct

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Date:   Wed, 28 Aug 2019 13:25:31 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Keith Busch <keith.busch@...el.com>,
        Ira Weiny <ira.weiny@...el.com>, linux-nvdimm@...ts.01.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] libnvdimm, region: Use struct_size() in kzalloc()

On Wed, Aug 28, 2019 at 01:30:24PM -0500, Gustavo A. R. Silva wrote:
> Hi all,
> 
> Friendly ping:
> 
> Who can take this, please?
> 
> Thanks
> --
> Gustavo
> 
> On 6/10/19 4:06 PM, 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@...eddedor.com>

FWIW,

Reviewed-by: Kees Cook <keescook@...omium.org>

-Kees

> > ---
> >  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;
> >  	}
> >  
> > 

-- 
Kees Cook