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

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

[Gustavo A. R. Silva]

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@embeddedor.com>
---
 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;
 	}
 
-- 
2.21.0

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

[Gustavo A. R. Silva]

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@embeddedor.com>
> ---
>  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;
>  	}
>  
> 

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@embeddedor.com>
> ---
>  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

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

[Gustavo A. R. Silva]

Hi Vishal,

On 8/28/19 1:51 PM, Verma, Vishal L wrote:

[..]

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

struct_size() does not apply to those scenarios. See below...

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

struct_size() only applies to structures of the following kind:

struct foo {
   int stuff;
   struct boo entry[];
};

and this scenario includes two different structures:

struct nd_region {

	...

        struct nd_mapping mapping[0];
};

struct nd_blk_region {

	...

        struct nd_region nd_region;
};

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

In this scenario struct_size() does not apply directly because of the following
logic before the call to devm_kzalloc():

 	size_t flush_data_size = sizeof(void *);
	
	[..]

        for (i = 0; i < nd_region->ndr_mappings; i++) {

		[..]

                /* at least one null hint slot per-dimm for the "no-hint" case */
                flush_data_size += sizeof(void *);
		
		[..]

                flush_data_size += nvdimm->num_flush * sizeof(void *);
        }

Thanks
--
Gustavo

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

[Verma, Vishal L]

On Wed, 2019-08-28 at 14:36 -0500, Gustavo A. R. Silva wrote:

> struct_size() does not apply to those scenarios. See below...
> 
> > [1]: 
> > https://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm.git/tree/drivers/nvdimm/region_devs.c#n1030
> 
> struct_size() only applies to structures of the following kind:
> 
> struct foo {
>    int stuff;
>    struct boo entry[];
> };
> 
> and this scenario includes two different structures:
> 
> struct nd_region {
> 	...
>         struct nd_mapping mapping[0];
> };
> 
> struct nd_blk_region {
> 	...
>         struct nd_region nd_region;
> };

Yep - I neglected to actually look at the structures involved - you're
right, it doesn't apply here.

> 
> > [2]: 
> > https://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm.git/tree/drivers/nvdimm/region_devs.c#n96
> > 
> 
> In this scenario struct_size() does not apply directly because of the
> following
> logic before the call to devm_kzalloc():

Agreed, I missed that the calculation was more involved here.

Thanks for the clarifications, you can add:
Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>

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

[Kees Cook]

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@embeddedor.com>

FWIW,

Reviewed-by: Kees Cook <keescook@chromium.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

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

[Dan Williams]

On Wed, Aug 28, 2019 at 1:24 PM Verma, Vishal L
<vishal.l.verma@intel.com> wrote:
>
> On Wed, 2019-08-28 at 14:36 -0500, Gustavo A. R. Silva wrote:
>
> > struct_size() does not apply to those scenarios. See below...
> >
> > > [1]:
> > > https://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm.git/tree/drivers/nvdimm/region_devs.c#n1030
> >
> > struct_size() only applies to structures of the following kind:
> >
> > struct foo {
> >    int stuff;
> >    struct boo entry[];
> > };
> >
> > and this scenario includes two different structures:
> >
> > struct nd_region {
> >       ...
> >         struct nd_mapping mapping[0];
> > };
> >
> > struct nd_blk_region {
> >       ...
> >         struct nd_region nd_region;
> > };
>
> Yep - I neglected to actually look at the structures involved - you're
> right, it doesn't apply here.
>
> >
> > > [2]:
> > > https://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm.git/tree/drivers/nvdimm/region_devs.c#n96
> > >
> >
> > In this scenario struct_size() does not apply directly because of the
> > following
> > logic before the call to devm_kzalloc():
>
> Agreed, I missed that the calculation was more involved here.
>
> Thanks for the clarifications, you can add:
> Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>

Thanks, applied.

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

[Gustavo A. R. Silva]

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 foo {
    int stuff;
    struct boo entry[];
};

instance = kzalloc(sizeof(struct foo) + count * sizeof(struct boo), 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, entry, count), GFP_KERNEL);

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
 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 e2818f94f292..d36cb5df9683 100644
--- a/drivers/nvdimm/region_devs.c
+++ b/drivers/nvdimm/region_devs.c
@@ -1020,10 +1020,9 @@ 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;
 	}
 
-- 
2.20.1