[PATCH] dmaengine: pxa_dma: Prefer struct_size over open coded arithmetic

[PATCH] dmaengine: pxa_dma: Prefer struct_size over open coded arithmetic

[Len Baker]

As noted in the "Deprecated Interfaces, Language Features, Attributes,
and Conventions" documentation [1], size calculations (especially
multiplication) should not be performed in memory allocator (or similar)
function arguments due to the risk of them overflowing. This could lead
to values wrapping around and a smaller allocation being made than the
caller was expecting. Using those allocations could lead to linear
overflows of heap memory and other misbehaviors.

So, use the struct_size() helper to do the arithmetic instead of the
argument "size + count * size" in the kzalloc() function.

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments

Signed-off-by: Len Baker <len.baker@gmx.com>
---
 drivers/dma/pxa_dma.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/dma/pxa_dma.c b/drivers/dma/pxa_dma.c
index 4a2a796e348c..52d04641e361 100644
--- a/drivers/dma/pxa_dma.c
+++ b/drivers/dma/pxa_dma.c
@@ -742,8 +742,7 @@ pxad_alloc_desc(struct pxad_chan *chan, unsigned int nb_hw_desc)
 	dma_addr_t dma;
 	int i;

-	sw_desc = kzalloc(sizeof(*sw_desc) +
-			  nb_hw_desc * sizeof(struct pxad_desc_hw *),
+	sw_desc = kzalloc(struct_size(sw_desc, hw_desc, nb_hw_desc),
 			  GFP_NOWAIT);
 	if (!sw_desc)
 		return NULL;
--
2.25.1

Re: [PATCH] dmaengine: pxa_dma: Prefer struct_size over open coded arithmetic

[Gustavo A. R. Silva]

On 9/18/21 05:40, Len Baker wrote:
> As noted in the "Deprecated Interfaces, Language Features, Attributes,
> and Conventions" documentation [1], size calculations (especially
> multiplication) should not be performed in memory allocator (or similar)
> function arguments due to the risk of them overflowing. This could lead
> to values wrapping around and a smaller allocation being made than the
> caller was expecting. Using those allocations could lead to linear
> overflows of heap memory and other misbehaviors.
> 
> So, use the struct_size() helper to do the arithmetic instead of the
> argument "size + count * size" in the kzalloc() function.
> 
> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments
> 
> Signed-off-by: Len Baker <len.baker@gmx.com>

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>

> ---
>  drivers/dma/pxa_dma.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/dma/pxa_dma.c b/drivers/dma/pxa_dma.c
> index 4a2a796e348c..52d04641e361 100644
> --- a/drivers/dma/pxa_dma.c
> +++ b/drivers/dma/pxa_dma.c
> @@ -742,8 +742,7 @@ pxad_alloc_desc(struct pxad_chan *chan, unsigned int nb_hw_desc)
>  	dma_addr_t dma;
>  	int i;
> 
> -	sw_desc = kzalloc(sizeof(*sw_desc) +
> -			  nb_hw_desc * sizeof(struct pxad_desc_hw *),
> +	sw_desc = kzalloc(struct_size(sw_desc, hw_desc, nb_hw_desc),
>  			  GFP_NOWAIT);
>  	if (!sw_desc)
>  		return NULL;
> --
> 2.25.1
> 

Re: [PATCH] dmaengine: pxa_dma: Prefer struct_size over open coded arithmetic

[Gustavo A. R. Silva]

On Mon, Sep 20, 2021 at 07:00:58PM -0500, Gustavo A. R. Silva wrote:
> 
> 
> On 9/18/21 05:40, Len Baker wrote:
> > As noted in the "Deprecated Interfaces, Language Features, Attributes,
> > and Conventions" documentation [1], size calculations (especially
> > multiplication) should not be performed in memory allocator (or similar)
> > function arguments due to the risk of them overflowing. This could lead
> > to values wrapping around and a smaller allocation being made than the
> > caller was expecting. Using those allocations could lead to linear
> > overflows of heap memory and other misbehaviors.
> > 
> > So, use the struct_size() helper to do the arithmetic instead of the
> > argument "size + count * size" in the kzalloc() function.
> > 
> > [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments
> > 
> > Signed-off-by: Len Baker <len.baker@gmx.com>
> 
> Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>

I'm taking this in my -next tree.

Thanks
--
Gustavo