linux-kernel - Re: [PATCH] dmaengine: pxa_dma: Prefer struct

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Date:   Mon, 20 Sep 2021 19:00:58 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Len Baker <len.baker@....com>, Daniel Mack <daniel@...que.org>,
        Haojian Zhuang <haojian.zhuang@...il.com>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        Vinod Koul <vkoul@...nel.org>
Cc:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        linux-arm-kernel@...ts.infradead.org, dmaengine@...r.kernel.org,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dmaengine: pxa_dma: Prefer struct_size over open coded
 arithmetic



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@....com>

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