Re: [PATCH 03/21] dmaengine: axi-dmac: Annotate struct axi_dmac_desc with __counted_by

[Gustavo A. R. Silva]

On 8/17/23 17:58, Kees Cook wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
>
> As found with Coccinelle[1], add __counted_by for struct axi_dmac_desc.
> Additionally, since the element count member must be set before accessing
> the annotated flexible array member, move its initialization earlier.
>
> [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
>
> Cc: Vinod Koul <vkoul@xxxxxxxxxx>
> Cc: Lars-Peter Clausen <lars@xxxxxxxxxx>
> Cc: dmaengine@xxxxxxxxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

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

Thanks
--
Gustavo

> ---
>   drivers/dma/dma-axi-dmac.c | 5 ++---
>   1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/dma/dma-axi-dmac.c b/drivers/dma/dma-axi-dmac.c
> index fc7cdad37161..b9f85cb20d3e 100644
> --- a/drivers/dma/dma-axi-dmac.c
> +++ b/drivers/dma/dma-axi-dmac.c
> @@ -117,7 +117,7 @@ struct axi_dmac_desc {
>   	unsigned int num_submitted;
>   	unsigned int num_completed;
>   	unsigned int num_sgs;
> -	struct axi_dmac_sg sg[];
> +	struct axi_dmac_sg sg[] __counted_by(num_sgs);
>   };
>   
>   struct axi_dmac_chan {
> @@ -484,12 +484,11 @@ static struct axi_dmac_desc *axi_dmac_alloc_desc(unsigned int num_sgs)
>   	desc = kzalloc(struct_size(desc, sg, num_sgs), GFP_NOWAIT);
>   	if (!desc)
>   		return NULL;
> +	desc->num_sgs = num_sgs;
>   
>   	for (i = 0; i < num_sgs; i++)
>   		desc->sg[i].id = AXI_DMAC_SG_UNUSED;
>   
> -	desc->num_sgs = num_sgs;
> -
>   	return desc;
>   }
>