Re: [PATCH 13/21] dmaengine: stm32-mdma: Annotate struct stm32_mdma_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 stm32_mdma_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: Maxime Coquelin <mcoquelin.stm32@xxxxxxxxx>
> Cc: Alexandre Torgue <alexandre.torgue@xxxxxxxxxxx>
> Cc: dmaengine@xxxxxxxxxxxxxxx
> Cc: linux-stm32@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

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

Thanks
--
Gustavo

> ---
>   drivers/dma/stm32-mdma.c | 5 ++---
>   1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/dma/stm32-mdma.c b/drivers/dma/stm32-mdma.c
> index 0de234022c6d..926d6ecf1274 100644
> --- a/drivers/dma/stm32-mdma.c
> +++ b/drivers/dma/stm32-mdma.c
> @@ -224,7 +224,7 @@ struct stm32_mdma_desc {
>   	u32 ccr;
>   	bool cyclic;
>   	u32 count;
> -	struct stm32_mdma_desc_node node[];
> +	struct stm32_mdma_desc_node node[] __counted_by(count);
>   };
>   
>   struct stm32_mdma_dma_config {
> @@ -321,6 +321,7 @@ static struct stm32_mdma_desc *stm32_mdma_alloc_desc(
>   	desc = kzalloc(struct_size(desc, node, count), GFP_NOWAIT);
>   	if (!desc)
>   		return NULL;
> +	desc->count = count;
>   
>   	for (i = 0; i < count; i++) {
>   		desc->node[i].hwdesc =
> @@ -330,8 +331,6 @@ static struct stm32_mdma_desc *stm32_mdma_alloc_desc(
>   			goto err;
>   	}
>   
> -	desc->count = count;
> -
>   	return desc;
>   
>   err: