Re: [PATCH v4 1/3] fpga: dfl: add bounds check in dfh_get_param_size()

[Xu Yilun]

On Tue, Apr 07, 2026 at 11:22:15AM -0600, Sebastian Alba Vives wrote:
> dfh_get_param_size() can return a parameter size larger than the feature
> region because the loop bounds check is evaluated before incrementing
> size. If the EOP (End of Parameters) bit is set in the same iteration,
> the inflated size is returned without re-validation against max.
> 
> This can cause create_feature_instance() to call memcpy_fromio() with a
> size exceeding the ioremap'd region when a malicious FPGA device provides
> crafted DFHv1 parameter headers.
> 
> Add a bounds check after the size increment to ensure the accumulated
> size never exceeds the feature boundary.
> 
> Fixes: a80a4b2b2e4f ("fpga: dfl: add support for DFHv1")
> Signed-off-by: Sebastian Alba Vives <sebasjosue84@xxxxxxxxx>
> ---
> Changes in v4:
>   - Resubmit as full series per maintainer request.
> Changes in v2:
>   - Use (size > max) instead of (size + DFHv1_PARAM_HDR > max).
>     The previous check unnecessarily guarded against the next parameter
>     header, which is not relevant at this point in the loop.
>     Suggested by Xu Yilun.
> ---
>  drivers/fpga/dfl.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/fpga/dfl.c b/drivers/fpga/dfl.c
> index 4087a36..81d7a68 100644
> --- a/drivers/fpga/dfl.c
> +++ b/drivers/fpga/dfl.c
> @@ -1132,7 +1132,8 @@ static int dfh_get_param_size(void __iomem *dfh_base, resource_size_t max)
>  			return -EINVAL;
>  
>  		size += next * sizeof(u64);
> -
> +		if (size > max)
> +			return -EINVAL;

I'd prefer a blank line here.

>  		if (FIELD_GET(DFHv1_PARAM_HDR_NEXT_EOP, v))
>  			return size;
>  	}
> -- 
> 2.43.0
> 
>