fpga: dfl: add bounds check in dfh_get_param_size()

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: 4747ab8 ("fpga: dfl: add basic support for DFHv1")
Cc: stable@vger.kernel.org
Signed-off-by: Sebastian Alba Vives <sebasjosue84@gmail.com>
Reviewed-by: Xu Yilun <yilun.xu@intel.com>
Link: https://lore.kernel.org/r/20260518190742.61426-2-sebasjosue84@gmail.com
Signed-off-by: Xu Yilun <yilun.xu@linux.intel.com>

Author: Sebasteuo

drivers/fpga/dfl.c

@@ -1132,6 +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;
 
 		if (FIELD_GET(DFHv1_PARAM_HDR_NEXT_EOP, v))
 			return size;