iommufd: Reject non-zero data_type if no data_len is provided

Since the current design doesn't forward the data_type to the driver to
check unless there is a data_len/uptr for a driver specific struct we
should check and ensure that data_type is 0 if data_len is 0. Otherwise
any value is permitted.

Fixes: bd529db ("iommufd: Add a nested HW pagetable object")
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Kevin Tian <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>

Author: jgunthorpe

drivers/iommu/iommufd/hw_pagetable.c

@@ -263,7 +263,8 @@ int iommufd_hwpt_alloc(struct iommufd_ucmd *ucmd)
 
 	if (cmd->__reserved)
 		return -EOPNOTSUPP;
-	if (cmd->data_type == IOMMU_HWPT_DATA_NONE && cmd->data_len)
+	if ((cmd->data_type == IOMMU_HWPT_DATA_NONE && cmd->data_len) ||
+	    (cmd->data_type != IOMMU_HWPT_DATA_NONE && !cmd->data_len))
 		return -EINVAL;
 
 	idev = iommufd_get_device(ucmd, cmd->dev_id);