iommu: Fix two issues in iommu_copy_struct_from_user()

In the review for iommu_copy_struct_to_user() helper, Matt pointed out that
a NULL pointer should be rejected prior to dereferencing it:
https://lore.kernel.org/all/[email protected]

And Alok pointed out a typo at the same time:
https://lore.kernel.org/all/[email protected]

Since both issues were copied from iommu_copy_struct_from_user(), fix them
first in the current header.

Fixes: e9d36c0 ("iommu: Add iommu_copy_struct_from_user helper")
Cc: [email protected]
Signed-off-by: Nicolin Chen <[email protected]>
Reviewed-by: Kevin Tian <[email protected]>
Acked-by: Alok Tiwari <[email protected]>
Reviewed-by: Matthew R. Ochs <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Joerg Roedel <[email protected]>

Author: nicolinc

include/linux/iommu.h

@@ -440,10 +440,10 @@ static inline int __iommu_copy_struct_from_user(
 	void *dst_data, const struct iommu_user_data *src_data,
 	unsigned int data_type, size_t data_len, size_t min_len)
 {
-	if (src_data->type != data_type)
-		return -EINVAL;
 	if (WARN_ON(!dst_data || !src_data))
 		return -EINVAL;
+	if (src_data->type != data_type)
+		return -EINVAL;
 	if (src_data->len < min_len || data_len < src_data->len)
 		return -EINVAL;
 	return copy_struct_from_user(dst_data, data_len, src_data->uptr,
@@ -456,8 +456,8 @@ static inline int __iommu_copy_struct_from_user(
  *        include/uapi/linux/iommufd.h
  * @user_data: Pointer to a struct iommu_user_data for user space data info
  * @data_type: The data type of the @kdst. Must match with @user_data->type
- * @min_last: The last memember of the data structure @kdst points in the
- *            initial version.
+ * @min_last: The last member of the data structure @kdst points in the initial
+ *            version.
  * Return 0 for success, otherwise -error.
  */
 #define iommu_copy_struct_from_user(kdst, user_data, data_type, min_last) \