VMCI: Remove handle_arr_calc_size()

Use struct_size() instead of handle_arr_calc_size().
This is much more conventional.

While at it, use size_add() when computing the needed size in
vmci_handle_arr_append_entry(). This prevents from (unlikely) overflow
when computing the new size to reallocate.
Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/84e7f2d8e7c4c2eab68f958307d56546978f76e3.1702125347.git.christophe.jaillet@wanadoo.frSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/vmw_vmci/vmci_handle_array.c

@@ -8,12 +8,6 @@
 #include <linux/slab.h>
 #include "vmci_handle_array.h"
 
-static size_t handle_arr_calc_size(u32 capacity)
-{
-	return VMCI_HANDLE_ARRAY_HEADER_SIZE +
-	    capacity * sizeof(struct vmci_handle);
-}
-
 struct vmci_handle_arr *vmci_handle_arr_create(u32 capacity, u32 max_capacity)
 {
 	struct vmci_handle_arr *array;
@@ -25,7 +19,7 @@ struct vmci_handle_arr *vmci_handle_arr_create(u32 capacity, u32 max_capacity)
 		capacity = min((u32)VMCI_HANDLE_ARRAY_DEFAULT_CAPACITY,
 			       max_capacity);
 
-	array = kmalloc(handle_arr_calc_size(capacity), GFP_ATOMIC);
+	array = kmalloc(struct_size(array, entries, capacity), GFP_ATOMIC);
 	if (!array)
 		return NULL;
 
@@ -51,8 +45,8 @@ int vmci_handle_arr_append_entry(struct vmci_handle_arr **array_ptr,
 		struct vmci_handle_arr *new_array;
 		u32 capacity_bump = min(array->max_capacity - array->capacity,
 					array->capacity);
-		size_t new_size = handle_arr_calc_size(array->capacity +
-						       capacity_bump);
+		size_t new_size = struct_size(array, entries,
+					      size_add(array->capacity, capacity_bump));
 
 		if (array->size >= array->max_capacity)
 			return VMCI_ERROR_NO_MEM;