Convert infiniband uverbs to struct_size

The flows were hidden from the C compiler; expose them as a zero-length
array to allow struct_size to work.
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

drivers/infiniband/core/uverbs_cmd.c

@@ -3559,8 +3559,8 @@ int ib_uverbs_ex_create_flow(struct ib_uverbs_file *file,
 		goto err_uobj;
 	}
 
-	flow_attr = kzalloc(sizeof(*flow_attr) + cmd.flow_attr.num_of_specs *
-			    sizeof(union ib_flow_spec), GFP_KERNEL);
+	flow_attr = kzalloc(struct_size(flow_attr, flows,
+				cmd.flow_attr.num_of_specs), GFP_KERNEL);
 	if (!flow_attr) {
 		err = -ENOMEM;
 		goto err_put;

include/rdma/ib_verbs.h

@@ -2093,10 +2093,7 @@ struct ib_flow_attr {
 	u32	     flags;
 	u8	     num_of_specs;
 	u8	     port;
-	/* Following are the optional layers according to user request
-	 * struct ib_flow_spec_xxx
-	 * struct ib_flow_spec_yyy
-	 */
+	union ib_flow_spec flows[];
 };
 
 struct ib_flow {