libsepol/cil: Create new first child helper function for building AST

In order to find statements not allowed in tunableifs, in-statements,
macros, and booleanifs, there are tree node pointers that point to
each of these kinds of statements when its block is being parsed.
If the pointer is non-NULL, then the rule being parsed is in the block
of that kind of statement.

The tree node pointers were being updated at the wrong point which
prevented an invalid statement from being found if it was the first
statement in the block of a tunableif, in-statement, macro, or
booleanif.

Create a first child helper function for walking the parse tree and
in that function set the appropriate tree node pointer if the
current AST node is a tunableif, in-statement, macro, or booleanif.
This also makes the code symmetrical with the last child helper
where the tree node pointers are set to NULL.

Signed-off-by: James Carter <jwcart2@gmail.com>

libsepol/cil/src/cil_build_ast.c

@@ -6429,22 +6429,6 @@ int __cil_build_ast_node_helper(struct cil_tree_node *parse_current, uint32_t *f
 
 	if (rc == SEPOL_OK) {
 		if (ast_current->cl_head == NULL) {
-			if (ast_current->flavor == CIL_TUNABLEIF) {
-				args->tunif = ast_current;
-			}
-
-			if (ast_current->flavor == CIL_IN) {
-				args->in = ast_current;
-			}
-
-			if (ast_current->flavor == CIL_MACRO) {
-				args->macro = ast_current;
-			}
-
-			if (ast_current->flavor == CIL_BOOLEANIF) {
-				args->boolif = ast_current;
-			}
-
 			ast_current->cl_head = ast_node;
 		} else {
 			ast_current->cl_tail->next = ast_node;
@@ -6460,6 +6444,30 @@ int __cil_build_ast_node_helper(struct cil_tree_node *parse_current, uint32_t *f
 	return rc;
 }
 
+int __cil_build_ast_first_child_helper(__attribute__((unused)) struct cil_tree_node *parse_current, void *extra_args)
+{
+	struct cil_args_build *args = extra_args;
+	struct cil_tree_node *ast = args->ast;
+
+	if (ast->flavor == CIL_TUNABLEIF) {
+		args->tunif = ast;
+	}
+
+	if (ast->flavor == CIL_IN) {
+		args->in = ast;
+	}
+
+	if (ast->flavor == CIL_MACRO) {
+		args->macro = ast;
+	}
+
+	if (ast->flavor == CIL_BOOLEANIF) {
+		args->boolif = ast;
+	}
+
+	return SEPOL_OK;
+}
+
 int __cil_build_ast_last_child_helper(struct cil_tree_node *parse_current, void *extra_args)
 {
 	struct cil_args_build *args = extra_args;
@@ -6513,7 +6521,7 @@ int cil_build_ast(struct cil_db *db, struct cil_tree_node *parse_tree, struct ci
 	extra_args.macro = NULL;
 	extra_args.boolif = NULL;
 
-	rc = cil_tree_walk(parse_tree, __cil_build_ast_node_helper, NULL, __cil_build_ast_last_child_helper, &extra_args);
+	rc = cil_tree_walk(parse_tree, __cil_build_ast_node_helper, __cil_build_ast_first_child_helper, __cil_build_ast_last_child_helper, &extra_args);
 	if (rc != SEPOL_OK) {
 		goto exit;
 	}