Python: Refactor StringKind.getTaintOfMethodResult

no need to match on ControlFlowNodes manually anymore 🎉

Author: RasmusWL

python/ql/src/semmle/python/security/strings/Basic.qll

@@ -7,10 +7,14 @@ abstract class StringKind extends TaintKind {
     bindingset[this]
     StringKind() { this = this }
 
+    override TaintKind getTaintOfMethodResult(string name) {
+        name in ["strip", "format", "lstrip", "rstrip", "ljust", "rjust", "title", "capitalize"] and
+        result = this
+    }
+
     override TaintKind getTaintForFlowStep(ControlFlowNode fromnode, ControlFlowNode tonode) {
         result = this and
         (
-            str_method_call(fromnode, tonode) or
             slice(fromnode, tonode) or
             tonode.(BinaryExprNode).getAnOperand() = fromnode or
             os_path_join(fromnode, tonode) or
@@ -50,20 +54,6 @@ private class StringEqualitySanitizer extends Sanitizer {
     }
 }
 
-/* tonode = fromnode.xxx() where the call to xxx returns an identical or similar string */
-private predicate str_method_call(ControlFlowNode fromnode, CallNode tonode) {
-    exists(string method_name | tonode.getFunction().(AttrNode).getObject(method_name) = fromnode |
-        method_name = "strip" or
-        method_name = "format" or
-        method_name = "lstrip" or
-        method_name = "rstrip" or
-        method_name = "ljust" or
-        method_name = "rjust" or
-        method_name = "title" or
-        method_name = "capitalize"
-    )
-}
-
 /* tonode = ....format(fromnode) */
 private predicate str_format(ControlFlowNode fromnode, CallNode tonode) {
     tonode.getFunction().(AttrNode).getName() = "format" and