Teach CleartextLogging not to track through error.Error() and `fm…

…t.Stringer.String()`.

These two are very heavily overloaded and cause all sorts of false positives.

ql/src/semmle/go/security/CleartextLogging.qll

@@ -32,7 +32,15 @@ module CleartextLogging {
 
     override predicate isSink(DataFlow::Node sink) { sink instanceof Sink }
 
-    override predicate isBarrier(DataFlow::Node node) { node instanceof Barrier }
+    override predicate isBarrier(DataFlow::Node node) {
+      node instanceof Barrier
+      or
+      exists(DataFlow::CallNode call | node = call.getResult() |
+        call.getTarget() = Builtin::error().getType().getMethod("Error")
+        or
+        call.getTarget().(Method).hasQualifiedName("fmt", "Stringer", "String")
+      )
+    }
 
     override predicate isAdditionalFlowStep(DataFlow::Node src, DataFlow::Node trg) {
       // A taint propagating data-flow edge through structs: a tainted write taints the entire struct.

ql/test/query-tests/Security/CWE-312/CleartextLogging.expected

@@ -1,6 +1,7 @@
 edges
 | klog.go:20:30:20:37 | selection of Header : Header | klog.go:22:15:22:20 | header |
 | klog.go:28:13:28:20 | selection of Header : Header | klog.go:28:13:28:41 | call to Get |
+| overrides.go:9:9:9:16 | password : string | overrides.go:13:14:13:23 | call to String |
 | passwords.go:8:12:8:12 | definition of x : string | passwords.go:9:14:9:14 | x |
 | passwords.go:30:8:30:15 | password : string | passwords.go:8:12:8:12 | definition of x : string |
 | passwords.go:34:28:34:35 | password : string | passwords.go:34:14:34:35 | ...+... |
@@ -30,6 +31,8 @@ nodes
 | klog.go:28:13:28:41 | call to Get | semmle.label | call to Get |
 | main.go:15:14:15:21 | password | semmle.label | password |
 | main.go:17:12:17:19 | password | semmle.label | password |
+| overrides.go:9:9:9:16 | password : string | semmle.label | password : string |
+| overrides.go:13:14:13:23 | call to String | semmle.label | call to String |
 | passwords.go:8:12:8:12 | definition of x : string | semmle.label | definition of x : string |
 | passwords.go:9:14:9:14 | x | semmle.label | x |
 | passwords.go:25:14:25:21 | password | semmle.label | password |
@@ -75,6 +78,7 @@ nodes
 | klog.go:28:13:28:41 | call to Get | klog.go:28:13:28:20 | selection of Header : Header | klog.go:28:13:28:41 | call to Get | Sensitive data returned by $@ is logged here. | klog.go:28:13:28:20 | selection of Header | HTTP request headers |
 | main.go:15:14:15:21 | password | main.go:15:14:15:21 | password | main.go:15:14:15:21 | password | Sensitive data returned by $@ is logged here. | main.go:15:14:15:21 | password | an access to password |
 | main.go:17:12:17:19 | password | main.go:17:12:17:19 | password | main.go:17:12:17:19 | password | Sensitive data returned by $@ is logged here. | main.go:17:12:17:19 | password | an access to password |
+| overrides.go:13:14:13:23 | call to String | overrides.go:9:9:9:16 | password : string | overrides.go:13:14:13:23 | call to String | Sensitive data returned by $@ is logged here. | overrides.go:9:9:9:16 | password | an access to password |
 | passwords.go:9:14:9:14 | x | passwords.go:30:8:30:15 | password : string | passwords.go:9:14:9:14 | x | Sensitive data returned by $@ is logged here. | passwords.go:30:8:30:15 | password | an access to password |
 | passwords.go:25:14:25:21 | password | passwords.go:25:14:25:21 | password | passwords.go:25:14:25:21 | password | Sensitive data returned by $@ is logged here. | passwords.go:25:14:25:21 | password | an access to password |
 | passwords.go:26:14:26:23 | selection of password | passwords.go:26:14:26:23 | selection of password | passwords.go:26:14:26:23 | selection of password | Sensitive data returned by $@ is logged here. | passwords.go:26:14:26:23 | selection of password | an access to password |