python: not is confusing our logic

- added `is_unsafe`
- added "negated version" of two tests.
These versions do not use `not` and the analysis gets the taint right.

Author: yoff

python/ql/test/experimental/dataflow/tainttracking/customSanitizer/InlineTaintTest.expected

@@ -6,12 +6,14 @@ isSanitizer
 | TestTaintTrackingConfiguration | test.py:34:39:34:39 | ControlFlowNode for s |
 | TestTaintTrackingConfiguration | test.py:52:28:52:28 | ControlFlowNode for s |
 | TestTaintTrackingConfiguration | test.py:66:10:66:29 | ControlFlowNode for emulated_escaping() |
-| TestTaintTrackingConfiguration | test_logical.py:30:28:30:28 | ControlFlowNode for s |
-| TestTaintTrackingConfiguration | test_logical.py:45:28:45:28 | ControlFlowNode for s |
-| TestTaintTrackingConfiguration | test_logical.py:50:28:50:28 | ControlFlowNode for s |
-| TestTaintTrackingConfiguration | test_logical.py:89:28:89:28 | ControlFlowNode for s |
-| TestTaintTrackingConfiguration | test_logical.py:100:28:100:28 | ControlFlowNode for s |
-| TestTaintTrackingConfiguration | test_logical.py:145:28:145:28 | ControlFlowNode for s |
+| TestTaintTrackingConfiguration | test_logical.py:33:28:33:28 | ControlFlowNode for s |
+| TestTaintTrackingConfiguration | test_logical.py:48:28:48:28 | ControlFlowNode for s |
+| TestTaintTrackingConfiguration | test_logical.py:53:28:53:28 | ControlFlowNode for s |
+| TestTaintTrackingConfiguration | test_logical.py:92:28:92:28 | ControlFlowNode for s |
+| TestTaintTrackingConfiguration | test_logical.py:103:28:103:28 | ControlFlowNode for s |
 | TestTaintTrackingConfiguration | test_logical.py:148:28:148:28 | ControlFlowNode for s |
-| TestTaintTrackingConfiguration | test_logical.py:155:28:155:28 | ControlFlowNode for s |
+| TestTaintTrackingConfiguration | test_logical.py:151:28:151:28 | ControlFlowNode for s |
+| TestTaintTrackingConfiguration | test_logical.py:158:28:158:28 | ControlFlowNode for s |
+| TestTaintTrackingConfiguration | test_logical.py:176:24:176:24 | ControlFlowNode for s |
+| TestTaintTrackingConfiguration | test_logical.py:193:24:193:24 | ControlFlowNode for s |
 | TestTaintTrackingConfiguration | test_reference.py:31:28:31:28 | ControlFlowNode for s |

python/ql/test/experimental/dataflow/tainttracking/customSanitizer/InlineTaintTest.ql

@@ -6,6 +6,12 @@ predicate isSafeCheck(DataFlow::GuardNode g, ControlFlowNode node, boolean branc
   branch = true
 }
 
+predicate isUnsafeCheck(DataFlow::GuardNode g, ControlFlowNode node, boolean branch) {
+  g.(CallNode).getNode().getFunc().(Name).getId() in ["is_unsafe", "emulated_is_unsafe"] and
+  node = g.(CallNode).getAnArg() and
+  branch = false
+}
+
 class CustomSanitizerOverrides extends TestTaintTrackingConfiguration {
   override predicate isSanitizer(DataFlow::Node node) {
     exists(Call call |
@@ -16,6 +22,8 @@ class CustomSanitizerOverrides extends TestTaintTrackingConfiguration {
     node.asExpr().(Call).getFunc().(Name).getId() = "emulated_escaping"
     or
     node = DataFlow::BarrierGuard<isSafeCheck/3>::getABarrierNode()
+    or
+    node = DataFlow::BarrierGuard<isUnsafeCheck/3>::getABarrierNode()
   }
 }
 

python/ql/test/experimental/dataflow/tainttracking/customSanitizer/test_logical.py

@@ -22,6 +22,9 @@ def random_choice():
 def is_safe(arg):
     return arg == "safe"
 
+def is_unsafe(arg):
+    return arg == TAINTED_STRING
+
 
 def test_basic():
     s = TAINTED_STRING
@@ -164,6 +167,15 @@ def test_with_return():
     ensure_not_tainted(s) # $ SPURIOUS: tainted
 
 
+def test_with_return_neg():
+    s = TAINTED_STRING
+
+    if is_unsafe(s):
+        return
+
+    ensure_not_tainted(s)
+
+
 def test_with_exception():
     s = TAINTED_STRING
 
@@ -172,6 +184,14 @@ def test_with_exception():
 
     ensure_not_tainted(s) # $ SPURIOUS: tainted
 
+def test_with_exception_neg():
+    s = TAINTED_STRING
+
+    if is_unsafe(s):
+        raise Exception("unsafe")
+
+    ensure_not_tainted(s)
+
 # Make tests runable
 
 test_basic()
@@ -182,7 +202,12 @@ def test_with_exception():
 test_nesting_not()
 test_nesting_not_with_and_true()
 test_with_return()
+test_with_return_neg()
 try:
     test_with_exception()
 except:
     pass
+try:
+    test_with_exception_neg()
+except:
+    pass