bpo-17288: Prevent jumps from 'return' and 'exception' trace events. (GH-6107)

(cherry picked from commit e32bbaf376)

Lib/test/test_sys_settrace.py

@@ -555,20 +555,35 @@ class RaisingTraceFuncTestCase(unittest.TestCase):
 class JumpTracer:
     """Defines a trace function that jumps from one place to another."""
 
-    def __init__(self, function, jumpFrom, jumpTo):
-        self.function = function
+    def __init__(self, function, jumpFrom, jumpTo, event='line',
+                 decorated=False):
+        self.code = function.__code__
         self.jumpFrom = jumpFrom
         self.jumpTo = jumpTo
+        self.event = event
+        self.firstLine = None if decorated else self.code.co_firstlineno
         self.done = False
 
     def trace(self, frame, event, arg):
-        if not self.done and frame.f_code == self.function.__code__:
-            firstLine = frame.f_code.co_firstlineno
-            if event == 'line' and frame.f_lineno == firstLine + self.jumpFrom:
+        if self.done:
+            return
+        # frame.f_code.co_firstlineno is the first line of the decorator when
+        # 'function' is decorated and the decorator may be written using
+        # multiple physical lines when it is too long. Use the first line
+        # trace event in 'function' to find the first line of 'function'.
+        if (self.firstLine is None and frame.f_code == self.code and
+                event == 'line'):
+            self.firstLine = frame.f_lineno - 1
+        if (event == self.event and self.firstLine and
+                frame.f_lineno == self.firstLine + self.jumpFrom):
+            f = frame
+            while f is not None and f.f_code != self.code:
+                f = f.f_back
+            if f is not None:
                 # Cope with non-integer self.jumpTo (because of
                 # no_jump_to_non_integers below).
                 try:
-                    frame.f_lineno = firstLine + self.jumpTo
+                    frame.f_lineno = self.firstLine + self.jumpTo
                 except TypeError:
                     frame.f_lineno = self.jumpTo
                 self.done = True
@@ -608,8 +623,9 @@ class JumpTestCase(unittest.TestCase):
                        "Expected: " + repr(expected) + "\n" +
                        "Received: " + repr(received))
 
-    def run_test(self, func, jumpFrom, jumpTo, expected, error=None):
-        tracer = JumpTracer(func, jumpFrom, jumpTo)
+    def run_test(self, func, jumpFrom, jumpTo, expected, error=None,
+                 event='line', decorated=False):
+        tracer = JumpTracer(func, jumpFrom, jumpTo, event, decorated)
         sys.settrace(tracer.trace)
         output = []
         if error is None:
@@ -620,15 +636,15 @@ class JumpTestCase(unittest.TestCase):
         sys.settrace(None)
         self.compare_jump_output(expected, output)
 
-    def jump_test(jumpFrom, jumpTo, expected, error=None):
+    def jump_test(jumpFrom, jumpTo, expected, error=None, event='line'):
         """Decorator that creates a test that makes a jump
         from one place to another in the following code.
         """
         def decorator(func):
             @wraps(func)
             def test(self):
-                # +1 to compensate a decorator line
-                self.run_test(func, jumpFrom+1, jumpTo+1, expected, error)
+                self.run_test(func, jumpFrom, jumpTo, expected,
+                              error=error, event=event, decorated=True)
             return test
         return decorator
 
@@ -1128,6 +1144,36 @@ output.append(4)
         sys.settrace(None)
         self.compare_jump_output([2, 3, 2, 3, 4], namespace["output"])
 
+    @jump_test(2, 3, [1], event='call', error=(ValueError, "can't jump from"
+               " the 'call' trace event of a new frame"))
+    def test_no_jump_from_call(output):
+        output.append(1)
+        def nested():
+            output.append(3)
+        nested()
+        output.append(5)
+
+    @jump_test(2, 1, [1], event='return', error=(ValueError,
+               "can only jump from a 'line' trace event"))
+    def test_no_jump_from_return_event(output):
+        output.append(1)
+        return
+
+    @jump_test(2, 1, [1], event='exception', error=(ValueError,
+               "can only jump from a 'line' trace event"))
+    def test_no_jump_from_exception_event(output):
+        output.append(1)
+        1 / 0
+
+    @jump_test(3, 2, [2], event='return', error=(ValueError,
+               "can't jump from a yield statement"))
+    def test_no_jump_from_yield(output):
+        def gen():
+            output.append(2)
+            yield 3
+        next(gen())
+        output.append(5)
+
 
 if __name__ == "__main__":
     unittest.main()