[3.7] bpo-17288: Prevent jumps from 'return' and 'exception' trace events. (GH-5928)

1 files changed, 36 insertions, 4 deletions

diff --git a/Objects/frameobject.c b/Objects/frameobject.c
index 2825041e63..f518dc4856 100644
--- a/Objects/frameobject.c
+++ b/Objects/frameobject.c
@@ -59,6 +59,9 @@ frame_getlineno(PyFrameObject *f, void *closure)
  *  o 'try'/'for'/'while' blocks can't be jumped into because the blockstack
  *    needs to be set up before their code runs, and for 'for' loops the
  *    iterator needs to be on the stack.
+ *  o Jumps cannot be made from within a trace function invoked with a
+ *    'return' or 'exception' event since the eval loop has been exited at
+ *    that time.
  */
 static int
 frame_setlineno(PyFrameObject *f, PyObject* p_new_lineno)
@@ -94,13 +97,32 @@ frame_setlineno(PyFrameObject *f, PyObject* p_new_lineno)
         return -1;
     }
 
+    /* Upon the 'call' trace event of a new frame, f->f_lasti is -1 and
+     * f->f_trace is NULL, check first on the first condition.
+     * Forbidding jumps from the 'call' event of a new frame is a side effect
+     * of allowing to set f_lineno only from trace functions. */
+    if (f->f_lasti == -1) {
+        PyErr_Format(PyExc_ValueError,
+                     "can't jump from the 'call' trace event of a new frame");
+        return -1;
+    }
+
     /* You can only do this from within a trace function, not via
      * _getframe or similar hackery. */
-    if (!f->f_trace)
-    {
+    if (!f->f_trace) {
         PyErr_Format(PyExc_ValueError,
-                     "f_lineno can only be set by a"
-                     " line trace function");
+                     "f_lineno can only be set by a trace function");
+        return -1;
+    }
+
+    /* Forbid jumps upon a 'return' trace event (except after executing a
+     * YIELD_VALUE or YIELD_FROM opcode, f_stacktop is not NULL in that case)
+     * and upon an 'exception' trace event.
+     * Jumps from 'call' trace events have already been forbidden above for new
+     * frames, so this check does not change anything for 'call' events. */
+    if (f->f_stacktop == NULL) {
+        PyErr_SetString(PyExc_ValueError,
+                "can only jump from a 'line' trace event");
         return -1;
     }
 
@@ -159,6 +181,16 @@ frame_setlineno(PyFrameObject *f, PyObject* p_new_lineno)
 
     /* We're now ready to look at the bytecode. */
     PyBytes_AsStringAndSize(f->f_code->co_code, (char **)&code, &code_len);
+
+    /* The trace function is called with a 'return' trace event after the
+     * execution of a yield statement. */
+    assert(f->f_lasti != -1);
+    if (code[f->f_lasti] == YIELD_VALUE || code[f->f_lasti] == YIELD_FROM) {
+        PyErr_SetString(PyExc_ValueError,
+                "can't jump from a yield statement");
+        return -1;
+    }
+
     min_addr = Py_MIN(new_lasti, f->f_lasti);
     max_addr = Py_MAX(new_lasti, f->f_lasti);