gh-94510: Raise on re-entrant calls to sys.setprofile and sys.settrace (GH-94511)

Co-authored-by: Łukasz Langa <lukasz@langa.pl>

1 files changed, 24 insertions, 2 deletions

diff --git a/Python/ceval.c b/Python/ceval.c
index 4fcdf9b..cdb14d8 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -6973,10 +6973,20 @@ _PyEval_SetProfile(PyThreadState *tstate, Py_tracefunc func, PyObject *arg)
     /* The caller must hold the GIL */
     assert(PyGILState_Check());
 
+    static int reentrant = 0;
+    if (reentrant) {
+        _PyErr_SetString(tstate, PyExc_RuntimeError, "Cannot install a profile function "
+                         "while another profile function is being installed");
+        reentrant = 0;
+        return -1;
+    }
+    reentrant = 1;
+
     /* Call _PySys_Audit() in the context of the current thread state,
        even if tstate is not the current thread state. */
     PyThreadState *current_tstate = _PyThreadState_GET();
     if (_PySys_Audit(current_tstate, "sys.setprofile", NULL) < 0) {
+        reentrant = 0;
         return -1;
     }
 
@@ -6994,6 +7004,7 @@ _PyEval_SetProfile(PyThreadState *tstate, Py_tracefunc func, PyObject *arg)
 
     /* Flag that tracing or profiling is turned on */
     _PyThreadState_UpdateTracingState(tstate);
+    reentrant = 0;
     return 0;
 }
 
@@ -7014,10 +7025,21 @@ _PyEval_SetTrace(PyThreadState *tstate, Py_tracefunc func, PyObject *arg)
     /* The caller must hold the GIL */
     assert(PyGILState_Check());
 
+    static int reentrant = 0;
+
+    if (reentrant) {
+        _PyErr_SetString(tstate, PyExc_RuntimeError, "Cannot install a trace function "
+                         "while another trace function is being installed");
+        reentrant = 0;
+        return -1;
+    }
+    reentrant = 1;
+
     /* Call _PySys_Audit() in the context of the current thread state,
        even if tstate is not the current thread state. */
     PyThreadState *current_tstate = _PyThreadState_GET();
     if (_PySys_Audit(current_tstate, "sys.settrace", NULL) < 0) {
+        reentrant = 0;
         return -1;
     }
 
@@ -7027,15 +7049,15 @@ _PyEval_SetTrace(PyThreadState *tstate, Py_tracefunc func, PyObject *arg)
     tstate->c_traceobj = NULL;
     /* Must make sure that profiling is not ignored if 'traceobj' is freed */
     _PyThreadState_UpdateTracingState(tstate);
-    Py_XDECREF(traceobj);
-
     Py_XINCREF(arg);
+    Py_XDECREF(traceobj);
     tstate->c_traceobj = arg;
     tstate->c_tracefunc = func;
 
     /* Flag that tracing or profiling is turned on */
     _PyThreadState_UpdateTracingState(tstate);
 
+    reentrant = 0;
     return 0;
 }