Fix usage of PyCFunction_GET_FLAGS in pysidesignal.cpp

Using PyCFunction_GET_FLAGS is unsafe, because it does not check
whether the argument given is actually a PyCFunction object. This
macro needs to be replaced with the function equivalent
PyCFunction_GetFlags for stable ABI patch, but this will cause a crash
in PyCFunction_Call because we don't check the return value of
PyCFunction_GetFlags to see if it fails.

Rather than checking the return value, it is safe to preemptively
add a PyCFunction_Check before calling the GetFlags function. This
does not modify the logic behind signalCall function.

The crashing test was homonymoussignalandmethod_test.py, so no
new test is needed.

Task-number: PYSIDE-593
Change-Id: Id9ac9c0dec454e8e1ce9516dc68af924372a34a9
Reviewed-by: Christian Tismer <tismer@stackless.com>

1 files changed, 11 insertions, 2 deletions

diff --git a/sources/pyside2/libpyside/pysidesignal.cpp b/sources/pyside2/libpyside/pysidesignal.cpp
index 9f60d2a41..04b1cf1f4 100644
--- a/sources/pyside2/libpyside/pysidesignal.cpp
+++ b/sources/pyside2/libpyside/pysidesignal.cpp
@@ -564,17 +564,26 @@ PyObject* signalCall(PyObject* self, PyObject* args, PyObject* kw)
 {
     PySideSignal* signal = reinterpret_cast<PySideSignal*>(self);
 
+    // Native C++ signals can't be called like functions, thus we throw an exception.
+    // The only way calling a signal can succeed (the Python equivalent of C++'s operator() )
+    // is when a method with the same name as the signal is attached to an object.
+    // An example is QProcess::error() (don't check the docs, but the source code of qprocess.h).
     if (!signal->homonymousMethod) {
         PyErr_SetString(PyExc_TypeError, "native Qt signal is not callable");
         return 0;
     }
 
     descrgetfunc getDescriptor = signal->homonymousMethod->ob_type->tp_descr_get;
-    Shiboken::AutoDecRef homonymousMethod(getDescriptor(signal->homonymousMethod, 0, 0));
 
-    if (PyCFunction_GET_FLAGS(homonymousMethod.object()) & METH_STATIC)
+    // Check if there exists a method with the same name as the signal, which is also a static
+    // method in C++ land.
+    Shiboken::AutoDecRef homonymousMethod(getDescriptor(signal->homonymousMethod, 0, 0));
+    if (PyCFunction_Check(homonymousMethod)
+            && (PyCFunction_GET_FLAGS(homonymousMethod.object()) & METH_STATIC)) {
         return PyCFunction_Call(homonymousMethod, args, kw);
+    }
 
+    // Assumes homonymousMethod is not a static method.
     ternaryfunc callFunc = signal->homonymousMethod->ob_type->tp_call;
     return callFunc(homonymousMethod, args, kw);
 }