Hello!
Please can you give some example code to clarify what behaviour you're expecting as I'm not sure I fully understand the question.

class MyData:
def init(self):
self.a = None
self.b = None
self.x = None
self.y = None
def a_callback(self, msg):
self.a = msg
def b_callback(self, msg):
self.b = msg
def get_x(self):
self.x = self.a +self.b
def talker(self):
pub = rospy.Publisher('C', Float64MultiArray, queue_size=10)
rospy.init_node('talker', anonymous=True)
rate = rospy.Rate(10) # 10hz
while not rospy.is_shutdown():
pub.publish(self.x)
rate.sleep()
if name == 'main':
rospy.init_node('listener')
mydata = MyData()
rospy.Subscriber('a', Float64MultiArray , mydata.a_callback)
mydata.get_x()
mydata.talker()

The above statement that is bold uses callback (a_callback) but the 'msg' in callback does not gets tainted at all giving us no vulnerability as a result but it give vulnerability. My source is supposed to be rospy.Subscriber and sink is rospy.Publisher . I hope I made it a little clear.