Does this trap hold water in it?
If it is dry, then the smell comes up because there is nothing to hold it back. Thats what the water is for. Obviously stuffing a rag in it will stop the smell, but that is not a cure. Also, sewer gas can be a very deadly issue if not dealt with.
The vent pipe usually terminates approx 12" above the roof ,its approx 3" in diam. Look for a nest or some other type of blockage in it. Sometimes putting a water hose down it with a stream of water will open any small blockage.
But firstly, check your basement floor drain trap to see if its holding water. Good luck Hube