A bowler can sling to a degree where his arms dont go below a level where his arms wud b when extended sideways parallel to the ground, lest it would be termed underarm bowling which is banned from the modern game after our coach disgraced himself and his brother using it.

Ofcourse Malinga can sling and its fine....
Also his arm does bend but by how much is debatory as I dont think he bends it all the time...
The aussies where aghast seeing his action...
They kept saying they couldnt see where his arm came from and had trouble sighting....