Noting that 'Marital rape' has not been recognised as an offence in India, the Madhya Pradesh High Court has observed that any sexual intercourse, including unnatural sex by a man with a wife,...
MAY 2 - Madhya Pradesh High Court reaffirms the Indian Penal Code, rules that marital rape is legal
Looks like it's basically the same idea as "sodomy".
CW explicit SA
So anal raping their wife, something that AFAIK can be incredibly painful and even damaging if not done right, is perfectly legal.