Question about blinds

This is a question that I thought I knew the answer to, but it came up recently in a home game.

If a player gets in a hand, but doesn't have enough chips to match the big blind, how many chips is that player eligible to win? Can he win as much as the blinds or only as much as he put in?

As much as he puts in from each player in the hand.

IE
Allin player has 100 chips.

Sb is 200
BB is 400

One person limps in
Player with 100 chips goes all in
Sb folds
BB checks

Main pot is 400, this is what the player all in can only win. 100 from the sb, bb and limper and his own 100.

Side pot is 700, all in player cannot win this. 400+400+200+100-400=700