Lori pretty much answered your question. When I "cook" all I am doing is boiling water, pouring it into a freezer bag and letting it hydrate. Smells are generally minimal.

FWIW if I didn't have to "cook" in the vestibule I wouldn't. On the rare occasions that I do take an actual tent then I will just pitch the rain fly or even the ground sheet as a make-shift shelter, cook my meal, eat and then continue hiking for a few more miles. In nicer weather I won't even bother pitching anything.

The only time I cook in a vestibule is when I simply backpack in and set-up camp for X amount of days.