I use Bar Keeper's Friend, found in the grocery store, by the Ajax and Comet.
Using a soft toothbrush, get the fabric wet, Rub some product in to the stain, and scrub with a soft toothbrush. It effectively removes rust stains from clothing.
I used to have a washing machine where the drum had chips in it, and those chips turned to rust. If i let my clothes sit in the chipped tub too long, I got rust stains on everything. It was awful. Bar Keeper's Friend was an inexpensive way to get the rust out of my laundry. I was so glad to get rid of that washer!
Hope this helps.