C - segfault when I do "cmd | cmd | cmd ; exit"

I have to recode a shell in C and when i'm try to do, for exemple, "ls | ls | ls ; exit", i have a Segmentation fault. Its like my exit was running before the end of my "ls | ls | ls" but if there are only 1 pipe its work. If you have an idea, or if you want a piece of my code please tell me !

(sorry for my bad english)