Run the commands,
~$ chmod u+s /challenge/getroot
~$ /challenge/getroot
SUCCESS! You have set the suid bit on this program, and it is running as root!
Here is your shell...
~# cat /flag
We obtain the flag pwn.college{4H-UoCzHphHwA_rURXGwzz26klo.dNTM2QDL3kTO0czW}