For this one, you need to be especially careful, while inspecting the source code, pay attention to the line:
if(fd=open("/home/mistake/password",O_RDONLY,0400) < 0){Here, the programmer meant to to save the return value of open() to fd, but they forgot to use braces so instead they save the result of the comparison to fd. So, if the comparison fails, fd is set to 0. That is STDIN. Hence, all we need to do is input a 10 character string first and after that the string with each byte XORed with 1.
mistake@pwnable:/tmp/fr1nge_mistake$ ~/mistake
do not bruteforce...
0000000000
input password : 1111111111
Password OK
Mommy, the operator priority always confuses me :(