Practicing what SHOULD be a simple crackme. Program calls strlen() but never returns

Question

I'm trying out a crackme from the "LSE CTF" called "Blue Box" worth only 10 points. I've attempted this inside GDB and radare2...

It is very simple, takes one argument and first checks to make sure it has that arg then it calls strlen later in the code. I set a breakpoint before the call and after but during the call to strlen I get a SIGTRAP signal which I continue but it never comes back to main, it just exits, even if I step through it all.

I'm stumped and would appreciate any help with this one, just to figure out this one part, I'm not asking for the answer or anything.

If you don't have an account with the CTF I uploaded the file here: https://ufile.io/te97v

Answer 1

Hopefully, this will get you moving in the right direction. Look closely at what is being passed to the strlen function; does the address make sense?