False positive feedback on Computing 101 / Output and Input / Hardcoding the Filename

[travelling-salesman-git]

When compiling the challenge binary using the following incorrect assembly code, the /challenge/check/ mistakenly tells the user their solution is correct, even though the binary never prints the flag.

challenge.s assembly file

mov BYTE PTR [rsp], '/'
mov BYTE PTR [rsp+1], 'f'
mov BYTE PTR [rsp+2], 'l'
mov BYTE PTR [rsp+3], 'a'
mov BYTE PTR [rsp+4], 'g'
mov BYTE PTR [rsp+5], 0
mov rdi, [rsp] # this should be rsp, not [rsp], as open expects a pointer
mov rsi, 0
mov rax, 2
syscall

Output from /challenge/check

ubuntu@hello-hackers~hardcoding-the-filename:~$ as challenge.s -o challenge.o; ld challenge.o -o challenge; /challenge/check challenge

/nix/store/v9zpzmigqkcjrw1jpf0zjc49y47cm55s-binutils-2.44/bin/ld: warning: cannot find entry symbol _start; defaulting to 0000000000401000

Checking the assembly code...
Your assembly looks correct!

Let's run your program and see if it can read the flag!

hacker@hello-hackers~hardcoding-the-filename:/home/hacker$ challenge
hacker@hello-hackers~hardcoding-the-filename:/home/hacker$ echo $?
42
hacker@hello-hackers~hardcoding-the-filename:/home/hacker$ 

Your program opened, read, and wrote the flag!