将0x20、0x00、0x0d，0x0a字节传递给strcmp（）

Question

I'm trying to do a challenge where there's a strange strcmp. It is the following:

if(strcmp(argv[1],"\x00")) return 0;
if(strcmp(argv[2],"\x20\x0a\x0d")) return 0;

I've tried to pass the arguments through Python but the bytes aren't read in the correct way. This is what I tried:

./program $(python -c 'import sys;sys.stdout.write("\x00 \x20\x0a\x0d")')

I also tried to use their repr but that didn't work too. They are currently being evaluated for what every byte actually represents: how do I "pass them as they are" correctly?

Answer 1

If you don't want the backslash escapes to be evaluated, you need to escape them.

This:

if(strcmp(argv[1], "\\x20\\x0a\\x0d")) return 0;

compares against the literal string "\\x20\\x0a\\x0d" , which has 12 characters.

From a command-line perspective, the first argument should be an empty string (typically written as "" in most shells), and the second should be the tree-character string " \\n\\r" in Python notation.

Not sure what Python has to do with things here, from eg bash you should be able to do:

$ ./program "" $'\n\r'