Loading raw code from C program

Question

I\'m writing a program that loads and executes code from file. But i got a problem: \"write\" syscall does not work. Code successfully loads and executes, but does not displ

Answer 1

One thing: you should open the file as binary.

FILE* fp = fopen(argv[1],"rb"); 

Answer 2

Why are you not using .so files to dynamically load your code? Are you testing a security scenario or really trying to dynamically load and run code?

Read here on how to compile code as a .so, load it dynamically within a program, and execute exported functions out of it.

http://www.yolinux.com/TUTORIALS/LibraryArchives-StaticAndDynamic.html

Answer 3

Your approach can't work: shellcode must be position-independant, but your code refers to the absolute address str. The unconditional jump can also be either relative or absolute: make sure you get the relative verison (opcodes EB and E9 on x86).

See The Technique of Writing Portable Shell Code for more information.

Answer 4

You don't specify the details of your CPU, but you might be running afoul of the NX bit. I would expect your code to SEGFAULT though rather than run to completion.

This is precisely what happens on my box (Linux 2.6.32-28-generic #55-Ubuntu SMP Mon Jan 10 23:42:43 UTC 2011 x86_64 GNU/Linux) running on Intel Xeon E5410.