I'm working on a homework problem that requires disabling compiler optimization protection for it to work. I'm using gcc 4.4.1 on ubuntu linux, but can't figure out which flags are are the right ones. I realize it's architecture dependant - my machine runs w/ 32-bit Intel processor.
That's a good problem. In order to solve that problem you will also have to disable ASLR otherwise the address of g() will be unpredictable.
sudo bash -c 'echo 0 > /proc/sys/kernel/randomize_va_space'
gcc overflow.c -o overflow -fno-stack-protector
After canaries and ASLR are disabled it should be a straight forward attack like the ones described in Smashing the Stack for Fun and Profit
Here is a list of security features used in ubuntu: https://wiki.ubuntu.com/Security/Features You don't have to worry about NX bits, the address of g() will always be in a executable region of memory because it is within the TEXT memory segment. NX bits only come into play if you are trying to execute shellcode on the stack or heap, which is not required for this assignment.
Now go and clobber that EIP!