I am attempting to learn about buffer overflows. I have written a simple C program that calls a function called checkpw() which allocates a char array of 10 bytes large. When I analyze the op code I see that it actually allocates 16 bytes on the stack.
My goal was to overflow that buffer and write over the return pointer address, which I have successfully done. I have pointed it to a bit further down the buffer where I have shell code, where the first instruction is xor eax,eax.
During the GDB disassembly I can si single step through the op codes successfully until the rip (instruction pointer) points exactly where I want it to point (0x00007fffffffde40).
I even see the => when I examine that memory location with the x/i 0x00007fffffffde40 which then displays the op code xor eax,eax.
The problem is as soon as I engage in the next instruction with si I get a SEGFAULT.
When I compiled the program, I made sure to include the switch -fno-stack-protector setting, and I also performed echo 0 > /proc/sys/kernel/randomize_va_space
Other than that, I am stuck. Why I am getting a SEGFAULT instead of executing the xor?
