Re: locating exploits in open source

["Littlefield, Tyler" <tyler () tysdomain com>]

Thanks all for the info. I really appreciated it. Luckaly I have some 
experience with asm, though it is limited. The videos are nice, though I 
am going to have to supplement them with extra materials more than 
usual, since I am blind and it's hard to tell what he is doing all the time.

Anyway, again I appreciate the help. I do have a question.
If I am going to use a buffer overflow, I want to make sure I understand 
this right.
If I have a function like:
void foo(char* x);
that means that I'd need to push an argument and call foo.
push eax
call foo
now that I've called foo, it's going to set up the stack:
gcc's disasm does something like:
push ebp
mov ebp, esp
so now we have:
ebp+8 >> x
ebp+4 >> return
ebp >> old ebp (?)
so lets say that I declare a static buffer (you would sub ebp, 4) for 
that extra variable and it was a buffer. so if it was ebp-4, I could 
store an int there.
now if I wanted to overflow that, I would have to fill ebp-4, which is 
the variable, ebp which is the pointer to the old frame (explaination 
there would be cool--I am kind of confused on what the "old frame" is); 
is it just the point on the stack (esp) where the previous frame's 
locals and that are stored? and then ebp+4. So I would have to feed that 
buffer 12 bytes to overwrite the return.
so, this leads me to two final questions.
First, is there a way perhaps to return backwards? So if I could manage 
to squeeze shellcode into those first 8 bytes (is that a possibility?) I 
could return to that and execute that? If I return to a funtion, how do 
I make that function do what I want? Being able to run any function in 
the code seems nice, but calling printf for example doesn't really do 
much for me. It would also require that I somehow get my arguments on 
the stack.
Finally, lets say I found a function with GDB. With ASLR, is that not 
guaranteed to change when I execute the program again?

Hopefully this is the right place for these questions--if not, I would 
appreciate other resources where this could be asked.
Thanks,
Ty


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