Re: Buffer Overflow Experiment

Hi,
Since you are using Fedora, have you disabled kernel.exec-shield ?
the va randomize i.e. kernel.exec-shield-randomize is only one of the
exec-shield features... So you may want to disable the whole
exec-shiedl to test your code.

regards,
Rick

On 9/13/07, Alcides <alcides.hercules@xxxxxxxxx> wrote:
Hi List,
I was wondering if someone has already done this.
I'm testing a small program written in C, especially coded for testing
buffer overflow.
In source code, I have assigned char buffer[512]; I compile with gcc and
run on bash.

As soon as I pass "512" characters as argument("A"x512--being precise),
the program gives " Segmentation fault (core dumped )" -->as desired.

1] Using GDB debugger, it has been verified that the extended
instruction pointer EIP has been overwritten, as expected.
(EIP-->0x41414141)
2] But, on passing "513" chars. argument, the EIP becomes 0x0 -->WHY
3]On passing 520 chars. argument, EIP takes 'some' value and EBP
becomes 0x41414141
4]Thereafter, every increment by 1 --> in input characters causes EIP to
remain the same as that 'some' value and EBP to take various incremental
values.
every time, for several unit increments

[I am using: 2.6.21-1.3194.fc7 kernel, i686, Disabled VA randomization]

Any views that help me understand why EIP becomes 0, are welcome.


Thanks.

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