Re: Need -fno-stack-protector to prevent stack corruption

[Henning Brauer <lists-openbsdtech@bsws.de>]

On Mon, Jun 23, 2003 at 11:29:09AM +0100, Barry Scott wrote:
> We're just got to the bottom of a stack corruption in a python extension
> written in C++.
> 
> I do not know the exact nature of the corruption but adding
> -fno-stack-protector fixes the crash.
> What we see is that the value returned from new is corrupted. The value
> of this at the end of
> the c'tor was reasonable.
> 
> I can supply source code and test scripts that demonstrates the problem
> against
> OpenBSD 3.3 Release.

it is quite easy to run into this trap.

say you have an application "X", compiled on an older OpenBSD version.
lets look at ldd output:
        -lpng.1 => /usr/local/lib/libpng.so.1.8
        -lc.25 => /usr/lib/libc.so.25.2
(I just left those two that are needed to demonstrate the problem).
we see it links to an older libc - it doesn't have __guard.
but you updated libpng. thus it needs __guard. libc is already loaded. 
no __guard symbol. kaboom.

clean solution: recompile the binary.

ugly hack:
  rm libc.so.25.2 && ln -s libc.so.29.0 libc.so.25.2
and hope the best.
This is so ugly and error prone that you better don't do it.
you've been warned.

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