Stack smash protection: Automated (de)bugging?

[John Richard Moser]

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Dan Kegel wrote:
> On 7/11/06, John Richard Moser <nigelenki at comcast.net> wrote:
>> I am planning to rewrite libssp0 clean and produce a version that takes
>> advantage of an external daemon
> 
> I've been wanting to do something similar, but with a
> preload library, kind of like catchsegv uses libSegFault.so,
> instead of trying to jam the external daemon hook into the toolchain.

It won't be in the toolchain, the changes will go like this:

 * toolchain supplies a __stack_chk_fail2() in libssp0

 * toolchain uses __stack_chk_fail2() to handle stack smashes

 * glibc provides its own minimal __stack_chk_fail2() (it provides a
   __stack_chk_fail() now)

 * we modify the glibc __stack_chk_fail2() to use a library under
   certain conditions

 * We supply a libssp that talks to our daemon

 * We tell glibc to use that libssp for stack_chk_fail2()

Our daemon and hooks to talk to it will be completely external to the
toolchain.  In fact the final result can remove our libssp and behave
exactly as any other system.

> You might want to consider the same.
> (Hmm,  been thinking about it for three years now, never got around to
> it... http://sources.redhat.com/ml/libc-alpha/2003-05/msg00006.html )
> 
> The nice thing about this approach is that users who want to get rid
> of the feature can just unset LD_PRELOAD.
> - Dan

Has problems, mainly in a multi-lib environment; I want a robust
solution that won't break on distributions that want to run 32- and
64-bit code at the same time.  Also LD_PRELOAD is more a debugging tool
than anything else.  (yes ironically this is a debugging tool as well
but...)

> 

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