Linux-kernel mailing list archive 2000-40,: Re: execve replacement.

# Re: execve replacement.

John Levon (moz@compsoc.man.ac.uk)
Wed, 4 Oct 2000 16:07:21 +0100 (BST)

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On Wed, 4 Oct 2000, Brian Gerst wrote:

> John Levon wrote:
> > anyway, you can just put refcounts in your hijacked system calls; that is
> > the safe way to do it, and doesn't require any kernel patches, just extra
> > cost in the intercepted system calls.
> >
> > e.g. :
> >
> > my_syswhatever(...)
> > {
> > MOD_INC_USE_COUNT;
> > original_syswhatever(...);
> > MOD_DEC_USE_COUNT;
> > }
> >
> > Can you explain to me the race with this approach ?
>
> There is a small period of time between the last MOD_DEC_USE_COUNT and
> the return of the function where the module could be unloaded by another
> CPU (SMP only). It is a tiny race window, but still possible.
>

Wouldn't this require another module to be loaded inbetween the
MOD_DEC_USE_COUNT, and the function exit, to actually be dangerous ?
I don't know ...

john

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