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SubjectRe: Stack Smashing and no-exec
On Fri, 7 Aug 1998, Kragen wrote:

> On Fri, 7 Aug 1998, Jon M. Taylor wrote:
> > On Fri, 7 Aug 1998, Kragen wrote:
> > > On Fri, 7 Aug 1998, Jon M. Taylor wrote:
> > > > As long as Linux is a traditional monolithic Unix-like kernel, I
> > > > think this is a reasonable attitude to have. Linus is correct. The suid
> > > > root programs should be fixed. If that task is difficult, use bounds
> > > > checking or whatever you need to be able to fix the problems.
> > >
> > > I think some kind of small-interface solution like bounds-checking
> > > compilers should help considerably -- but, of course, it's not a
> > > panacea.
> >
> > Right. The point is that the primary responsibility must lie with
> > the suid root code. The kernel can help catch these bugs, as can various
> > other tools like the compiler, but ultimately the code needs to be fixed.
>
> No, that wasn't what I meant. If you have a compiler that does
> bounds-checking in a reliable fashion, you may indeed be able to avoid
> adding features to the code to make sure it doesn't buffer-overflow.
> In fact, you might be better off that way.

This sort of checking cannot be made deterministic, though, right?

> What I meant was that there are (many!) other security bugs that are
> not the result of wild pointers, and so you can't rely on your compiler
> to catch them.

That is also true. It may be harder to imagine a bug which makes
a suid root program fall over and spew garbage all over /proc/kmem, but it
is not impossible. Should the kernel watch for this? No, it assumes that
suid root code knows what it is doing. That means no special treatment.
I think you could say that if the stack-smashing thing isn't a problem for
non-root code, it just plain is not a bug period, at least not in the same
sense. Suid root code does not get the same guarantees from the kernel as
regular userspace code does. That extends to the right to tell the kernel
what is and is not correct behavior.

Jon


---
'Cloning and the reprogramming of DNA is the first serious step in
becoming one with God.'
- Scientist G. Richard Seed


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