Re: RFC: disablenetwork facility. (v4)

[Serge E. Hallyn]

Quoting Eric W. Biederman (ebiederm@xxxxxxxxxxxx):
> Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> writes:
> 
> >> > Execute != read. The executable file may contain secrets which must not
> >> > be available to the user running the setuid program. If you fail the
> >> > setuid, the user will be able to ptrace() and then the secret is
> >> > revealed.
> >> >
> >> > It's amazing how many security holes appear from what seems like a very
> >> > simple request.
> >> 
> >> Do we have a security hole in nosuid mount option?
> >> Can someone write a patch to fix it?
> >
> > If a setuid app can read a key when its erroneously not set setuid then
> > the user can read it too.
> >
> > Anything you can do with ptrace you can do yourself !
> 
> Now that I think about it this is really something completely separate
> from setuid.  This is about being able to read the text segment with
> ptrace when you on have execute permissions on the file.
> 
> I just skimmed through fs/exec.c and we set the undumpable process
> flag in that case so ptrace should not work in that case.

And in fact you can't do a new ptrace_attach, but if you're already
tracing the task when it execs the unreadable-but-executable file,
then the ptrace can continue.

Just looking at the code, it appears 2.2 was the same way (though I
could be missing where it used to enforce that).

So, is that intended?  What exactly would we do about it if not?
Just refuse exec of a unreadable-but-executable file if we're
being traced?

> So short of a bug in the implementation we have no security hole.
> 
> Eric
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