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    SubjectRe: ext2 attribute immutable
    On  1 Apr 96 at 22:50, sct@dcs.ed.ac.uk wrote:

    > Hi,
    >
    > On Fri, 29 Mar 1996 19:52:32 -0800 (PST), Snow Cat
    > <snowcat@math.csufresno.edu> said:
    >
    > > sct@dcs.ed.ac.uk once wrote:
    > >>
    > >> ... A non-zero securelev prevents even root from bypassing or
    > >> removing the immutable (or the append-only) flag on an ext2 file.
    > >>
    > >> Not even root is allowed to decrease the securelev again. The only
    > >> process ever allowed to decrement securelev is init.
    >
    > > So, how does one need to modify /proc/1/mem to decrease the secure-level
    > > after getting root access? :)
    >
    > You don't need to. You can just do a ptrace() on init, or create your
    > OWN init process --- by using a careful, controlled fork bomb we can
    > easily create new processes until we are about to wrap pid, then kill
    > init and wait until one of our forks has a pid of 1.

    Does the kernel really reassign PID 1? What about a panic as soon as
    PID 1 dies?

    >
    > The securelevel code is now fully implemented, but of course it is
    > still insecure if there are other vulnerabilities in the security
    > regime which permit arbitrary access to kernel memory or to the init
    > process. A complete security mechanism, capable of defeating even a
    > root attack, has GOT to be more complex than Linux can currently
    > achieve. There's nothing new about this!
    >
    > However, one thing which could be done fairly easily would be to (a)
    > protect init from all attacks, making it immune to ptrace, kill -9
    > etc; and (b) disable all direct kernel access (such as /dev/mem or
    > loading new kernel modules) once securelev is sufficiently high.
    >
    > Cheers,
    > Stephen.
    > --
    > Stephen Tweedie <sct@dcs.ed.ac.uk>
    > Department of Computer Science, Edinburgh University, Scotland.

    Ulrich


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