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    SubjectRe: seccomp for 2.6.11-rc1-bk8

    * Ingo Molnar <mingo@elte.hu> wrote:

    > > > This is the seccomp patch ported to 2.6.11-rc1-bk8, that I need for
    > > > Cpushare (until trusted computing will hit the hardware market).
    > > > [...]
    > >
    > > why do you need any kernel code for this? This seems to be a limited
    > > ptrace implementation: restricting untrusted userspace code to only be
    > > able to exec read/write/sigreturn.
    > >
    > > So this patch, unless i'm missing something, duplicates in essence what
    > > ptrace can do [...]
    >
    > there's one thing ptrace wont do: if the ptrace parent dies
    > unexpectedly and the child was 'running' (there is a small window
    > where the child might not be stopped and where this may happen) then
    > the child can get runaway. While i think this is theoretical (UML
    > doesnt suffer from this problem), it is simple to fix - find below a
    > proof-of-concept patch that introduces PTRACE_ATTACH_JAIL - ptraced
    > children can never escape out of such a jail. (barely tested - but you
    > get the idea.)

    maybe this could even be fit into existing ptrace semantics, without any
    need for PTRACE_ATTACH_JAIL. What we need is to catch the case where a
    ptraced child is running (i.e. the signal_wake_up() has already been
    done, and the parent is waiting for the child to stop again), and the
    ptrace parent is killed unexpectedly. Would it be a correct fix to just
    unconditionally stop the child in this case (and leave it hanging in
    such a state)? Or to kill it right away?

    Ingo
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