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    SubjectRe: [PATCH 3/5] v2 seccomp_filters: Enable ftrace-based system call filtering

    * <> wrote:

    > On Thu, 26 May 2011, Ingo Molnar wrote:
    > >* Linus Torvalds <> wrote:
    > >
    > >>It also gets rid of all configuration - one of the things that
    > >>makes most security frameworks (look at selinux, but also just
    > >>ACL's etc) such a crazy rats nest is the whole "set up for other
    > >>processes". If it's designed very much to be about just the "self"
    > >>process (after initialization etc), then I think that avoids pretty
    > >>much all the serious issues.
    > >
    > >That's how the event filters work currently: even when inherited they
    > >get removed when exec-ing a setuid task, so they cannot leak into
    > >privileged context and cannot modify execution there.
    > >
    > >Inheritance works when requested, covering only same-credential child
    > >tasks, not privileged successors.
    > this is a very reasonable default, but there should be some way of
    > saying that you want the restrictions to carry over to the suid
    > task (I really know what I'm doing switch)

    Unless you mean that root should be able to do it it's a security
    hole both for events and for filters:

    - for example we dont want really finegrained events to be used to
    BTS hw-trace sshd and thus enable it to discover cryptographic
    properties of the private key sshd is using.

    - we do not want to *modify* the execution flow of a setuid program,
    that can lead to exploits: by pushing the privileged codepath into
    a condition that can never occur on a normal system - and thus can
    push it into doing something it was not intended to do.

    data damage could be done as well: for example if the privileged
    code is logging into a system file then modifying execution can
    damage the log file.

    So it's not a good idea in general to allow unprivileged code to
    modify the execution of privileged code. In fact it's not a good idea
    to allow it to simply *observe* privileged code. It must remain a
    black box with very few information leaking outwards.



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