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    SubjectRe: [PATCH 3/5] v2 seccomp_filters: Enable ftrace-based system call filtering
    On Thu, May 26, 2011 at 11:46 AM, Linus Torvalds
    <> wrote:
    > On Thu, May 26, 2011 at 9:33 AM, Will Drewry <> wrote:
    >> FWIW, none of the patches deal with privilege escalation via setuid
    >> files or file capabilities.
    > That is NOT AT ALL what I'm talking about.
    > I'm talking about the "setuid()" system call (and all its cousins:
    > setgit/setreuid etc). And the whole thread has been about filtering
    > system calls, no?
    > Do a google code search for setuid.
    > In good code, it will look something like
    >  uid = getuid();
    >  if (setuid(uid)) {
    >    fprintf(stderr, "Unable to drop provileges\n");
    >    exit(1);
    >  }
    > but I guarantee you that there are cases where people just blindly
    > drop privileges. google code search found me at least the "heirloom"
    > source code doing exactly that.
    > And if you filter system calls, it's entirely possible that you can
    > attack suid executables through such a vector. Your "limit system
    > calls for security" security suddenly turned into "avoid the system
    > call that made things secure"!
    > See what I'm saying?

    Absolutely - that was what I meant :/ The patches do not currently
    check creds at creation or again at use, which would lead to
    unprivileged filters being used in a privileged context. Right now,
    though, if setuid() is not allowed by the seccomp-filter, the process
    will be immediately killed with do_exit(SIGKILL) on call -- thus
    avoiding a silent failure. I mentioned file capabilities because they
    can have setuid-like side effects, too. As long as system call
    rejection results in a process death, I *think* it helps with some of
    this complexity, but I haven't fully vetted the patches for these
    scenarios to be 100% confident.

    Sorry I wasn't clear!
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