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    SubjectRe: [RFC 1/3] seccomp: add a return code to trap to userspace
    On Wed, Feb 14, 2018 at 9:19 AM, Andy Lutomirski <luto@amacapital.net> wrote:
    > On Wed, Feb 14, 2018 at 3:29 PM, Tycho Andersen <tycho@tycho.ws> wrote:
    >> On Tue, Feb 13, 2018 at 01:09:20PM -0800, Kees Cook wrote:
    >>> On Sun, Feb 4, 2018 at 2:49 AM, Tycho Andersen <tycho@tycho.ws> wrote:
    >>> I wonder if this communication should be netlink, which gives a more
    >>> well-structured way to describe what's on the wire? The reason I ask
    >>> is because if we ever change the seccomp_data structure, we'll now
    >>> have two places where we need to deal with it (the first being within
    >>> the BPF itself). My initial idea was to prefix the communication with
    >>> a size field, then send the structure, and then I had nightmares, and
    >>> realized this was basically netlink reinvented.
    >>
    >> I suggested netlink in LA, and everyone (especially Andy) groaned very
    >> loudly :). I'm happy to switch it to netlink if you like, although i
    >> think memcpy() of structs should be safe here, since the return value
    >> from read or write can indicate the size of things.
    >
    > I could easily get on board with "netlink" (i.e. NLA) messages sent
    > over an fd. I will object strongly to the use of netlink *sockets*.

    Yeah, I was thinking NLA over the fd; not a netlink socket.

    >>> An ERRNO filter would block a USER_NOTIF because it's unconditional.
    >>> TRACE could be either, USER_NOTIF could be either.
    >>>
    >>> This means TRACE rules would be bumped by a USER_NOTIF... hmm.
    >>
    >> Yes, I didn't exactly know what to do here. ERRNO, TRAP, and KILL all
    >> seemed more important than USER_NOTIF, but TRACE didn't. I don't have
    >> a strong opinion about what to do here, because users can adjust their
    >> filters accordingly. Let me know what you prefer.
    >
    > If we switched to eBPF functions, this whole issue goes away.

    Yeah, though we'd still need some kind of "wait for answer" eBPF
    function. It feels wrong to re-use maps for that...

    -Kees

    --
    Kees Cook
    Pixel Security

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