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    SubjectRe: [RFC 1/3] seccomp: add a return code to trap to userspace
    Hi Andy,

    On Sun, Feb 04, 2018 at 05:36:33PM +0000, Andy Lutomirski wrote:
    > > The actual implementation of this is fairly small, although getting the
    > > synchronization right was/is slightly complex. Also worth noting that there
    > > is one race still present:
    > >
    > > 1. a task does a SECCOMP_RET_USER_NOTIF
    > > 2. the userspace handler reads this notification
    > > 3. the task dies
    > > 4. a new task with the same pid starts
    > > 5. this new task does a SECCOMP_RET_USER_NOTIF, gets the same cookie id
    > > that the previous one did
    > > 6. the userspace handler writes a response
    >
    > I'm slightly confused. I thought the id was never reused for a given
    > struct seccomp_filter. (Also, shouldn't the id be u64, not u32?)

    Well, what happens when u32/64 overflows? Eventually it will wrap.

    > On very quick reading, I have a question. What happens if a process
    > has two seccomp_filters attached, one of them returns
    > SECCOMP_RET_USER_NOTIF, and the *other* one has a listener?

    Good question, in seccomp_run_filters(), the first (lowest, last
    applied) filter who returns SECCOMP_RET_USER_NOTIF is the one that
    gets the notification and the other receives nothing.

    I don't really have any reason to prefer this behavior, it's just what
    happened without much thought.

    Cheers,

    Tycho

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