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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.



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