SECCOMP_IOCTL_NOTIF_ADDFD race condition

[Tycho Andersen]

On Mon, Nov 30, 2020 at 06:20:09PM -0500, Tycho Andersen wrote:
> Idea 1 sounds best to me, but maybe that's because it's the way I
> originally did the fd support that never landed :)
> 
> But here's an Idea 4: we add a way to remotely close an fd (I don't
> see that the current infra can do this, but perhaps I didn't look hard
> enough), and then when you get ENOENT you have to close the fd. Of
> course, this can't be via seccomp, so maybe it's even more racy.

Or better yet: what if the kernel closed everything it had added via
ADDFD if it didn't get a valid response from the supervisor? Then
everyone gets this bug fixed for free.

Tycho