On Tue, Dec 01, 2020 at 08:13:34AM -0500, Tycho Andersen wrote: > On Tue, Dec 01, 2020 at 01:08:25PM +0000, Sargun Dhillon wrote: > > On Tue, Dec 01, 2020 at 07:41:05AM -0500, Tycho Andersen wrote: > > > 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 > > > _______________________________________________ > > > Containers mailing list > > > Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx > > > https://lists.linuxfoundation.org/mailman/listinfo/containers > > > > This doesn't solve the problem universally because of the (Go) preemption > > problem. Unless we can guarantee that the supervisor can always handle the > > request in fewer than 10ms, or if it implements resumption behaviour. I know > > that resumption behaviour is a requirement no matter what, but the easier we can > > make it to implement resumption, the better chance we are giving users to get > > this right. > > Doesn't automatic cleanup of fds make things easier? I'm not sure I > understand the argument. I doubt Al would ever allow the "cleanup" approach: his observation was that the instant a file has been added to the fdtable, it's not possible to "unwind" that ever, since it could be cloned away, etc, etc. > I agree it doesn't fix the problem of uncooperative userspace. IIUC, I see two issues: - a slow monitor might cause a child to loop forever retrying the same interrupted syscall. - a syscall-interrupted process may have had an fd added that it has no idea about. The former problem seems like a userspace issue. :P But, to help, yeah, is signal blocking best? Either explicit (at filter apply time) or implicit (all user_notif-triggering syscalls get all signals blocks automatically)? For the latter problem, I think we need to get back to Tycho's original method: add fd and finish syscall in a single action. I can't see any other way to get around the need for atomicity... -- Kees Cook _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
