Messages in this thread | | | Date | Wed, 24 Apr 2019 17:23:06 +0200 | From | Christian Brauner <> | Subject | Re: SECCOMP_RET_USER_NOTIF: listener improvements |
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On Wed, Apr 24, 2019 at 09:20:01AM -0600, Tycho Andersen wrote: > On Wed, Apr 24, 2019 at 05:04:26PM +0200, Christian Brauner wrote: > > Hey everyone, > > > > So I was working on making use of the seccomp listener stuff and I > > stumbled upon a problem. Imagine a scenario where: > > > > 1. Task T1 installs Filter F1 and gets and listener fd for that filter FD1 > > 2. T1 sends FD1 via SCM_RIGHTS to task T2 > > T2 now holds a reference to the same underlying struct file as FD1 via FD2 > > 3. T2 registers FD2 in an event loop and starts listening for events > > 4. T1 exits and wipes FD1 > > > > Now, T2 still holds a reference to the filter via FD2 which references > > the same underlying file as FD1 which has the seccomp filter stashed in > > private_data. > > So T2 will never get notified that the filter is essentially unused and > > doesn't know when to exit, i.e. it has no way of telling when T1 and all > > of its children using the same filter are gone. > > > > I think we should have a way to do this > > Since the only way we ever allow creating a struct file * that points > to a struct seccomp_filter *, if there is a notifier attached, the > number of tasks still being monitored by a particular filter should be > filter->usage - 1 (assuming there is a notifier attached). So we could > augment __put_seccomp_filter() to check for this and send out a > message with a SECCOMP_NOTIF_FLAG_DEAD flag or something. > > > *or* alternatively have a way to attach a process to an existing > > filter. > > I also think this wouldn't be too hard, since the struct file * has a > reference to the filter. So I guess the question is: which of these > makes more sense?
Or we do both... But overall I'm very much in favor of the option to attach a task to an existing filter. Re-creating a seccomp context is extremely brittle and error-prone. This would take a way a major pain point.
Christian
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