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? Tycho
