On Sun, Feb 04, 2018 at 08:33:25PM +0000, Andy Lutomirski wrote: > On Sun, Feb 4, 2018 at 8:01 PM, Tycho Andersen <tycho@xxxxxxxx> wrote: > > 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. > > I think we can safely assume that u64 won't overflow. Even if we > processed one user return notification on a given seccomp_filter every > nanosecond (which would be insanely fast), that's 584 years. Yes, fair point r.e. u64. I'll make the change. > > > >> 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. > > Hmm. This won't nest right. Maybe we should just disallow a > user-notification-using filter from being applied if there is already > one in the stack. Then, if anyone cares about making these things > nest right, they can fix it. Sounds fine to me, I'll add a check. Cheers, Tycho _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
