On Thu, Aug 11, 2016 at 11:18 AM, Kees Cook <keesc...@chromium.org> wrote: > On Thu, Aug 11, 2016 at 8:12 AM, Oleg Nesterov <o...@redhat.com> wrote: >> On 08/10, Kees Cook wrote: >>> >>> This fixes a ptrace vs fatal pending signals bug as manifested in seccomp >>> now that ptrace was reordered to happen after ptrace. The short version is >>> that seccomp should not attempt to call do_exit() while fatal signals are >>> pending under a tracer. This was needlessly paranoid. Instead, the syscall >>> can just be skipped and normal signal handling, tracer notification, and >>> process death can happen. >> >> ACK. >> >> I think this change is fine in any case, but... >> >>> The bug happens because when __seccomp_filter() detects >>> fatal_signal_pending(), it calls do_exit() without dequeuing the fatal >>> signal. When do_exit() sends the PTRACE_EVENT_EXIT >> >> I _never_ understood what PTRACE_EVENT_EXIT should actually do. I mean, >> when it should actually stop. This was never defined. > > Yeah, agreed. I spent some time reading through what should happen to > __TASK_TRACED during exit and my head spun. :) > >>> notification and >>> that task is descheduled, __schedule() notices that there is a fatal >>> signal pending and changes its state from TASK_TRACED to TASK_RUNNING. >> >> And this can happen anyway, with or without this change, with or without >> seccomp. Because another fatal signal can be pending. So PTRACE_EVENT_EXIT >> actually depends on /dev/random. >> >> Perhaps we should finally define what it should do. Say, it should only >> stop if SIGKILL was sent "implicitely" by exit/exec. But as for exec, >> there are more (off-topic) complications, not sure we actually want this... >> >> Nevermind, the main problem is that _any_ change in this area can break >> something. This code is sooooooo old. >> >> But let me repeat, I think this change is fine anyway. >> >> Acked-by: Oleg Nesterov <o...@redhat.com> > > Awesome, thanks!
Hi folks, Can't help but notice this didn't make it into rc3. Not sure if it's bubbling up somewhere I can't see, but we'd really like this to get into 4.8 so we don't have to work around the regression. Thanks! - Kyle