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! -Kees -- Kees Cook Nexus Security
