Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1460935

Re: [PATCH] seccomp: Fix tracer exit notifications during fatal signals

Show all headers | View raw

Thanks!

On Fri, Aug 12, 2016 at 3:12 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> > 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.
>
> > 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.

True. But at least (as Kees alluded to later) this patch ensures
PTRACE_EVENT_EXIT delivery when exit is due to exit_group() and no
genuine fatal signals are involved.

> 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...

The ptrace man page currently says:
> A SIGKILL signal may still cause a PTRACE_EVENT_EXIT stop before actual signal death.  This may be changed in the future; SIGKILL is meant to always immediately kill tasks even under ptrace.  Last confirmed on Linux 3.13.

In practice, a PTRACE_EVENT_EXIT is almost always observed after
SIGKILL. That's nice for rr, because it lets us observe the process's
final state. But it allows a process to stay alive indefinitely after
receiving SIGKILL, so I can see why you might want to change it.

Rob
-- 
lbir ye,ea yer.tnietoehr  rdn rdsme,anea lurpr  edna e hnysnenh hhe uresyf toD
selthor  stor  edna  siewaoeodm  or v sstvr  esBa  kbvted,t rdsme,aoreseoouoto
o l euetiuruewFa  kbn e hnystoivateweh uresyf tulsa rehr  rdm  or rnea lurpr
.a war hsrer holsa rodvted,t  nenh hneireseoouot.tniesiewaoeivatewt sstvr  esn

Back to linux.kernel | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

[PATCH] seccomp: Fix tracer exit notifications during fatal signals Kees Cook <keescook@chromium.org> - 2016-08-11 01:40 +0200
  Re: [PATCH] seccomp: Fix tracer exit notifications during fatal signals Kyle Huey <me@kylehuey.com> - 2016-08-11 02:20 +0200
  Re: [PATCH] seccomp: Fix tracer exit notifications during fatal signals Andy Lutomirski <luto@amacapital.net> - 2016-08-11 09:30 +0200
    Re: [PATCH] seccomp: Fix tracer exit notifications during fatal signals Kees Cook <keescook@chromium.org> - 2016-08-11 20:10 +0200
  Re: [PATCH] seccomp: Fix tracer exit notifications during fatal  signals Oleg Nesterov <oleg@redhat.com> - 2016-08-11 17:20 +0200
    Re: [PATCH] seccomp: Fix tracer exit notifications during fatal signals Kees Cook <keescook@chromium.org> - 2016-08-11 20:20 +0200
      Re: [PATCH] seccomp: Fix tracer exit notifications during fatal signals Kyle Huey <me@kylehuey.com> - 2016-08-23 05:30 +0200
        Re: [PATCH] seccomp: Fix tracer exit notifications during fatal signals Kees Cook <keescook@chromium.org> - 2016-08-23 22:00 +0200
    Re: [PATCH] seccomp: Fix tracer exit notifications during fatal signals "Robert O'Callahan" <robert@ocallahan.org> - 2016-08-12 05:30 +0200

csiph-web