On 04/27, Eric W. Biederman wrote:
>
> Oleg Nesterov <o...@redhat.com> writes:
>
> > On 04/26, Eric W. Biederman wrote:
> >>
> >> @@ -253,7 +252,7 @@ static int ptrace_check_attach(struct task_struct
> >> *child, bool ignore_state)
> >> */
> >> if (lock_task_sighand(child, &flags)) {
> >> if (child->ptrace && child->parent == current) {
> >> - WARN_ON(READ_ONCE(child->__state) == __TASK_TRACED);
> >> + WARN_ON(child->jobctl & JOBCTL_DELAY_WAKEKILL);
> >
> > This WARN_ON() doesn't look right.
> >
> > It is possible that this child was traced by another task and
> > PTRACE_DETACH'ed,
> > but it didn't clear DELAY_WAKEKILL.
>
> That would be a bug. That would mean that PTRACE_DETACHED process can
> not be SIGKILL'd.
Why? The tracee will take siglock, clear JOBCTL_DELAY_WAKEKILL and notice
SIGKILL after that.
Oleg.
> > If the new debugger attaches and calls ptrace() before the child takes
> > siglock
> > ptrace_freeze_traced() will fail, but we can hit this WARN_ON().
>
> Eric
>
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