Re: Race in ptrace.

[Oleg Nesterov]

On 02/11, Salman Qazi wrote:
>
> >> >                // the tracee is STOPPED as requested, not TRACED,
> >> >                // SIGCONT wakes it up
> >> >                kill(pid, SIGCONT);
>
> I am still missing something.  There's probably a gap in my
> understanding, so let's try to clarify it.  The last "kill" call,
> sends a SIGCONT.  But, shouldn't this SIGCONT be intercepted by the
> tracer before the tracee sees it?

No. The tracee resumes (again: because it was STOPPED, not TRACED),
dequeues SIGCONT, reports the signal and stops in TASK_TRACED,
see ptrace_signal(). Meanwhile, until it calls ptrace_stop(), it is
TASK_RUNNING and ptrace() fails.

Oleg.

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