[PATCH 9/9] ptrace: Don't change __state

[Eric W. Biederman]

Oleg Nesterov <oleg at 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.

> 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