Re: siginfo pid not populated from ptrace?

Eric W. Biederman
2018-12-10T17:37:19Z

Oleg Nesterov <oleg@redhat.com> writes:

> On 12/06, Eric W. Biederman wrote:
>>
>> The challenge is that we could be delivering this to a zombie signal
>> group leader.
>
> ...
>
>> Sigh it is probably time that I dig in and figure out how to avoid that
>> case which we need to fix anyway because we can get the permission
>> checks wrong for multi-threaded processes that call setuid and friends.
>
> this is another issue... I am sure we have already discussed this, but I
> failed to find any link to the previous discussion.

Now that we have PIDTYPE_TGID I think we are closer to being able to
solve that issue. You are absolutely right it is another issue.

>> Once that is sorted your small change will at least be safe.
>
> I don't think so, any sub-thread can dequeue SIGSTOP unless type == PIDTYPE_PID,
> this has nothing to do with the problems connected to zombie leader, or I
> misunderstood you.

I forgot to check what wants_signal does in this case. I thought
SIGSTOP was like SIGKILL and being unblockable would always be delivered
to the thread we are aiming at. With a zombie leader being the
exception.

Having reread wants_signal you are absolutely correct. SIGSTOP can be
delivered to any thread so this won't help. I don't understand why for
SIGSTOP we don't treat SIGSTOP like SIGKILL, but that is also another
conversation. It feels like the differences between SIGSTOP and SIGKILL
in wants_signal are silly. I don't see them leading to incorrect behavior.

Eric