Re: [PATCH] signal: Avoid corrupting si_pid and si_uid in do_notify_parent

[Christian Brauner]

On Tue, Apr 21, 2020 at 01:11:40PM +0200, Oleg Nesterov wrote:
> Sorry Christian, I don't understand...

In my original mail, it was really just a clarification question. I
said the patch is correct from looking at the codepaths. :) I was just
trying to see whether there was a potential corner-case we're missing
where "force" could be _validly_ true.

> 
> > because child subreapers can't come from outside the pid namespace. If
> > they could you could create a scenario where the signal is generated
> > from a sibling pid namespace in which case it would be correctly set to
> > true.
> 
> not sure I understand, but probably the answer is "yes"...

(This is really purely academic now since it isn't possible, but for
pure amusement assume that a child subreaper could cross namespace
boundaries (which they don't). A marks itself as a subreaper and creates
a new process B in a new pid namespace <pidnsB>, process B setnses into
<pidnsC> which is a sibling pid namespace, B clones a new proces in
<pidnsC> which is now a full member of <pidnsC>, B dies and C is
reparented to A, B exits and then you'd be getting a sigchld from a pid
in a pid namespace in which you have no pid nr.)