linux-kernel - Re: [PATCH] signal: Avoid corrupting si_pid and si_uid in do_notify

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Message-ID: <20200421113802.z7f3di3qp5tyowrk@wittgenstein>
Date:   Tue, 21 Apr 2020 13:38:02 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        linux-kernel@...r.kernel.org,
        Linux Containers <containers@...ts.linux-foundation.org>,
        Christof Meerwald <cmeerw@...erw.org>
Subject: Re: [PATCH] signal: Avoid corrupting si_pid and si_uid in
 do_notify_parent

On Tue, Apr 21, 2020 at 01:28:31PM +0200, Oleg Nesterov wrote:
> On 04/21, Oleg Nesterov wrote:
> >
> > The corner case is release_task() when the last exiting sub-thread sends
> > a signal on behalf of its ->group_leader, and at this point all the tsk's
> > pid pointers are NULL, that is why "force" can be falsely "true".
> 
> Or do_notify_parent() can be called by debugger from the parent namespace,
> in this case "force" can be falsely "true" too.

That's an interesting scenario to think about as well. Cross-pid-namespace
interactions are fun... That's why the cross-pid-namespace-signal
sending aspects we discussed a while back on-list though pretty nice to
have at some point are somewhat scary.

Christian