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

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Message-ID: <20200421092846.GB6787@redhat.com>
Date:   Tue, 21 Apr 2020 11:28:47 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Christian Brauner <christian.brauner@...ntu.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 04/21, Christian Brauner wrote:
>
> > -		__group_send_sig_info(sig, &info, tsk->parent);
> > +		__send_signal(sig, &info, tsk->parent, PIDTYPE_TGID, false);
>
> So below you switch to __send_signal() but set the "force" argument to
> to "false".

it must be false, the signal is generated from the parent's namespace or
its descendant

> Before that, if the signal was generated from another pid
> namespace and we fixed up si_pid and si_uid the "force" argument was set
> to "true",

before that the "force" argument could be falsely true by the same reason,
task_pid_nr_ns(tsk, tsk->parent) can return 0 because "tsk" no longer have
pids after __unhash_process().

Oleg.