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Date: Sun, 9 Oct 2011 21:00:22 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: "Serge E. Hallyn" <serge.hallyn@canonical.com>
Cc: lkml <linux-kernel@vger.kernel.org>, richard@nod.at,
        Andrew Morton <akpm@google.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>, Tejun Heo <tj@kernel.org>,
        serge@hallyn.com
Subject: Re: [PATCH] user namespace: make signal.c respect user namespaces
Message-ID: <20111009190022.GA13853@redhat.com>
References: <20110920174849.GB22317@redhat.com> <20110920185354.GA19629@sergelap> <20110921175357.GA25590@redhat.com> <20110923163113.GA3820@sergelap> <20110923173656.GA5233@redhat.com> <20110923212025.GA21330@sergelap> <20110924163709.GA6776@redhat.com> <20110925201723.GA5288@sergelap> <20110926160619.GA13736@redhat.com> <20111004174213.GA24179@sergelap>
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Sorry, I missed this email...

On 10/04, Serge E. Hallyn wrote:
>
> Quoting Oleg Nesterov (oleg@redhat.com):
> > --- x/kernel/signal.c
> > +++ x/kernel/signal.c
> > @@ -1019,6 +1019,27 @@ static inline int legacy_queue(struct si
> >  	return (sig < SIGRTMIN) && sigismember(&signals->signal, sig);
> >  }
> >
> > +static inline fixup_uid(struct siginfo *info, struct task_struct *t)
> > +{
> > +#ifdef CONFIG_USER_NS
> > +	if (current_user_ns() == task_cred_xxx(t, user_ns)))
> > +#endif
> > +		return;
> > +
> > +	if (SI_FROMKERNEL(info))
> > +		switch (info->si_code & __SI_MASK) {
> > +			default:
> > +				return;
> > +
> > +			case __SI_CHLD:
>
> If I'm reading this right, this will catch do_notify_parent, which is
> sending signals not from current.

Argh, indeed. So we need to modify the callers.

OTOH, this is only possible if the debugger notifies tracee->real_parent,
or we reparent to /sbin/init.

Anyways, yes, I forgot about this. Thanks.

Oleg.

Not sure of the best way to avoid
> this.  For pids that case is being ignored by not using the __SI_MASK,
> so CLD_EXITED etc will cause from_ancestor_ns to be false.  Could we
> do that here too, and then translate the pids in do_notify_parent?
> 
> > +			case __SI_MESGQ:
> > +				break;
> > +		}
> > +
> > +	info->si_uid = user_ns_map_uid(task_cred_xxx(t, user_ns),
> > +					current_cred(), info->si_uid);
> > +}
> > +
> >  static int __send_signal(int sig, struct siginfo *info, struct task_struct *t,
> >  			int group, int from_ancestor_ns)
> >  {
> > @@ -1088,6 +1109,9 @@ static int __send_signal(int sig, struct
> >  				q->info.si_pid = 0;
> >  			break;
> >  		}
> > +
> > +		fixup_uid(info, t);
> > +
> >  	} else if (!is_si_special(info)) {
> >  		if (sig >= SIGRTMIN && info->si_code != SI_USER) {
> >  			/*
> >