linux-kernel - Re: SIGNAL_UNKILLABLE and init again

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Message-ID: <20170814093124.vvpa6e7ntcukghub@cedar>
Date:   Mon, 14 Aug 2017 10:31:24 +0100
From:   Jamie Iles <jamie.iles@...cle.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: SIGNAL_UNKILLABLE and init again

Hi Oleg,

On Thu, Apr 27, 2017 at 01:16:51PM +0100, Jamie Iles wrote:
> On Wed, Apr 26, 2017 at 05:18:58PM +0200, Oleg Nesterov wrote:
> > Hi Jamie,
> > 
> > On 04/25, Jamie Iles wrote:
> > >
> > > Hi Oleg,
> > >
> > > I'm back looking at SIGNAL_UNKILLABLE and debugging child reapers again, 
> > > and the current issue is when running code in the target process, 
> > > SIGTRAP firing and that causing SIGNAL_UNKILLABLE protection to be 
> > > removed in force_sig_info():
> > >
> > > 	if (action->sa.sa_handler == SIG_DFL)
> > > 		t->signal->flags &= ~SIGNAL_UNKILLABLE;
> > 
> > Yes, this is what I meant when I said force_sig_info() needs changes too.
> > I was going to fix it "tomorrow" but I was distracted and then forgot.
> > 
> > >   @@ -1185,7 +1185,7 @@ force_sig_info(int sig, struct siginfo *info, struct task_struct *t)
> > >    			recalc_sigpending_and_wake(t);
> > >    		}
> > >    	}
> > >   -	if (action->sa.sa_handler == SIG_DFL)
> > >   +	if (action->sa.sa_handler == SIG_DFL && !t->ptrace)
> > >    		t->signal->flags &= ~SIGNAL_UNKILLABLE;
> > >    	ret = specific_send_sig_info(sig, info, t);
> > >    	spin_unlock_irqrestore(&t->sighand->siglock, flags);
> > 
> > Not sure, let me think a bit more... and this is not enough anyway.
> > 
> > perhaps we should start with this simple change, but the "real" fix
> > needs a lot of cleanups, although I am not sure if we will ever do this.
> 
> Okay, sounds good.  I'm happy to spend more time looking at this if you 
> have suggestions - in the context of namespaces and containers this 
> seems more relevant than when it was just the system init that we were 
> protecting.

Any objections to moving ahead with this patch?

Thanks,

Jamie