linux-kernel - Re: [PATCH 5/5] ptrace: it is fun to strace /sbin/init

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Date:	Fri, 21 Mar 2008 04:15:54 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Pavel Machek <pavel@....cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Davide Libenzi <davidel@...ilserver.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...e.hu>,
	Laurent Riffard <laurent.riffard@...e.fr>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] ptrace: it is fun to strace /sbin/init

On 03/21, Pavel Machek wrote:
>
> On Thu 2008-03-20 19:57:56, Oleg Nesterov wrote:
> > On 03/20, Pavel Machek wrote:
> > > 
> > > > Ptracing of /sbin/init is not allowed. Of course, this is very dangerous, but
> > > > may be useful. Introduce the kernel boot parameter to allow this.
> > > ...
> > > > @@ -803,6 +803,8 @@ and is between 256 and 4096 characters. 
> > > >  			Run specified binary instead of /sbin/init as init
> > > >  			process.
> > > >  
> > > > +	init_ptrace	[KNL] Allows to ptrace init. Very dangerous. Don't use.
> > > > +
> > > 
> > > I don't know what ptracing init is good for, and I believe people
> > > wanting to do this kind of special stuff can patch their own kernel...
> > 
> > Yes sure. But could you explain why this can be bad given that ptracing
> > init needs the explicit boot parameter? IOW, could you explain why you
> > don't like this small and trivial change which adds a minimal impact?
> 
> "It can't be bad, its optional".
> 
> It is bad exactly _because_ it is optional. Anything that adds boot
> parameter is *not* trivial... 

You are right. I'd prefer to make /sbin/init ptraceable unconditionally,
the root should know what it does. But this will change the historical
behaviour.

> Why not add
> 
> please_randomly_corrupt_memory boot parameter? It may be useful for
> something...
> 								Pavel

Nice argument.

Oleg.

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