linux-kernel - Re: [PATCH 2/2] exit_notify: kill the wrong capable(CAP

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Message-ID: <20090225220324.GA14667@redhat.com>
Date:	Wed, 25 Feb 2009 23:03:24 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	Roland McGrath <roland@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Chris Evans <scarybeasts@...il.com>,
	David Howells <dhowells@...hat.com>,
	Don Howard <dhoward@...hat.com>,
	Eugene Teo <eugene@...hat.com>,
	Michael Kerrisk <mtk.manpages@...glemail.com>,
	Tavis Ormandy <taviso@....lonestar.org>,
	Vitaly Mayatskikh <vmayatsk@...hat.com>, stable@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] exit_notify: kill the wrong capable(CAP_KILL) check

On 02/25, Serge E. Hallyn wrote:
>
> Quoting Roland McGrath (roland@...hat.com):
> > > I can't understand why exit_notify() checks capable(CAP_KILL), but this
> > > looks just wrong.
> >
> > I don't know either why it's there.  My guess is that it was not actually
> > thought out specifically, just a "unless capable" exception added when the
> > security-motivated exclusions (exec_id stuff) were added.
> >
> > I can't think of any reason not to drop this check.
>
> Because of the following test?
>
> #include <stdio.h>
> #include <sched.h>
> #include <signal.h>
> #include <stdlib.h>
>
> int childfn(void *data)
> {
> 	printf("hi there, i'm the child\n");
> 	sleep(10);
> 	exit(0);
> }
>
> int main()
> {
> 	int stacksize = 4*getpagesize();
> 	void *stack, *stacktop;
>
> 	stack = malloc(stacksize);
> 	stacktop = stack + stacksize;
>
> 	int p = clone(childfn, stacktop, CLONE_PARENT|SIGSTOP, NULL);
> 	exit(0);
> }

Can't understand... Why do you think CAP_KILL makes things better?

Actually, how can it make any difference in this case?

Oleg.

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