linux-kernel - Re: CAP_SYSLOG, 2.6.38 and user space

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Message-ID: <20110206011831.GB15805@mail.hallyn.com>
Date:	Sun, 6 Feb 2011 01:18:31 +0000
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	david@...g.hm
Cc:	"Serge E. Hallyn" <serge@...lyn.com>,
	Gergely Nagy <algernon@...abit.hu>,
	James Morris <jmorris@...ei.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: CAP_SYSLOG, 2.6.38 and user space

Quoting david@...g.hm (david@...g.hm):
> On Fri, 4 Feb 2011, Serge E. Hallyn wrote:
> 
> >Quoting Gergely Nagy (algernon@...abit.hu):
> >>On Fri, 2011-02-04 at 16:05 +0000, Serge E. Hallyn wrote:
> >>>Quoting Serge E. Hallyn (serge@...lyn.com):
> >>>>>From 2d7408541dd3a6e19a4265b028233789be6a40f4 Mon Sep 17 00:00:00 2001
> >>>>From: Serge Hallyn <serge@....(none)>
> >>>>
> >>>>At 2.6.39 or 2.6.40, let's add a sysctl which defaults to 0.  When
> >>>>0, refuse if cap_sys_admin, if 1, then allow.  This will allow
> >>>>users to acknowledge (permanently, if they must, using /etc/sysctl.conf)
> >>>>that they've seen the syslog message about cap_sys_admin being
> >>>>deprecated for syslog.
> >>>>
> >>>>Signed-off-by: Serge Hallyn <serge@...lyn.com>
> >-			goto warn; /* switch to return -EPERM after 2.6.39 */
> >+		     !capable(CAP_SYSLOG)) {
> >+			/* remove after 2.6.39 */
> >+			if (capable(CAP_SYS_ADMIN))
> >+				WARN_ONCE(1, "Attempt to access syslog with CAP_SYS_ADMIN "
> >+				  "but no CAP_SYSLOG (deprecated).\n");
> >+			else
> >+				return -EPERM;
> >+		}
> >	}
> 
> why does this need to be removed after 2.6.39?
> 
> whenever you go to remove it you will break userspace, what's the
> benifit of breaking userspace?
> 
> I can understand that it's better to have a syslog daemon with
> CAP_SYSLOG instead of CAP_SYS_ADMIN, but does "it would be better to
> have userspace changed" really translate into "it's so important to
> have userspace changed that we need to break any userspace that
> hasn't changed"?
> 
> I really don't think so.

I think I agree with you.  If someone wants to grant one of the other
CAP_SYS_ADMIN powers without CAP_SYSLOG, then they can break that into
yet another, i.e. CAP_IPCSET.  Makes sense.

thanks,
-serge
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