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

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Date:	Wed, 9 Feb 2011 13:34:18 -0800 (PST)
From:	david@...g.hm
To:	Gergely Nagy <algernon@...abit.hu>
cc:	"Serge E. Hallyn" <serge@...lyn.com>,
	James Morris <jmorris@...ei.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: CAP_SYSLOG, 2.6.38 and user space

On Wed, 9 Feb 2011, Gergely Nagy wrote:

> On Wed, 2011-02-09 at 21:23 +0000, Serge E. Hallyn wrote:
>> So if that's how we're leaning, then the following patch is much more
>> concise.  I'll send this to Linus and any appropriate -stable tomorrow
>>  if noone objects.
>>
>> From 5166e114d6a7c508addbadd763322089eb0b02f5 Mon Sep 17 00:00:00 2001
>> From: Serge Hallyn <serge@...lyn.com>
>> Date: Thu, 3 Feb 2011 09:26:15 -0600
>> Subject: [PATCH 1/1] cap_syslog: don't refuse cap_sys_admin for now (v2)
>>
>> It'd be nice to do that later, but it's not strictly necessary,
>> and it'll be hard to do without breaking somebody's userspace.
>>
>> Signed-off-by: Serge Hallyn <serge@...lyn.com>
>> ---
>>  kernel/printk.c |   14 ++++----------
>>  1 files changed, 4 insertions(+), 10 deletions(-)
>
> Personally, I'd prefer the sysctl idea in the long run, because
> userspace can easily and automatically adapt to the running kernel then.
> Ie, this patch is fine for 2.6.38, but later on, a sysctl could be
> introduced, that when set (but defaulting to unset, as to not break
> userspace), would make CAP_SYS_ADMIN return -EPERM. That way, syslogds
> could look at the setting, and act accordingly. This would mean that old
> userspace wouldn't break, and upgraded userspace could work on both old
> and new kernels, depending on the setting. Distros or admins could then
> enable the sysctl once they made sure that all neccessary applications
> have been upgraded.

what is your justification for ever having CAP_SYS_ADMIN return -EPERM? 
what's the value in blocking this.

David Lang

> But this works too, for now. My immediate concern is making sure 2.6.38
> doesn't break capability-using syslogds.
>
>
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