linux-kernel - Re: [PATCH] kmsg: Honor dmesg

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Message-ID: <20130227181311.GI2071@hansolo.jdub.homelinux.org>
Date:	Wed, 27 Feb 2013 13:13:11 -0500
From:	Josh Boyer <jwboyer@...hat.com>
To:	Kees Cook <kees@...flux.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	eparis@...hat.com, Christian Kujau <lists@...dbynature.de>,
	stable@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kmsg: Honor dmesg_restrict sysctl on /dev/kmsg

On Wed, Feb 27, 2013 at 10:05:47AM -0800, Kees Cook wrote:
> Hi,
> 
> On Fri, Feb 22, 2013 at 01:18:57PM -0500, Josh Boyer wrote:
> > Originally, the addition of dmesg_restrict covered both the syslog
> > method of accessing dmesg, as well as /dev/kmsg itself.  This was done
> > indirectly by security_syslog calling cap_syslog before doing any LSM
> > checks.
> 
> Actually, are the security_syslog() checks in /dev/kmsg correct? There is
> only one used in devkmsg_open which uses SYSLOG_ACTION_READ_ALL. Shouldn't
> it be using SYSLOG_ACTION_OPEN? And have SYSLOG_ACTION_READ_ALL added to
> devkmsg_read? (And should we add one for write?)

You ask wonderful questions!  I have no idea.  Either way, it needs to
still somehow check for capable(CAP_SYSLOG) which security_syslog
doesn't do.  So either what I have already, or your suggestion of using
the existing function with SYSLOG_ACTION_OPEN in devkmsg_open.

josh
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