linux-kernel - Re: [PATCH] kernel/printk/printk.c: check_syslog

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Date:	Fri, 15 May 2015 12:22:06 +0300
From:	Vasily Averin <vvs@...n.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
	Josh Boyer <jwboyer@...hat.com>, Eric Paris <eparis@...hat.com>
Subject: Re: [PATCH] kernel/printk/printk.c: check_syslog_permissions() cleanup



On 15.05.2015 10:41, Vasily Averin wrote:
> On 15.05.2015 01:01, Andrew Morton wrote:
>> On Sun, 10 May 2015 09:35:53 +0300 Vasily Averin <vvs@...n.com> wrote:
>>
>>> Fixes: 637241a900cb ("kmsg: honor dmesg_restrict sysctl on /dev/kmsg")
>>>
>>> Final version of patch 637241a900cb ("kmsg: honor dmesg_restrict sysctl
>>> on /dev/kmsg") lost few hooks. As result security_syslog() is not checked
>>> inside check_syslog_permissions() if dmesg_restrict is set,
>>> or it can be called twice in do_syslog().
>>
>> I'm not seeing how security_syslog() is called twice from do_syslog(). 
>> Put more details in the changelog, please.
> 
> For example, if dmesg_restrict is not set and SYSLOG_ACTION_OPEN is requested.

no, SYSLOG_ACTION_OPEN does not fit.

syslog_action_restricted() should return 0,
so it should be SYSLOG_ACTION_READ_ALL or SYSLOG_ACTION_SIZE_BUFFER commands
and from_file should be set to SYSLOG_FROM_READER.

> In this case do_syslog() calls check_syslog_permissions() 
> where security_syslog() is called first time and approves the operation,
> then do_syslog() itself calls security_syslog() 2nd time.
>
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