linux-kernel - Re: selinux_msg_queue

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Date:	Thu, 7 Feb 2013 13:16:05 +0400
From:	Stanislav Kinsbursky <skinsbursky@...allels.com>
To:	Tommi Rantala <tt.rantala@...il.com>
CC:	Stephen Smalley <sds@...ho.nsa.gov>,
	James Morris <james.l.morris@...cle.com>,
	Eric Paris <eparis@...isplace.org>,
	<linux-security-module@...r.kernel.org>,
	Dave Jones <davej@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: selinux_msg_queue_msgrcv() oops

06.02.2013 23:51, Tommi Rantala пишет:
> 2013/2/6 Stephen Smalley <sds@...ho.nsa.gov>:
>> On 02/06/2013 10:21 AM, Tommi Rantala wrote:
>>>
>>> 2013/2/6 Stephen Smalley <sds@...ho.nsa.gov>:
>>>>
>>>> On 02/06/2013 07:56 AM, Tommi Rantala wrote:
>>>>>
>>>>>
>>>>> Hello,
>>>>>
>>>>> I'm hitting an oops in selinux_msg_queue_msgrcv() when fuzzing with
>>>>> Trinity as the root user (in a qemu VM):
>>>>
>>>>
>>>>
>>>> NULL msg->security at that point is a bug in the ipc subsystem; SELinux
>>>> is
>>>> just the messenger.  Normally msg->security is set for every allocated
>>>> msg
>>>> by load_msg() -> security_msg_msg_alloc() ->
>>>> selinux_msg_msg_alloc_security(), and freed/cleared upon free_msg() ->
>>>> security_msg_msg_free() -> selinux_msg_msg_free_security().  Looking
>>>> around,
>>>> I see copy_msg() introduced for checkpoint-restore initializes
>>>> dst->security
>>>> to NULL but never sets it properly?
>>>
>>>
>>> I am indeed building with CONFIG_CHECKPOINT_RESTORE=y, so your
>>> analysis seems to be correct.
>>
>>
>> (cc originator of the bug)
>>
>> If I am reading this correctly, then when the copy msg was created, a msg
>> security struct was already allocated
>> (prepare_copy->load_msg->security_msg_msg_alloc).  So having copy_msg()
>> clear dst->security is also a memory leak in addition to leading to this
>> oops.  Attached is a possible, un-tested fix.
>
> I can still reproduce the exact same oops with the patch applied. I
> also wanted to be sure that copy_msg() is called, so I added a warning
> there, but that never gets triggered. So I suppose the problem is not
> actually related to CONFIG_CHECKPOINT_RESTORE.
>

Hello.
Unfortunately, you are not the first one, who experience problems with Trinity running in KVM.

copy_msg() won't be called unless you'll specify the MSG_COPY flag in msgrcv() flags parameter.

Could you make a small investigation around the problem?
For example, does this problem appear, is you disable CONFIG_CHECKPOINT_RESTORE config option?


-- 
Best regards,
Stanislav Kinsbursky
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