Re: [Part1 PATCH 00/22] Add namespace support for audit

[Gao feng]

On 06/20/2013 09:02 PM, Eric Paris wrote:
> On Thu, 2013-06-20 at 11:02 +0800, Gao feng wrote:
>> On 06/20/2013 04:51 AM, Eric Paris wrote:
>>> On Wed, 2013-06-19 at 16:49 -0400, Aristeu Rozanski wrote:
>>>> On Wed, Jun 19, 2013 at 09:53:32AM +0800, Gao feng wrote:
>>>>> This patchset is first part of namespace support for audit.
>>>>> in this patchset, the mainly resources of audit system have
>>>>> been isolated. the audit filter, rules havn't been isolated
>>>>> now. It will be implemented in Part2. We finished the isolation
>>>>> of user audit message in this patchset.
>>>>>
>>>>> I choose to assign audit to the user namespace.
>>>>> Right now,there are six kinds of namespaces, such as
>>>>> net, mount, ipc, pid, uts and user. the first five
>>>>> namespaces have special usage. the audit isn't suitable to
>>>>> belong to these five namespaces, And since the flag of system
>>>>> call clone is in short supply, we can't provide a new flag such
>>>>> as CLONE_NEWAUDIT to enable audit namespace separately. so the
>>>>> user namespace may be the best choice.
>>>>
>>>> I thought it was said on the last submission that to tie userns and
>>>> audit namespace would be a bad idea?
>>>
>>> I consider it a non-starter.  unpriv users are allowed to launch their
>>> own user namespace.  The whole point of audit is to have only a priv
>>> user be allowed to make changes.  If you tied audit namespace to user
>>> namespace you grant an unpriv user the ability to modify audit.
>>>
>>
>> I understand your views.
>>
>> But ven the unpriv user are allowed to make changes, they can do no harm.
>> they can only make changes on the audit namespace they created.they can
>> only communicate with the audit namespace they created.
> 
> Imagine I set up my machine to audit all user access to super secret
> information.  With your patch set all an malicious user has to do is
> create a new user namespace.  Now when he accesses the super secret
> information it will be logged inside the user namespace he created.  So
> he can just dump those logs in the trash.
> 

No, my v1 patchset only log the user audit message(which generated through
auditctl -m "xxx") inside user namespace.

I agree with that we should not simply log audit message in the child
audit namespace. for some global resource related audit messages, they
should be logged in init audit namespace too.

> I believe that each audit namespace should require priv
> (CAP_AUDIT_CONTROL) in the user namespace that created the current audit
> namespace.  So lets say the machine boots and we are in the init_user
> and init_audit namespace.  Creating a new audit namespace should require
> CAP_AUDIT_CONTROL in the init_user namespace.  If instead we spawned a
> new user namespace userns1 and try to create a new audit namespace, we
> should STILL check for CAP_AUDIT_CONTROL in the init_user namespace.
> 

Ok, I can add this permission check in next version, though this seems a
litter strictness when we make sure child audit namespace won't fool the
init audit namespace,

> Assuming we've spawned auditns1 in userns1 and want to spawn auditns2 it
> should require CAP_AUDIT_CONTROL in userns1.  So now you only have
> permission to change your audit config (create a new audit namespace) if
> you already had permission to change your current audit config.
> 
> Now how to handle coding this...
> 
> When the kernel receives an audit message on the netlink socket it can
> always check the current->[whatever] to figure out which audit namespace
> it came from.  Then it can be processed accordingly...

Yes, this situation is easy to handle, since we are in process context...
but in some situations, we are not running in process context... as I
mentioned, audit messages generated by netfilter rules. current process
is untrustable. we can only get meaningful net namespace in this situation.
Actually, it's meaningful to send net related audit messages to the user
namespace which creates this net namespace.


> 
> Sending messages to the userspace auditd is a little more tricky.  We
> need to somehow map the audit namespace to a socket connected to auditd
> in userspace.  I'd imagine we'd have to either have per auditns backlog
> queues and run one kauditd per audit namespace, or we'd have to tag the
> skb's with the intended namespace somehow and then find the right socket
> in kauditd.  Either way it doesn't seem too onerous (although I admit, I
> don't know how to code the per namespace kauditd right offhand)
> 

As I said in "[PATCH 04/22] netlink: Add compare function for netlink_table",
netlink and socket are private resources of net namespace. socket has no
idea which audit namespace it belongs to,unless we add a field to mark this.
Through I think we can archive audit namespace in your way,but maybe we should
hack into the net namespace. I don't think the network guys will like it.

There is one more thing we have to do if we don't tie audit namespace to user
namespace. we have to implement the audit proc file(/proc/<pid>/ns/audit) and
the clone/unshare/setns parts.

I still this my way is the simplest and can satisfy your requirement.
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