linux-kernel - Re: [RFC][PATCH 00/10] Mount, FS, Block and Keyrings notifications [ver #3]

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Date:   Thu, 6 Jun 2019 11:51:01 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Casey Schaufler <casey@...aufler-ca.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        David Howells <dhowells@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        USB list <linux-usb@...r.kernel.org>, raven@...maw.net,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        linux-block@...r.kernel.org, keyrings@...r.kernel.org,
        LSM List <linux-security-module@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Paul Moore <paul@...l-moore.com>
Subject: Re: [RFC][PATCH 00/10] Mount, FS, Block and Keyrings notifications [ver #3]



> On Jun 6, 2019, at 11:33 AM, Casey Schaufler <casey@...aufler-ca.com> wrote:
> 
>> On 6/6/2019 10:11 AM, Andy Lutomirski wrote:
>>> On Thu, Jun 6, 2019 at 9:43 AM Casey Schaufler <casey@...aufler-ca.com> wrote:
>>> ...
>>> I don't agree. That is, I don't believe it is sufficient.
>>> There is no guarantee that being able to set a watch on an
>>> object implies that every process that can trigger the event
>>> can send it to you.
>>> 
>>>        Watcher has Smack label W
>>>        Triggerer has Smack label T
>>>        Watched object has Smack label O
>>> 
>>>        Relevant Smack rules are
>>> 
>>>        W O rw
>>>        T O rw
>>> 
>>> The watcher will be able to set the watch,
>>> the triggerer will be able to trigger the event,
>>> but there is nothing that would allow the watcher
>>> to receive the event. This is not a case of watcher
>>> reading the watched object, as the event is delivered
>>> without any action by watcher.
>> I think this is an example of a bogus policy that should not be
>> supported by the kernel.
> 
> At this point it's pretty hard for me to care much what
> you think. You don't seem to have any insight into the
> implications of the features you're advocating, or their
> potential consequences.
> 
> 

Can you try to spell it out, then?  A mostly or fully worked out example might help.

As Stephen said, it looks like you are considering cases where there is already a full communication channel between two processes, and you’re concerned that this new mechanism might add a side channel too.  If this is wrong, can you explain how?