Re: [RFC PATCH v3 5/5] selinux: introduce kdbus access controls

[Stephen Smalley <sds@tycho.nsa.gov>]

On 10/09/2015 11:39 AM, Paul Moore wrote:
> On Friday, October 09, 2015 11:05:58 AM Stephen Smalley wrote:
>> On 10/07/2015 07:08 PM, Paul Moore wrote:
>>> +static int selinux_kdbus_init_inode(struct inode *inode,
>>> +				    const struct cred *creds)
>>> +{
>>> +	struct inode_security_struct *isec = inode->i_security;
>>> +	u32 sid = cred_sid(creds);
>>> +
>>> +	/* XXX - this is very simple, e.g. no transitions, no special object
>>> +	 *       class, etc. since this inode is basically an IPC socket ...
>>> +	 *       however, is this too simple?  do we want transitions?  if we
>>> +	 *       do, we should do the transition in kdbus_node_init() and not
>>> +	 *       here so that endpoint is labeled correctly and not just this
>>> +	 *       inode */
>>> +
>>> +	isec->inode = inode;
>>> +	isec->task_sid = sid;
>>> +	isec->sid = sid;
>>> +	isec->sclass = SECCLASS_FILE;
>>> +	isec->initialized = 1;
>>
>> These are used for files exposed in the filesystem namespace, unlike
>> sockets (sockfs can't be mounted by userspace, and the socket objects
>> themselves have their own class, so there is no ambiguity).  Currently
>> the only such files that are labeled with the same SID as the associated
>> task are /proc files.  So if we label the kdbusfs files with the same
>> SID, then you can't allow read/write to kdbusfs nodes owned by another
>> task without also exposing its /proc/pid files in the same manner.
>> Doubt we want that.  Probably should compute a transition from the task
>> SID and the kdbusfs SID.
>
> Okay, that was one of my main concerns; your suggestion makes sense to me.
>
> I'm also thinking that is we do a file transition using the task label and the
> kdbusfs superblock label we should limit it to just the inode label and not
> the kdbus endpoint as I suggested in the comment above (the bit about
> kdbus_node_init()), yes?

Yes, it only needs to be done for the inode, not the endpoint.
Analogy with sockets:  Can I write to the socket file (kdbus file) bound 
to the socket (endpoint)?  Can I connectto/sendto the socket (endpoint)?