Re: [PATCH RFC 4/4] NFSD: Prototype support for IMA on NFS (server)

[Chuck Lever <chuck.lever@oracle.com>]

> On Mar 1, 2019, at 10:04 AM, Bruce Fields <bfields@fieldses.org> wrote:
> 
> On Mon, Feb 18, 2019 at 02:41:24PM -0500, Chuck Lever wrote:
>> 
>> 
>>> On Feb 18, 2019, at 2:32 PM, bfields@fieldses.org wrote:
>>> 
>>> On Thu, Feb 14, 2019 at 03:43:26PM -0500, Chuck Lever wrote:
>>>> When NFSv4 Security Label support is enabled and kernel Integrity
>>>> and IMA support is enabled (via CONFIG), then build in code to
>>>> handle the "security.ima" xattr. The NFS server converts incoming
>>>> GETATTR and SETATTR calls to acesses and updates of the xattr.
>>>> 
>>>> The FATTR4 bit is made up; meaning we still have to go through a
>>>> standards process to allocate a bit that all NFS vendors agree on.
>>>> Thus there is no guarantee this prototype will interoperate with
>>>> others or with a future standards-based implementation.
>>> 
>>> Why the dependence on CONFIG_NFSD_V4_SECURITY_LABEL?
>> 
>> Hrm, well there is some mechanism on the client side that IMA
>> needs that is behind CONFIG_NFS_V4_SECURITY_LABEL. I guess I
>> didn't think about not doing the same thing on the server. It
>> may just be an artifact of an earlier version of this code.
>> 
>> 
>>> (Also, I wonder if we actually need CONFIG_NFSD_V4_SECURITY_LABEL or if
>>> we could just remove it, or replace it by CONFIG_SECURITY where
>>> necessary.)
>> 
>> On the server, there is already a (run-time) export option to
>> enable and disable security labels. Is there a reason a
>> distribution would want to disable client or server support
>> for security labels at build time?
> 
> Distributions tend to want kernels that can do anything, with run time
> controls that are adequate to handle any use cases.
> 
> So given that we need adequate run-time configuration, why might someone
> also want the ability to disable at build time?  Some reasons I can
> think of:
> 
> 	- they need a really small kernel.
> 	- the feature is too hard to support, or they think it
> 	  introduces security risks, so they don't want their users
> 	  turning it on at all.
> 
> I could see any of those being reasons for someone not to want NFSD_V4
> or SECURITY at all, but is there likely to be a big need to configure in
> both of those things but configure out NFSD_V4_SECURITY_LABEL?  That
> seems unnecessarily fine grained.

I'm not clear, then. Are you proposing to control support for IMA labels
with the "security_labels" export option?


--
Chuck Lever