[Gluster-users] Restrict root clients / experimental patch

[Pierre C]

On Fri, Sep 22, 2017 at 10:37 AM, Soumya Koduri <skoduri at redhat.com> wrote:

> Hi,
>
> On 09/21/2017 07:32 PM, Pierre C wrote:
>
>> Hi All,
>>
>> I would like to use glusterfs in an environment where storage servers are
>> managed by an IT service - myself :) - and several users in the
>> organization can mount the distributed fs. The users are root on their
>> machines.
>> As far as I know about glusterfs, a root client user may impersonate any
>> uid/gid since it provides its uid/gid itself when it talks to the bricks
>> (like nfsv3).
>> The thing is, we want to enforce permissions, i.e. user X may only access
>> files shared with him even if he's root on his machine.
>> I found a draft spec about glusterfs+kerberos <
>> https://github.com/gluster/glusterfs-specs/blob/master/unde
>> r_review/Kerberos.md> but not much more so I think it's not possible
>> with glusterfs right now, correct?
>> (Also I feel that kerberos would be a bit heavy to manage)
>>
>
> I am not much familiar with how ssl is handled. But from what I understand
> from your statement above, you need to restrict root users. Isn't
> root-squash option enough for it?
>
> Option: server.root-squash
> Default Value: off
> Description: Map requests from uid/gid 0 to the anonymous uid/gid. Note
> that this does not apply to any other uids or gids that might be equally
> sensitive, such as user bin or group staff.
>
> Option: server.anonuid
> Default Value: 65534
> Description: value of the uid used for the anonymous user/nfsnobody when
> root-squash is enabled.
>
> Option: server.anongid
> Default Value: 65534
> Description: value of the gid used for the anonymous user/nfsnobody when
> root-squash is enabled.
>
>
Hi Soumya,

This is not sufficient because the glusterfs protocol lets the client
choose its uid/gid/groups when the client connects to a server. (done there
https://github.com/gluster/glusterfs/blob/master/rpc/rpc-lib/src/auth-glusterfs.c#L177
)
So the current implementation relies on the client being trustworthy. A
slightly modified client can pretend to be any user.

Do you see what I mean?

Cheers,
Pierre
eshard



>
> Thanks,
> Soumya
>
>
>> ---
>>
>> An simple hack that I found is to add custom uid/gid fields in clients'
>> ssl certificates. The bricks use the client's uid/gid specified in its
>> certificate rather than using one specified by the user. This solution has
>> no effect on performance and there's no need for a central authentication.
>> The thing that changes is the way client certificates are generated and
>> glusterfsd needs a small patch.
>>
>> I did an experimental implementation <https://github.com/eshard/glu
>> sterfs/commit/768bf63154fdc59ba67d5788743adab8679ec5ab> of this idea.
>> Custom fields "1.2.3.4.5.6.7" and "1.2.3.4.5.6.8" are used for uid and gid.
>> I tried it with custom CA trusted by all bricks and I issued a few client
>> certificates.
>> No server configuration is needed when a new client is added, when a
>> client is revoked the a CRL <https://en.wikipedia.org/wiki
>> /Certificate_revocation_list> must updated and pushed to all servers.
>> By the way I didn't get glusterfs servers to accept my CRLs, do some
>> people use it?
>>
>> Notes:
>>   * groups are not handled right now and since users may change groups
>> regularly I don't think it would be a great idea to freeze them in a
>> certificate. The bricks could possibly do an ldap lookup in order to
>> retrieve and cache the groups for an uid.
>>   * Clients obviously can't modify their certificates because they are
>> signed by CA
>>
>> What do you think of this implementation, is it safe?
>> Do all client operationsuse auth_glusterfs_v2_authenticate or did I miss
>> other codepaths?
>>
>> Thanks!
>>
>> Pierre Carru
>> eshard
>>
>> PS: By the way I found the source code very clean and well organized,
>> nice job :)
>>
>>
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>>
>>
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