Internet DRAFT - draft-cel-fedfs-security-addendum
draft-cel-fedfs-security-addendum
NFSv4 C. Lever
Internet-Draft Oracle
Intended status: Standards Track July 11, 2013
Expires: January 12, 2014
Federated Filesystem Security Addendum
draft-cel-fedfs-security-addendum-01
Abstract
This document addresses critical security-related items that are
missing from existing FedFS proposed standards.
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Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on January 12, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Problem Statement: GSSAPI service name for ADMIN . . . . . 4
1.2. Problem Statement: Compromised NSDBs . . . . . . . . . . . 4
1.3. Scope Of This Document . . . . . . . . . . . . . . . . . . 6
2. GSSAPI Service Name for the FedFS ADMIN protocol . . . . . . . 7
3. Fencing Compromised NSDBs . . . . . . . . . . . . . . . . . . 8
4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.1. Normative References . . . . . . . . . . . . . . . . . . . 12
7.2. Informative References . . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
Requirements for federated filesystems are described in [RFC5716].
Specification of the protocol used by administrators to configure
fileservers and construct namespaces is provided in [FEDFS-ADMIN].
Specification of the protocol allowing fileservers to store namespace
information is provided in [FEDFS-NSDB].
These documents are now immutable. However, some security-related
concerns have arisen that should be addressed immediately rather than
waiting for another version of these protocols to be ratified.
1.1. Problem Statement: GSSAPI service name for ADMIN
After IESG review, the Security Considerations chapter of
[FEDFS-ADMIN] now specifically requires that implementations of this
protocol support GSSAPI security mechanisms.
ADMIN protocol clients must use a service principal to establish a
GSS context shared with an ADMIN server. To construct the service
principal, clients need to know a priori the protocol's GSSAPI
service name. The form of that service name is described in chapter
4 of [RFC2724].
According to [RFC2743], requesting an addition to the "GSSAPI/
Kerberos/SASL Service Names" registry requires a specification.
Because [FEDFS-ADMIN] cannot be changed, a new specification must be
provided.
1.2. Problem Statement: Compromised NSDBs
The FedFS ADMIN RPC protocol provides a mechanism for provisioning
NSDBs on remote fileservers. The operations it provides are
FEDFS_SET_NSDB_PARAMS, FEDFS_GET_NSDB_PARAMS, and
FEDFS_GET_LIMITED_NSDB_PARAMS.
FEDFS_SET_NSDB_PARAMS specifies the name of an NSDB and the security
mode to use when connecting to this NSDB. The fileserver connects to
an NSDB in order to resolve a FedFS junction. The ADMIN protocol
specification further says:
On success, this operation returns FEDFS_OK. When the operation
returns, the new connection parameters SHOULD be used for all
subsequent LDAP connections to the given NSDB. Existing
connections MAY be terminated and re-established using the new
connection parameters. The connection parameters SHOULD be
durable across fileserver reboots.
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There are two security modes defined in the protocol specification:
FEDFS_SEC_NONE, which does not authenticate the LDAP server; and
FEDFS_SEC_TLS, which uses START_TLS (RFC 4513) to authenticate the
LDAP server.
When FEDFS_SEC_TLS is specified with the FEDFS_SET_NSDB_PARAMS
operation, an x.509v3 certificate chain is also provided to the
fileserver. The fileserver uses the provided certificate to
authenticate subsequent connections to this NSDB. The
FEDFS_SET_NSDB_PARAMS operation can change the connection security
used by a fileserver to connect to a particular NSDB from NONE to TLS
or TLS to NONE.
Over time, domain administrators add NSDB connection parameters to
each of their fileservers to enable FedFS junction resolution. The
specified NSDB may be the domain's own, or it might be an NSDB in a
foreign domain.
Many junctions on multiple fileservers can be created that use a
particular NSDB. There is no way to find such junctions without an
exhaustive search. Since filesystem namespace topology can evolve
arbitrarily over time, a recorded pathname of any junction is almost
guaranteed to become stale.
Now suppose we have two FedFS domains: example.net and
university.edu. Suppose university.edu fileservers have a number of
junctions that refer to locations maintained by example.net, and thus
university.net's fileservers are configured to resolve junctions on
example.net's NSDB.
One day Mallory compromises example.net's NSDB, but the domain
administrator there is on a long vacation. The administrator at
university.net discovers the compromise immediately, but has no
control over the foreign NSDB and cannot create a fresh x.509
certificate or verify that the contents of the NSDB are unmolested.
The only choice is to find and remove every junction in the
university.edu domain that contains the compromised NSDB.
If university.edu is using a good implementation of FedFS, the
administrative tools it provides might allow an administrator to
simply visit each of its fileservers and mark the example.net NSDB as
compromised. Any junction resolution that attempts to use that NSDB
would fail, but all junctions remain in place. When example.net's
administrator gets back from holiday and cleans up the mess, the
university.edu administrator can then update each of her fileservers
with fresh connection parameters for that NSDB.
However, none of this can be done remotely using the FedFS ADMIN
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protocol. It does not have a mechanism for removing NSDB connection
parameters or for fencing a compromised NSDB.
1.3. Scope Of This Document
This document specifies additional requirements for the FedFS ADMIN
protocol specified in [FEDFS-ADMIN], which is a standards track
specification.
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2. GSSAPI Service Name for the FedFS ADMIN protocol
Section 6 of [FEDFS-ADMIN] requires a FedFS ADMIN server to support
the RPCSEC_GSS framework [RFC2203]. The present document specifies
the GSSAPI service name, as described in Section 4.1 of [RFC2743], to
be used for the FedFS ADMIN protocol.
Regardless of what security mechanism under RPCSEC_GSS is in use, a
FedFS ADMIN server MUST identify itself in GSSAPI via a
GSS_C_NT_HOSTBASED_SERVICE name type. GSS_C_NT_HOSTBASED_SERVICE
names are of the form:
service@hostname
For the ADMIN protocol, the "service" element is
fedfs-admin
Implementations of security mechanisms will convert
fedfs-admin@hostname to various different forms. For Kerberos V5,
the following form is RECOMMENDED:
fedfs-admin/hostname
This service name SHOULD NOT be used to authenticate other GSSAPI
services.
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3. Fencing Compromised NSDBs
An NSDB is considered "foreign" relative to a particular FedFS domain
if that domain's administrator has no administrative access to that
NSDB.
When a FedFS domain administrator is faced with a foreign NSDB that
is compromised or otherwise unusable, and in the absense of an
implementation-provided mechanism for fencing an NSDB, the
administrator can fence that NSDB using the following technique.
1. The administrator locally generates a new certificate for the
compromised foreign NSDB. The certificate can be self-signed, or
signed by the administrator's local certificate authority.
2. The administrator distributes this certificate to all of her
domain's fileservers using the FedFS ADMIN protocol or some other
secure means. The connection security for the foreign NSDB is
set to FEDFS_SEC_TLS on each of the local domain's fileservers.
3. The administrator requests fresh certificate material from the
administrator of the foreign NSDB.
4. When the threat has passed and the foreign NSDB is safe to use
again, the administrator can distribute the new valid certificate
material to her domain's fileservers.
No change to the ADMIN protocol as specified in [FEDFS-ADMIN] is
required to fence a compromised NSDB. Step 2 guarantees that, on
fileservers in the administrator's local FedFS domain, resolving a
junction that references the compromised foreign NSDB will fail until
updated certificate material is provided.
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4. Security Considerations
There are no additional security considerations.
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5. IANA Considerations
In accordance with Section 4.1 of [RFC2743], the service name "fedfs-
admin" will be registered in the GSSAPI Service Name registry at
http://www.iana.org/assignments/gssapi-service-names/ gssapi-service-
names.xml
The new entry should reference the present document as the
specification.
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6. Acknowledgements
The author of this document gratefully acknowledges the contributions
of Nico Williams, Spencer Shepler, Tom Haynes, and David Noveck.
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7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2203] Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol
Specification", RFC 2203, September 1997.
[RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000.
7.2. Informative References
[FEDFS-ADMIN]
Lentini, J., Everhart, C., Ellard, D., Tewari, R., and M.
Naik, "Administration Protocol for Federated Filesystems",
draft-ietf-nfsv4-federated-fs-admin (Work In Progress),
2010.
[FEDFS-NSDB]
Lentini, J., Everhart, C., Ellard, D., Tewari, R., and M.
Naik, "NSDB Protocol for Federated Filesystems",
draft-ietf-nfsv4-federated-fs-protocol (Work In Progress),
2010.
[RFC2724] Handelman, S., Stibler, S., Brownlee, N., and G. Ruth,
"RTFM: New Attributes for Traffic Flow Measurement",
RFC 2724, October 1999.
[RFC5716] Lentini, J., Everhart, C., Ellard, D., Tewari, R., and M.
Naik, "Requirements for Federated File Systems", RFC 5716,
January 2010.
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Author's Address
Charles Lever
Oracle Corporation
1015 Granger Avenue
Ann Arbor, MI 48104
US
Phone: +1 734 274 2396
Email: chuck.lever@oracle.com
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