[redhat-lspp] [RFC] [MLSXFRM 00/04] Granular IPSec associations for use in MLS environments

[Venkat Yekkirala]

The current approach to labeling Security Associations for SELinux purposes
uses a one-to-one mapping between xfrm policy rules and security associations.
This doesn’t address the needs of real world MLS (Multi-level System, traditional
Bell-LaPadula) environments where a single xfrm policy rule (pertaining to a range,
classified to secret for example) might need to map to multiple Security Associations
(one each for classified, secret, top secret and all the compartments applicable to
these security levels).

This patch set addresses the above problem by allowing for the mapping of a single
xfrm policy rule to multiple security associations, with each association used in
the security context it is defined for. It also includes the security context to be
used in IKE negotiation in the acquire messages sent to the IKE daemon so that a unique
SA can be negotiated for each unique security context. A couple of bug fixes are also
included; checks to make sure the SAs used by a packet match policy (security context-wise)
on the inbound and also that the bundle used for the outbound matches the security context
of the flow. This patch set also makes the use of the SELinux sid in flow cache lookups
seemless by including the sid in the flow key itself.

The exact differences between the "OLD" and "NEW" behavior this patch set entails are
described later in the below under "Description of changes".

Patch is relative to 2.6.17-rc6-mm2. A policy patch is also included for reference.
A patch to ipsec-tools/racoon will follow later on the ipsectools-devel list.
ipsec-tools 0.6.5 src in FC rawhide already has the setkey changes needed to work with this.

DETAILS:

The basic idea is to have the IPSec policy specify an MLS range and have unique SAs
generated/used for each of the levels that fall in the range. SAs for different levels
can either be manually loaded (using setkey and such) or negotiated using IKE (racoon, etc.).

Example:

Let's say we have the following in the SPD (Security Policy Database):

spdadd 9.2.9.15 9.2.9.17 any -ctx 1 1 "system_u:object_r:zzyzx_t:s0-s9:c0-c127"
-P in ipsec esp/transport//require ;
spdadd 9.2.9.17 9.2.9.15 any -ctx 1 1 "system_u:object_r:zzyzx_t:s0-s9:c0-c127"
-P out ipsec esp/transport//require ;

with nothing in the SAD (Security Association Database) initially. When the kernel
runs into the first packet with the label s2:c4 destined for 9.2.9.17, it will see
that there's no SA available to encrypt it with. So, it will call upon racoon/IKE
to generate an SA. Racoon will obtain the label (s2:c4) from the kernel, do the
negotiation with its peer, including the label (s2:c4) also in the payload/proposals.
The negotiation will result in a dynamically generated SPI that is unique to the label
(s2:c4) plus the other normal parameters involved. It will then insert the SA (along
with the SPI) such as the following into the SAD in the kernel:

add 9.2.9.15 9.2.9.17 esp 0x123456
-ctx 1 1 "system_u:object_r:zzyzx_t:s2:c4"
-E des-cbc 0x0000000000000000;

If the kernel subsequently runs into a packet at a different label (say s2:c5) for which
there's no SA available, it will again call upon racoon (which will get s2:c5 from the
kernel this time) and a different SA (with a different SPI) will be negotiated.

Description of changes:

A "sid" member has been added to the flow cache key resulting in the sid being available
at all needed locations and the flow cache lookups automatically using the sid. The flow
sid is derived from the socket on the outbound and the SAs (unlabeled where an SA was not
used) on the inbound.

Outbound case:
1. Find policy for the socket.

2. OLD: Find an SA that matches the policy.
 NEW: Find an SA that matches BOTH the policy and the flow/socket.
      This is necessary since not every SA that matches the policy
      can be used for the flow/socket. Consider policy range Secret-TS,
      and SAs each for Secret and TS. We don't want a TS socket to
      use the Secret SA. Hence the additional check for the SA Vs. flow/socket.

3. NEW: When looking thru bundles for a policy, make sure the flow/socket can use the
   bundle. If a bundle is not found, create one, calling for IKE if necessary. If using IKE,
   include the security context in the acquire message to the IKE daemon.

Inbound case:
1. OLD: Find policy for the socket.
   NEW: Find policy for the incoming packet based on the sid of the SA(s) it used or the
   unlabeled sid if no SAs were used. (Consider a case where a socket is "authorized" for
   two policies (unclassified-confidential, secret-top_secret). If the packet has come in
   using a secret SA, we really ought to be using the latter policy (secret-top_secret).)

2. OLD: BUG: No check to see if the SAs used by the packet agree with the policy sec_ctx-wise.
   (It was indicated in selinux_xfrm_sock_rcv_skb() that this was being accomplished by
    (x->id.spi == tmpl->id.spi || !tmpl->id.spi) in xfrm_state_ok, but it turns out tmpl->id.spi
    would normally be zero (unless xfrm policy rules specify one at the template level, which
    they usually don't).
   NEW: The socket is checked for access to the SAs used (based on the sid of the SAs) in
   selinux_xfrm_sock_rcv_skb().

Outstanding items/issues:
- xfrm_user needs to be altered also to include the security context in acquire messages. This
  patch set already includes changes for PF_KEY/acquire.
- Timewait acknowledgements and such are generated in the current/upstream implementation using
  a NULL socket resulting in the any_socket sid (SYSTEM_HIGH) to be used. This problem is not
  addressed by this patch set.

include/linux/security.h                     |  104 ++++++++-
include/net/flow.h                           |    5 
net/core/flow.c                              |    7 
net/core/sock.c                              |    4 
net/key/af_key.c                             |   24 ++
net/xfrm/xfrm_policy.c                       |   28 +-
net/xfrm/xfrm_state.c                        |   12 -
net/xfrm/xfrm_user.c                         |    2 
security/dummy.c                             |   23 ++
security/selinux/hooks.c                     |   27 +-
security/selinux/include/av_perm_to_string.h |    1 
security/selinux/include/av_permissions.h    |    1 
security/selinux/include/objsec.h            |    1 
security/selinux/include/security.h          |    2 
security/selinux/include/xfrm.h              |    9 
security/selinux/ss/mls.c                    |   20 -
security/selinux/ss/mls.h                    |   20 +
security/selinux/ss/services.c               |   48 ++++
security/selinux/xfrm.c                      |  185 ++++++++++++++---
19 files changed, 426 insertions(+), 97 deletions(-)