Re: [PATCH v2] Improve network_support.md

[Dominick Grift <dominick.grift@defensec.nl>]

Topi Miettinen <toiwoton@gmail.com> writes:

> On 27.7.2020 16.57, Dominick Grift wrote:
>> Topi Miettinen <toiwoton@gmail.com> writes:
>>
>>> List all access control methods available for networking and provide
>>> examples for each.
>>>
>>> Signed-off-by: Topi Miettinen <toiwoton@gmail.com>
>>>
>>> ---
>>> v2: address comments from Richard Haines
>>> ---
>>>   src/network_statements.md |   2 +-
>>>   src/network_support.md    | 170 +++++++++++++++++++++++++++++++++-----
>>>   2 files changed, 150 insertions(+), 22 deletions(-)
>>>
>>> diff --git a/src/network_statements.md b/src/network_statements.md
>>> index ef1c873..357c3b1 100644
>>> --- a/src/network_statements.md
>>> +++ b/src/network_statements.md
>>> @@ -102,7 +102,7 @@ the interface to a security context.
>>>   <tr>
>>>   <td><code>packet_context</code></td>
>>>   <td><p>The security context allocated packets. Note that these are defined but unused.</p>
>>> -<p>The iptables(8)/nftables(8) <a href="network_support.md#secmark">SECMARK services</a> should be used to label packets.</p></td>
>>> +<p>The iptables(8)/nftables(8) <a
>>> href="network_support.md#internal-labeling-secmark">SECMARK
>>> services</a> should be used to label packets.</p></td>
>>>   </tr>
>>>   </tbody>
>>>   </table>
>>> diff --git a/src/network_support.md b/src/network_support.md
>>> index 309e863..6f9896b 100644
>>> --- a/src/network_support.md
>>> +++ b/src/network_support.md
>>> @@ -1,20 +1,17 @@
>>>   # SELinux Networking Support
>>>   -SELinux supports the following types of network labeling:
>>> +SELinux supports several methods for access control of networks. These are
>>>   -**Internal labeling** - This is where network objects are
>>> labeled and
>>> -managed internally within a single machine (i.e. their labels are not
>>> -transmitted as part of the session with remote systems). There are two
>>> -types supported: SECMARK and NetLabel. There was a service known as
>>> -'compat_net' controls, however that was removed in kernel 2.6.30.
>>> +* Packet labeling: class `packet`
>>> +* Peer labeling: class `peer`
>>> +* Interface control: class `netif`
>>> +* Network node control: class `node`
>>> +* TCP/UDP/SCTP/DCCP ports: class `port`
>>>   -**Labeled Networking** - This is where labels are passed to/from
>>> remote
>>> -systems where they can be interpreted and a MAC policy enforced on each
>>> -system. There are three types supported: Labeled IPSec, CIPSO
>>> -(Commercial IP Security Option) and CALIPSO (Common Architecture Label
>>> -IPv6 Security Option)
>>> +Networking support is not enabled by default. It can be enabled either
>>> +the policy capabilities or by loading SECMARK rules.
>>>   -There are two policy capability options that can be set within
>>> policy
>>> +There are three policy capability options that can be set within policy
>>>   using the `policycap` statement that affect networking configuration:
>>>     **`network_peer_controls`** - This is always enabled in the
>>> latest
>>> @@ -37,8 +34,22 @@ The policy capability settings are available in userspace via the
>>>   SELinux filesystem as shown in the
>>>   [**SELinux Filesystem**](lsm_selinux.md#selinux-filesystem) section.
>>>   -To support peer labeling, CIPSO and CALIPSO the NetLabel tools
>>> need to
>>> -be installed:
>>> +SELinux supports the following types of network labeling:
>>> +
>>> +**Internal labeling** - This is where network objects are labeled and
>>> +managed internally within a single machine (i.e. their labels are not
>>> +transmitted as part of the session with remote systems). There are two
>>> +types supported: SECMARK and NetLabel. There was a service known as
>>> +'compat_net' controls, however that was removed in kernel 2.6.30.
>>> +
>>> +**Labeled Networking** - This is where labels are passed to/from remote
>>> +systems where they can be interpreted and a MAC policy enforced on each
>>> +system. There are three types supported: Labeled IPSec, CIPSO
>>> +(Commercial IP Security Option) and CALIPSO (Common Architecture Label
>>> +IPv6 Security Option).
>>> +
>>> +To support peer labeling with CIPSO and CALIPSO or fallback labeling,
>>> +the NetLabel tools need to be installed:
>>>     `dnf install netlabel_tools`
>>>   @@ -52,8 +63,12 @@ OpenSwan but is now distributed as LibreSwan:
>>>   `dnf install libreswan`
>>>     It is important to note that the kernel must be configured to
>>> support
>>> -these services. The Fedora kernels are configured to handle all the above
>>> -services.
>>> +these services (`CONFIG_NETLABEL`, `CONFIG_NETWORK_SECMARK`,
>>> +`CONFIG_NF_CONNTRACK_SECMARK`,
>>> +`CONFIG_NETFILTER_XT_TARGET_CONNSECMARK`,
>>> +`CONFIG_NETFILTER_XT_TARGET_SECMARK`, `CONFIG_IP_NF_SECURITY`,
>>> +`CONFIG_IP6_NF_SECURITY`). At least Fedora and Debian kernels are
>>> +configured to handle all the above services.
>>>     The Linux networking package *iproute* has an SELinux aware
>>> socket
>>>   statistics command ***ss**(8)* that will show the SELinux context of
>>> @@ -65,7 +80,7 @@ to achieve this).
>>>     <br>
>>>   -## SECMARK
>>> +## Internal labeling: SECMARK
>>>     SECMARK makes use of the standard kernel NetFilter framework
>>> that
>>>   underpins the GNU / Linux IP networking sub-system. NetFilter services
>>> @@ -73,7 +88,7 @@ automatically inspects all incoming and outgoing packets and can place
>>>   controls on interfaces, IP addresses (nodes) and ports with the added
>>>   advantage of connection tracking. The SECMARK security extensions allow
>>>   security contexts to be added to packets (SECMARK) or sessions
>>> -(CONNSECMARK).
>>> +(CONNSECMARK), belonging to object class of `packet`.
>>>     The NetFilter framework inspects and tag packets with labels as
>>> defined
>>>   within ***iptables**(8)* (also 'nftables' ***nft**(8)* from version 9.3 with
>>> @@ -172,6 +187,16 @@ table ip6 security {
>>>   }
>>>   ```
>>>   +Before the SECMARK rules can be loaded, TE rules must be added
>>> to
>>> +define the types, and also allow domains to send and/or receive
>>> +objects of `packet` class:
>>> +
>>> +```
>>> +type test_server_packet_t, packet_type;
>>> +
>>> +allow my_server_t test_server_packet_t:packet { send recv };
>>> +```
>>> +
>>>   The following articles explain the SECMARK service:
>>>   -   [*Transitioning to Secmark*](http://paulmoore.livejournal.com/4281.html)
>>>   -   [New secmark-based network controls for SELinux](http://james-morris.livejournal.com/11010.html)
>>> @@ -179,7 +204,7 @@ The following articles explain the SECMARK service:
>>>     <br>
>>>   -## NetLabel - Fallback Peer Labeling
>>> +## Internal labeling: NetLabel - Fallback Peer Labeling
>>>     Fallback labeling can optionally be implemented on a system if
>>> the
>>>   Labeled IPSec or CIPSO/CALIPSO is not being used (hence 'fallback
>>> @@ -217,9 +242,20 @@ netlabelctl -p map list
>>>   Note that the security contexts must be valid in the policy otherwise the
>>>   commands will fail.
>>>   +Before the NetLabel rules can be loaded, TE rules must be added
>>> to
>>> +define the types. Then the rules can allow domains to receive data
>>> +from objects of `peer` class:
>>> +
>>> +```
>>> +type netlabel_sctp_peer_t;
>>> +
>>> +allow my_server_t netlabel_sctp_peer_t:peer recv;
>>> +```
>>> +Note that sending can't be controlled with `peer` class.
>>> +
>>>   <br>
>>>   -## NetLabel – CIPSO/CALIPSO
>>> +## Labeled Networking: NetLabel – CIPSO/CALIPSO
>>>     To allow MLS [**security levels**](mls_mcs.md#security-levels)
>>> to be passed
>>>   over a network between MLS
>>> @@ -288,7 +324,7 @@ section, plus the standard Fedora 'targeted' policy for the tests.
>>>     <br>
>>>   -## Labeled IPSec
>>> +## Labeled Networking: Labeled IPSec
>>>     Labeled IPSec has been built into the standard GNU / Linux
>>> IPSec
>>>   services as described in the
>>> @@ -451,6 +487,98 @@ The *selinux-testsuite tools/nfs.sh* tests labeled NFS using various labels.
>>>     <br>
>>>   +## Access Control for Network Interfaces
>>> +
>>> +SELinux domains can be restricted to use only specific network
>>> +interfaces. TE rules must define the interface types and then allow a
>>> +domain to `egress` in class `netif` for the defined interface types:
>>> +
>>> +```
>>> +require {
>>> +        attribute netif_type;
>>> +}
>>> +
>>> +type external_if_t, netif_type;
>>> +type loopback_if_t, netif_type;
>>> +
>>> +allow my_server_t external_if_t:netif egress;
>>> +allow my_server_t loopback_if_t:netif egress;
>>> +```
>>> +
>>> +The interfaces must also be labeled with ***semanage**(8)* (or by
>>> +using `netifcon` statements in the policy):
>>> +```
>>> +semanage interface -a -t loopback_if_t -r s0 lo
>>> +semanage interface -a -t external_if_t -r s0 eth0
>>> +```
>>> +
>>> +Note that reception can't be controlled with `netif` class.
>>
>> Probably nothing but I did not understand this: Is reception not
>> controlled with the netif ingress permission?
>
> I'm no expert, but the only netif ingress rules which I have are
> rather generic:
>
> allow internet_peer_t external_if_t:netif ingress;
> allow link_local_peer_t external_if_t:netif ingress;
> allow localnet_peer_t external_if_t:netif ingress;
> allow multicast_peer_t external_if_t:netif ingress;
> allow loopback_peer_t loopback_if_t:netif ingress;
>
> `peer` types above have been added with NetLabel rules like:
>
> netlabelctl unlbl add default address:2000::/3
> label:system_u:object_r:internet_peer_t:s0
>
> Perhaps this would be better:
>
> Note that reception for application domains can't be controlled with
> `netif` class.
>

I look at it this way: peers *are* processes, You seem to
essentually use peers as nodes above.

It would become more clear if you would try this out with labeled ipsec.
A peer, in my experience is kind of the same as an association in the
labeled ipsec scenario (the classes actually overlap). That is also why
you should probably disable the netlabel_peer_controls polcap if you use
labeled ipsec.

>>
>>> +
>>> +<br>
>>> +
>>> +## Access Control for Network Nodes
>>> +
>>> +Domains can be restricted by SELinux to access and bind sockets to
>>> +only dedicated network nodes (in practice, IP addresses).
>>> +
>>> +The node types must be defined and then the node types can be used for
>>> +TE rules as target context. TE rules to allow a domain to `sendto` for
>>> +class `node` and to `node_bind` (for incoming connections) for class
>>> +`tcp_socket`:
>>> +
>>> +```
>>> +require {
>>> +        attribute node_type;
>>> +}
>>> +
>>> +type loopback_node_t, node_type;
>>> +type internet_node_t, node_type;
>>> +type link_local_node_t, node_type;
>>> +type multicast_node_t, node_type;
>>> +
>>> +allow my_server_t loopback_node_t:node sendto;
>>> +allow my_server_t loopback_node_t:tcp_socket node_bind;
>>> +allow my_server_t internet_node_t:node sendto;
>>> +```
>>> +
>>> +After the types have been defined, corresponding node rules can be
>>> +added with `semanage` (or `nodecon` statements):
>>> +```
>>> +semanage node -a -M /128 -p ipv6 -t loopback_node_t -r s0 ::1
>>> +semanage node -a -M /3 -p ipv6 -t internet_node_t -r s0 2000::
>>> +semanage node -a -M /8 -p ipv6 -t link_local_node_t -r s0 fe00::
>>> +semanage node -a -M /8 -p ipv6 -t multicast_node_t -r s0 ff00::
>>> +```
>>> +
>>> +<br>
>>> +
>>> +## Access Control for Network Ports
>>> +
>>> +SELinux policy can also control access to ports used by various
>>> +networking protocols such as TCP, UDP, SCTP and DCCP. TE rules must
>>> +define the port types and then allow a domain to `name_connect`
>>> +(outgoing) or `name_bind` (incoming) in class `tcp_socket` (or
>>> +`udp_socket` etc) for the defined port types:
>>> +
>>> +```
>>> +require {
>>> +        attribute port_type;
>>> +}
>>> +
>>> +type my_server_port_t, port_type;
>>> +
>>> +allow my_server_t my_server_port_t:tcp_socket name_connect;
>>> +allow my_server_t my_server_port_t:tcp_socket name_bind;
>>> +```
>>> +
>>> +The ports must also be labeled with `semanage` (or `portcon`
>>> +statements):
>>> +```
>>> +semanage port -a -t my_server_port_t -p tcp -r s0 12345
>>> +```
>>> +
>>> +<br>
>>> +
>>>   <section class="footnotes">
>>>   <ol>
>>>   <li id="fnn1"><p>For example, an ftp session where the server is
>>> listening on a specific port (the destination port) but the client
>>> will be assigned a random source port. The CONNSECMARK will ensure
>>> that all packets for the ftp session are marked with the same label.<a
>>> href="#fnnet1" class="footnote-back">↩</a></p></li>
>>
>

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Dominick Grift