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* [PATCH v3] Improve network_support.md
@ 2020-08-01  9:26 Topi Miettinen
  0 siblings, 0 replies; only message in thread
From: Topi Miettinen @ 2020-08-01  9:26 UTC (permalink / raw)
  To: selinux; +Cc: Topi Miettinen

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
v3: address comments from Paul Moore
---
 src/network_statements.md |   2 +-
 src/network_support.md    | 225 ++++++++++++++++++++++++++++++++++----
 2 files changed, 207 insertions(+), 20 deletions(-)

diff --git a/src/network_statements.md b/src/network_statements.md
index ef1c873..a2213d4 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#packet-controls-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..e3101ee 100644
--- a/src/network_support.md
+++ b/src/network_support.md
@@ -1,20 +1,51 @@
 # SELinux Networking Support
 
-SELinux supports the following types of network labeling:
+SELinux controls network access in kernel at two locations: at the
+socket interface, and when packets are processed by the protocol
+stacks. Controls at socket interface are invoked when a task makes
+network related system calls and thus the access permission checks
+mimic the sockets programming interface (e.g. ***bind**(2)*
+vs. `node_bind`). Packet controls are more distant from applications
+and they are invoked whenever any packets are received, forwarded or
+sent.
+
+Packet level controls include:
+* Packet labeling with SECMARK: class `packet`
+* Peer labeling with Labeled IPSec or NetLabel: class `peer`
+* Interface control: class `netif`
+* Network node control: class `node`
+
+Controls at socket interface include:
+* TCP/UDP/SCTP/DCCP ports: class `port`
+
+Packet controls can be organized further according to the source of
+the label for the packets, which can be internal or external:
 
 **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
+types supported: SECMARK and NetLabel. As an example, SECMARK access
+controls could restrict `firefox_t` to talking only to network
+services on TCP port 80 while NetLabel fallback/static rules could
+restrict `firefox_t` to only receive data from specific IP addresses
+on a specific network interface.  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)
+IPv6 Security Option). With labeled networking, it's possible to
+compare the security attributes (SELinux label) of the sending peer
+with the security context of the receiving peer. A simple example with
+Labeled IPSec is restricting `firefox_t` to talking only to `httpd_t`,
+while CIPSO/CALIPSO could restrict domains with MLS security level
+`s32` not to talk with domains with level `s31`.
 
-There are two policy capability options that can be set within policy
+Networking support is not enabled by default. It can be enabled either
+the policy capabilities or by loading SECMARK rules.
+
+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 +68,14 @@ 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:
+NetLabel is a framework for explicit network labeling that abstracts
+away the underlying labeling protocol from the LSMs. Labeled IPsec and
+the NetLabel framework are the current access controls for class
+`peer`, with NetLabel supporting CIPSO for IPv4, CALIPSO for IPv6, and
+a fallback/static labeling for unlabeled IPv4 and IPv6 networks.
+
+To support peer labeling with CIPSO and CALIPSO or fallback labeling,
+the NetLabel tools need to be installed:
 
 `dnf install netlabel_tools`
 
@@ -52,8 +89,12 @@ 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 +106,7 @@ to achieve this).
 
 <br>
 
-## SECMARK
+## Packet controls: SECMARK
 
 SECMARK makes use of the standard kernel NetFilter framework that
 underpins the GNU / Linux IP networking sub-system. NetFilter services
@@ -73,7 +114,7 @@ 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 +213,16 @@ 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 +230,7 @@ The following articles explain the SECMARK service:
 
 <br>
 
-## NetLabel - Fallback Peer Labeling
+## Packet controls: 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
@@ -217,13 +268,24 @@ 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
+## Packet controls: NetLabel – CIPSO/CALIPSO
 
-To allow MLS [**security levels**](mls_mcs.md#security-levels) to be passed
-over a network between MLS
-systems<a href="#fnn2" class="footnote-ref" id="fnnet2"><strong><sup>2</sup></strong></a>,
+To allow MLS or MCS [**security levels**](mls_mcs.md#security-levels)
+to be passed over a network between MLS or MCS systems<a href="#fnn2"
+class="footnote-ref" id="fnnet2"><strong><sup>2</sup></strong></a>,
 the Commercial IP Security Option (CIPSO) protocol is used. This is defined in the
 [**CIPSO Internet Draft**](http://tools.ietf.org/html/draft-ietf-cipso-ipsecurity-01)
 document (this is an obsolete document, however the protocol is still in
@@ -234,9 +296,9 @@ The Common Architecture Label IPv6 Security Option (CALIPSO) protocol
 described in [**rfc 5570**](http://ietf.org/rfc/rfc5570.txt) is supported in
 kernels from 4.8.
 
-CIPSO/CALIPSO will only pass the MLS component of the security context
-over the network, however in loopback mode CIPSO allows the full
-security context to be passed as explained in the
+CIPSO/CALIPSO will only pass the MLS or MCS component of the security
+context over the network, however in loopback mode CIPSO allows the
+full security context to be passed as explained in the
 "**Full SELinux Labels Over Loopback with NetLabel and CIPSO**" available at
 <http://paulmoore.livejournal.com/7234.html>.
 
@@ -288,7 +350,7 @@ section, plus the standard Fedora 'targeted' policy for the tests.
 
 <br>
 
-## Labeled IPSec
+## Packet controls: Labeled IPSec
 
 Labeled IPSec has been built into the standard GNU / Linux IPSec
 services as described in the
@@ -451,6 +513,131 @@ The *selinux-testsuite tools/nfs.sh* tests labeled NFS using various labels.
 
 <br>
 
+## Packet controls: 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;
+		class netif { egress ingress };
+}
+
+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
+```
+
+The checks for `ingress` in class `netif` however use the peer label
+of the remote peer (not the receiving task on the local system) as
+subject:
+
+```
+type internet_peer_t;
+
+allow internet_peer_t external_if_t:netif ingress;
+```
+
+The peers must also be labeled with various methods provided by
+***netlabelctl**(8)*. A simple example with fallback/static labeling is:
+
+```
+netlabelctl unlbl add default address:2000::/3 label:system_u:object_r:internet_peer_t:s0
+```
+
+<br>
+
+## Packet controls: 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;
+		class node { sendto recvfrom };
+		class tcp_socket node_bind;
+}
+
+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::
+```
+
+The checks for `recvfrom` in class `node` however use the peer label
+as subject:
+
+```
+allow internet_peer_t internet_node_t:node { recvfrom sendto };
+```
+
+<br>
+
+## Socket controls: 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. In contrast to
+packet level controls, port controls are close to how networked
+applications use the socket system calls. Thus the controls typically
+involve checking if a task can perform an operation on a network
+socket, e.g. ***bind**(2)* would cause an access check for
+`node_bind`. These are usually easy to understand and don't require
+any special network configuration.
+
+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;
+		class tcp_socket { name_bind name_connect };
+}
+
+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>
-- 
2.27.0


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