1.. SPDX-License-Identifier: GPL-2.0
2
3====
4SCTP
5====
6
7SCTP LSM Support
8================
9
10Security Hooks
11--------------
12
13For security module support, three SCTP specific hooks have been implemented::
14
15    security_sctp_assoc_request()
16    security_sctp_bind_connect()
17    security_sctp_sk_clone()
18
19Also the following security hook has been utilised::
20
21    security_inet_conn_established()
22
23The usage of these hooks are described below with the SELinux implementation
24described in the `SCTP SELinux Support`_ chapter.
25
26
27security_sctp_assoc_request()
28~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
29Passes the ``@ep`` and ``@chunk->skb`` of the association INIT packet to the
30security module. Returns 0 on success, error on failure.
31::
32
33    @ep - pointer to sctp endpoint structure.
34    @skb - pointer to skbuff of association packet.
35
36
37security_sctp_bind_connect()
38~~~~~~~~~~~~~~~~~~~~~~~~~~~~
39Passes one or more ipv4/ipv6 addresses to the security module for validation
40based on the ``@optname`` that will result in either a bind or connect
41service as shown in the permission check tables below.
42Returns 0 on success, error on failure.
43::
44
45    @sk      - Pointer to sock structure.
46    @optname - Name of the option to validate.
47    @address - One or more ipv4 / ipv6 addresses.
48    @addrlen - The total length of address(s). This is calculated on each
49               ipv4 or ipv6 address using sizeof(struct sockaddr_in) or
50               sizeof(struct sockaddr_in6).
51
52  ------------------------------------------------------------------
53  |                     BIND Type Checks                           |
54  |       @optname             |         @address contains         |
55  |----------------------------|-----------------------------------|
56  | SCTP_SOCKOPT_BINDX_ADD     | One or more ipv4 / ipv6 addresses |
57  | SCTP_PRIMARY_ADDR          | Single ipv4 or ipv6 address       |
58  | SCTP_SET_PEER_PRIMARY_ADDR | Single ipv4 or ipv6 address       |
59  ------------------------------------------------------------------
60
61  ------------------------------------------------------------------
62  |                   CONNECT Type Checks                          |
63  |       @optname             |         @address contains         |
64  |----------------------------|-----------------------------------|
65  | SCTP_SOCKOPT_CONNECTX      | One or more ipv4 / ipv6 addresses |
66  | SCTP_PARAM_ADD_IP          | One or more ipv4 / ipv6 addresses |
67  | SCTP_SENDMSG_CONNECT       | Single ipv4 or ipv6 address       |
68  | SCTP_PARAM_SET_PRIMARY     | Single ipv4 or ipv6 address       |
69  ------------------------------------------------------------------
70
71A summary of the ``@optname`` entries is as follows::
72
73    SCTP_SOCKOPT_BINDX_ADD - Allows additional bind addresses to be
74                             associated after (optionally) calling
75                             bind(3).
76                             sctp_bindx(3) adds a set of bind
77                             addresses on a socket.
78
79    SCTP_SOCKOPT_CONNECTX - Allows the allocation of multiple
80                            addresses for reaching a peer
81                            (multi-homed).
82                            sctp_connectx(3) initiates a connection
83                            on an SCTP socket using multiple
84                            destination addresses.
85
86    SCTP_SENDMSG_CONNECT  - Initiate a connection that is generated by a
87                            sendmsg(2) or sctp_sendmsg(3) on a new asociation.
88
89    SCTP_PRIMARY_ADDR     - Set local primary address.
90
91    SCTP_SET_PEER_PRIMARY_ADDR - Request peer sets address as
92                                 association primary.
93
94    SCTP_PARAM_ADD_IP          - These are used when Dynamic Address
95    SCTP_PARAM_SET_PRIMARY     - Reconfiguration is enabled as explained below.
96
97
98To support Dynamic Address Reconfiguration the following parameters must be
99enabled on both endpoints (or use the appropriate **setsockopt**\(2))::
100
101    /proc/sys/net/sctp/addip_enable
102    /proc/sys/net/sctp/addip_noauth_enable
103
104then the following *_PARAM_*'s are sent to the peer in an
105ASCONF chunk when the corresponding ``@optname``'s are present::
106
107          @optname                      ASCONF Parameter
108         ----------                    ------------------
109    SCTP_SOCKOPT_BINDX_ADD     ->   SCTP_PARAM_ADD_IP
110    SCTP_SET_PEER_PRIMARY_ADDR ->   SCTP_PARAM_SET_PRIMARY
111
112
113security_sctp_sk_clone()
114~~~~~~~~~~~~~~~~~~~~~~~~
115Called whenever a new socket is created by **accept**\(2)
116(i.e. a TCP style socket) or when a socket is 'peeled off' e.g userspace
117calls **sctp_peeloff**\(3).
118::
119
120    @ep - pointer to current sctp endpoint structure.
121    @sk - pointer to current sock structure.
122    @sk - pointer to new sock structure.
123
124
125security_inet_conn_established()
126~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
127Called when a COOKIE ACK is received::
128
129    @sk  - pointer to sock structure.
130    @skb - pointer to skbuff of the COOKIE ACK packet.
131
132
133Security Hooks used for Association Establishment
134-------------------------------------------------
135
136The following diagram shows the use of ``security_sctp_bind_connect()``,
137``security_sctp_assoc_request()``, ``security_inet_conn_established()`` when
138establishing an association.
139::
140
141      SCTP endpoint "A"                                SCTP endpoint "Z"
142      =================                                =================
143    sctp_sf_do_prm_asoc()
144 Association setup can be initiated
145 by a connect(2), sctp_connectx(3),
146 sendmsg(2) or sctp_sendmsg(3).
147 These will result in a call to
148 security_sctp_bind_connect() to
149 initiate an association to
150 SCTP peer endpoint "Z".
151         INIT --------------------------------------------->
152                                                   sctp_sf_do_5_1B_init()
153                                                 Respond to an INIT chunk.
154                                             SCTP peer endpoint "A" is
155                                             asking for an association. Call
156                                             security_sctp_assoc_request()
157                                             to set the peer label if first
158                                             association.
159                                             If not first association, check
160                                             whether allowed, IF so send:
161          <----------------------------------------------- INIT ACK
162          |                                  ELSE audit event and silently
163          |                                       discard the packet.
164          |
165    COOKIE ECHO ------------------------------------------>
166                                                          |
167                                                          |
168                                                          |
169          <------------------------------------------- COOKIE ACK
170          |                                               |
171    sctp_sf_do_5_1E_ca                                    |
172 Call security_inet_conn_established()                    |
173 to set the peer label.                                   |
174          |                                               |
175          |                               If SCTP_SOCKET_TCP or peeled off
176          |                               socket security_sctp_sk_clone() is
177          |                               called to clone the new socket.
178          |                                               |
179      ESTABLISHED                                    ESTABLISHED
180          |                                               |
181    ------------------------------------------------------------------
182    |                     Association Established                    |
183    ------------------------------------------------------------------
184
185
186SCTP SELinux Support
187====================
188
189Security Hooks
190--------------
191
192The `SCTP LSM Support`_ chapter above describes the following SCTP security
193hooks with the SELinux specifics expanded below::
194
195    security_sctp_assoc_request()
196    security_sctp_bind_connect()
197    security_sctp_sk_clone()
198    security_inet_conn_established()
199
200
201security_sctp_assoc_request()
202~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
203Passes the ``@ep`` and ``@chunk->skb`` of the association INIT packet to the
204security module. Returns 0 on success, error on failure.
205::
206
207    @ep - pointer to sctp endpoint structure.
208    @skb - pointer to skbuff of association packet.
209
210The security module performs the following operations:
211     IF this is the first association on ``@ep->base.sk``, then set the peer
212     sid to that in ``@skb``. This will ensure there is only one peer sid
213     assigned to ``@ep->base.sk`` that may support multiple associations.
214
215     ELSE validate the ``@ep->base.sk peer_sid`` against the ``@skb peer sid``
216     to determine whether the association should be allowed or denied.
217
218     Set the sctp ``@ep sid`` to socket's sid (from ``ep->base.sk``) with
219     MLS portion taken from ``@skb peer sid``. This will be used by SCTP
220     TCP style sockets and peeled off connections as they cause a new socket
221     to be generated.
222
223     If IP security options are configured (CIPSO/CALIPSO), then the ip
224     options are set on the socket.
225
226
227security_sctp_bind_connect()
228~~~~~~~~~~~~~~~~~~~~~~~~~~~~
229Checks permissions required for ipv4/ipv6 addresses based on the ``@optname``
230as follows::
231
232  ------------------------------------------------------------------
233  |                   BIND Permission Checks                       |
234  |       @optname             |         @address contains         |
235  |----------------------------|-----------------------------------|
236  | SCTP_SOCKOPT_BINDX_ADD     | One or more ipv4 / ipv6 addresses |
237  | SCTP_PRIMARY_ADDR          | Single ipv4 or ipv6 address       |
238  | SCTP_SET_PEER_PRIMARY_ADDR | Single ipv4 or ipv6 address       |
239  ------------------------------------------------------------------
240
241  ------------------------------------------------------------------
242  |                 CONNECT Permission Checks                      |
243  |       @optname             |         @address contains         |
244  |----------------------------|-----------------------------------|
245  | SCTP_SOCKOPT_CONNECTX      | One or more ipv4 / ipv6 addresses |
246  | SCTP_PARAM_ADD_IP          | One or more ipv4 / ipv6 addresses |
247  | SCTP_SENDMSG_CONNECT       | Single ipv4 or ipv6 address       |
248  | SCTP_PARAM_SET_PRIMARY     | Single ipv4 or ipv6 address       |
249  ------------------------------------------------------------------
250
251
252`SCTP LSM Support`_ gives a summary of the ``@optname``
253entries and also describes ASCONF chunk processing when Dynamic Address
254Reconfiguration is enabled.
255
256
257security_sctp_sk_clone()
258~~~~~~~~~~~~~~~~~~~~~~~~
259Called whenever a new socket is created by **accept**\(2) (i.e. a TCP style
260socket) or when a socket is 'peeled off' e.g userspace calls
261**sctp_peeloff**\(3). ``security_sctp_sk_clone()`` will set the new
262sockets sid and peer sid to that contained in the ``@ep sid`` and
263``@ep peer sid`` respectively.
264::
265
266    @ep - pointer to current sctp endpoint structure.
267    @sk - pointer to current sock structure.
268    @sk - pointer to new sock structure.
269
270
271security_inet_conn_established()
272~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
273Called when a COOKIE ACK is received where it sets the connection's peer sid
274to that in ``@skb``::
275
276    @sk  - pointer to sock structure.
277    @skb - pointer to skbuff of the COOKIE ACK packet.
278
279
280Policy Statements
281-----------------
282The following class and permissions to support SCTP are available within the
283kernel::
284
285    class sctp_socket inherits socket { node_bind }
286
287whenever the following policy capability is enabled::
288
289    policycap extended_socket_class;
290
291SELinux SCTP support adds the ``name_connect`` permission for connecting
292to a specific port type and the ``association`` permission that is explained
293in the section below.
294
295If userspace tools have been updated, SCTP will support the ``portcon``
296statement as shown in the following example::
297
298    portcon sctp 1024-1036 system_u:object_r:sctp_ports_t:s0
299
300
301SCTP Peer Labeling
302------------------
303An SCTP socket will only have one peer label assigned to it. This will be
304assigned during the establishment of the first association. Any further
305associations on this socket will have their packet peer label compared to
306the sockets peer label, and only if they are different will the
307``association`` permission be validated. This is validated by checking the
308socket peer sid against the received packets peer sid to determine whether
309the association should be allowed or denied.
310
311NOTES:
312   1) If peer labeling is not enabled, then the peer context will always be
313      ``SECINITSID_UNLABELED`` (``unlabeled_t`` in Reference Policy).
314
315   2) As SCTP can support more than one transport address per endpoint
316      (multi-homing) on a single socket, it is possible to configure policy
317      and NetLabel to provide different peer labels for each of these. As the
318      socket peer label is determined by the first associations transport
319      address, it is recommended that all peer labels are consistent.
320
321   3) **getpeercon**\(3) may be used by userspace to retrieve the sockets peer
322      context.
323
324   4) While not SCTP specific, be aware when using NetLabel that if a label
325      is assigned to a specific interface, and that interface 'goes down',
326      then the NetLabel service will remove the entry. Therefore ensure that
327      the network startup scripts call **netlabelctl**\(8) to set the required
328      label (see **netlabel-config**\(8) helper script for details).
329
330   5) The NetLabel SCTP peer labeling rules apply as discussed in the following
331      set of posts tagged "netlabel" at: https://www.paul-moore.com/blog/t.
332
333   6) CIPSO is only supported for IPv4 addressing: ``socket(AF_INET, ...)``
334      CALIPSO is only supported for IPv6 addressing: ``socket(AF_INET6, ...)``
335
336      Note the following when testing CIPSO/CALIPSO:
337         a) CIPSO will send an ICMP packet if an SCTP packet cannot be
338            delivered because of an invalid label.
339         b) CALIPSO does not send an ICMP packet, just silently discards it.
340
341   7) IPSEC is not supported as RFC 3554 - sctp/ipsec support has not been
342      implemented in userspace (**racoon**\(8) or **ipsec_pluto**\(8)),
343      although the kernel supports SCTP/IPSEC.
344