Documentation/security/SCTP.rst

   1 .. SPDX-License-Identifier: GPL-2.0
   2
   3 ====
   4 SCTP
   5 ====
   6
   7 SCTP LSM Support
   8 ================
   9
  10 Security Hooks
  11 --------------
  12
  13 For 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
  19 Also the following security hook has been utilised::
  20
  21     security_inet_conn_established()
  22
  23 The usage of these hooks are described below with the SELinux implementation
  24 described in the `SCTP SELinux Support`_ chapter.
  25
  26
  27 security_sctp_assoc_request()
  28 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  29 Passes the ``@ep`` and ``@chunk->skb`` of the association INIT packet to the
  30 security 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
  37 security_sctp_bind_connect()
  38 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  39 Passes one or more ipv4/ipv6 addresses to the security module for validation
  40 based on the ``@optname`` that will result in either a bind or connect
  41 service as shown in the permission check tables below.
  42 Returns 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
  71 A 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
  98 To support Dynamic Address Reconfiguration the following parameters must be
  99 enabled 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
 104 then the following *_PARAM_*'s are sent to the peer in an
 105 ASCONF 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
 113 security_sctp_sk_clone()
 114 ~~~~~~~~~~~~~~~~~~~~~~~~
 115 Called 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
 117 calls **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
 125 security_inet_conn_established()
 126 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 127 Called 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
 133 Security Hooks used for Association Establishment
 134 -------------------------------------------------
 135
 136 The following diagram shows the use of ``security_sctp_bind_connect()``,
 137 ``security_sctp_assoc_request()``, ``security_inet_conn_established()`` when
 138 establishing 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
 186 SCTP SELinux Support
 187 ====================
 188
 189 Security Hooks
 190 --------------
 191
 192 The `SCTP LSM Support`_ chapter above describes the following SCTP security
 193 hooks 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
 201 security_sctp_assoc_request()
 202 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 203 Passes the ``@ep`` and ``@chunk->skb`` of the association INIT packet to the
 204 security 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
 210 The 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
 227 security_sctp_bind_connect()
 228 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 229 Checks permissions required for ipv4/ipv6 addresses based on the ``@optname``
 230 as 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``
 253 entries and also describes ASCONF chunk processing when Dynamic Address
 254 Reconfiguration is enabled.
 255
 256
 257 security_sctp_sk_clone()
 258 ~~~~~~~~~~~~~~~~~~~~~~~~
 259 Called whenever a new socket is created by **accept**\(2) (i.e. a TCP style
 260 socket) or when a socket is 'peeled off' e.g userspace calls
 261 **sctp_peeloff**\(3). ``security_sctp_sk_clone()`` will set the new
 262 sockets 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
 271 security_inet_conn_established()
 272 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 273 Called when a COOKIE ACK is received where it sets the connection's peer sid
 274 to that in ``@skb``::
 275
 276     @sk  - pointer to sock structure.
 277     @skb - pointer to skbuff of the COOKIE ACK packet.
 278
 279
 280 Policy Statements
 281 -----------------
 282 The following class and permissions to support SCTP are available within the
 283 kernel::
 284
 285     class sctp_socket inherits socket { node_bind }
 286
 287 whenever the following policy capability is enabled::
 288
 289     policycap extended_socket_class;
 290
 291 SELinux SCTP support adds the ``name_connect`` permission for connecting
 292 to a specific port type and the ``association`` permission that is explained
 293 in the section below.
 294
 295 If userspace tools have been updated, SCTP will support the ``portcon``
 296 statement as shown in the following example::
 297
 298     portcon sctp 1024-1036 system_u:object_r:sctp_ports_t:s0
 299
 300
 301 SCTP Peer Labeling
 302 ------------------
 303 An SCTP socket will only have one peer label assigned to it. This will be
 304 assigned during the establishment of the first association. Any further
 305 associations on this socket will have their packet peer label compared to
 306 the sockets peer label, and only if they are different will the
 307 ``association`` permission be validated. This is validated by checking the
 308 socket peer sid against the received packets peer sid to determine whether
 309 the association should be allowed or denied.
 310
 311 NOTES:
 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.