| 1 | |
| 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 | security_sctp_assoc_established()
|
| 19 |
|
| 20 | The usage of these hooks are described below with the SELinux implementation
|
| 21 | described in the `SCTP SELinux Support`_ chapter.
|
| 22 |
|
| 23 |
|
| 24 | security_sctp_assoc_request()
|
| 25 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
| 26 | Passes the ``@asoc`` and ``@chunk->skb`` of the association INIT packet to the
|
| 27 | security module. Returns 0 on success, error on failure.
|
| 28 | ::
|
| 29 |
|
| 30 | @asoc - pointer to sctp association structure.
|
| 31 | @skb - pointer to skbuff of association packet.
|
| 32 |
|
| 33 |
|
| 34 | security_sctp_bind_connect()
|
| 35 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
| 36 | Passes one or more ipv4/ipv6 addresses to the security module for validation
|
| 37 | based on the ``@optname`` that will result in either a bind or connect
|
| 38 | service as shown in the permission check tables below.
|
| 39 | Returns 0 on success, error on failure.
|
| 40 | ::
|
| 41 |
|
| 42 | @sk - Pointer to sock structure.
|
| 43 | @optname - Name of the option to validate.
|
| 44 | @address - One or more ipv4 / ipv6 addresses.
|
| 45 | @addrlen - The total length of address(s). This is calculated on each
|
| 46 | ipv4 or ipv6 address using sizeof(struct sockaddr_in) or
|
| 47 | sizeof(struct sockaddr_in6).
|
| 48 |
|
| 49 | ------------------------------------------------------------------
|
| 50 | | BIND Type Checks |
|
| 51 | | @optname | @address contains |
|
| 52 | |----------------------------|-----------------------------------|
|
| 53 | | SCTP_SOCKOPT_BINDX_ADD | One or more ipv4 / ipv6 addresses |
|
| 54 | | SCTP_PRIMARY_ADDR | Single ipv4 or ipv6 address |
|
| 55 | | SCTP_SET_PEER_PRIMARY_ADDR | Single ipv4 or ipv6 address |
|
| 56 | ------------------------------------------------------------------
|
| 57 |
|
| 58 | ------------------------------------------------------------------
|
| 59 | | CONNECT Type Checks |
|
| 60 | | @optname | @address contains |
|
| 61 | |----------------------------|-----------------------------------|
|
| 62 | | SCTP_SOCKOPT_CONNECTX | One or more ipv4 / ipv6 addresses |
|
| 63 | | SCTP_PARAM_ADD_IP | One or more ipv4 / ipv6 addresses |
|
| 64 | | SCTP_SENDMSG_CONNECT | Single ipv4 or ipv6 address |
|
| 65 | | SCTP_PARAM_SET_PRIMARY | Single ipv4 or ipv6 address |
|
| 66 | ------------------------------------------------------------------
|
| 67 |
|
| 68 | A summary of the ``@optname`` entries is as follows::
|
| 69 |
|
| 70 | SCTP_SOCKOPT_BINDX_ADD - Allows additional bind addresses to be
|
| 71 | associated after (optionally) calling
|
| 72 | bind(3).
|
| 73 | sctp_bindx(3) adds a set of bind
|
| 74 | addresses on a socket.
|
| 75 |
|
| 76 | SCTP_SOCKOPT_CONNECTX - Allows the allocation of multiple
|
| 77 | addresses for reaching a peer
|
| 78 | (multi-homed).
|
| 79 | sctp_connectx(3) initiates a connection
|
| 80 | on an SCTP socket using multiple
|
| 81 | destination addresses.
|
| 82 |
|
| 83 | SCTP_SENDMSG_CONNECT - Initiate a connection that is generated by a
|
| 84 | sendmsg(2) or sctp_sendmsg(3) on a new association.
|
| 85 |
|
| 86 | SCTP_PRIMARY_ADDR - Set local primary address.
|
| 87 |
|
| 88 | SCTP_SET_PEER_PRIMARY_ADDR - Request peer sets address as
|
| 89 | association primary.
|
| 90 |
|
| 91 | SCTP_PARAM_ADD_IP - These are used when Dynamic Address
|
| 92 | SCTP_PARAM_SET_PRIMARY - Reconfiguration is enabled as explained below.
|
| 93 |
|
| 94 |
|
| 95 | To support Dynamic Address Reconfiguration the following parameters must be
|
| 96 | enabled on both endpoints (or use the appropriate **setsockopt**\(2))::
|
| 97 |
|
| 98 | /proc/sys/net/sctp/addip_enable
|
| 99 | /proc/sys/net/sctp/addip_noauth_enable
|
| 100 |
|
| 101 | then the following *_PARAM_*'s are sent to the peer in an
|
| 102 | ASCONF chunk when the corresponding ``@optname``'s are present::
|
| 103 |
|
| 104 | @optname ASCONF Parameter
|
| 105 | ---------- ------------------
|
| 106 | SCTP_SOCKOPT_BINDX_ADD -> SCTP_PARAM_ADD_IP
|
| 107 | SCTP_SET_PEER_PRIMARY_ADDR -> SCTP_PARAM_SET_PRIMARY
|
| 108 |
|
| 109 |
|
| 110 | security_sctp_sk_clone()
|
| 111 | ~~~~~~~~~~~~~~~~~~~~~~~~
|
| 112 | Called whenever a new socket is created by **accept**\(2)
|
| 113 | (i.e. a TCP style socket) or when a socket is 'peeled off' e.g userspace
|
| 114 | calls **sctp_peeloff**\(3).
|
| 115 | ::
|
| 116 |
|
| 117 | @asoc - pointer to current sctp association structure.
|
| 118 | @sk - pointer to current sock structure.
|
| 119 | @newsk - pointer to new sock structure.
|
| 120 |
|
| 121 |
|
| 122 | security_sctp_assoc_established()
|
| 123 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
| 124 | Called when a COOKIE ACK is received, and the peer secid will be
|
| 125 | saved into ``@asoc->peer_secid`` for client::
|
| 126 |
|
| 127 | @asoc - pointer to sctp association structure.
|
| 128 | @skb - pointer to skbuff of the COOKIE ACK packet.
|
| 129 |
|
| 130 |
|
| 131 | Security Hooks used for Association Establishment
|
| 132 | -------------------------------------------------
|
| 133 |
|
| 134 | The following diagram shows the use of ``security_sctp_bind_connect()``,
|
| 135 | ``security_sctp_assoc_request()``, ``security_sctp_assoc_established()`` when
|
| 136 | establishing an association.
|
| 137 | ::
|
| 138 |
|
| 139 | SCTP endpoint "A" SCTP endpoint "Z"
|
| 140 | ================= =================
|
| 141 | sctp_sf_do_prm_asoc()
|
| 142 | Association setup can be initiated
|
| 143 | by a connect(2), sctp_connectx(3),
|
| 144 | sendmsg(2) or sctp_sendmsg(3).
|
| 145 | These will result in a call to
|
| 146 | security_sctp_bind_connect() to
|
| 147 | initiate an association to
|
| 148 | SCTP peer endpoint "Z".
|
| 149 | INIT --------------------------------------------->
|
| 150 | sctp_sf_do_5_1B_init()
|
| 151 | Respond to an INIT chunk.
|
| 152 | SCTP peer endpoint "A" is asking
|
| 153 | for a temporary association.
|
| 154 | Call security_sctp_assoc_request()
|
| 155 | to set the peer label if first
|
| 156 | association.
|
| 157 | If not first association, check
|
| 158 | whether allowed, IF so send:
|
| 159 | <----------------------------------------------- INIT ACK
|
| 160 | | ELSE audit event and silently
|
| 161 | | discard the packet.
|
| 162 | |
|
| 163 | COOKIE ECHO ------------------------------------------>
|
| 164 | sctp_sf_do_5_1D_ce()
|
| 165 | Respond to an COOKIE ECHO chunk.
|
| 166 | Confirm the cookie and create a
|
| 167 | permanent association.
|
| 168 | Call security_sctp_assoc_request() to
|
| 169 | do the same as for INIT chunk Response.
|
| 170 | <------------------------------------------- COOKIE ACK
|
| 171 | | |
|
| 172 | sctp_sf_do_5_1E_ca |
|
| 173 | Call security_sctp_assoc_established() |
|
| 174 | to set the peer label. |
|
| 175 | | |
|
| 176 | | If SCTP_SOCKET_TCP or peeled off
|
| 177 | | socket security_sctp_sk_clone() is
|
| 178 | | called to clone the new socket.
|
| 179 | | |
|
| 180 | ESTABLISHED ESTABLISHED
|
| 181 | | |
|
| 182 | ------------------------------------------------------------------
|
| 183 | | Association Established |
|
| 184 | ------------------------------------------------------------------
|
| 185 |
|
| 186 |
|
| 187 | SCTP SELinux Support
|
| 188 | ====================
|
| 189 |
|
| 190 | Security Hooks
|
| 191 | --------------
|
| 192 |
|
| 193 | The `SCTP LSM Support`_ chapter above describes the following SCTP security
|
| 194 | hooks with the SELinux specifics expanded below::
|
| 195 |
|
| 196 | security_sctp_assoc_request()
|
| 197 | security_sctp_bind_connect()
|
| 198 | security_sctp_sk_clone()
|
| 199 | security_sctp_assoc_established()
|
| 200 |
|
| 201 |
|
| 202 | security_sctp_assoc_request()
|
| 203 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
| 204 | Passes the ``@asoc`` and ``@chunk->skb`` of the association INIT packet to the
|
| 205 | security module. Returns 0 on success, error on failure.
|
| 206 | ::
|
| 207 |
|
| 208 | @asoc - pointer to sctp association structure.
|
| 209 | @skb - pointer to skbuff of association packet.
|
| 210 |
|
| 211 | The security module performs the following operations:
|
| 212 | IF this is the first association on ``@asoc->base.sk``, then set the peer
|
| 213 | sid to that in ``@skb``. This will ensure there is only one peer sid
|
| 214 | assigned to ``@asoc->base.sk`` that may support multiple associations.
|
| 215 |
|
| 216 | ELSE validate the ``@asoc->base.sk peer_sid`` against the ``@skb peer sid``
|
| 217 | to determine whether the association should be allowed or denied.
|
| 218 |
|
| 219 | Set the sctp ``@asoc sid`` to socket's sid (from ``asoc->base.sk``) with
|
| 220 | MLS portion taken from ``@skb peer sid``. This will be used by SCTP
|
| 221 | TCP style sockets and peeled off connections as they cause a new socket
|
| 222 | to be generated.
|
| 223 |
|
| 224 | If IP security options are configured (CIPSO/CALIPSO), then the ip
|
| 225 | options are set on the socket.
|
| 226 |
|
| 227 |
|
| 228 | security_sctp_bind_connect()
|
| 229 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
| 230 | Checks permissions required for ipv4/ipv6 addresses based on the ``@optname``
|
| 231 | as follows::
|
| 232 |
|
| 233 | ------------------------------------------------------------------
|
| 234 | | BIND Permission Checks |
|
| 235 | | @optname | @address contains |
|
| 236 | |----------------------------|-----------------------------------|
|
| 237 | | SCTP_SOCKOPT_BINDX_ADD | One or more ipv4 / ipv6 addresses |
|
| 238 | | SCTP_PRIMARY_ADDR | Single ipv4 or ipv6 address |
|
| 239 | | SCTP_SET_PEER_PRIMARY_ADDR | Single ipv4 or ipv6 address |
|
| 240 | ------------------------------------------------------------------
|
| 241 |
|
| 242 | ------------------------------------------------------------------
|
| 243 | | CONNECT Permission Checks |
|
| 244 | | @optname | @address contains |
|
| 245 | |----------------------------|-----------------------------------|
|
| 246 | | SCTP_SOCKOPT_CONNECTX | One or more ipv4 / ipv6 addresses |
|
| 247 | | SCTP_PARAM_ADD_IP | One or more ipv4 / ipv6 addresses |
|
| 248 | | SCTP_SENDMSG_CONNECT | Single ipv4 or ipv6 address |
|
| 249 | | SCTP_PARAM_SET_PRIMARY | Single ipv4 or ipv6 address |
|
| 250 | ------------------------------------------------------------------
|
| 251 |
|
| 252 |
|
| 253 | `SCTP LSM Support`_ gives a summary of the ``@optname``
|
| 254 | entries and also describes ASCONF chunk processing when Dynamic Address
|
| 255 | Reconfiguration is enabled.
|
| 256 |
|
| 257 |
|
| 258 | security_sctp_sk_clone()
|
| 259 | ~~~~~~~~~~~~~~~~~~~~~~~~
|
| 260 | Called whenever a new socket is created by **accept**\(2) (i.e. a TCP style
|
| 261 | socket) or when a socket is 'peeled off' e.g userspace calls
|
| 262 | **sctp_peeloff**\(3). ``security_sctp_sk_clone()`` will set the new
|
| 263 | sockets sid and peer sid to that contained in the ``@asoc sid`` and
|
| 264 | ``@asoc peer sid`` respectively.
|
| 265 | ::
|
| 266 |
|
| 267 | @asoc - pointer to current sctp association structure.
|
| 268 | @sk - pointer to current sock structure.
|
| 269 | @newsk - pointer to new sock structure.
|
| 270 |
|
| 271 |
|
| 272 | security_sctp_assoc_established()
|
| 273 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
| 274 | Called when a COOKIE ACK is received where it sets the connection's peer sid
|
| 275 | to that in ``@skb``::
|
| 276 |
|
| 277 | @asoc - pointer to sctp association structure.
|
| 278 | @skb - pointer to skbuff of the COOKIE ACK packet.
|
| 279 |
|
| 280 |
|
| 281 | Policy Statements
|
| 282 | -----------------
|
| 283 | The following class and permissions to support SCTP are available within the
|
| 284 | kernel::
|
| 285 |
|
| 286 | class sctp_socket inherits socket { node_bind }
|
| 287 |
|
| 288 | whenever the following policy capability is enabled::
|
| 289 |
|
| 290 | policycap extended_socket_class;
|
| 291 |
|
| 292 | SELinux SCTP support adds the ``name_connect`` permission for connecting
|
| 293 | to a specific port type and the ``association`` permission that is explained
|
| 294 | in the section below.
|
| 295 |
|
| 296 | If userspace tools have been updated, SCTP will support the ``portcon``
|
| 297 | statement as shown in the following example::
|
| 298 |
|
| 299 | portcon sctp 1024-1036 system_u:object_r:sctp_ports_t:s0
|
| 300 |
|
| 301 |
|
| 302 | SCTP Peer Labeling
|
| 303 | ------------------
|
| 304 | An SCTP socket will only have one peer label assigned to it. This will be
|
| 305 | assigned during the establishment of the first association. Any further
|
| 306 | associations on this socket will have their packet peer label compared to
|
| 307 | the sockets peer label, and only if they are different will the
|
| 308 | ``association`` permission be validated. This is validated by checking the
|
| 309 | socket peer sid against the received packets peer sid to determine whether
|
| 310 | the association should be allowed or denied.
|
| 311 |
|
| 312 | NOTES:
|
| 313 | 1) If peer labeling is not enabled, then the peer context will always be
|
| 314 | ``SECINITSID_UNLABELED`` (``unlabeled_t`` in Reference Policy).
|
| 315 |
|
| 316 | 2) As SCTP can support more than one transport address per endpoint
|
| 317 | (multi-homing) on a single socket, it is possible to configure policy
|
| 318 | and NetLabel to provide different peer labels for each of these. As the
|
| 319 | socket peer label is determined by the first associations transport
|
| 320 | address, it is recommended that all peer labels are consistent.
|
| 321 |
|
| 322 | 3) **getpeercon**\(3) may be used by userspace to retrieve the sockets peer
|
| 323 | context.
|
| 324 |
|
| 325 | 4) While not SCTP specific, be aware when using NetLabel that if a label
|
| 326 | is assigned to a specific interface, and that interface 'goes down',
|
| 327 | then the NetLabel service will remove the entry. Therefore ensure that
|
| 328 | the network startup scripts call **netlabelctl**\(8) to set the required
|
| 329 | label (see **netlabel-config**\(8) helper script for details).
|
| 330 |
|
| 331 | 5) The NetLabel SCTP peer labeling rules apply as discussed in the following
|
| 332 | set of posts tagged "netlabel" at: https://www.paul-moore.com/blog/t.
|
| 333 |
|
| 334 | 6) CIPSO is only supported for IPv4 addressing: ``socket(AF_INET, ...)``
|
| 335 | CALIPSO is only supported for IPv6 addressing: ``socket(AF_INET6, ...)``
|
| 336 |
|
| 337 | Note the following when testing CIPSO/CALIPSO:
|
| 338 | a) CIPSO will send an ICMP packet if an SCTP packet cannot be
|
| 339 | delivered because of an invalid label.
|
| 340 | b) CALIPSO does not send an ICMP packet, just silently discards it.
|
| 341 |
|
| 342 | 7) IPSEC is not supported as RFC 3554 - sctp/ipsec support has not been
|
| 343 | implemented in userspace (**racoon**\(8) or **ipsec_pluto**\(8)),
|
| 344 | although the kernel supports SCTP/IPSEC.
|