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LSM-sctp.rst

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SCTP LSM Support

For security module support, three SCTP specific hooks have been implemented:

security_sctp_assoc_request()
security_sctp_bind_connect()
security_sctp_sk_clone()

Also the following security hook has been utilised:

security_inet_conn_established()

The usage of these hooks are described below with the SELinux implementation described in Documentation/security/SELinux-sctp.rst

security_sctp_assoc_request()

Passes the @ep and @chunk->skb of the association INIT packet to the security module. Returns 0 on success, error on failure.

@ep - pointer to sctp endpoint structure.
@skb - pointer to skbuff of association packet.

security_sctp_bind_connect()

Passes one or more ipv4/ipv6 addresses to the security module for validation based on the @optname that will result in either a bind or connect service as shown in the permission check tables below. Returns 0 on success, error on failure.

  @sk      - Pointer to sock structure.
  @optname - Name of the option to validate.
  @address - One or more ipv4 / ipv6 addresses.
  @addrlen - The total length of address(s). This is calculated on each
             ipv4 or ipv6 address using sizeof(struct sockaddr_in) or
             sizeof(struct sockaddr_in6).

------------------------------------------------------------------
|                     BIND Type Checks                           |
|       @optname             |         @address contains         |
|----------------------------|-----------------------------------|
| SCTP_SOCKOPT_BINDX_ADD     | One or more ipv4 / ipv6 addresses |
| SCTP_PRIMARY_ADDR          | Single ipv4 or ipv6 address       |
| SCTP_SET_PEER_PRIMARY_ADDR | Single ipv4 or ipv6 address       |
------------------------------------------------------------------

------------------------------------------------------------------
|                   CONNECT Type Checks                          |
|       @optname             |         @address contains         |
|----------------------------|-----------------------------------|
| SCTP_SOCKOPT_CONNECTX      | One or more ipv4 / ipv6 addresses |
| SCTP_PARAM_ADD_IP          | One or more ipv4 / ipv6 addresses |
| SCTP_SENDMSG_CONNECT       | Single ipv4 or ipv6 address       |
| SCTP_PARAM_SET_PRIMARY     | Single ipv4 or ipv6 address       |
------------------------------------------------------------------

A summary of the @optname entries is as follows:

SCTP_SOCKOPT_BINDX_ADD - Allows additional bind addresses to be
                         associated after (optionally) calling
                         bind(3).
                         sctp_bindx(3) adds a set of bind
                         addresses on a socket.

SCTP_SOCKOPT_CONNECTX - Allows the allocation of multiple
                        addresses for reaching a peer
                        (multi-homed).
                        sctp_connectx(3) initiates a connection
                        on an SCTP socket using multiple
                        destination addresses.

SCTP_SENDMSG_CONNECT  - Initiate a connection that is generated by a
                        sendmsg(2) or sctp_sendmsg(3) on a new asociation.

SCTP_PRIMARY_ADDR     - Set local primary address.

SCTP_SET_PEER_PRIMARY_ADDR - Request peer sets address as
                             association primary.

SCTP_PARAM_ADD_IP          - These are used when Dynamic Address
SCTP_PARAM_SET_PRIMARY     - Reconfiguration is enabled as explained below.

To support Dynamic Address Reconfiguration the following parameters must be enabled on both endpoints (or use the appropriate setsockopt(2)):

/proc/sys/net/sctp/addip_enable
/proc/sys/net/sctp/addip_noauth_enable

then the following _PARAM_'s are sent to the peer in an ASCONF chunk when the corresponding @optname's are present:

      @optname                      ASCONF Parameter
     ----------                    ------------------
SCTP_SOCKOPT_BINDX_ADD     ->   SCTP_PARAM_ADD_IP
SCTP_SET_PEER_PRIMARY_ADDR ->   SCTP_PARAM_SET_PRIMARY

security_sctp_sk_clone()

Called whenever a new socket is created by accept(2) (i.e. a TCP style socket) or when a socket is 'peeled off' e.g userspace calls sctp_peeloff(3).

@ep - pointer to current sctp endpoint structure.
@sk - pointer to current sock structure.
@sk - pointer to new sock structure.

security_inet_conn_established()

Called when a COOKIE ACK is received:

@sk  - pointer to sock structure.
@skb - pointer to skbuff of the COOKIE ACK packet.

Security Hooks used for Association Establishment

The following diagram shows the use of security_sctp_bind_connect(), security_sctp_assoc_request(), security_inet_conn_established() when establishing an association.

     SCTP endpoint "A"                                SCTP endpoint "Z"
     =================                                =================
   sctp_sf_do_prm_asoc()
Association setup can be initiated
by a connect(2), sctp_connectx(3),
sendmsg(2) or sctp_sendmsg(3).
These will result in a call to
security_sctp_bind_connect() to
initiate an association to
SCTP peer endpoint "Z".
        INIT --------------------------------------------->
                                                  sctp_sf_do_5_1B_init()
                                                Respond to an INIT chunk.
                                            SCTP peer endpoint "A" is
                                            asking for an association. Call
                                            security_sctp_assoc_request()
                                            to set the peer label if first
                                            association.
                                            If not first association, check
                                            whether allowed, IF so send:
         <----------------------------------------------- INIT ACK
         |                                  ELSE audit event and silently
         |                                       discard the packet.
         |
   COOKIE ECHO ------------------------------------------>
                                                         |
                                                         |
                                                         |
         <------------------------------------------- COOKIE ACK
         |                                               |
   sctp_sf_do_5_1E_ca                                    |
Call security_inet_conn_established()                    |
to set the peer label.                                   |
         |                                               |
         |                               If SCTP_SOCKET_TCP or peeled off
         |                               socket security_sctp_sk_clone() is
         |                               called to clone the new socket.
         |                                               |
     ESTABLISHED                                    ESTABLISHED
         |                                               |
   ------------------------------------------------------------------
   |                     Association Established                    |
   ------------------------------------------------------------------