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SCTP SELinux Support

Security Hooks

Documentation/security/LSM-sctp.rst describes the following SCTP security hooks with the SELinux specifics expanded below:

security_sctp_assoc_request()
security_sctp_bind_connect()
security_sctp_sk_clone()
security_inet_conn_established()

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.
The security module performs the following operations:

IF this is the first association on @ep->base.sk, then set the peer sid to that in @skb. This will ensure there is only one peer sid assigned to @ep->base.sk that may support multiple associations.

ELSE validate the @ep->base.sk peer_sid against the @skb peer sid to determine whether the association should be allowed or denied.

Set the sctp @ep sid to socket's sid (from ep->base.sk) with MLS portion taken from @skb peer sid. This will be used by SCTP TCP style sockets and peeled off connections as they cause a new socket to be generated.

If IP security options are configured (CIPSO/CALIPSO), then the ip options are set on the socket.

security_sctp_bind_connect()

Checks permissions required for ipv4/ipv6 addresses based on the @optname as follows:

------------------------------------------------------------------
|                   BIND Permission 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 Permission 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       |
------------------------------------------------------------------

Documentation/security/LSM-sctp.rst gives a summary of the @optname entries and also describes ASCONF chunk processing when Dynamic Address Reconfiguration is enabled.

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). security_sctp_sk_clone() will set the new sockets sid and peer sid to that contained in the @ep sid and @ep peer sid respectively.

@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 where it sets the connection's peer sid to that in @skb:

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

Policy Statements

The following class and permissions to support SCTP are available within the kernel:

class sctp_socket inherits socket { node_bind }

whenever the following policy capability is enabled:

policycap extended_socket_class;

SELinux SCTP support adds the name_connect permission for connecting to a specific port type and the association permission that is explained in the section below.

If userspace tools have been updated, SCTP will support the portcon statement as shown in the following example:

portcon sctp 1024-1036 system_u:object_r:sctp_ports_t:s0

SCTP Peer Labeling

An SCTP socket will only have one peer label assigned to it. This will be assigned during the establishment of the first association. Any further associations on this socket will have their packet peer label compared to the sockets peer label, and only if they are different will the association permission be validated. This is validated by checking the socket peer sid against the received packets peer sid to determine whether the association should be allowed or denied.

NOTES:
  1. If peer labeling is not enabled, then the peer context will always be SECINITSID_UNLABELED (unlabeled_t in Reference Policy).

  2. As SCTP can support more than one transport address per endpoint (multi-homing) on a single socket, it is possible to configure policy and NetLabel to provide different peer labels for each of these. As the socket peer label is determined by the first associations transport address, it is recommended that all peer labels are consistent.

  3. getpeercon(3) may be used by userspace to retrieve the sockets peer context.

  4. While not SCTP specific, be aware when using NetLabel that if a label is assigned to a specific interface, and that interface 'goes down', then the NetLabel service will remove the entry. Therefore ensure that the network startup scripts call netlabelctl(8) to set the required label (see netlabel-config(8) helper script for details).

  5. The NetLabel SCTP peer labeling rules apply as discussed in the following set of posts tagged "netlabel" at: http://www.paul-moore.com/blog/t.

  6. CIPSO is only supported for IPv4 addressing: socket(AF_INET, ...) CALIPSO is only supported for IPv6 addressing: socket(AF_INET6, ...)

    Note the following when testing CIPSO/CALIPSO:
    1. CIPSO will send an ICMP packet if an SCTP packet cannot be delivered because of an invalid label.
    2. CALIPSO does not send an ICMP packet, just silently discards it.
  7. IPSEC is not supported as RFC 3554 - sctp/ipsec support has not been implemented in userspace (racoon(8) or ipsec_pluto(8)), although the kernel supports SCTP/IPSEC.