| .. SPDX-License-Identifier: GPL-2.0 |
| |
| ==== |
| SCTP |
| ==== |
| |
| SCTP LSM Support |
| ================ |
| |
| Security Hooks |
| -------------- |
| |
| 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 the `SCTP SELinux Support`_ chapter. |
| |
| |
| 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 | |
| ------------------------------------------------------------------ |
| |
| |
| SCTP SELinux Support |
| ==================== |
| |
| Security Hooks |
| -------------- |
| |
| The `SCTP LSM Support`_ chapter above 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 | |
| ------------------------------------------------------------------ |
| |
| |
| `SCTP LSM Support`_ 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: https://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: |
| a) CIPSO will send an ICMP packet if an SCTP packet cannot be |
| delivered because of an invalid label. |
| b) 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. |
