344 lines
14 KiB
ReStructuredText
344 lines
14 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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====
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SCTP
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====
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SCTP LSM Support
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================
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Security Hooks
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--------------
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For security module support, three SCTP specific hooks have been implemented::
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security_sctp_assoc_request()
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security_sctp_bind_connect()
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security_sctp_sk_clone()
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Also the following security hook has been utilised::
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security_inet_conn_established()
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The usage of these hooks are described below with the SELinux implementation
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described in the `SCTP SELinux Support`_ chapter.
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security_sctp_assoc_request()
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Passes the ``@ep`` and ``@chunk->skb`` of the association INIT packet to the
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security module. Returns 0 on success, error on failure.
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::
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@ep - pointer to sctp endpoint structure.
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@skb - pointer to skbuff of association packet.
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security_sctp_bind_connect()
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Passes one or more ipv4/ipv6 addresses to the security module for validation
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based on the ``@optname`` that will result in either a bind or connect
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service as shown in the permission check tables below.
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Returns 0 on success, error on failure.
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::
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@sk - Pointer to sock structure.
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@optname - Name of the option to validate.
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@address - One or more ipv4 / ipv6 addresses.
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@addrlen - The total length of address(s). This is calculated on each
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ipv4 or ipv6 address using sizeof(struct sockaddr_in) or
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sizeof(struct sockaddr_in6).
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------------------------------------------------------------------
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| BIND Type Checks |
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| @optname | @address contains |
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|----------------------------|-----------------------------------|
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| SCTP_SOCKOPT_BINDX_ADD | One or more ipv4 / ipv6 addresses |
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| SCTP_PRIMARY_ADDR | Single ipv4 or ipv6 address |
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| SCTP_SET_PEER_PRIMARY_ADDR | Single ipv4 or ipv6 address |
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------------------------------------------------------------------
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------------------------------------------------------------------
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| CONNECT Type Checks |
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| @optname | @address contains |
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|----------------------------|-----------------------------------|
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| SCTP_SOCKOPT_CONNECTX | One or more ipv4 / ipv6 addresses |
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| SCTP_PARAM_ADD_IP | One or more ipv4 / ipv6 addresses |
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| SCTP_SENDMSG_CONNECT | Single ipv4 or ipv6 address |
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| SCTP_PARAM_SET_PRIMARY | Single ipv4 or ipv6 address |
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------------------------------------------------------------------
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A summary of the ``@optname`` entries is as follows::
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SCTP_SOCKOPT_BINDX_ADD - Allows additional bind addresses to be
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associated after (optionally) calling
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bind(3).
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sctp_bindx(3) adds a set of bind
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addresses on a socket.
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SCTP_SOCKOPT_CONNECTX - Allows the allocation of multiple
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addresses for reaching a peer
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(multi-homed).
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sctp_connectx(3) initiates a connection
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on an SCTP socket using multiple
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destination addresses.
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SCTP_SENDMSG_CONNECT - Initiate a connection that is generated by a
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sendmsg(2) or sctp_sendmsg(3) on a new asociation.
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SCTP_PRIMARY_ADDR - Set local primary address.
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SCTP_SET_PEER_PRIMARY_ADDR - Request peer sets address as
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association primary.
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SCTP_PARAM_ADD_IP - These are used when Dynamic Address
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SCTP_PARAM_SET_PRIMARY - Reconfiguration is enabled as explained below.
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To support Dynamic Address Reconfiguration the following parameters must be
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enabled on both endpoints (or use the appropriate **setsockopt**\(2))::
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/proc/sys/net/sctp/addip_enable
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/proc/sys/net/sctp/addip_noauth_enable
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then the following *_PARAM_*'s are sent to the peer in an
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ASCONF chunk when the corresponding ``@optname``'s are present::
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@optname ASCONF Parameter
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---------- ------------------
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SCTP_SOCKOPT_BINDX_ADD -> SCTP_PARAM_ADD_IP
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SCTP_SET_PEER_PRIMARY_ADDR -> SCTP_PARAM_SET_PRIMARY
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security_sctp_sk_clone()
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~~~~~~~~~~~~~~~~~~~~~~~~
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Called whenever a new socket is created by **accept**\(2)
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(i.e. a TCP style socket) or when a socket is 'peeled off' e.g userspace
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calls **sctp_peeloff**\(3).
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::
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@ep - pointer to current sctp endpoint structure.
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@sk - pointer to current sock structure.
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@sk - pointer to new sock structure.
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security_inet_conn_established()
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Called when a COOKIE ACK is received::
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@sk - pointer to sock structure.
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@skb - pointer to skbuff of the COOKIE ACK packet.
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Security Hooks used for Association Establishment
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-------------------------------------------------
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The following diagram shows the use of ``security_sctp_bind_connect()``,
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``security_sctp_assoc_request()``, ``security_inet_conn_established()`` when
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establishing an association.
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::
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SCTP endpoint "A" SCTP endpoint "Z"
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================= =================
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sctp_sf_do_prm_asoc()
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Association setup can be initiated
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by a connect(2), sctp_connectx(3),
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sendmsg(2) or sctp_sendmsg(3).
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These will result in a call to
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security_sctp_bind_connect() to
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initiate an association to
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SCTP peer endpoint "Z".
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INIT --------------------------------------------->
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sctp_sf_do_5_1B_init()
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Respond to an INIT chunk.
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SCTP peer endpoint "A" is
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asking for an association. Call
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security_sctp_assoc_request()
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to set the peer label if first
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association.
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If not first association, check
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whether allowed, IF so send:
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<----------------------------------------------- INIT ACK
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| ELSE audit event and silently
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| discard the packet.
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COOKIE ECHO ------------------------------------------>
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<------------------------------------------- COOKIE ACK
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sctp_sf_do_5_1E_ca |
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Call security_inet_conn_established() |
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to set the peer label. |
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| If SCTP_SOCKET_TCP or peeled off
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| socket security_sctp_sk_clone() is
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| called to clone the new socket.
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ESTABLISHED ESTABLISHED
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------------------------------------------------------------------
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| Association Established |
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------------------------------------------------------------------
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SCTP SELinux Support
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====================
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Security Hooks
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--------------
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The `SCTP LSM Support`_ chapter above describes the following SCTP security
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hooks with the SELinux specifics expanded below::
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security_sctp_assoc_request()
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security_sctp_bind_connect()
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security_sctp_sk_clone()
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security_inet_conn_established()
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security_sctp_assoc_request()
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Passes the ``@ep`` and ``@chunk->skb`` of the association INIT packet to the
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security module. Returns 0 on success, error on failure.
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::
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@ep - pointer to sctp endpoint structure.
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@skb - pointer to skbuff of association packet.
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The security module performs the following operations:
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IF this is the first association on ``@ep->base.sk``, then set the peer
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sid to that in ``@skb``. This will ensure there is only one peer sid
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assigned to ``@ep->base.sk`` that may support multiple associations.
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ELSE validate the ``@ep->base.sk peer_sid`` against the ``@skb peer sid``
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to determine whether the association should be allowed or denied.
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Set the sctp ``@ep sid`` to socket's sid (from ``ep->base.sk``) with
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MLS portion taken from ``@skb peer sid``. This will be used by SCTP
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TCP style sockets and peeled off connections as they cause a new socket
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to be generated.
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If IP security options are configured (CIPSO/CALIPSO), then the ip
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options are set on the socket.
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security_sctp_bind_connect()
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Checks permissions required for ipv4/ipv6 addresses based on the ``@optname``
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as follows::
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------------------------------------------------------------------
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| BIND Permission Checks |
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| @optname | @address contains |
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|----------------------------|-----------------------------------|
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| SCTP_SOCKOPT_BINDX_ADD | One or more ipv4 / ipv6 addresses |
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| SCTP_PRIMARY_ADDR | Single ipv4 or ipv6 address |
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| SCTP_SET_PEER_PRIMARY_ADDR | Single ipv4 or ipv6 address |
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------------------------------------------------------------------
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------------------------------------------------------------------
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| CONNECT Permission Checks |
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| @optname | @address contains |
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|----------------------------|-----------------------------------|
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| SCTP_SOCKOPT_CONNECTX | One or more ipv4 / ipv6 addresses |
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| SCTP_PARAM_ADD_IP | One or more ipv4 / ipv6 addresses |
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| SCTP_SENDMSG_CONNECT | Single ipv4 or ipv6 address |
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| SCTP_PARAM_SET_PRIMARY | Single ipv4 or ipv6 address |
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------------------------------------------------------------------
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`SCTP LSM Support`_ gives a summary of the ``@optname``
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entries and also describes ASCONF chunk processing when Dynamic Address
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Reconfiguration is enabled.
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security_sctp_sk_clone()
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~~~~~~~~~~~~~~~~~~~~~~~~
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Called whenever a new socket is created by **accept**\(2) (i.e. a TCP style
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socket) or when a socket is 'peeled off' e.g userspace calls
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**sctp_peeloff**\(3). ``security_sctp_sk_clone()`` will set the new
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sockets sid and peer sid to that contained in the ``@ep sid`` and
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``@ep peer sid`` respectively.
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::
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@ep - pointer to current sctp endpoint structure.
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@sk - pointer to current sock structure.
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@sk - pointer to new sock structure.
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security_inet_conn_established()
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Called when a COOKIE ACK is received where it sets the connection's peer sid
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to that in ``@skb``::
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@sk - pointer to sock structure.
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@skb - pointer to skbuff of the COOKIE ACK packet.
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Policy Statements
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-----------------
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The following class and permissions to support SCTP are available within the
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kernel::
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class sctp_socket inherits socket { node_bind }
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whenever the following policy capability is enabled::
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policycap extended_socket_class;
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SELinux SCTP support adds the ``name_connect`` permission for connecting
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to a specific port type and the ``association`` permission that is explained
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in the section below.
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If userspace tools have been updated, SCTP will support the ``portcon``
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statement as shown in the following example::
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portcon sctp 1024-1036 system_u:object_r:sctp_ports_t:s0
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SCTP Peer Labeling
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------------------
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An SCTP socket will only have one peer label assigned to it. This will be
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assigned during the establishment of the first association. Any further
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associations on this socket will have their packet peer label compared to
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the sockets peer label, and only if they are different will the
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``association`` permission be validated. This is validated by checking the
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socket peer sid against the received packets peer sid to determine whether
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the association should be allowed or denied.
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NOTES:
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1) If peer labeling is not enabled, then the peer context will always be
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``SECINITSID_UNLABELED`` (``unlabeled_t`` in Reference Policy).
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2) As SCTP can support more than one transport address per endpoint
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(multi-homing) on a single socket, it is possible to configure policy
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and NetLabel to provide different peer labels for each of these. As the
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socket peer label is determined by the first associations transport
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address, it is recommended that all peer labels are consistent.
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3) **getpeercon**\(3) may be used by userspace to retrieve the sockets peer
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context.
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4) While not SCTP specific, be aware when using NetLabel that if a label
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is assigned to a specific interface, and that interface 'goes down',
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then the NetLabel service will remove the entry. Therefore ensure that
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the network startup scripts call **netlabelctl**\(8) to set the required
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label (see **netlabel-config**\(8) helper script for details).
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5) The NetLabel SCTP peer labeling rules apply as discussed in the following
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set of posts tagged "netlabel" at: https://www.paul-moore.com/blog/t.
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6) CIPSO is only supported for IPv4 addressing: ``socket(AF_INET, ...)``
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CALIPSO is only supported for IPv6 addressing: ``socket(AF_INET6, ...)``
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Note the following when testing CIPSO/CALIPSO:
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a) CIPSO will send an ICMP packet if an SCTP packet cannot be
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delivered because of an invalid label.
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b) CALIPSO does not send an ICMP packet, just silently discards it.
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7) IPSEC is not supported as RFC 3554 - sctp/ipsec support has not been
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implemented in userspace (**racoon**\(8) or **ipsec_pluto**\(8)),
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although the kernel supports SCTP/IPSEC.
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