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authorKees Cook <keescook@chromium.org>2019-02-17 14:08:36 -0800
committerJonathan Corbet <corbet@lwn.net>2019-02-22 08:51:40 -0700
commitd61330c689df2ef7ac76b63be2bd0a8561e47fd9 (patch)
tree1dd5dd449f49ea47435fd895ea43e4c6faec6ca0 /Documentation/security/SCTP.rst
parent3203561d6d081fa53d3b448d99fb9ffd933b3123 (diff)
doc: sctp: Merge and clean up rst files
The SCTP sections were ending up at the top-level table of contents under the security section when they should have be sections with the SCTP chapters. In addition to correcting the section and subsection headings, this merges the SCTP documents into a single file to organize the chapters more clearly, internally linkifies them, and adds the missing SPDX header. Signed-off-by: Kees Cook <keescook@chromium.org> Acked-by: Paul Moore <paul@paul-moore.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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+.. 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: 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:
+ 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.