345 lines
14 KiB
ReStructuredText
345 lines
14 KiB
ReStructuredText
.. 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()
|
|
security_sctp_assoc_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 ``@asoc`` and ``@chunk->skb`` of the association INIT packet to the
|
|
security module. Returns 0 on success, error on failure.
|
|
::
|
|
|
|
@asoc - pointer to sctp association 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).
|
|
::
|
|
|
|
@asoc - pointer to current sctp association structure.
|
|
@sk - pointer to current sock structure.
|
|
@newsk - pointer to new sock structure.
|
|
|
|
|
|
security_sctp_assoc_established()
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
Called when a COOKIE ACK is received, and the peer secid will be
|
|
saved into ``@asoc->peer_secid`` for client::
|
|
|
|
@asoc - pointer to sctp association 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_sctp_assoc_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 a temporary 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 ------------------------------------------>
|
|
sctp_sf_do_5_1D_ce()
|
|
Respond to an COOKIE ECHO chunk.
|
|
Confirm the cookie and create a
|
|
permanent association.
|
|
Call security_sctp_assoc_request() to
|
|
do the same as for INIT chunk Response.
|
|
<------------------------------------------- COOKIE ACK
|
|
| |
|
|
sctp_sf_do_5_1E_ca |
|
|
Call security_sctp_assoc_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_sctp_assoc_established()
|
|
|
|
|
|
security_sctp_assoc_request()
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
Passes the ``@asoc`` and ``@chunk->skb`` of the association INIT packet to the
|
|
security module. Returns 0 on success, error on failure.
|
|
::
|
|
|
|
@asoc - pointer to sctp association structure.
|
|
@skb - pointer to skbuff of association packet.
|
|
|
|
The security module performs the following operations:
|
|
IF this is the first association on ``@asoc->base.sk``, then set the peer
|
|
sid to that in ``@skb``. This will ensure there is only one peer sid
|
|
assigned to ``@asoc->base.sk`` that may support multiple associations.
|
|
|
|
ELSE validate the ``@asoc->base.sk peer_sid`` against the ``@skb peer sid``
|
|
to determine whether the association should be allowed or denied.
|
|
|
|
Set the sctp ``@asoc sid`` to socket's sid (from ``asoc->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 ``@asoc sid`` and
|
|
``@asoc peer sid`` respectively.
|
|
::
|
|
|
|
@asoc - pointer to current sctp association structure.
|
|
@sk - pointer to current sock structure.
|
|
@newsk - pointer to new sock structure.
|
|
|
|
|
|
security_sctp_assoc_established()
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
Called when a COOKIE ACK is received where it sets the connection's peer sid
|
|
to that in ``@skb``::
|
|
|
|
@asoc - pointer to sctp association 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.
|