Skip to content

Latest commit

 

History

History
175 lines (139 loc) · 7.53 KB

LSM-sctp.rst

File metadata and controls

175 lines (139 loc) · 7.53 KB
Raw

SCTP LSM Support

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 Documentation/security/SELinux-sctp.rst

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 | ------------------------------------------------------------------