linux/net/sctp/sm_statefuns.c

// SPDX-License-Identifier: GPL-2.0-or-later
/* SCTP kernel implementation
 * (C) Copyright IBM Corp. 2001, 2004
 * Copyright (c) 1999-2000 Cisco, Inc.
 * Copyright (c) 1999-2001 Motorola, Inc.
 * Copyright (c) 2001-2002 Intel Corp.
 * Copyright (c) 2002      Nokia Corp.
 *
 * This is part of the SCTP Linux Kernel Implementation.
 *
 * These are the state functions for the state machine.
 *
 * Please send any bug reports or fixes you make to the
 * email address(es):
 *    lksctp developers <[email protected]>
 *
 * Written or modified by:
 *    La Monte H.P. Yarroll <[email protected]>
 *    Karl Knutson          <[email protected]>
 *    Mathew Kotowsky       <[email protected]>
 *    Sridhar Samudrala     <[email protected]>
 *    Jon Grimm             <[email protected]>
 *    Hui Huang 	    <[email protected]>
 *    Dajiang Zhang 	    <[email protected]>
 *    Daisy Chang	    <[email protected]>
 *    Ardelle Fan	    <[email protected]>
 *    Ryan Layer	    <[email protected]>
 *    Kevin Gao		    <[email protected]>
 */

#define pr_fmt(fmt) …

#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/net.h>
#include <linux/inet.h>
#include <linux/slab.h>
#include <net/sock.h>
#include <net/proto_memory.h>
#include <net/inet_ecn.h>
#include <linux/skbuff.h>
#include <net/sctp/sctp.h>
#include <net/sctp/sm.h>
#include <net/sctp/structs.h>

#define CREATE_TRACE_POINTS
#include <trace/events/sctp.h>

static struct sctp_packet *sctp_abort_pkt_new(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					struct sctp_chunk *chunk,
					const void *payload, size_t paylen);
static int sctp_eat_data(const struct sctp_association *asoc,
			 struct sctp_chunk *chunk,
			 struct sctp_cmd_seq *commands);
static struct sctp_packet *sctp_ootb_pkt_new(
					struct net *net,
					const struct sctp_association *asoc,
					const struct sctp_chunk *chunk);
static void sctp_send_stale_cookie_err(struct net *net,
				       const struct sctp_endpoint *ep,
				       const struct sctp_association *asoc,
				       const struct sctp_chunk *chunk,
				       struct sctp_cmd_seq *commands,
				       struct sctp_chunk *err_chunk);
static enum sctp_disposition sctp_sf_do_5_2_6_stale(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands);
static enum sctp_disposition sctp_sf_shut_8_4_5(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands);
static enum sctp_disposition sctp_sf_tabort_8_4_8(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands);
static enum sctp_disposition sctp_sf_new_encap_port(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands);
static struct sctp_sackhdr *sctp_sm_pull_sack(struct sctp_chunk *chunk);

static enum sctp_disposition sctp_stop_t1_and_abort(
					struct net *net,
					struct sctp_cmd_seq *commands,
					__be16 error, int sk_err,
					const struct sctp_association *asoc,
					struct sctp_transport *transport);

static enum sctp_disposition sctp_sf_abort_violation(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					void *arg,
					struct sctp_cmd_seq *commands,
					const __u8 *payload,
					const size_t paylen);

static enum sctp_disposition sctp_sf_violation_chunklen(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands);

static enum sctp_disposition sctp_sf_violation_paramlen(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg, void *ext,
					struct sctp_cmd_seq *commands);

static enum sctp_disposition sctp_sf_violation_ctsn(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands);

static enum sctp_disposition sctp_sf_violation_chunk(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands);

static enum sctp_ierror sctp_sf_authenticate(
					const struct sctp_association *asoc,
					struct sctp_chunk *chunk);

static enum sctp_disposition __sctp_sf_do_9_1_abort(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands);

static enum sctp_disposition
__sctp_sf_do_9_2_reshutack(struct net *net, const struct sctp_endpoint *ep,
			   const struct sctp_association *asoc,
			   const union sctp_subtype type, void *arg,
			   struct sctp_cmd_seq *commands);

/* Small helper function that checks if the chunk length
 * is of the appropriate length.  The 'required_length' argument
 * is set to be the size of a specific chunk we are testing.
 * Return Values:  true  = Valid length
 * 		   false = Invalid length
 *
 */
static inline bool sctp_chunk_length_valid(struct sctp_chunk *chunk,
					   __u16 required_length)
{ … }

/* Check for format error in an ABORT chunk */
static inline bool sctp_err_chunk_valid(struct sctp_chunk *chunk)
{ … }

/**********************************************************
 * These are the state functions for handling chunk events.
 **********************************************************/

/*
 * Process the final SHUTDOWN COMPLETE.
 *
 * Section: 4 (C) (diagram), 9.2
 * Upon reception of the SHUTDOWN COMPLETE chunk the endpoint will verify
 * that it is in SHUTDOWN-ACK-SENT state, if it is not the chunk should be
 * discarded. If the endpoint is in the SHUTDOWN-ACK-SENT state the endpoint
 * should stop the T2-shutdown timer and remove all knowledge of the
 * association (and thus the association enters the CLOSED state).
 *
 * Verification Tag: 8.5.1(C), sctpimpguide 2.41.
 * C) Rules for packet carrying SHUTDOWN COMPLETE:
 * ...
 * - The receiver of a SHUTDOWN COMPLETE shall accept the packet
 *   if the Verification Tag field of the packet matches its own tag and
 *   the T bit is not set
 *   OR
 *   it is set to its peer's tag and the T bit is set in the Chunk
 *   Flags.
 *   Otherwise, the receiver MUST silently discard the packet
 *   and take no further action.  An endpoint MUST ignore the
 *   SHUTDOWN COMPLETE if it is not in the SHUTDOWN-ACK-SENT state.
 *
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_do_4_C(struct net *net,
				     const struct sctp_endpoint *ep,
				     const struct sctp_association *asoc,
				     const union sctp_subtype type,
				     void *arg, struct sctp_cmd_seq *commands)
{ … }

/*
 * Respond to a normal INIT chunk.
 * We are the side that is being asked for an association.
 *
 * Section: 5.1 Normal Establishment of an Association, B
 * B) "Z" shall respond immediately with an INIT ACK chunk.  The
 *    destination IP address of the INIT ACK MUST be set to the source
 *    IP address of the INIT to which this INIT ACK is responding.  In
 *    the response, besides filling in other parameters, "Z" must set the
 *    Verification Tag field to Tag_A, and also provide its own
 *    Verification Tag (Tag_Z) in the Initiate Tag field.
 *
 * Verification Tag: Must be 0.
 *
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_do_5_1B_init(struct net *net,
					   const struct sctp_endpoint *ep,
					   const struct sctp_association *asoc,
					   const union sctp_subtype type,
					   void *arg,
					   struct sctp_cmd_seq *commands)
{ … }

/*
 * Respond to a normal INIT ACK chunk.
 * We are the side that is initiating the association.
 *
 * Section: 5.1 Normal Establishment of an Association, C
 * C) Upon reception of the INIT ACK from "Z", "A" shall stop the T1-init
 *    timer and leave COOKIE-WAIT state. "A" shall then send the State
 *    Cookie received in the INIT ACK chunk in a COOKIE ECHO chunk, start
 *    the T1-cookie timer, and enter the COOKIE-ECHOED state.
 *
 *    Note: The COOKIE ECHO chunk can be bundled with any pending outbound
 *    DATA chunks, but it MUST be the first chunk in the packet and
 *    until the COOKIE ACK is returned the sender MUST NOT send any
 *    other packets to the peer.
 *
 * Verification Tag: 3.3.3
 *   If the value of the Initiate Tag in a received INIT ACK chunk is
 *   found to be 0, the receiver MUST treat it as an error and close the
 *   association by transmitting an ABORT.
 *
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_do_5_1C_ack(struct net *net,
					  const struct sctp_endpoint *ep,
					  const struct sctp_association *asoc,
					  const union sctp_subtype type,
					  void *arg,
					  struct sctp_cmd_seq *commands)
{ … }

static bool sctp_auth_chunk_verify(struct net *net, struct sctp_chunk *chunk,
				   const struct sctp_association *asoc)
{ … }

/*
 * Respond to a normal COOKIE ECHO chunk.
 * We are the side that is being asked for an association.
 *
 * Section: 5.1 Normal Establishment of an Association, D
 * D) Upon reception of the COOKIE ECHO chunk, Endpoint "Z" will reply
 *    with a COOKIE ACK chunk after building a TCB and moving to
 *    the ESTABLISHED state. A COOKIE ACK chunk may be bundled with
 *    any pending DATA chunks (and/or SACK chunks), but the COOKIE ACK
 *    chunk MUST be the first chunk in the packet.
 *
 *   IMPLEMENTATION NOTE: An implementation may choose to send the
 *   Communication Up notification to the SCTP user upon reception
 *   of a valid COOKIE ECHO chunk.
 *
 * Verification Tag: 8.5.1 Exceptions in Verification Tag Rules
 * D) Rules for packet carrying a COOKIE ECHO
 *
 * - When sending a COOKIE ECHO, the endpoint MUST use the value of the
 *   Initial Tag received in the INIT ACK.
 *
 * - The receiver of a COOKIE ECHO follows the procedures in Section 5.
 *
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_do_5_1D_ce(struct net *net,
					 const struct sctp_endpoint *ep,
					 const struct sctp_association *asoc,
					 const union sctp_subtype type,
					 void *arg,
					 struct sctp_cmd_seq *commands)
{ … }

/*
 * Respond to a normal COOKIE ACK chunk.
 * We are the side that is asking for an association.
 *
 * RFC 2960 5.1 Normal Establishment of an Association
 *
 * E) Upon reception of the COOKIE ACK, endpoint "A" will move from the
 *    COOKIE-ECHOED state to the ESTABLISHED state, stopping the T1-cookie
 *    timer. It may also notify its ULP about the successful
 *    establishment of the association with a Communication Up
 *    notification (see Section 10).
 *
 * Verification Tag:
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_do_5_1E_ca(struct net *net,
					 const struct sctp_endpoint *ep,
					 const struct sctp_association *asoc,
					 const union sctp_subtype type,
					 void *arg,
					 struct sctp_cmd_seq *commands)
{ … }

/* Generate and sendout a heartbeat packet.  */
static enum sctp_disposition sctp_sf_heartbeat(
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/* Generate a HEARTBEAT packet on the given transport.  */
enum sctp_disposition sctp_sf_sendbeat_8_3(struct net *net,
					   const struct sctp_endpoint *ep,
					   const struct sctp_association *asoc,
					   const union sctp_subtype type,
					   void *arg,
					   struct sctp_cmd_seq *commands)
{ … }

/* resend asoc strreset_chunk.  */
enum sctp_disposition sctp_sf_send_reconf(struct net *net,
					  const struct sctp_endpoint *ep,
					  const struct sctp_association *asoc,
					  const union sctp_subtype type,
					  void *arg,
					  struct sctp_cmd_seq *commands)
{ … }

/* send hb chunk with padding for PLPMUTD.  */
enum sctp_disposition sctp_sf_send_probe(struct net *net,
					 const struct sctp_endpoint *ep,
					 const struct sctp_association *asoc,
					 const union sctp_subtype type,
					 void *arg,
					 struct sctp_cmd_seq *commands)
{ … }

/*
 * Process an heartbeat request.
 *
 * Section: 8.3 Path Heartbeat
 * The receiver of the HEARTBEAT should immediately respond with a
 * HEARTBEAT ACK that contains the Heartbeat Information field copied
 * from the received HEARTBEAT chunk.
 *
 * Verification Tag:  8.5 Verification Tag [Normal verification]
 * When receiving an SCTP packet, the endpoint MUST ensure that the
 * value in the Verification Tag field of the received SCTP packet
 * matches its own Tag. If the received Verification Tag value does not
 * match the receiver's own tag value, the receiver shall silently
 * discard the packet and shall not process it any further except for
 * those cases listed in Section 8.5.1 below.
 *
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_beat_8_3(struct net *net,
				       const struct sctp_endpoint *ep,
				       const struct sctp_association *asoc,
				       const union sctp_subtype type,
				       void *arg, struct sctp_cmd_seq *commands)
{ … }

/*
 * Process the returning HEARTBEAT ACK.
 *
 * Section: 8.3 Path Heartbeat
 * Upon the receipt of the HEARTBEAT ACK, the sender of the HEARTBEAT
 * should clear the error counter of the destination transport
 * address to which the HEARTBEAT was sent, and mark the destination
 * transport address as active if it is not so marked. The endpoint may
 * optionally report to the upper layer when an inactive destination
 * address is marked as active due to the reception of the latest
 * HEARTBEAT ACK. The receiver of the HEARTBEAT ACK must also
 * clear the association overall error count as well (as defined
 * in section 8.1).
 *
 * The receiver of the HEARTBEAT ACK should also perform an RTT
 * measurement for that destination transport address using the time
 * value carried in the HEARTBEAT ACK chunk.
 *
 * Verification Tag:  8.5 Verification Tag [Normal verification]
 *
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_backbeat_8_3(struct net *net,
					   const struct sctp_endpoint *ep,
					   const struct sctp_association *asoc,
					   const union sctp_subtype type,
					   void *arg,
					   struct sctp_cmd_seq *commands)
{ … }

/* Helper function to send out an abort for the restart
 * condition.
 */
static int sctp_sf_send_restart_abort(struct net *net, union sctp_addr *ssa,
				      struct sctp_chunk *init,
				      struct sctp_cmd_seq *commands)
{ … }

static bool list_has_sctp_addr(const struct list_head *list,
			       union sctp_addr *ipaddr)
{ … }
/* A restart is occurring, check to make sure no new addresses
 * are being added as we may be under a takeover attack.
 */
static int sctp_sf_check_restart_addrs(const struct sctp_association *new_asoc,
				       const struct sctp_association *asoc,
				       struct sctp_chunk *init,
				       struct sctp_cmd_seq *commands)
{ … }

/* Populate the verification/tie tags based on overlapping INIT
 * scenario.
 *
 * Note: Do not use in CLOSED or SHUTDOWN-ACK-SENT state.
 */
static void sctp_tietags_populate(struct sctp_association *new_asoc,
				  const struct sctp_association *asoc)
{ … }

/*
 * Compare vtag/tietag values to determine unexpected COOKIE-ECHO
 * handling action.
 *
 * RFC 2960 5.2.4 Handle a COOKIE ECHO when a TCB exists.
 *
 * Returns value representing action to be taken.   These action values
 * correspond to Action/Description values in RFC 2960, Table 2.
 */
static char sctp_tietags_compare(struct sctp_association *new_asoc,
				 const struct sctp_association *asoc)
{ … }

/* Common helper routine for both duplicate and simultaneous INIT
 * chunk handling.
 */
static enum sctp_disposition sctp_sf_do_unexpected_init(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Handle simultaneous INIT.
 * This means we started an INIT and then we got an INIT request from
 * our peer.
 *
 * Section: 5.2.1 INIT received in COOKIE-WAIT or COOKIE-ECHOED State (Item B)
 * This usually indicates an initialization collision, i.e., each
 * endpoint is attempting, at about the same time, to establish an
 * association with the other endpoint.
 *
 * Upon receipt of an INIT in the COOKIE-WAIT or COOKIE-ECHOED state, an
 * endpoint MUST respond with an INIT ACK using the same parameters it
 * sent in its original INIT chunk (including its Verification Tag,
 * unchanged). These original parameters are combined with those from the
 * newly received INIT chunk. The endpoint shall also generate a State
 * Cookie with the INIT ACK. The endpoint uses the parameters sent in its
 * INIT to calculate the State Cookie.
 *
 * After that, the endpoint MUST NOT change its state, the T1-init
 * timer shall be left running and the corresponding TCB MUST NOT be
 * destroyed. The normal procedures for handling State Cookies when
 * a TCB exists will resolve the duplicate INITs to a single association.
 *
 * For an endpoint that is in the COOKIE-ECHOED state it MUST populate
 * its Tie-Tags with the Tag information of itself and its peer (see
 * section 5.2.2 for a description of the Tie-Tags).
 *
 * Verification Tag: Not explicit, but an INIT can not have a valid
 * verification tag, so we skip the check.
 *
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_do_5_2_1_siminit(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Handle duplicated INIT messages.  These are usually delayed
 * restransmissions.
 *
 * Section: 5.2.2 Unexpected INIT in States Other than CLOSED,
 * COOKIE-ECHOED and COOKIE-WAIT
 *
 * Unless otherwise stated, upon reception of an unexpected INIT for
 * this association, the endpoint shall generate an INIT ACK with a
 * State Cookie.  In the outbound INIT ACK the endpoint MUST copy its
 * current Verification Tag and peer's Verification Tag into a reserved
 * place within the state cookie.  We shall refer to these locations as
 * the Peer's-Tie-Tag and the Local-Tie-Tag.  The outbound SCTP packet
 * containing this INIT ACK MUST carry a Verification Tag value equal to
 * the Initiation Tag found in the unexpected INIT.  And the INIT ACK
 * MUST contain a new Initiation Tag (randomly generated see Section
 * 5.3.1).  Other parameters for the endpoint SHOULD be copied from the
 * existing parameters of the association (e.g. number of outbound
 * streams) into the INIT ACK and cookie.
 *
 * After sending out the INIT ACK, the endpoint shall take no further
 * actions, i.e., the existing association, including its current state,
 * and the corresponding TCB MUST NOT be changed.
 *
 * Note: Only when a TCB exists and the association is not in a COOKIE-
 * WAIT state are the Tie-Tags populated.  For a normal association INIT
 * (i.e. the endpoint is in a COOKIE-WAIT state), the Tie-Tags MUST be
 * set to 0 (indicating that no previous TCB existed).  The INIT ACK and
 * State Cookie are populated as specified in section 5.2.1.
 *
 * Verification Tag: Not specified, but an INIT has no way of knowing
 * what the verification tag could be, so we ignore it.
 *
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_do_5_2_2_dupinit(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }


/*
 * Unexpected INIT-ACK handler.
 *
 * Section 5.2.3
 * If an INIT ACK received by an endpoint in any state other than the
 * COOKIE-WAIT state, the endpoint should discard the INIT ACK chunk.
 * An unexpected INIT ACK usually indicates the processing of an old or
 * duplicated INIT chunk.
*/
enum sctp_disposition sctp_sf_do_5_2_3_initack(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

static int sctp_sf_do_assoc_update(struct sctp_association *asoc,
				   struct sctp_association *new,
				   struct sctp_cmd_seq *cmds)
{ … }

/* Unexpected COOKIE-ECHO handler for peer restart (Table 2, action 'A')
 *
 * Section 5.2.4
 *  A)  In this case, the peer may have restarted.
 */
static enum sctp_disposition sctp_sf_do_dupcook_a(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					struct sctp_chunk *chunk,
					struct sctp_cmd_seq *commands,
					struct sctp_association *new_asoc)
{ … }

/* Unexpected COOKIE-ECHO handler for setup collision (Table 2, action 'B')
 *
 * Section 5.2.4
 *   B) In this case, both sides may be attempting to start an association
 *      at about the same time but the peer endpoint started its INIT
 *      after responding to the local endpoint's INIT
 */
/* This case represents an initialization collision.  */
static enum sctp_disposition sctp_sf_do_dupcook_b(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					struct sctp_chunk *chunk,
					struct sctp_cmd_seq *commands,
					struct sctp_association *new_asoc)
{ … }

/* Unexpected COOKIE-ECHO handler for setup collision (Table 2, action 'C')
 *
 * Section 5.2.4
 *  C) In this case, the local endpoint's cookie has arrived late.
 *     Before it arrived, the local endpoint sent an INIT and received an
 *     INIT-ACK and finally sent a COOKIE ECHO with the peer's same tag
 *     but a new tag of its own.
 */
/* This case represents an initialization collision.  */
static enum sctp_disposition sctp_sf_do_dupcook_c(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					struct sctp_chunk *chunk,
					struct sctp_cmd_seq *commands,
					struct sctp_association *new_asoc)
{ … }

/* Unexpected COOKIE-ECHO handler lost chunk (Table 2, action 'D')
 *
 * Section 5.2.4
 *
 * D) When both local and remote tags match the endpoint should always
 *    enter the ESTABLISHED state, if it has not already done so.
 */
/* This case represents an initialization collision.  */
static enum sctp_disposition sctp_sf_do_dupcook_d(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					struct sctp_chunk *chunk,
					struct sctp_cmd_seq *commands,
					struct sctp_association *new_asoc)
{ … }

/*
 * Handle a duplicate COOKIE-ECHO.  This usually means a cookie-carrying
 * chunk was retransmitted and then delayed in the network.
 *
 * Section: 5.2.4 Handle a COOKIE ECHO when a TCB exists
 *
 * Verification Tag: None.  Do cookie validation.
 *
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_do_5_2_4_dupcook(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Process an ABORT.  (SHUTDOWN-PENDING state)
 *
 * See sctp_sf_do_9_1_abort().
 */
enum sctp_disposition sctp_sf_shutdown_pending_abort(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Process an ABORT.  (SHUTDOWN-SENT state)
 *
 * See sctp_sf_do_9_1_abort().
 */
enum sctp_disposition sctp_sf_shutdown_sent_abort(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Process an ABORT.  (SHUTDOWN-ACK-SENT state)
 *
 * See sctp_sf_do_9_1_abort().
 */
enum sctp_disposition sctp_sf_shutdown_ack_sent_abort(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Handle an Error received in COOKIE_ECHOED state.
 *
 * Only handle the error type of stale COOKIE Error, the other errors will
 * be ignored.
 *
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_cookie_echoed_err(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Handle a Stale COOKIE Error
 *
 * Section: 5.2.6 Handle Stale COOKIE Error
 * If the association is in the COOKIE-ECHOED state, the endpoint may elect
 * one of the following three alternatives.
 * ...
 * 3) Send a new INIT chunk to the endpoint, adding a Cookie
 *    Preservative parameter requesting an extension to the lifetime of
 *    the State Cookie. When calculating the time extension, an
 *    implementation SHOULD use the RTT information measured based on the
 *    previous COOKIE ECHO / ERROR exchange, and should add no more
 *    than 1 second beyond the measured RTT, due to long State Cookie
 *    lifetimes making the endpoint more subject to a replay attack.
 *
 * Verification Tag:  Not explicit, but safe to ignore.
 *
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
static enum sctp_disposition sctp_sf_do_5_2_6_stale(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Process an ABORT.
 *
 * Section: 9.1
 * After checking the Verification Tag, the receiving endpoint shall
 * remove the association from its record, and shall report the
 * termination to its upper layer.
 *
 * Verification Tag: 8.5.1 Exceptions in Verification Tag Rules
 * B) Rules for packet carrying ABORT:
 *
 *  - The endpoint shall always fill in the Verification Tag field of the
 *    outbound packet with the destination endpoint's tag value if it
 *    is known.
 *
 *  - If the ABORT is sent in response to an OOTB packet, the endpoint
 *    MUST follow the procedure described in Section 8.4.
 *
 *  - The receiver MUST accept the packet if the Verification Tag
 *    matches either its own tag, OR the tag of its peer. Otherwise, the
 *    receiver MUST silently discard the packet and take no further
 *    action.
 *
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_do_9_1_abort(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

static enum sctp_disposition __sctp_sf_do_9_1_abort(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Process an ABORT.  (COOKIE-WAIT state)
 *
 * See sctp_sf_do_9_1_abort() above.
 */
enum sctp_disposition sctp_sf_cookie_wait_abort(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Process an incoming ICMP as an ABORT.  (COOKIE-WAIT state)
 */
enum sctp_disposition sctp_sf_cookie_wait_icmp_abort(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Process an ABORT.  (COOKIE-ECHOED state)
 */
enum sctp_disposition sctp_sf_cookie_echoed_abort(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Stop T1 timer and abort association with "INIT failed".
 *
 * This is common code called by several sctp_sf_*_abort() functions above.
 */
static enum sctp_disposition sctp_stop_t1_and_abort(
					struct net *net,
					struct sctp_cmd_seq *commands,
					__be16 error, int sk_err,
					const struct sctp_association *asoc,
					struct sctp_transport *transport)
{ … }

/*
 * sctp_sf_do_9_2_shut
 *
 * Section: 9.2
 * Upon the reception of the SHUTDOWN, the peer endpoint shall
 *  - enter the SHUTDOWN-RECEIVED state,
 *
 *  - stop accepting new data from its SCTP user
 *
 *  - verify, by checking the Cumulative TSN Ack field of the chunk,
 *    that all its outstanding DATA chunks have been received by the
 *    SHUTDOWN sender.
 *
 * Once an endpoint as reached the SHUTDOWN-RECEIVED state it MUST NOT
 * send a SHUTDOWN in response to a ULP request. And should discard
 * subsequent SHUTDOWN chunks.
 *
 * If there are still outstanding DATA chunks left, the SHUTDOWN
 * receiver shall continue to follow normal data transmission
 * procedures defined in Section 6 until all outstanding DATA chunks
 * are acknowledged; however, the SHUTDOWN receiver MUST NOT accept
 * new data from its SCTP user.
 *
 * Verification Tag:  8.5 Verification Tag [Normal verification]
 *
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_do_9_2_shutdown(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * sctp_sf_do_9_2_shut_ctsn
 *
 * Once an endpoint has reached the SHUTDOWN-RECEIVED state,
 * it MUST NOT send a SHUTDOWN in response to a ULP request.
 * The Cumulative TSN Ack of the received SHUTDOWN chunk
 * MUST be processed.
 */
enum sctp_disposition sctp_sf_do_9_2_shut_ctsn(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/* RFC 2960 9.2
 * If an endpoint is in SHUTDOWN-ACK-SENT state and receives an INIT chunk
 * (e.g., if the SHUTDOWN COMPLETE was lost) with source and destination
 * transport addresses (either in the IP addresses or in the INIT chunk)
 * that belong to this association, it should discard the INIT chunk and
 * retransmit the SHUTDOWN ACK chunk.
 */
static enum sctp_disposition
__sctp_sf_do_9_2_reshutack(struct net *net, const struct sctp_endpoint *ep,
			   const struct sctp_association *asoc,
			   const union sctp_subtype type, void *arg,
			   struct sctp_cmd_seq *commands)
{ … }

enum sctp_disposition
sctp_sf_do_9_2_reshutack(struct net *net, const struct sctp_endpoint *ep,
			 const struct sctp_association *asoc,
			 const union sctp_subtype type, void *arg,
			 struct sctp_cmd_seq *commands)
{ … }

/*
 * sctp_sf_do_ecn_cwr
 *
 * Section:  Appendix A: Explicit Congestion Notification
 *
 * CWR:
 *
 * RFC 2481 details a specific bit for a sender to send in the header of
 * its next outbound TCP segment to indicate to its peer that it has
 * reduced its congestion window.  This is termed the CWR bit.  For
 * SCTP the same indication is made by including the CWR chunk.
 * This chunk contains one data element, i.e. the TSN number that
 * was sent in the ECNE chunk.  This element represents the lowest
 * TSN number in the datagram that was originally marked with the
 * CE bit.
 *
 * Verification Tag: 8.5 Verification Tag [Normal verification]
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_do_ecn_cwr(struct net *net,
					 const struct sctp_endpoint *ep,
					 const struct sctp_association *asoc,
					 const union sctp_subtype type,
					 void *arg,
					 struct sctp_cmd_seq *commands)
{ … }

/*
 * sctp_sf_do_ecne
 *
 * Section:  Appendix A: Explicit Congestion Notification
 *
 * ECN-Echo
 *
 * RFC 2481 details a specific bit for a receiver to send back in its
 * TCP acknowledgements to notify the sender of the Congestion
 * Experienced (CE) bit having arrived from the network.  For SCTP this
 * same indication is made by including the ECNE chunk.  This chunk
 * contains one data element, i.e. the lowest TSN associated with the IP
 * datagram marked with the CE bit.....
 *
 * Verification Tag: 8.5 Verification Tag [Normal verification]
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_do_ecne(struct net *net,
				      const struct sctp_endpoint *ep,
				      const struct sctp_association *asoc,
				      const union sctp_subtype type,
				      void *arg, struct sctp_cmd_seq *commands)
{ … }

/*
 * Section: 6.2  Acknowledgement on Reception of DATA Chunks
 *
 * The SCTP endpoint MUST always acknowledge the reception of each valid
 * DATA chunk.
 *
 * The guidelines on delayed acknowledgement algorithm specified in
 * Section 4.2 of [RFC2581] SHOULD be followed. Specifically, an
 * acknowledgement SHOULD be generated for at least every second packet
 * (not every second DATA chunk) received, and SHOULD be generated within
 * 200 ms of the arrival of any unacknowledged DATA chunk. In some
 * situations it may be beneficial for an SCTP transmitter to be more
 * conservative than the algorithms detailed in this document allow.
 * However, an SCTP transmitter MUST NOT be more aggressive than the
 * following algorithms allow.
 *
 * A SCTP receiver MUST NOT generate more than one SACK for every
 * incoming packet, other than to update the offered window as the
 * receiving application consumes new data.
 *
 * Verification Tag:  8.5 Verification Tag [Normal verification]
 *
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_eat_data_6_2(struct net *net,
					   const struct sctp_endpoint *ep,
					   const struct sctp_association *asoc,
					   const union sctp_subtype type,
					   void *arg,
					   struct sctp_cmd_seq *commands)
{ … }

/*
 * sctp_sf_eat_data_fast_4_4
 *
 * Section: 4 (4)
 * (4) In SHUTDOWN-SENT state the endpoint MUST acknowledge any received
 *    DATA chunks without delay.
 *
 * Verification Tag:  8.5 Verification Tag [Normal verification]
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_eat_data_fast_4_4(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Section: 6.2  Processing a Received SACK
 * D) Any time a SACK arrives, the endpoint performs the following:
 *
 *     i) If Cumulative TSN Ack is less than the Cumulative TSN Ack Point,
 *     then drop the SACK.   Since Cumulative TSN Ack is monotonically
 *     increasing, a SACK whose Cumulative TSN Ack is less than the
 *     Cumulative TSN Ack Point indicates an out-of-order SACK.
 *
 *     ii) Set rwnd equal to the newly received a_rwnd minus the number
 *     of bytes still outstanding after processing the Cumulative TSN Ack
 *     and the Gap Ack Blocks.
 *
 *     iii) If the SACK is missing a TSN that was previously
 *     acknowledged via a Gap Ack Block (e.g., the data receiver
 *     reneged on the data), then mark the corresponding DATA chunk
 *     as available for retransmit:  Mark it as missing for fast
 *     retransmit as described in Section 7.2.4 and if no retransmit
 *     timer is running for the destination address to which the DATA
 *     chunk was originally transmitted, then T3-rtx is started for
 *     that destination address.
 *
 * Verification Tag:  8.5 Verification Tag [Normal verification]
 *
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_eat_sack_6_2(struct net *net,
					   const struct sctp_endpoint *ep,
					   const struct sctp_association *asoc,
					   const union sctp_subtype type,
					   void *arg,
					   struct sctp_cmd_seq *commands)
{ … }

/*
 * Generate an ABORT in response to a packet.
 *
 * Section: 8.4 Handle "Out of the blue" Packets, sctpimpguide 2.41
 *
 * 8) The receiver should respond to the sender of the OOTB packet with
 *    an ABORT.  When sending the ABORT, the receiver of the OOTB packet
 *    MUST fill in the Verification Tag field of the outbound packet
 *    with the value found in the Verification Tag field of the OOTB
 *    packet and set the T-bit in the Chunk Flags to indicate that the
 *    Verification Tag is reflected.  After sending this ABORT, the
 *    receiver of the OOTB packet shall discard the OOTB packet and take
 *    no further action.
 *
 * Verification Tag:
 *
 * The return value is the disposition of the chunk.
*/
static enum sctp_disposition sctp_sf_tabort_8_4_8(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/* Handling of SCTP Packets Containing an INIT Chunk Matching an
 * Existing Associations when the UDP encap port is incorrect.
 *
 * From Section 4 at draft-tuexen-tsvwg-sctp-udp-encaps-cons-03.
 */
static enum sctp_disposition sctp_sf_new_encap_port(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Received an ERROR chunk from peer.  Generate SCTP_REMOTE_ERROR
 * event as ULP notification for each cause included in the chunk.
 *
 * API 5.3.1.3 - SCTP_REMOTE_ERROR
 *
 * The return value is the disposition of the chunk.
*/
enum sctp_disposition sctp_sf_operr_notify(struct net *net,
					   const struct sctp_endpoint *ep,
					   const struct sctp_association *asoc,
					   const union sctp_subtype type,
					   void *arg,
					   struct sctp_cmd_seq *commands)
{ … }

/*
 * Process an inbound SHUTDOWN ACK.
 *
 * From Section 9.2:
 * Upon the receipt of the SHUTDOWN ACK, the SHUTDOWN sender shall
 * stop the T2-shutdown timer, send a SHUTDOWN COMPLETE chunk to its
 * peer, and remove all record of the association.
 *
 * The return value is the disposition.
 */
enum sctp_disposition sctp_sf_do_9_2_final(struct net *net,
					   const struct sctp_endpoint *ep,
					   const struct sctp_association *asoc,
					   const union sctp_subtype type,
					   void *arg,
					   struct sctp_cmd_seq *commands)
{ … }

/*
 * RFC 2960, 8.4 - Handle "Out of the blue" Packets, sctpimpguide 2.41.
 *
 * 5) If the packet contains a SHUTDOWN ACK chunk, the receiver should
 *    respond to the sender of the OOTB packet with a SHUTDOWN COMPLETE.
 *    When sending the SHUTDOWN COMPLETE, the receiver of the OOTB
 *    packet must fill in the Verification Tag field of the outbound
 *    packet with the Verification Tag received in the SHUTDOWN ACK and
 *    set the T-bit in the Chunk Flags to indicate that the Verification
 *    Tag is reflected.
 *
 * 8) The receiver should respond to the sender of the OOTB packet with
 *    an ABORT.  When sending the ABORT, the receiver of the OOTB packet
 *    MUST fill in the Verification Tag field of the outbound packet
 *    with the value found in the Verification Tag field of the OOTB
 *    packet and set the T-bit in the Chunk Flags to indicate that the
 *    Verification Tag is reflected.  After sending this ABORT, the
 *    receiver of the OOTB packet shall discard the OOTB packet and take
 *    no further action.
 */
enum sctp_disposition sctp_sf_ootb(struct net *net,
				   const struct sctp_endpoint *ep,
				   const struct sctp_association *asoc,
				   const union sctp_subtype type,
				   void *arg, struct sctp_cmd_seq *commands)
{ … }

/*
 * Handle an "Out of the blue" SHUTDOWN ACK.
 *
 * Section: 8.4 5, sctpimpguide 2.41.
 *
 * 5) If the packet contains a SHUTDOWN ACK chunk, the receiver should
 *    respond to the sender of the OOTB packet with a SHUTDOWN COMPLETE.
 *    When sending the SHUTDOWN COMPLETE, the receiver of the OOTB
 *    packet must fill in the Verification Tag field of the outbound
 *    packet with the Verification Tag received in the SHUTDOWN ACK and
 *    set the T-bit in the Chunk Flags to indicate that the Verification
 *    Tag is reflected.
 *
 * Inputs
 * (endpoint, asoc, type, arg, commands)
 *
 * Outputs
 * (enum sctp_disposition)
 *
 * The return value is the disposition of the chunk.
 */
static enum sctp_disposition sctp_sf_shut_8_4_5(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Handle SHUTDOWN ACK in COOKIE_ECHOED or COOKIE_WAIT state.
 *
 * Verification Tag:  8.5.1 E) Rules for packet carrying a SHUTDOWN ACK
 *   If the receiver is in COOKIE-ECHOED or COOKIE-WAIT state the
 *   procedures in section 8.4 SHOULD be followed, in other words it
 *   should be treated as an Out Of The Blue packet.
 *   [This means that we do NOT check the Verification Tag on these
 *   chunks. --piggy ]
 *
 */
enum sctp_disposition sctp_sf_do_8_5_1_E_sa(struct net *net,
					    const struct sctp_endpoint *ep,
					    const struct sctp_association *asoc,
					    const union sctp_subtype type,
					    void *arg,
					    struct sctp_cmd_seq *commands)
{ … }

/* ADDIP Section 4.2 Upon reception of an ASCONF Chunk.  */
enum sctp_disposition sctp_sf_do_asconf(struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

static enum sctp_disposition sctp_send_next_asconf(
					struct net *net,
					const struct sctp_endpoint *ep,
					struct sctp_association *asoc,
					const union sctp_subtype type,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * ADDIP Section 4.3 General rules for address manipulation
 * When building TLV parameters for the ASCONF Chunk that will add or
 * delete IP addresses the D0 to D13 rules should be applied:
 */
enum sctp_disposition sctp_sf_do_asconf_ack(struct net *net,
					    const struct sctp_endpoint *ep,
					    const struct sctp_association *asoc,
					    const union sctp_subtype type,
					    void *arg,
					    struct sctp_cmd_seq *commands)
{ … }

/* RE-CONFIG Section 5.2 Upon reception of an RECONF Chunk. */
enum sctp_disposition sctp_sf_do_reconf(struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * PR-SCTP Section 3.6 Receiver Side Implementation of PR-SCTP
 *
 * When a FORWARD TSN chunk arrives, the data receiver MUST first update
 * its cumulative TSN point to the value carried in the FORWARD TSN
 * chunk, and then MUST further advance its cumulative TSN point locally
 * if possible.
 * After the above processing, the data receiver MUST stop reporting any
 * missing TSNs earlier than or equal to the new cumulative TSN point.
 *
 * Verification Tag:  8.5 Verification Tag [Normal verification]
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_eat_fwd_tsn(struct net *net,
					  const struct sctp_endpoint *ep,
					  const struct sctp_association *asoc,
					  const union sctp_subtype type,
					  void *arg,
					  struct sctp_cmd_seq *commands)
{ … }

enum sctp_disposition sctp_sf_eat_fwd_tsn_fast(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * SCTP-AUTH Section 6.3 Receiving authenticated chunks
 *
 *    The receiver MUST use the HMAC algorithm indicated in the HMAC
 *    Identifier field.  If this algorithm was not specified by the
 *    receiver in the HMAC-ALGO parameter in the INIT or INIT-ACK chunk
 *    during association setup, the AUTH chunk and all chunks after it MUST
 *    be discarded and an ERROR chunk SHOULD be sent with the error cause
 *    defined in Section 4.1.
 *
 *    If an endpoint with no shared key receives a Shared Key Identifier
 *    other than 0, it MUST silently discard all authenticated chunks.  If
 *    the endpoint has at least one endpoint pair shared key for the peer,
 *    it MUST use the key specified by the Shared Key Identifier if a
 *    key has been configured for that Shared Key Identifier.  If no
 *    endpoint pair shared key has been configured for that Shared Key
 *    Identifier, all authenticated chunks MUST be silently discarded.
 *
 * Verification Tag:  8.5 Verification Tag [Normal verification]
 *
 * The return value is the disposition of the chunk.
 */
static enum sctp_ierror sctp_sf_authenticate(
					const struct sctp_association *asoc,
					struct sctp_chunk *chunk)
{ … }

enum sctp_disposition sctp_sf_eat_auth(struct net *net,
				       const struct sctp_endpoint *ep,
				       const struct sctp_association *asoc,
				       const union sctp_subtype type,
				       void *arg, struct sctp_cmd_seq *commands)
{ … }

/*
 * Process an unknown chunk.
 *
 * Section: 3.2. Also, 2.1 in the implementor's guide.
 *
 * Chunk Types are encoded such that the highest-order two bits specify
 * the action that must be taken if the processing endpoint does not
 * recognize the Chunk Type.
 *
 * 00 - Stop processing this SCTP packet and discard it, do not process
 *      any further chunks within it.
 *
 * 01 - Stop processing this SCTP packet and discard it, do not process
 *      any further chunks within it, and report the unrecognized
 *      chunk in an 'Unrecognized Chunk Type'.
 *
 * 10 - Skip this chunk and continue processing.
 *
 * 11 - Skip this chunk and continue processing, but report in an ERROR
 *      Chunk using the 'Unrecognized Chunk Type' cause of error.
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_unk_chunk(struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Discard the chunk.
 *
 * Section: 0.2, 5.2.3, 5.2.5, 5.2.6, 6.0, 8.4.6, 8.5.1c, 9.2
 * [Too numerous to mention...]
 * Verification Tag: No verification needed.
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_discard_chunk(struct net *net,
					    const struct sctp_endpoint *ep,
					    const struct sctp_association *asoc,
					    const union sctp_subtype type,
					    void *arg,
					    struct sctp_cmd_seq *commands)
{ … }

/*
 * Discard the whole packet.
 *
 * Section: 8.4 2)
 *
 * 2) If the OOTB packet contains an ABORT chunk, the receiver MUST
 *    silently discard the OOTB packet and take no further action.
 *
 * Verification Tag: No verification necessary
 *
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_pdiscard(struct net *net,
				       const struct sctp_endpoint *ep,
				       const struct sctp_association *asoc,
				       const union sctp_subtype type,
				       void *arg, struct sctp_cmd_seq *commands)
{ … }


/*
 * The other end is violating protocol.
 *
 * Section: Not specified
 * Verification Tag: Not specified
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * We simply tag the chunk as a violation.  The state machine will log
 * the violation and continue.
 */
enum sctp_disposition sctp_sf_violation(struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Common function to handle a protocol violation.
 */
static enum sctp_disposition sctp_sf_abort_violation(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					void *arg,
					struct sctp_cmd_seq *commands,
					const __u8 *payload,
					const size_t paylen)
{ … }

/*
 * Handle a protocol violation when the chunk length is invalid.
 * "Invalid" length is identified as smaller than the minimal length a
 * given chunk can be.  For example, a SACK chunk has invalid length
 * if its length is set to be smaller than the size of struct sctp_sack_chunk.
 *
 * We inform the other end by sending an ABORT with a Protocol Violation
 * error code.
 *
 * Section: Not specified
 * Verification Tag:  Nothing to do
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (reply_msg, msg_up, counters)
 *
 * Generate an  ABORT chunk and terminate the association.
 */
static enum sctp_disposition sctp_sf_violation_chunklen(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Handle a protocol violation when the parameter length is invalid.
 * If the length is smaller than the minimum length of a given parameter,
 * or accumulated length in multi parameters exceeds the end of the chunk,
 * the length is considered as invalid.
 */
static enum sctp_disposition sctp_sf_violation_paramlen(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg, void *ext,
					struct sctp_cmd_seq *commands)
{ … }

/* Handle a protocol violation when the peer trying to advance the
 * cumulative tsn ack to a point beyond the max tsn currently sent.
 *
 * We inform the other end by sending an ABORT with a Protocol Violation
 * error code.
 */
static enum sctp_disposition sctp_sf_violation_ctsn(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/* Handle protocol violation of an invalid chunk bundling.  For example,
 * when we have an association and we receive bundled INIT-ACK, or
 * SHUTDOWN-COMPLETE, our peer is clearly violating the "MUST NOT bundle"
 * statement from the specs.  Additionally, there might be an attacker
 * on the path and we may not want to continue this communication.
 */
static enum sctp_disposition sctp_sf_violation_chunk(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }
/***************************************************************************
 * These are the state functions for handling primitive (Section 10) events.
 ***************************************************************************/
/*
 * sctp_sf_do_prm_asoc
 *
 * Section: 10.1 ULP-to-SCTP
 * B) Associate
 *
 * Format: ASSOCIATE(local SCTP instance name, destination transport addr,
 * outbound stream count)
 * -> association id [,destination transport addr list] [,outbound stream
 * count]
 *
 * This primitive allows the upper layer to initiate an association to a
 * specific peer endpoint.
 *
 * The peer endpoint shall be specified by one of the transport addresses
 * which defines the endpoint (see Section 1.4).  If the local SCTP
 * instance has not been initialized, the ASSOCIATE is considered an
 * error.
 * [This is not relevant for the kernel implementation since we do all
 * initialization at boot time.  It we hadn't initialized we wouldn't
 * get anywhere near this code.]
 *
 * An association id, which is a local handle to the SCTP association,
 * will be returned on successful establishment of the association. If
 * SCTP is not able to open an SCTP association with the peer endpoint,
 * an error is returned.
 * [In the kernel implementation, the struct sctp_association needs to
 * be created BEFORE causing this primitive to run.]
 *
 * Other association parameters may be returned, including the
 * complete destination transport addresses of the peer as well as the
 * outbound stream count of the local endpoint. One of the transport
 * address from the returned destination addresses will be selected by
 * the local endpoint as default primary path for sending SCTP packets
 * to this peer.  The returned "destination transport addr list" can
 * be used by the ULP to change the default primary path or to force
 * sending a packet to a specific transport address.  [All of this
 * stuff happens when the INIT ACK arrives.  This is a NON-BLOCKING
 * function.]
 *
 * Mandatory attributes:
 *
 * o local SCTP instance name - obtained from the INITIALIZE operation.
 *   [This is the argument asoc.]
 * o destination transport addr - specified as one of the transport
 * addresses of the peer endpoint with which the association is to be
 * established.
 *  [This is asoc->peer.active_path.]
 * o outbound stream count - the number of outbound streams the ULP
 * would like to open towards this peer endpoint.
 * [BUG: This is not currently implemented.]
 * Optional attributes:
 *
 * None.
 *
 * The return value is a disposition.
 */
enum sctp_disposition sctp_sf_do_prm_asoc(struct net *net,
					  const struct sctp_endpoint *ep,
					  const struct sctp_association *asoc,
					  const union sctp_subtype type,
					  void *arg,
					  struct sctp_cmd_seq *commands)
{ … }

/*
 * Process the SEND primitive.
 *
 * Section: 10.1 ULP-to-SCTP
 * E) Send
 *
 * Format: SEND(association id, buffer address, byte count [,context]
 *         [,stream id] [,life time] [,destination transport address]
 *         [,unorder flag] [,no-bundle flag] [,payload protocol-id] )
 * -> result
 *
 * This is the main method to send user data via SCTP.
 *
 * Mandatory attributes:
 *
 *  o association id - local handle to the SCTP association
 *
 *  o buffer address - the location where the user message to be
 *    transmitted is stored;
 *
 *  o byte count - The size of the user data in number of bytes;
 *
 * Optional attributes:
 *
 *  o context - an optional 32 bit integer that will be carried in the
 *    sending failure notification to the ULP if the transportation of
 *    this User Message fails.
 *
 *  o stream id - to indicate which stream to send the data on. If not
 *    specified, stream 0 will be used.
 *
 *  o life time - specifies the life time of the user data. The user data
 *    will not be sent by SCTP after the life time expires. This
 *    parameter can be used to avoid efforts to transmit stale
 *    user messages. SCTP notifies the ULP if the data cannot be
 *    initiated to transport (i.e. sent to the destination via SCTP's
 *    send primitive) within the life time variable. However, the
 *    user data will be transmitted if SCTP has attempted to transmit a
 *    chunk before the life time expired.
 *
 *  o destination transport address - specified as one of the destination
 *    transport addresses of the peer endpoint to which this packet
 *    should be sent. Whenever possible, SCTP should use this destination
 *    transport address for sending the packets, instead of the current
 *    primary path.
 *
 *  o unorder flag - this flag, if present, indicates that the user
 *    would like the data delivered in an unordered fashion to the peer
 *    (i.e., the U flag is set to 1 on all DATA chunks carrying this
 *    message).
 *
 *  o no-bundle flag - instructs SCTP not to bundle this user data with
 *    other outbound DATA chunks. SCTP MAY still bundle even when
 *    this flag is present, when faced with network congestion.
 *
 *  o payload protocol-id - A 32 bit unsigned integer that is to be
 *    passed to the peer indicating the type of payload protocol data
 *    being transmitted. This value is passed as opaque data by SCTP.
 *
 * The return value is the disposition.
 */
enum sctp_disposition sctp_sf_do_prm_send(struct net *net,
					  const struct sctp_endpoint *ep,
					  const struct sctp_association *asoc,
					  const union sctp_subtype type,
					  void *arg,
					  struct sctp_cmd_seq *commands)
{ … }

/*
 * Process the SHUTDOWN primitive.
 *
 * Section: 10.1:
 * C) Shutdown
 *
 * Format: SHUTDOWN(association id)
 * -> result
 *
 * Gracefully closes an association. Any locally queued user data
 * will be delivered to the peer. The association will be terminated only
 * after the peer acknowledges all the SCTP packets sent.  A success code
 * will be returned on successful termination of the association. If
 * attempting to terminate the association results in a failure, an error
 * code shall be returned.
 *
 * Mandatory attributes:
 *
 *  o association id - local handle to the SCTP association
 *
 * Optional attributes:
 *
 * None.
 *
 * The return value is the disposition.
 */
enum sctp_disposition sctp_sf_do_9_2_prm_shutdown(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Process the ABORT primitive.
 *
 * Section: 10.1:
 * C) Abort
 *
 * Format: Abort(association id [, cause code])
 * -> result
 *
 * Ungracefully closes an association. Any locally queued user data
 * will be discarded and an ABORT chunk is sent to the peer.  A success code
 * will be returned on successful abortion of the association. If
 * attempting to abort the association results in a failure, an error
 * code shall be returned.
 *
 * Mandatory attributes:
 *
 *  o association id - local handle to the SCTP association
 *
 * Optional attributes:
 *
 *  o cause code - reason of the abort to be passed to the peer
 *
 * None.
 *
 * The return value is the disposition.
 */
enum sctp_disposition sctp_sf_do_9_1_prm_abort(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/* We tried an illegal operation on an association which is closed.  */
enum sctp_disposition sctp_sf_error_closed(struct net *net,
					   const struct sctp_endpoint *ep,
					   const struct sctp_association *asoc,
					   const union sctp_subtype type,
					   void *arg,
					   struct sctp_cmd_seq *commands)
{ … }

/* We tried an illegal operation on an association which is shutting
 * down.
 */
enum sctp_disposition sctp_sf_error_shutdown(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * sctp_cookie_wait_prm_shutdown
 *
 * Section: 4 Note: 2
 * Verification Tag:
 * Inputs
 * (endpoint, asoc)
 *
 * The RFC does not explicitly address this issue, but is the route through the
 * state table when someone issues a shutdown while in COOKIE_WAIT state.
 *
 * Outputs
 * (timers)
 */
enum sctp_disposition sctp_sf_cookie_wait_prm_shutdown(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * sctp_cookie_echoed_prm_shutdown
 *
 * Section: 4 Note: 2
 * Verification Tag:
 * Inputs
 * (endpoint, asoc)
 *
 * The RFC does not explicitly address this issue, but is the route through the
 * state table when someone issues a shutdown while in COOKIE_ECHOED state.
 *
 * Outputs
 * (timers)
 */
enum sctp_disposition sctp_sf_cookie_echoed_prm_shutdown(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * sctp_sf_cookie_wait_prm_abort
 *
 * Section: 4 Note: 2
 * Verification Tag:
 * Inputs
 * (endpoint, asoc)
 *
 * The RFC does not explicitly address this issue, but is the route through the
 * state table when someone issues an abort while in COOKIE_WAIT state.
 *
 * Outputs
 * (timers)
 */
enum sctp_disposition sctp_sf_cookie_wait_prm_abort(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * sctp_sf_cookie_echoed_prm_abort
 *
 * Section: 4 Note: 3
 * Verification Tag:
 * Inputs
 * (endpoint, asoc)
 *
 * The RFC does not explcitly address this issue, but is the route through the
 * state table when someone issues an abort while in COOKIE_ECHOED state.
 *
 * Outputs
 * (timers)
 */
enum sctp_disposition sctp_sf_cookie_echoed_prm_abort(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * sctp_sf_shutdown_pending_prm_abort
 *
 * Inputs
 * (endpoint, asoc)
 *
 * The RFC does not explicitly address this issue, but is the route through the
 * state table when someone issues an abort while in SHUTDOWN-PENDING state.
 *
 * Outputs
 * (timers)
 */
enum sctp_disposition sctp_sf_shutdown_pending_prm_abort(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * sctp_sf_shutdown_sent_prm_abort
 *
 * Inputs
 * (endpoint, asoc)
 *
 * The RFC does not explicitly address this issue, but is the route through the
 * state table when someone issues an abort while in SHUTDOWN-SENT state.
 *
 * Outputs
 * (timers)
 */
enum sctp_disposition sctp_sf_shutdown_sent_prm_abort(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * sctp_sf_cookie_echoed_prm_abort
 *
 * Inputs
 * (endpoint, asoc)
 *
 * The RFC does not explcitly address this issue, but is the route through the
 * state table when someone issues an abort while in COOKIE_ECHOED state.
 *
 * Outputs
 * (timers)
 */
enum sctp_disposition sctp_sf_shutdown_ack_sent_prm_abort(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Process the REQUESTHEARTBEAT primitive
 *
 * 10.1 ULP-to-SCTP
 * J) Request Heartbeat
 *
 * Format: REQUESTHEARTBEAT(association id, destination transport address)
 *
 * -> result
 *
 * Instructs the local endpoint to perform a HeartBeat on the specified
 * destination transport address of the given association. The returned
 * result should indicate whether the transmission of the HEARTBEAT
 * chunk to the destination address is successful.
 *
 * Mandatory attributes:
 *
 * o association id - local handle to the SCTP association
 *
 * o destination transport address - the transport address of the
 *   association on which a heartbeat should be issued.
 */
enum sctp_disposition sctp_sf_do_prm_requestheartbeat(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * ADDIP Section 4.1 ASCONF Chunk Procedures
 * When an endpoint has an ASCONF signaled change to be sent to the
 * remote endpoint it should do A1 to A9
 */
enum sctp_disposition sctp_sf_do_prm_asconf(struct net *net,
					    const struct sctp_endpoint *ep,
					    const struct sctp_association *asoc,
					    const union sctp_subtype type,
					    void *arg,
					    struct sctp_cmd_seq *commands)
{ … }

/* RE-CONFIG Section 5.1 RECONF Chunk Procedures */
enum sctp_disposition sctp_sf_do_prm_reconf(struct net *net,
					    const struct sctp_endpoint *ep,
					    const struct sctp_association *asoc,
					    const union sctp_subtype type,
					    void *arg,
					    struct sctp_cmd_seq *commands)
{ … }

/*
 * Ignore the primitive event
 *
 * The return value is the disposition of the primitive.
 */
enum sctp_disposition sctp_sf_ignore_primitive(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/***************************************************************************
 * These are the state functions for the OTHER events.
 ***************************************************************************/

/*
 * When the SCTP stack has no more user data to send or retransmit, this
 * notification is given to the user. Also, at the time when a user app
 * subscribes to this event, if there is no data to be sent or
 * retransmit, the stack will immediately send up this notification.
 */
enum sctp_disposition sctp_sf_do_no_pending_tsn(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Start the shutdown negotiation.
 *
 * From Section 9.2:
 * Once all its outstanding data has been acknowledged, the endpoint
 * shall send a SHUTDOWN chunk to its peer including in the Cumulative
 * TSN Ack field the last sequential TSN it has received from the peer.
 * It shall then start the T2-shutdown timer and enter the SHUTDOWN-SENT
 * state. If the timer expires, the endpoint must re-send the SHUTDOWN
 * with the updated last sequential TSN received from its peer.
 *
 * The return value is the disposition.
 */
enum sctp_disposition sctp_sf_do_9_2_start_shutdown(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Generate a SHUTDOWN ACK now that everything is SACK'd.
 *
 * From Section 9.2:
 *
 * If it has no more outstanding DATA chunks, the SHUTDOWN receiver
 * shall send a SHUTDOWN ACK and start a T2-shutdown timer of its own,
 * entering the SHUTDOWN-ACK-SENT state. If the timer expires, the
 * endpoint must re-send the SHUTDOWN ACK.
 *
 * The return value is the disposition.
 */
enum sctp_disposition sctp_sf_do_9_2_shutdown_ack(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * Ignore the event defined as other
 *
 * The return value is the disposition of the event.
 */
enum sctp_disposition sctp_sf_ignore_other(struct net *net,
					   const struct sctp_endpoint *ep,
					   const struct sctp_association *asoc,
					   const union sctp_subtype type,
					   void *arg,
					   struct sctp_cmd_seq *commands)
{ … }

/************************************************************
 * These are the state functions for handling timeout events.
 ************************************************************/

/*
 * RTX Timeout
 *
 * Section: 6.3.3 Handle T3-rtx Expiration
 *
 * Whenever the retransmission timer T3-rtx expires for a destination
 * address, do the following:
 * [See below]
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_do_6_3_3_rtx(struct net *net,
					   const struct sctp_endpoint *ep,
					   const struct sctp_association *asoc,
					   const union sctp_subtype type,
					   void *arg,
					   struct sctp_cmd_seq *commands)
{ … }

/*
 * Generate delayed SACK on timeout
 *
 * Section: 6.2  Acknowledgement on Reception of DATA Chunks
 *
 * The guidelines on delayed acknowledgement algorithm specified in
 * Section 4.2 of [RFC2581] SHOULD be followed.  Specifically, an
 * acknowledgement SHOULD be generated for at least every second packet
 * (not every second DATA chunk) received, and SHOULD be generated
 * within 200 ms of the arrival of any unacknowledged DATA chunk.  In
 * some situations it may be beneficial for an SCTP transmitter to be
 * more conservative than the algorithms detailed in this document
 * allow. However, an SCTP transmitter MUST NOT be more aggressive than
 * the following algorithms allow.
 */
enum sctp_disposition sctp_sf_do_6_2_sack(struct net *net,
					  const struct sctp_endpoint *ep,
					  const struct sctp_association *asoc,
					  const union sctp_subtype type,
					  void *arg,
					  struct sctp_cmd_seq *commands)
{ … }

/*
 * sctp_sf_t1_init_timer_expire
 *
 * Section: 4 Note: 2
 * Verification Tag:
 * Inputs
 * (endpoint, asoc)
 *
 *  RFC 2960 Section 4 Notes
 *  2) If the T1-init timer expires, the endpoint MUST retransmit INIT
 *     and re-start the T1-init timer without changing state.  This MUST
 *     be repeated up to 'Max.Init.Retransmits' times.  After that, the
 *     endpoint MUST abort the initialization process and report the
 *     error to SCTP user.
 *
 * Outputs
 * (timers, events)
 *
 */
enum sctp_disposition sctp_sf_t1_init_timer_expire(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * sctp_sf_t1_cookie_timer_expire
 *
 * Section: 4 Note: 2
 * Verification Tag:
 * Inputs
 * (endpoint, asoc)
 *
 *  RFC 2960 Section 4 Notes
 *  3) If the T1-cookie timer expires, the endpoint MUST retransmit
 *     COOKIE ECHO and re-start the T1-cookie timer without changing
 *     state.  This MUST be repeated up to 'Max.Init.Retransmits' times.
 *     After that, the endpoint MUST abort the initialization process and
 *     report the error to SCTP user.
 *
 * Outputs
 * (timers, events)
 *
 */
enum sctp_disposition sctp_sf_t1_cookie_timer_expire(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/* RFC2960 9.2 If the timer expires, the endpoint must re-send the SHUTDOWN
 * with the updated last sequential TSN received from its peer.
 *
 * An endpoint should limit the number of retransmission of the
 * SHUTDOWN chunk to the protocol parameter 'Association.Max.Retrans'.
 * If this threshold is exceeded the endpoint should destroy the TCB and
 * MUST report the peer endpoint unreachable to the upper layer (and
 * thus the association enters the CLOSED state).  The reception of any
 * packet from its peer (i.e. as the peer sends all of its queued DATA
 * chunks) should clear the endpoint's retransmission count and restart
 * the T2-Shutdown timer,  giving its peer ample opportunity to transmit
 * all of its queued DATA chunks that have not yet been sent.
 */
enum sctp_disposition sctp_sf_t2_timer_expire(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*
 * ADDIP Section 4.1 ASCONF Chunk Procedures
 * If the T4 RTO timer expires the endpoint should do B1 to B5
 */
enum sctp_disposition sctp_sf_t4_timer_expire(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/* sctpimpguide-05 Section 2.12.2
 * The sender of the SHUTDOWN MAY also start an overall guard timer
 * 'T5-shutdown-guard' to bound the overall time for shutdown sequence.
 * At the expiration of this timer the sender SHOULD abort the association
 * by sending an ABORT chunk.
 */
enum sctp_disposition sctp_sf_t5_timer_expire(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/* Handle expiration of AUTOCLOSE timer.  When the autoclose timer expires,
 * the association is automatically closed by starting the shutdown process.
 * The work that needs to be done is same as when SHUTDOWN is initiated by
 * the user.  So this routine looks same as sctp_sf_do_9_2_prm_shutdown().
 */
enum sctp_disposition sctp_sf_autoclose_timer_expire(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const union sctp_subtype type,
					void *arg,
					struct sctp_cmd_seq *commands)
{ … }

/*****************************************************************************
 * These are sa state functions which could apply to all types of events.
 ****************************************************************************/

/*
 * This table entry is not implemented.
 *
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_not_impl(struct net *net,
				       const struct sctp_endpoint *ep,
				       const struct sctp_association *asoc,
				       const union sctp_subtype type,
				       void *arg, struct sctp_cmd_seq *commands)
{ … }

/*
 * This table entry represents a bug.
 *
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_bug(struct net *net,
				  const struct sctp_endpoint *ep,
				  const struct sctp_association *asoc,
				  const union sctp_subtype type,
				  void *arg, struct sctp_cmd_seq *commands)
{ … }

/*
 * This table entry represents the firing of a timer in the wrong state.
 * Since timer deletion cannot be guaranteed a timer 'may' end up firing
 * when the association is in the wrong state.   This event should
 * be ignored, so as to prevent any rearming of the timer.
 *
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * The return value is the disposition of the chunk.
 */
enum sctp_disposition sctp_sf_timer_ignore(struct net *net,
					   const struct sctp_endpoint *ep,
					   const struct sctp_association *asoc,
					   const union sctp_subtype type,
					   void *arg,
					   struct sctp_cmd_seq *commands)
{ … }

/********************************************************************
 * 2nd Level Abstractions
 ********************************************************************/

/* Pull the SACK chunk based on the SACK header. */
static struct sctp_sackhdr *sctp_sm_pull_sack(struct sctp_chunk *chunk)
{ … }

/* Create an ABORT packet to be sent as a response, with the specified
 * error causes.
 */
static struct sctp_packet *sctp_abort_pkt_new(
					struct net *net,
					const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					struct sctp_chunk *chunk,
					const void *payload, size_t paylen)
{ … }

/* Allocate a packet for responding in the OOTB conditions.  */
static struct sctp_packet *sctp_ootb_pkt_new(
					struct net *net,
					const struct sctp_association *asoc,
					const struct sctp_chunk *chunk)
{ … }

/* Free the packet allocated earlier for responding in the OOTB condition.  */
void sctp_ootb_pkt_free(struct sctp_packet *packet)
{ … }

/* Send a stale cookie error when a invalid COOKIE ECHO chunk is found  */
static void sctp_send_stale_cookie_err(struct net *net,
				       const struct sctp_endpoint *ep,
				       const struct sctp_association *asoc,
				       const struct sctp_chunk *chunk,
				       struct sctp_cmd_seq *commands,
				       struct sctp_chunk *err_chunk)
{ … }


/* Process a data chunk */
static int sctp_eat_data(const struct sctp_association *asoc,
			 struct sctp_chunk *chunk,
			 struct sctp_cmd_seq *commands)
{ … }