net/x25/x25_in.c - linux - Git at Google

 /*
  *	X.25 Packet Layer release 002
  *
  *	This is ALPHA test software. This code may break your machine,
  *	randomly fail to work with new releases, misbehave and/or generally
  *	screw up. It might even work.
  *
  *	This code REQUIRES 2.1.15 or higher
  *
  *	This module:
  *		This module is free software; you can redistribute it and/or
  *		modify it under the terms of the GNU General Public License
  *		as published by the Free Software Foundation; either version
  *		2 of the License, or (at your option) any later version.
  *
  *	History
  *	X.25 001	Jonathan Naylor	  Started coding.
  *	X.25 002	Jonathan Naylor	  Centralised disconnection code.
  *					  New timer architecture.
  *	2000-03-20	Daniela Squassoni Disabling/enabling of facilities
  *					  negotiation.
  *	2000-11-10	Henner Eisen	  Check and reset for out-of-sequence
  *					  i-frames.
  */

 #define pr_fmt(fmt) "X25: " fmt

 #include <linux/slab.h>
 #include <linux/errno.h>
 #include <linux/kernel.h>
 #include <linux/string.h>
 #include <linux/skbuff.h>
 #include <net/sock.h>
 #include <net/tcp_states.h>
 #include <net/x25.h>

 static int x25_queue_rx_frame(struct sock *sk, struct sk_buff *skb, int more)
 {
 	struct sk_buff *skbo, *skbn = skb;
 	struct x25_sock *x25 = x25_sk(sk);

 	if (more) {
 		x25->fraglen += skb->len;
 		skb_queue_tail(&x25->fragment_queue, skb);
 		skb_set_owner_r(skb, sk);
 		return 0;
 	}

 	if (!more && x25->fraglen > 0) {	/* End of fragment */
 		int len = x25->fraglen + skb->len;

 		if ((skbn = alloc_skb(len, GFP_ATOMIC)) == NULL){
 			kfree_skb(skb);
 			return 1;
 		}

 		skb_queue_tail(&x25->fragment_queue, skb);

 		skb_reset_transport_header(skbn);

 		skbo = skb_dequeue(&x25->fragment_queue);
 		skb_copy_from_linear_data(skbo, skb_put(skbn, skbo->len),
 					  skbo->len);
 		kfree_skb(skbo);

 		while ((skbo =
 			skb_dequeue(&x25->fragment_queue)) != NULL) {
 			skb_pull(skbo, (x25->neighbour->extended) ?
 					X25_EXT_MIN_LEN : X25_STD_MIN_LEN);
 			skb_copy_from_linear_data(skbo,
 						  skb_put(skbn, skbo->len),
 						  skbo->len);
 			kfree_skb(skbo);
 		}

 		x25->fraglen = 0;
 	}

 	skb_set_owner_r(skbn, sk);
 	skb_queue_tail(&sk->sk_receive_queue, skbn);
 	if (!sock_flag(sk, SOCK_DEAD))
 		sk->sk_data_ready(sk);

 	return 0;
 }

 /*
  * State machine for state 1, Awaiting Call Accepted State.
  * The handling of the timer(s) is in file x25_timer.c.
  * Handling of state 0 and connection release is in af_x25.c.
  */
 static int x25_state1_machine(struct sock *sk, struct sk_buff *skb, int frametype)
 {
 	struct x25_address source_addr, dest_addr;
 	int len;
 	struct x25_sock *x25 = x25_sk(sk);

 	switch (frametype) {
 	case X25_CALL_ACCEPTED: {

 		x25_stop_timer(sk);
 		x25->condition = 0x00;
 		x25->vs        = 0;
 		x25->va        = 0;
 		x25->vr        = 0;
 		x25->vl        = 0;
 		x25->state     = X25_STATE_3;
 		sk->sk_state   = TCP_ESTABLISHED;
 		/*
 		 *	Parse the data in the frame.
 		 */
 		if (!pskb_may_pull(skb, X25_STD_MIN_LEN))
 			goto out_clear;
 		skb_pull(skb, X25_STD_MIN_LEN);

 		len = x25_parse_address_block(skb, &source_addr,
 					      &dest_addr);
 		if (len > 0)
 			skb_pull(skb, len);
 		else if (len < 0)
 			goto out_clear;

 		len = x25_parse_facilities(skb, &x25->facilities,
 					   &x25->dte_facilities,
 					   &x25->vc_facil_mask);
 		if (len > 0)
 			skb_pull(skb, len);
 		else if (len < 0)
 			goto out_clear;
 		/*
 		 *	Copy any Call User Data.
 		 */
 		if (skb->len > 0) {
 			if (skb->len > X25_MAX_CUD_LEN)
 				goto out_clear;

 			skb_copy_bits(skb, 0, x25->calluserdata.cuddata,
 				skb->len);
 			x25->calluserdata.cudlength = skb->len;
 		}
 		if (!sock_flag(sk, SOCK_DEAD))
 			sk->sk_state_change(sk);
 		break;
 	}
 	case X25_CALL_REQUEST:
 		/* call collision */
 		x25->causediag.cause      = 0x01;
 		x25->causediag.diagnostic = 0x48;

 		x25_write_internal(sk, X25_CLEAR_REQUEST);
 		x25_disconnect(sk, EISCONN, 0x01, 0x48);
 		break;

 	case X25_CLEAR_REQUEST:
 		if (!pskb_may_pull(skb, X25_STD_MIN_LEN + 2))
 			goto out_clear;

 		x25_write_internal(sk, X25_CLEAR_CONFIRMATION);
 		x25_disconnect(sk, ECONNREFUSED, skb->data[3], skb->data[4]);
 		break;

 	default:
 		break;
 	}

 	return 0;

 out_clear:
 	x25_write_internal(sk, X25_CLEAR_REQUEST);
 	x25->state = X25_STATE_2;
 	x25_start_t23timer(sk);
 	return 0;
 }

 /*
  * State machine for state 2, Awaiting Clear Confirmation State.
  * The handling of the timer(s) is in file x25_timer.c
  * Handling of state 0 and connection release is in af_x25.c.
  */
 static int x25_state2_machine(struct sock *sk, struct sk_buff *skb, int frametype)
 {
 	switch (frametype) {

 		case X25_CLEAR_REQUEST:
 			if (!pskb_may_pull(skb, X25_STD_MIN_LEN + 2))
 				goto out_clear;

 			x25_write_internal(sk, X25_CLEAR_CONFIRMATION);
 			x25_disconnect(sk, 0, skb->data[3], skb->data[4]);
 			break;

 		case X25_CLEAR_CONFIRMATION:
 			x25_disconnect(sk, 0, 0, 0);
 			break;

 		default:
 			break;
 	}

 	return 0;

 out_clear:
 	x25_write_internal(sk, X25_CLEAR_REQUEST);
 	x25_start_t23timer(sk);
 	return 0;
 }

 /*
  * State machine for state 3, Connected State.
  * The handling of the timer(s) is in file x25_timer.c
  * Handling of state 0 and connection release is in af_x25.c.
  */
 static int x25_state3_machine(struct sock *sk, struct sk_buff *skb, int frametype, int ns, int nr, int q, int d, int m)
 {
 	int queued = 0;
 	int modulus;
 	struct x25_sock *x25 = x25_sk(sk);

 	modulus = (x25->neighbour->extended) ? X25_EMODULUS : X25_SMODULUS;

 	switch (frametype) {

 		case X25_RESET_REQUEST:
 			x25_write_internal(sk, X25_RESET_CONFIRMATION);
 			x25_stop_timer(sk);
 			x25->condition = 0x00;
 			x25->vs        = 0;
 			x25->vr        = 0;
 			x25->va        = 0;
 			x25->vl        = 0;
 			x25_requeue_frames(sk);
 			break;

 		case X25_CLEAR_REQUEST:
 			if (!pskb_may_pull(skb, X25_STD_MIN_LEN + 2))
 				goto out_clear;

 			x25_write_internal(sk, X25_CLEAR_CONFIRMATION);
 			x25_disconnect(sk, 0, skb->data[3], skb->data[4]);
 			break;

 		case X25_RR:
 		case X25_RNR:
 			if (!x25_validate_nr(sk, nr)) {
 				x25_clear_queues(sk);
 				x25_write_internal(sk, X25_RESET_REQUEST);
 				x25_start_t22timer(sk);
 				x25->condition = 0x00;
 				x25->vs        = 0;
 				x25->vr        = 0;
 				x25->va        = 0;
 				x25->vl        = 0;
 				x25->state     = X25_STATE_4;
 			} else {
 				x25_frames_acked(sk, nr);
 				if (frametype == X25_RNR) {
 					x25->condition |= X25_COND_PEER_RX_BUSY;
 				} else {
 					x25->condition &= ~X25_COND_PEER_RX_BUSY;
 				}
 			}
 			break;

 		case X25_DATA:	/* XXX */
 			x25->condition &= ~X25_COND_PEER_RX_BUSY;
 			if ((ns != x25->vr) || !x25_validate_nr(sk, nr)) {
 				x25_clear_queues(sk);
 				x25_write_internal(sk, X25_RESET_REQUEST);
 				x25_start_t22timer(sk);
 				x25->condition = 0x00;
 				x25->vs        = 0;
 				x25->vr        = 0;
 				x25->va        = 0;
 				x25->vl        = 0;
 				x25->state     = X25_STATE_4;
 				break;
 			}
 			x25_frames_acked(sk, nr);
 			if (ns == x25->vr) {
 				if (x25_queue_rx_frame(sk, skb, m) == 0) {
 					x25->vr = (x25->vr + 1) % modulus;
 					queued = 1;
 				} else {
 					/* Should never happen */
 					x25_clear_queues(sk);
 					x25_write_internal(sk, X25_RESET_REQUEST);
 					x25_start_t22timer(sk);
 					x25->condition = 0x00;
 					x25->vs        = 0;
 					x25->vr        = 0;
 					x25->va        = 0;
 					x25->vl        = 0;
 					x25->state     = X25_STATE_4;
 					break;
 				}
 				if (atomic_read(&sk->sk_rmem_alloc) >
 				    (sk->sk_rcvbuf >> 1))
 					x25->condition |= X25_COND_OWN_RX_BUSY;
 			}
 			/*
 			 *	If the window is full Ack it immediately, else
 			 *	start the holdback timer.
 			 */
 			if (((x25->vl + x25->facilities.winsize_in) % modulus) == x25->vr) {
 				x25->condition &= ~X25_COND_ACK_PENDING;
 				x25_stop_timer(sk);
 				x25_enquiry_response(sk);
 			} else {
 				x25->condition |= X25_COND_ACK_PENDING;
 				x25_start_t2timer(sk);
 			}
 			break;

 		case X25_INTERRUPT_CONFIRMATION:
 			clear_bit(X25_INTERRUPT_FLAG, &x25->flags);
 			break;

 		case X25_INTERRUPT:
 			if (sock_flag(sk, SOCK_URGINLINE))
 				queued = !sock_queue_rcv_skb(sk, skb);
 			else {
 				skb_set_owner_r(skb, sk);
 				skb_queue_tail(&x25->interrupt_in_queue, skb);
 				queued = 1;
 			}
 			sk_send_sigurg(sk);
 			x25_write_internal(sk, X25_INTERRUPT_CONFIRMATION);
 			break;

 		default:
 			pr_warn("unknown %02X in state 3\n", frametype);
 			break;
 	}

 	return queued;

 out_clear:
 	x25_write_internal(sk, X25_CLEAR_REQUEST);
 	x25->state = X25_STATE_2;
 	x25_start_t23timer(sk);
 	return 0;
 }

 /*
  * State machine for state 4, Awaiting Reset Confirmation State.
  * The handling of the timer(s) is in file x25_timer.c
  * Handling of state 0 and connection release is in af_x25.c.
  */
 static int x25_state4_machine(struct sock *sk, struct sk_buff *skb, int frametype)
 {
 	struct x25_sock *x25 = x25_sk(sk);

 	switch (frametype) {

 		case X25_RESET_REQUEST:
 			x25_write_internal(sk, X25_RESET_CONFIRMATION);
 			/* fall through */
 		case X25_RESET_CONFIRMATION: {
 			x25_stop_timer(sk);
 			x25->condition = 0x00;
 			x25->va        = 0;
 			x25->vr        = 0;
 			x25->vs        = 0;
 			x25->vl        = 0;
 			x25->state     = X25_STATE_3;
 			x25_requeue_frames(sk);
 			break;
 		}
 		case X25_CLEAR_REQUEST:
 			if (!pskb_may_pull(skb, X25_STD_MIN_LEN + 2))
 				goto out_clear;

 			x25_write_internal(sk, X25_CLEAR_CONFIRMATION);
 			x25_disconnect(sk, 0, skb->data[3], skb->data[4]);
 			break;

 		default:
 			break;
 	}

 	return 0;

 out_clear:
 	x25_write_internal(sk, X25_CLEAR_REQUEST);
 	x25->state = X25_STATE_2;
 	x25_start_t23timer(sk);
 	return 0;
 }

 /* Higher level upcall for a LAPB frame */
 int x25_process_rx_frame(struct sock *sk, struct sk_buff *skb)
 {
 	struct x25_sock *x25 = x25_sk(sk);
 	int queued = 0, frametype, ns, nr, q, d, m;

 	if (x25->state == X25_STATE_0)
 		return 0;

 	frametype = x25_decode(sk, skb, &ns, &nr, &q, &d, &m);

 	switch (x25->state) {
 	case X25_STATE_1:
 		queued = x25_state1_machine(sk, skb, frametype);
 		break;
 	case X25_STATE_2:
 		queued = x25_state2_machine(sk, skb, frametype);
 		break;
 	case X25_STATE_3:
 		queued = x25_state3_machine(sk, skb, frametype, ns, nr, q, d, m);
 		break;
 	case X25_STATE_4:
 		queued = x25_state4_machine(sk, skb, frametype);
 		break;
 	}

 	x25_kick(sk);

 	return queued;
 }

 int x25_backlog_rcv(struct sock *sk, struct sk_buff *skb)
 {
 	int queued = x25_process_rx_frame(sk, skb);

 	if (!queued)
 		kfree_skb(skb);

 	return 0;
 }
	/*
	* X.25 Packet Layer release 002
	*
	* This is ALPHA test software. This code may break your machine,
	* randomly fail to work with new releases, misbehave and/or generally
	* screw up. It might even work.
	*
	* This code REQUIRES 2.1.15 or higher
	*
	* This module:
	* This module is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License
	* as published by the Free Software Foundation; either version
	* 2 of the License, or (at your option) any later version.
	*
	* History
	* X.25 001 Jonathan Naylor Started coding.
	* X.25 002 Jonathan Naylor Centralised disconnection code.
	* New timer architecture.
	* 2000-03-20 Daniela Squassoni Disabling/enabling of facilities
	* negotiation.
	* 2000-11-10 Henner Eisen Check and reset for out-of-sequence
	* i-frames.
	*/

	#define pr_fmt(fmt) "X25: " fmt

	#include <linux/slab.h>
	#include <linux/errno.h>
	#include <linux/kernel.h>
	#include <linux/string.h>
	#include <linux/skbuff.h>
	#include <net/sock.h>
	#include <net/tcp_states.h>
	#include <net/x25.h>

	static int x25_queue_rx_frame(struct sock sk, struct sk_buff skb, int more)
	{
	struct sk_buff skbo, skbn = skb;
	struct x25_sock *x25 = x25_sk(sk);

	if (more) {
	x25->fraglen += skb->len;
	skb_queue_tail(&x25->fragment_queue, skb);
	skb_set_owner_r(skb, sk);
	return 0;
	}

	if (!more && x25->fraglen > 0) { /* End of fragment */
	int len = x25->fraglen + skb->len;

	if ((skbn = alloc_skb(len, GFP_ATOMIC)) == NULL){
	kfree_skb(skb);
	return 1;
	}

	skb_queue_tail(&x25->fragment_queue, skb);

	skb_reset_transport_header(skbn);

	skbo = skb_dequeue(&x25->fragment_queue);
	skb_copy_from_linear_data(skbo, skb_put(skbn, skbo->len),
	skbo->len);
	kfree_skb(skbo);

	while ((skbo =
	skb_dequeue(&x25->fragment_queue)) != NULL) {
	skb_pull(skbo, (x25->neighbour->extended) ?
	X25_EXT_MIN_LEN : X25_STD_MIN_LEN);
	skb_copy_from_linear_data(skbo,
	skb_put(skbn, skbo->len),
	skbo->len);
	kfree_skb(skbo);
	}

	x25->fraglen = 0;
	}

	skb_set_owner_r(skbn, sk);
	skb_queue_tail(&sk->sk_receive_queue, skbn);
	if (!sock_flag(sk, SOCK_DEAD))
	sk->sk_data_ready(sk);

	return 0;
	}

	/*
	* State machine for state 1, Awaiting Call Accepted State.
	* The handling of the timer(s) is in file x25_timer.c.
	* Handling of state 0 and connection release is in af_x25.c.
	*/
	static int x25_state1_machine(struct sock sk, struct sk_buff skb, int frametype)
	{
	struct x25_address source_addr, dest_addr;
	int len;
	struct x25_sock *x25 = x25_sk(sk);

	switch (frametype) {
	case X25_CALL_ACCEPTED: {

	x25_stop_timer(sk);
	x25->condition = 0x00;
	x25->vs = 0;
	x25->va = 0;
	x25->vr = 0;
	x25->vl = 0;
	x25->state = X25_STATE_3;
	sk->sk_state = TCP_ESTABLISHED;
	/*
	* Parse the data in the frame.
	*/
	if (!pskb_may_pull(skb, X25_STD_MIN_LEN))
	goto out_clear;
	skb_pull(skb, X25_STD_MIN_LEN);

	len = x25_parse_address_block(skb, &source_addr,
	&dest_addr);
	if (len > 0)
	skb_pull(skb, len);
	else if (len < 0)
	goto out_clear;

	len = x25_parse_facilities(skb, &x25->facilities,
	&x25->dte_facilities,
	&x25->vc_facil_mask);
	if (len > 0)
	skb_pull(skb, len);
	else if (len < 0)
	goto out_clear;
	/*
	* Copy any Call User Data.
	*/
	if (skb->len > 0) {
	if (skb->len > X25_MAX_CUD_LEN)
	goto out_clear;

	skb_copy_bits(skb, 0, x25->calluserdata.cuddata,
	skb->len);
	x25->calluserdata.cudlength = skb->len;
	}
	if (!sock_flag(sk, SOCK_DEAD))
	sk->sk_state_change(sk);
	break;
	}
	case X25_CALL_REQUEST:
	/* call collision */
	x25->causediag.cause = 0x01;
	x25->causediag.diagnostic = 0x48;

	x25_write_internal(sk, X25_CLEAR_REQUEST);
	x25_disconnect(sk, EISCONN, 0x01, 0x48);
	break;

	case X25_CLEAR_REQUEST:
	if (!pskb_may_pull(skb, X25_STD_MIN_LEN + 2))
	goto out_clear;

	x25_write_internal(sk, X25_CLEAR_CONFIRMATION);
	x25_disconnect(sk, ECONNREFUSED, skb->data[3], skb->data[4]);
	break;

	default:
	break;
	}

	return 0;

	out_clear:
	x25_write_internal(sk, X25_CLEAR_REQUEST);
	x25->state = X25_STATE_2;
	x25_start_t23timer(sk);
	return 0;
	}

	/*
	* State machine for state 2, Awaiting Clear Confirmation State.
	* The handling of the timer(s) is in file x25_timer.c
	* Handling of state 0 and connection release is in af_x25.c.
	*/
	static int x25_state2_machine(struct sock sk, struct sk_buff skb, int frametype)
	{
	switch (frametype) {

	case X25_CLEAR_REQUEST:
	if (!pskb_may_pull(skb, X25_STD_MIN_LEN + 2))
	goto out_clear;

	x25_write_internal(sk, X25_CLEAR_CONFIRMATION);
	x25_disconnect(sk, 0, skb->data[3], skb->data[4]);
	break;

	case X25_CLEAR_CONFIRMATION:
	x25_disconnect(sk, 0, 0, 0);
	break;

	default:
	break;
	}

	return 0;

	out_clear:
	x25_write_internal(sk, X25_CLEAR_REQUEST);
	x25_start_t23timer(sk);
	return 0;
	}

	/*
	* State machine for state 3, Connected State.
	* The handling of the timer(s) is in file x25_timer.c
	* Handling of state 0 and connection release is in af_x25.c.
	*/
	static int x25_state3_machine(struct sock sk, struct sk_buff skb, int frametype, int ns, int nr, int q, int d, int m)
	{
	int queued = 0;
	int modulus;
	struct x25_sock *x25 = x25_sk(sk);

	modulus = (x25->neighbour->extended) ? X25_EMODULUS : X25_SMODULUS;

	switch (frametype) {

	case X25_RESET_REQUEST:
	x25_write_internal(sk, X25_RESET_CONFIRMATION);
	x25_stop_timer(sk);
	x25->condition = 0x00;
	x25->vs = 0;
	x25->vr = 0;
	x25->va = 0;
	x25->vl = 0;
	x25_requeue_frames(sk);
	break;

	case X25_CLEAR_REQUEST:
	if (!pskb_may_pull(skb, X25_STD_MIN_LEN + 2))
	goto out_clear;

	x25_write_internal(sk, X25_CLEAR_CONFIRMATION);
	x25_disconnect(sk, 0, skb->data[3], skb->data[4]);
	break;

	case X25_RR:
	case X25_RNR:
	if (!x25_validate_nr(sk, nr)) {
	x25_clear_queues(sk);
	x25_write_internal(sk, X25_RESET_REQUEST);
	x25_start_t22timer(sk);
	x25->condition = 0x00;
	x25->vs = 0;
	x25->vr = 0;
	x25->va = 0;
	x25->vl = 0;
	x25->state = X25_STATE_4;
	} else {
	x25_frames_acked(sk, nr);
	if (frametype == X25_RNR) {
	x25->condition \|= X25_COND_PEER_RX_BUSY;
	} else {
	x25->condition &= ~X25_COND_PEER_RX_BUSY;
	}
	}
	break;

	case X25_DATA: /* XXX */
	x25->condition &= ~X25_COND_PEER_RX_BUSY;
	if ((ns != x25->vr) \|\| !x25_validate_nr(sk, nr)) {
	x25_clear_queues(sk);
	x25_write_internal(sk, X25_RESET_REQUEST);
	x25_start_t22timer(sk);
	x25->condition = 0x00;
	x25->vs = 0;
	x25->vr = 0;
	x25->va = 0;
	x25->vl = 0;
	x25->state = X25_STATE_4;
	break;
	}
	x25_frames_acked(sk, nr);
	if (ns == x25->vr) {
	if (x25_queue_rx_frame(sk, skb, m) == 0) {
	x25->vr = (x25->vr + 1) % modulus;
	queued = 1;
	} else {
	/* Should never happen */
	x25_clear_queues(sk);
	x25_write_internal(sk, X25_RESET_REQUEST);
	x25_start_t22timer(sk);
	x25->condition = 0x00;
	x25->vs = 0;
	x25->vr = 0;
	x25->va = 0;
	x25->vl = 0;
	x25->state = X25_STATE_4;
	break;
	}
	if (atomic_read(&sk->sk_rmem_alloc) >
	(sk->sk_rcvbuf >> 1))
	x25->condition \|= X25_COND_OWN_RX_BUSY;
	}
	/*
	* If the window is full Ack it immediately, else
	* start the holdback timer.
	*/
	if (((x25->vl + x25->facilities.winsize_in) % modulus) == x25->vr) {
	x25->condition &= ~X25_COND_ACK_PENDING;
	x25_stop_timer(sk);
	x25_enquiry_response(sk);
	} else {
	x25->condition \|= X25_COND_ACK_PENDING;
	x25_start_t2timer(sk);
	}
	break;

	case X25_INTERRUPT_CONFIRMATION:
	clear_bit(X25_INTERRUPT_FLAG, &x25->flags);
	break;

	case X25_INTERRUPT:
	if (sock_flag(sk, SOCK_URGINLINE))
	queued = !sock_queue_rcv_skb(sk, skb);
	else {
	skb_set_owner_r(skb, sk);
	skb_queue_tail(&x25->interrupt_in_queue, skb);
	queued = 1;
	}
	sk_send_sigurg(sk);
	x25_write_internal(sk, X25_INTERRUPT_CONFIRMATION);
	break;

	default:
	pr_warn("unknown %02X in state 3\n", frametype);
	break;
	}

	return queued;

	out_clear:
	x25_write_internal(sk, X25_CLEAR_REQUEST);
	x25->state = X25_STATE_2;
	x25_start_t23timer(sk);
	return 0;
	}

	/*
	* State machine for state 4, Awaiting Reset Confirmation State.
	* The handling of the timer(s) is in file x25_timer.c
	* Handling of state 0 and connection release is in af_x25.c.
	*/
	static int x25_state4_machine(struct sock sk, struct sk_buff skb, int frametype)
	{
	struct x25_sock *x25 = x25_sk(sk);

	switch (frametype) {

	case X25_RESET_REQUEST:
	x25_write_internal(sk, X25_RESET_CONFIRMATION);
	/* fall through */
	case X25_RESET_CONFIRMATION: {
	x25_stop_timer(sk);
	x25->condition = 0x00;
	x25->va = 0;
	x25->vr = 0;
	x25->vs = 0;
	x25->vl = 0;
	x25->state = X25_STATE_3;
	x25_requeue_frames(sk);
	break;
	}
	case X25_CLEAR_REQUEST:
	if (!pskb_may_pull(skb, X25_STD_MIN_LEN + 2))
	goto out_clear;

	x25_write_internal(sk, X25_CLEAR_CONFIRMATION);
	x25_disconnect(sk, 0, skb->data[3], skb->data[4]);
	break;

	default:
	break;
	}

	return 0;

	out_clear:
	x25_write_internal(sk, X25_CLEAR_REQUEST);
	x25->state = X25_STATE_2;
	x25_start_t23timer(sk);
	return 0;
	}

	/* Higher level upcall for a LAPB frame */
	int x25_process_rx_frame(struct sock sk, struct sk_buff skb)
	{
	struct x25_sock *x25 = x25_sk(sk);
	int queued = 0, frametype, ns, nr, q, d, m;

	if (x25->state == X25_STATE_0)
	return 0;

	frametype = x25_decode(sk, skb, &ns, &nr, &q, &d, &m);

	switch (x25->state) {
	case X25_STATE_1:
	queued = x25_state1_machine(sk, skb, frametype);
	break;
	case X25_STATE_2:
	queued = x25_state2_machine(sk, skb, frametype);
	break;
	case X25_STATE_3:
	queued = x25_state3_machine(sk, skb, frametype, ns, nr, q, d, m);
	break;
	case X25_STATE_4:
	queued = x25_state4_machine(sk, skb, frametype);
	break;
	}

	x25_kick(sk);

	return queued;
	}

	int x25_backlog_rcv(struct sock sk, struct sk_buff skb)
	{
	int queued = x25_process_rx_frame(sk, skb);

	if (!queued)
	kfree_skb(skb);

	return 0;
	}