net/ax25/ax25_std_in.c - kernel/common - Git at Google

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  *
  * Copyright (C) Alan Cox GW4PTS ([email protected])
  * Copyright (C) Jonathan Naylor G4KLX ([email protected])
  * Copyright (C) Joerg Reuter DL1BKE ([email protected])
  * Copyright (C) Hans-Joachim Hetscher DD8NE ([email protected])
  *
  * Most of this code is based on the SDL diagrams published in the 7th ARRL
  * Computer Networking Conference papers. The diagrams have mistakes in them,
  * but are mostly correct. Before you modify the code could you read the SDL
  * diagrams as the code is not obvious and probably very easy to break.
  */
 #include <linux/errno.h>
 #include <linux/types.h>
 #include <linux/socket.h>
 #include <linux/in.h>
 #include <linux/kernel.h>
 #include <linux/timer.h>
 #include <linux/string.h>
 #include <linux/sockios.h>
 #include <linux/net.h>
 #include <net/ax25.h>
 #include <linux/inet.h>
 #include <linux/netdevice.h>
 #include <linux/skbuff.h>
 #include <net/sock.h>
 #include <net/tcp_states.h>
 #include <linux/uaccess.h>
 #include <linux/fcntl.h>
 #include <linux/mm.h>
 #include <linux/interrupt.h>

 /*
  *	State machine for state 1, Awaiting Connection State.
  *	The handling of the timer(s) is in file ax25_std_timer.c.
  *	Handling of state 0 and connection release is in ax25.c.
  */
 static int ax25_std_state1_machine(ax25_cb *ax25, struct sk_buff *skb, int frametype, int pf, int type)
 {
 	switch (frametype) {
 	case AX25_SABM:
 		ax25->modulus = AX25_MODULUS;
 		ax25->window  = ax25->ax25_dev->values[AX25_VALUES_WINDOW];
 		ax25_send_control(ax25, AX25_UA, pf, AX25_RESPONSE);
 		break;

 	case AX25_SABME:
 		ax25->modulus = AX25_EMODULUS;
 		ax25->window  = ax25->ax25_dev->values[AX25_VALUES_EWINDOW];
 		ax25_send_control(ax25, AX25_UA, pf, AX25_RESPONSE);
 		break;

 	case AX25_DISC:
 		ax25_send_control(ax25, AX25_DM, pf, AX25_RESPONSE);
 		break;

 	case AX25_UA:
 		if (pf) {
 			ax25_calculate_rtt(ax25);
 			ax25_stop_t1timer(ax25);
 			ax25_start_t3timer(ax25);
 			ax25_start_idletimer(ax25);
 			ax25->vs      = 0;
 			ax25->va      = 0;
 			ax25->vr      = 0;
 			ax25->state   = AX25_STATE_3;
 			ax25->n2count = 0;
 			if (ax25->sk != NULL) {
 				bh_lock_sock(ax25->sk);
 				ax25->sk->sk_state = TCP_ESTABLISHED;
 				/* For WAIT_SABM connections we will produce an accept ready socket here */
 				if (!sock_flag(ax25->sk, SOCK_DEAD))
 					ax25->sk->sk_state_change(ax25->sk);
 				bh_unlock_sock(ax25->sk);
 			}
 		}
 		break;

 	case AX25_DM:
 		if (pf) {
 			if (ax25->modulus == AX25_MODULUS) {
 				ax25_disconnect(ax25, ECONNREFUSED);
 			} else {
 				ax25->modulus = AX25_MODULUS;
 				ax25->window  = ax25->ax25_dev->values[AX25_VALUES_WINDOW];
 			}
 		}
 		break;

 	default:
 		break;
 	}

 	return 0;
 }

 /*
  *	State machine for state 2, Awaiting Release State.
  *	The handling of the timer(s) is in file ax25_std_timer.c
  *	Handling of state 0 and connection release is in ax25.c.
  */
 static int ax25_std_state2_machine(ax25_cb *ax25, struct sk_buff *skb, int frametype, int pf, int type)
 {
 	switch (frametype) {
 	case AX25_SABM:
 	case AX25_SABME:
 		ax25_send_control(ax25, AX25_DM, pf, AX25_RESPONSE);
 		break;

 	case AX25_DISC:
 		ax25_send_control(ax25, AX25_UA, pf, AX25_RESPONSE);
 		ax25_disconnect(ax25, 0);
 		break;

 	case AX25_DM:
 	case AX25_UA:
 		if (pf)
 			ax25_disconnect(ax25, 0);
 		break;

 	case AX25_I:
 	case AX25_REJ:
 	case AX25_RNR:
 	case AX25_RR:
 		if (pf) ax25_send_control(ax25, AX25_DM, AX25_POLLON, AX25_RESPONSE);
 		break;

 	default:
 		break;
 	}

 	return 0;
 }

 /*
  *	State machine for state 3, Connected State.
  *	The handling of the timer(s) is in file ax25_std_timer.c
  *	Handling of state 0 and connection release is in ax25.c.
  */
 static int ax25_std_state3_machine(ax25_cb *ax25, struct sk_buff *skb, int frametype, int ns, int nr, int pf, int type)
 {
 	int queued = 0;

 	switch (frametype) {
 	case AX25_SABM:
 	case AX25_SABME:
 		if (frametype == AX25_SABM) {
 			ax25->modulus = AX25_MODULUS;
 			ax25->window  = ax25->ax25_dev->values[AX25_VALUES_WINDOW];
 		} else {
 			ax25->modulus = AX25_EMODULUS;
 			ax25->window  = ax25->ax25_dev->values[AX25_VALUES_EWINDOW];
 		}
 		ax25_send_control(ax25, AX25_UA, pf, AX25_RESPONSE);
 		ax25_stop_t1timer(ax25);
 		ax25_stop_t2timer(ax25);
 		ax25_start_t3timer(ax25);
 		ax25_start_idletimer(ax25);
 		ax25->condition = 0x00;
 		ax25->vs        = 0;
 		ax25->va        = 0;
 		ax25->vr        = 0;
 		ax25_requeue_frames(ax25);
 		break;

 	case AX25_DISC:
 		ax25_send_control(ax25, AX25_UA, pf, AX25_RESPONSE);
 		ax25_disconnect(ax25, 0);
 		break;

 	case AX25_DM:
 		ax25_disconnect(ax25, ECONNRESET);
 		break;

 	case AX25_RR:
 	case AX25_RNR:
 		if (frametype == AX25_RR)
 			ax25->condition &= ~AX25_COND_PEER_RX_BUSY;
 		else
 			ax25->condition |= AX25_COND_PEER_RX_BUSY;
 		if (type == AX25_COMMAND && pf)
 			ax25_std_enquiry_response(ax25);
 		if (ax25_validate_nr(ax25, nr)) {
 			ax25_check_iframes_acked(ax25, nr);
 		} else {
 			ax25_std_nr_error_recovery(ax25);
 			ax25->state = AX25_STATE_1;
 		}
 		break;

 	case AX25_REJ:
 		ax25->condition &= ~AX25_COND_PEER_RX_BUSY;
 		if (type == AX25_COMMAND && pf)
 			ax25_std_enquiry_response(ax25);
 		if (ax25_validate_nr(ax25, nr)) {
 			ax25_frames_acked(ax25, nr);
 			ax25_calculate_rtt(ax25);
 			ax25_stop_t1timer(ax25);
 			ax25_start_t3timer(ax25);
 			ax25_requeue_frames(ax25);
 		} else {
 			ax25_std_nr_error_recovery(ax25);
 			ax25->state = AX25_STATE_1;
 		}
 		break;

 	case AX25_I:
 		if (!ax25_validate_nr(ax25, nr)) {
 			ax25_std_nr_error_recovery(ax25);
 			ax25->state = AX25_STATE_1;
 			break;
 		}
 		if (ax25->condition & AX25_COND_PEER_RX_BUSY) {
 			ax25_frames_acked(ax25, nr);
 		} else {
 			ax25_check_iframes_acked(ax25, nr);
 		}
 		if (ax25->condition & AX25_COND_OWN_RX_BUSY) {
 			if (pf) ax25_std_enquiry_response(ax25);
 			break;
 		}
 		if (ns == ax25->vr) {
 			ax25->vr = (ax25->vr + 1) % ax25->modulus;
 			queued = ax25_rx_iframe(ax25, skb);
 			if (ax25->condition & AX25_COND_OWN_RX_BUSY)
 				ax25->vr = ns;	/* ax25->vr - 1 */
 			ax25->condition &= ~AX25_COND_REJECT;
 			if (pf) {
 				ax25_std_enquiry_response(ax25);
 			} else {
 				if (!(ax25->condition & AX25_COND_ACK_PENDING)) {
 					ax25->condition |= AX25_COND_ACK_PENDING;
 					ax25_start_t2timer(ax25);
 				}
 			}
 		} else {
 			if (ax25->condition & AX25_COND_REJECT) {
 				if (pf) ax25_std_enquiry_response(ax25);
 			} else {
 				ax25->condition |= AX25_COND_REJECT;
 				ax25_send_control(ax25, AX25_REJ, pf, AX25_RESPONSE);
 				ax25->condition &= ~AX25_COND_ACK_PENDING;
 			}
 		}
 		break;

 	case AX25_FRMR:
 	case AX25_ILLEGAL:
 		ax25_std_establish_data_link(ax25);
 		ax25->state = AX25_STATE_1;
 		break;

 	default:
 		break;
 	}

 	return queued;
 }

 /*
  *	State machine for state 4, Timer Recovery State.
  *	The handling of the timer(s) is in file ax25_std_timer.c
  *	Handling of state 0 and connection release is in ax25.c.
  */
 static int ax25_std_state4_machine(ax25_cb *ax25, struct sk_buff *skb, int frametype, int ns, int nr, int pf, int type)
 {
 	int queued = 0;

 	switch (frametype) {
 	case AX25_SABM:
 	case AX25_SABME:
 		if (frametype == AX25_SABM) {
 			ax25->modulus = AX25_MODULUS;
 			ax25->window  = ax25->ax25_dev->values[AX25_VALUES_WINDOW];
 		} else {
 			ax25->modulus = AX25_EMODULUS;
 			ax25->window  = ax25->ax25_dev->values[AX25_VALUES_EWINDOW];
 		}
 		ax25_send_control(ax25, AX25_UA, pf, AX25_RESPONSE);
 		ax25_stop_t1timer(ax25);
 		ax25_stop_t2timer(ax25);
 		ax25_start_t3timer(ax25);
 		ax25_start_idletimer(ax25);
 		ax25->condition = 0x00;
 		ax25->vs        = 0;
 		ax25->va        = 0;
 		ax25->vr        = 0;
 		ax25->state     = AX25_STATE_3;
 		ax25->n2count   = 0;
 		ax25_requeue_frames(ax25);
 		break;

 	case AX25_DISC:
 		ax25_send_control(ax25, AX25_UA, pf, AX25_RESPONSE);
 		ax25_disconnect(ax25, 0);
 		break;

 	case AX25_DM:
 		ax25_disconnect(ax25, ECONNRESET);
 		break;

 	case AX25_RR:
 	case AX25_RNR:
 		if (frametype == AX25_RR)
 			ax25->condition &= ~AX25_COND_PEER_RX_BUSY;
 		else
 			ax25->condition |= AX25_COND_PEER_RX_BUSY;
 		if (type == AX25_RESPONSE && pf) {
 			ax25_stop_t1timer(ax25);
 			ax25->n2count = 0;
 			if (ax25_validate_nr(ax25, nr)) {
 				ax25_frames_acked(ax25, nr);
 				if (ax25->vs == ax25->va) {
 					ax25_start_t3timer(ax25);
 					ax25->state   = AX25_STATE_3;
 				} else {
 					ax25_requeue_frames(ax25);
 				}
 			} else {
 				ax25_std_nr_error_recovery(ax25);
 				ax25->state = AX25_STATE_1;
 			}
 			break;
 		}
 		if (type == AX25_COMMAND && pf)
 			ax25_std_enquiry_response(ax25);
 		if (ax25_validate_nr(ax25, nr)) {
 			ax25_frames_acked(ax25, nr);
 		} else {
 			ax25_std_nr_error_recovery(ax25);
 			ax25->state = AX25_STATE_1;
 		}
 		break;

 	case AX25_REJ:
 		ax25->condition &= ~AX25_COND_PEER_RX_BUSY;
 		if (pf && type == AX25_RESPONSE) {
 			ax25_stop_t1timer(ax25);
 			ax25->n2count = 0;
 			if (ax25_validate_nr(ax25, nr)) {
 				ax25_frames_acked(ax25, nr);
 				if (ax25->vs == ax25->va) {
 					ax25_start_t3timer(ax25);
 					ax25->state   = AX25_STATE_3;
 				} else {
 					ax25_requeue_frames(ax25);
 				}
 			} else {
 				ax25_std_nr_error_recovery(ax25);
 				ax25->state = AX25_STATE_1;
 			}
 			break;
 		}
 		if (type == AX25_COMMAND && pf)
 			ax25_std_enquiry_response(ax25);
 		if (ax25_validate_nr(ax25, nr)) {
 			ax25_frames_acked(ax25, nr);
 			ax25_requeue_frames(ax25);
 		} else {
 			ax25_std_nr_error_recovery(ax25);
 			ax25->state = AX25_STATE_1;
 		}
 		break;

 	case AX25_I:
 		if (!ax25_validate_nr(ax25, nr)) {
 			ax25_std_nr_error_recovery(ax25);
 			ax25->state = AX25_STATE_1;
 			break;
 		}
 		ax25_frames_acked(ax25, nr);
 		if (ax25->condition & AX25_COND_OWN_RX_BUSY) {
 			if (pf)
 				ax25_std_enquiry_response(ax25);
 			break;
 		}
 		if (ns == ax25->vr) {
 			ax25->vr = (ax25->vr + 1) % ax25->modulus;
 			queued = ax25_rx_iframe(ax25, skb);
 			if (ax25->condition & AX25_COND_OWN_RX_BUSY)
 				ax25->vr = ns;	/* ax25->vr - 1 */
 			ax25->condition &= ~AX25_COND_REJECT;
 			if (pf) {
 				ax25_std_enquiry_response(ax25);
 			} else {
 				if (!(ax25->condition & AX25_COND_ACK_PENDING)) {
 					ax25->condition |= AX25_COND_ACK_PENDING;
 					ax25_start_t2timer(ax25);
 				}
 			}
 		} else {
 			if (ax25->condition & AX25_COND_REJECT) {
 				if (pf) ax25_std_enquiry_response(ax25);
 			} else {
 				ax25->condition |= AX25_COND_REJECT;
 				ax25_send_control(ax25, AX25_REJ, pf, AX25_RESPONSE);
 				ax25->condition &= ~AX25_COND_ACK_PENDING;
 			}
 		}
 		break;

 	case AX25_FRMR:
 	case AX25_ILLEGAL:
 		ax25_std_establish_data_link(ax25);
 		ax25->state = AX25_STATE_1;
 		break;

 	default:
 		break;
 	}

 	return queued;
 }

 /*
  *	Higher level upcall for a LAPB frame
  */
 int ax25_std_frame_in(ax25_cb *ax25, struct sk_buff *skb, int type)
 {
 	int queued = 0, frametype, ns, nr, pf;

 	frametype = ax25_decode(ax25, skb, &ns, &nr, &pf);

 	switch (ax25->state) {
 	case AX25_STATE_1:
 		queued = ax25_std_state1_machine(ax25, skb, frametype, pf, type);
 		break;
 	case AX25_STATE_2:
 		queued = ax25_std_state2_machine(ax25, skb, frametype, pf, type);
 		break;
 	case AX25_STATE_3:
 		queued = ax25_std_state3_machine(ax25, skb, frametype, ns, nr, pf, type);
 		break;
 	case AX25_STATE_4:
 		queued = ax25_std_state4_machine(ax25, skb, frametype, ns, nr, pf, type);
 		break;
 	}

 	ax25_kick(ax25);

 	return queued;
 }
	// SPDX-License-Identifier: GPL-2.0-or-later
	/*
	*
	* Copyright (C) Alan Cox GW4PTS ([email protected])
	* Copyright (C) Jonathan Naylor G4KLX ([email protected])
	* Copyright (C) Joerg Reuter DL1BKE ([email protected])
	* Copyright (C) Hans-Joachim Hetscher DD8NE ([email protected])
	*
	* Most of this code is based on the SDL diagrams published in the 7th ARRL
	* Computer Networking Conference papers. The diagrams have mistakes in them,
	* but are mostly correct. Before you modify the code could you read the SDL
	* diagrams as the code is not obvious and probably very easy to break.
	*/
	#include <linux/errno.h>
	#include <linux/types.h>
	#include <linux/socket.h>
	#include <linux/in.h>
	#include <linux/kernel.h>
	#include <linux/timer.h>
	#include <linux/string.h>
	#include <linux/sockios.h>
	#include <linux/net.h>
	#include <net/ax25.h>
	#include <linux/inet.h>
	#include <linux/netdevice.h>
	#include <linux/skbuff.h>
	#include <net/sock.h>
	#include <net/tcp_states.h>
	#include <linux/uaccess.h>
	#include <linux/fcntl.h>
	#include <linux/mm.h>
	#include <linux/interrupt.h>

	/*
	* State machine for state 1, Awaiting Connection State.
	* The handling of the timer(s) is in file ax25_std_timer.c.
	* Handling of state 0 and connection release is in ax25.c.
	*/
	static int ax25_std_state1_machine(ax25_cb ax25, struct sk_buff skb, int frametype, int pf, int type)
	{
	switch (frametype) {
	case AX25_SABM:
	ax25->modulus = AX25_MODULUS;
	ax25->window = ax25->ax25_dev->values[AX25_VALUES_WINDOW];
	ax25_send_control(ax25, AX25_UA, pf, AX25_RESPONSE);
	break;

	case AX25_SABME:
	ax25->modulus = AX25_EMODULUS;
	ax25->window = ax25->ax25_dev->values[AX25_VALUES_EWINDOW];
	ax25_send_control(ax25, AX25_UA, pf, AX25_RESPONSE);
	break;

	case AX25_DISC:
	ax25_send_control(ax25, AX25_DM, pf, AX25_RESPONSE);
	break;

	case AX25_UA:
	if (pf) {
	ax25_calculate_rtt(ax25);
	ax25_stop_t1timer(ax25);
	ax25_start_t3timer(ax25);
	ax25_start_idletimer(ax25);
	ax25->vs = 0;
	ax25->va = 0;
	ax25->vr = 0;
	ax25->state = AX25_STATE_3;
	ax25->n2count = 0;
	if (ax25->sk != NULL) {
	bh_lock_sock(ax25->sk);
	ax25->sk->sk_state = TCP_ESTABLISHED;
	/* For WAIT_SABM connections we will produce an accept ready socket here */
	if (!sock_flag(ax25->sk, SOCK_DEAD))
	ax25->sk->sk_state_change(ax25->sk);
	bh_unlock_sock(ax25->sk);
	}
	}
	break;

	case AX25_DM:
	if (pf) {
	if (ax25->modulus == AX25_MODULUS) {
	ax25_disconnect(ax25, ECONNREFUSED);
	} else {
	ax25->modulus = AX25_MODULUS;
	ax25->window = ax25->ax25_dev->values[AX25_VALUES_WINDOW];
	}
	}
	break;

	default:
	break;
	}

	return 0;
	}

	/*
	* State machine for state 2, Awaiting Release State.
	* The handling of the timer(s) is in file ax25_std_timer.c
	* Handling of state 0 and connection release is in ax25.c.
	*/
	static int ax25_std_state2_machine(ax25_cb ax25, struct sk_buff skb, int frametype, int pf, int type)
	{
	switch (frametype) {
	case AX25_SABM:
	case AX25_SABME:
	ax25_send_control(ax25, AX25_DM, pf, AX25_RESPONSE);
	break;

	case AX25_DISC:
	ax25_send_control(ax25, AX25_UA, pf, AX25_RESPONSE);
	ax25_disconnect(ax25, 0);
	break;

	case AX25_DM:
	case AX25_UA:
	if (pf)
	ax25_disconnect(ax25, 0);
	break;

	case AX25_I:
	case AX25_REJ:
	case AX25_RNR:
	case AX25_RR:
	if (pf) ax25_send_control(ax25, AX25_DM, AX25_POLLON, AX25_RESPONSE);
	break;

	default:
	break;
	}

	return 0;
	}

	/*
	* State machine for state 3, Connected State.
	* The handling of the timer(s) is in file ax25_std_timer.c
	* Handling of state 0 and connection release is in ax25.c.
	*/
	static int ax25_std_state3_machine(ax25_cb ax25, struct sk_buff skb, int frametype, int ns, int nr, int pf, int type)
	{
	int queued = 0;

	switch (frametype) {
	case AX25_SABM:
	case AX25_SABME:
	if (frametype == AX25_SABM) {
	ax25->modulus = AX25_MODULUS;
	ax25->window = ax25->ax25_dev->values[AX25_VALUES_WINDOW];
	} else {
	ax25->modulus = AX25_EMODULUS;
	ax25->window = ax25->ax25_dev->values[AX25_VALUES_EWINDOW];
	}
	ax25_send_control(ax25, AX25_UA, pf, AX25_RESPONSE);
	ax25_stop_t1timer(ax25);
	ax25_stop_t2timer(ax25);
	ax25_start_t3timer(ax25);
	ax25_start_idletimer(ax25);
	ax25->condition = 0x00;
	ax25->vs = 0;
	ax25->va = 0;
	ax25->vr = 0;
	ax25_requeue_frames(ax25);
	break;

	case AX25_DISC:
	ax25_send_control(ax25, AX25_UA, pf, AX25_RESPONSE);
	ax25_disconnect(ax25, 0);
	break;

	case AX25_DM:
	ax25_disconnect(ax25, ECONNRESET);
	break;

	case AX25_RR:
	case AX25_RNR:
	if (frametype == AX25_RR)
	ax25->condition &= ~AX25_COND_PEER_RX_BUSY;
	else
	ax25->condition \|= AX25_COND_PEER_RX_BUSY;
	if (type == AX25_COMMAND && pf)
	ax25_std_enquiry_response(ax25);
	if (ax25_validate_nr(ax25, nr)) {
	ax25_check_iframes_acked(ax25, nr);
	} else {
	ax25_std_nr_error_recovery(ax25);
	ax25->state = AX25_STATE_1;
	}
	break;

	case AX25_REJ:
	ax25->condition &= ~AX25_COND_PEER_RX_BUSY;
	if (type == AX25_COMMAND && pf)
	ax25_std_enquiry_response(ax25);
	if (ax25_validate_nr(ax25, nr)) {
	ax25_frames_acked(ax25, nr);
	ax25_calculate_rtt(ax25);
	ax25_stop_t1timer(ax25);
	ax25_start_t3timer(ax25);
	ax25_requeue_frames(ax25);
	} else {
	ax25_std_nr_error_recovery(ax25);
	ax25->state = AX25_STATE_1;
	}
	break;

	case AX25_I:
	if (!ax25_validate_nr(ax25, nr)) {
	ax25_std_nr_error_recovery(ax25);
	ax25->state = AX25_STATE_1;
	break;
	}
	if (ax25->condition & AX25_COND_PEER_RX_BUSY) {
	ax25_frames_acked(ax25, nr);
	} else {
	ax25_check_iframes_acked(ax25, nr);
	}
	if (ax25->condition & AX25_COND_OWN_RX_BUSY) {
	if (pf) ax25_std_enquiry_response(ax25);
	break;
	}
	if (ns == ax25->vr) {
	ax25->vr = (ax25->vr + 1) % ax25->modulus;
	queued = ax25_rx_iframe(ax25, skb);
	if (ax25->condition & AX25_COND_OWN_RX_BUSY)
	ax25->vr = ns; /* ax25->vr - 1 */
	ax25->condition &= ~AX25_COND_REJECT;
	if (pf) {
	ax25_std_enquiry_response(ax25);
	} else {
	if (!(ax25->condition & AX25_COND_ACK_PENDING)) {
	ax25->condition \|= AX25_COND_ACK_PENDING;
	ax25_start_t2timer(ax25);
	}
	}
	} else {
	if (ax25->condition & AX25_COND_REJECT) {
	if (pf) ax25_std_enquiry_response(ax25);
	} else {
	ax25->condition \|= AX25_COND_REJECT;
	ax25_send_control(ax25, AX25_REJ, pf, AX25_RESPONSE);
	ax25->condition &= ~AX25_COND_ACK_PENDING;
	}
	}
	break;

	case AX25_FRMR:
	case AX25_ILLEGAL:
	ax25_std_establish_data_link(ax25);
	ax25->state = AX25_STATE_1;
	break;

	default:
	break;
	}

	return queued;
	}

	/*
	* State machine for state 4, Timer Recovery State.
	* The handling of the timer(s) is in file ax25_std_timer.c
	* Handling of state 0 and connection release is in ax25.c.
	*/
	static int ax25_std_state4_machine(ax25_cb ax25, struct sk_buff skb, int frametype, int ns, int nr, int pf, int type)
	{
	int queued = 0;

	switch (frametype) {
	case AX25_SABM:
	case AX25_SABME:
	if (frametype == AX25_SABM) {
	ax25->modulus = AX25_MODULUS;
	ax25->window = ax25->ax25_dev->values[AX25_VALUES_WINDOW];
	} else {
	ax25->modulus = AX25_EMODULUS;
	ax25->window = ax25->ax25_dev->values[AX25_VALUES_EWINDOW];
	}
	ax25_send_control(ax25, AX25_UA, pf, AX25_RESPONSE);
	ax25_stop_t1timer(ax25);
	ax25_stop_t2timer(ax25);
	ax25_start_t3timer(ax25);
	ax25_start_idletimer(ax25);
	ax25->condition = 0x00;
	ax25->vs = 0;
	ax25->va = 0;
	ax25->vr = 0;
	ax25->state = AX25_STATE_3;
	ax25->n2count = 0;
	ax25_requeue_frames(ax25);
	break;

	case AX25_DISC:
	ax25_send_control(ax25, AX25_UA, pf, AX25_RESPONSE);
	ax25_disconnect(ax25, 0);
	break;

	case AX25_DM:
	ax25_disconnect(ax25, ECONNRESET);
	break;

	case AX25_RR:
	case AX25_RNR:
	if (frametype == AX25_RR)
	ax25->condition &= ~AX25_COND_PEER_RX_BUSY;
	else
	ax25->condition \|= AX25_COND_PEER_RX_BUSY;
	if (type == AX25_RESPONSE && pf) {
	ax25_stop_t1timer(ax25);
	ax25->n2count = 0;
	if (ax25_validate_nr(ax25, nr)) {
	ax25_frames_acked(ax25, nr);
	if (ax25->vs == ax25->va) {
	ax25_start_t3timer(ax25);
	ax25->state = AX25_STATE_3;
	} else {
	ax25_requeue_frames(ax25);
	}
	} else {
	ax25_std_nr_error_recovery(ax25);
	ax25->state = AX25_STATE_1;
	}
	break;
	}
	if (type == AX25_COMMAND && pf)
	ax25_std_enquiry_response(ax25);
	if (ax25_validate_nr(ax25, nr)) {
	ax25_frames_acked(ax25, nr);
	} else {
	ax25_std_nr_error_recovery(ax25);
	ax25->state = AX25_STATE_1;
	}
	break;

	case AX25_REJ:
	ax25->condition &= ~AX25_COND_PEER_RX_BUSY;
	if (pf && type == AX25_RESPONSE) {
	ax25_stop_t1timer(ax25);
	ax25->n2count = 0;
	if (ax25_validate_nr(ax25, nr)) {
	ax25_frames_acked(ax25, nr);
	if (ax25->vs == ax25->va) {
	ax25_start_t3timer(ax25);
	ax25->state = AX25_STATE_3;
	} else {
	ax25_requeue_frames(ax25);
	}
	} else {
	ax25_std_nr_error_recovery(ax25);
	ax25->state = AX25_STATE_1;
	}
	break;
	}
	if (type == AX25_COMMAND && pf)
	ax25_std_enquiry_response(ax25);
	if (ax25_validate_nr(ax25, nr)) {
	ax25_frames_acked(ax25, nr);
	ax25_requeue_frames(ax25);
	} else {
	ax25_std_nr_error_recovery(ax25);
	ax25->state = AX25_STATE_1;
	}
	break;

	case AX25_I:
	if (!ax25_validate_nr(ax25, nr)) {
	ax25_std_nr_error_recovery(ax25);
	ax25->state = AX25_STATE_1;
	break;
	}
	ax25_frames_acked(ax25, nr);
	if (ax25->condition & AX25_COND_OWN_RX_BUSY) {
	if (pf)
	ax25_std_enquiry_response(ax25);
	break;
	}
	if (ns == ax25->vr) {
	ax25->vr = (ax25->vr + 1) % ax25->modulus;
	queued = ax25_rx_iframe(ax25, skb);
	if (ax25->condition & AX25_COND_OWN_RX_BUSY)
	ax25->vr = ns; /* ax25->vr - 1 */
	ax25->condition &= ~AX25_COND_REJECT;
	if (pf) {
	ax25_std_enquiry_response(ax25);
	} else {
	if (!(ax25->condition & AX25_COND_ACK_PENDING)) {
	ax25->condition \|= AX25_COND_ACK_PENDING;
	ax25_start_t2timer(ax25);
	}
	}
	} else {
	if (ax25->condition & AX25_COND_REJECT) {
	if (pf) ax25_std_enquiry_response(ax25);
	} else {
	ax25->condition \|= AX25_COND_REJECT;
	ax25_send_control(ax25, AX25_REJ, pf, AX25_RESPONSE);
	ax25->condition &= ~AX25_COND_ACK_PENDING;
	}
	}
	break;

	case AX25_FRMR:
	case AX25_ILLEGAL:
	ax25_std_establish_data_link(ax25);
	ax25->state = AX25_STATE_1;
	break;

	default:
	break;
	}

	return queued;
	}

	/*
	* Higher level upcall for a LAPB frame
	*/
	int ax25_std_frame_in(ax25_cb ax25, struct sk_buff skb, int type)
	{
	int queued = 0, frametype, ns, nr, pf;

	frametype = ax25_decode(ax25, skb, &ns, &nr, &pf);

	switch (ax25->state) {
	case AX25_STATE_1:
	queued = ax25_std_state1_machine(ax25, skb, frametype, pf, type);
	break;
	case AX25_STATE_2:
	queued = ax25_std_state2_machine(ax25, skb, frametype, pf, type);
	break;
	case AX25_STATE_3:
	queued = ax25_std_state3_machine(ax25, skb, frametype, ns, nr, pf, type);
	break;
	case AX25_STATE_4:
	queued = ax25_std_state4_machine(ax25, skb, frametype, ns, nr, pf, type);
	break;
	}

	ax25_kick(ax25);

	return queued;
	}