xref: /openbmc/linux/net/ax25/ax25_subr.c (revision 7d8a3a47)
1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3  *
4  * Copyright (C) Alan Cox GW4PTS (alan@lxorguk.ukuu.org.uk)
5  * Copyright (C) Jonathan Naylor G4KLX (g4klx@g4klx.demon.co.uk)
6  * Copyright (C) Joerg Reuter DL1BKE (jreuter@yaina.de)
7  * Copyright (C) Frederic Rible F1OAT (frible@teaser.fr)
8  */
9 #include <linux/errno.h>
10 #include <linux/types.h>
11 #include <linux/socket.h>
12 #include <linux/in.h>
13 #include <linux/kernel.h>
14 #include <linux/timer.h>
15 #include <linux/string.h>
16 #include <linux/sockios.h>
17 #include <linux/net.h>
18 #include <linux/slab.h>
19 #include <net/ax25.h>
20 #include <linux/inet.h>
21 #include <linux/netdevice.h>
22 #include <linux/skbuff.h>
23 #include <net/sock.h>
24 #include <net/tcp_states.h>
25 #include <linux/uaccess.h>
26 #include <linux/fcntl.h>
27 #include <linux/mm.h>
28 #include <linux/interrupt.h>
29 
30 /*
31  *	This routine purges all the queues of frames.
32  */
ax25_clear_queues(ax25_cb * ax25)33 void ax25_clear_queues(ax25_cb *ax25)
34 {
35 	skb_queue_purge(&ax25->write_queue);
36 	skb_queue_purge(&ax25->ack_queue);
37 	skb_queue_purge(&ax25->reseq_queue);
38 	skb_queue_purge(&ax25->frag_queue);
39 }
40 
41 /*
42  * This routine purges the input queue of those frames that have been
43  * acknowledged. This replaces the boxes labelled "V(a) <- N(r)" on the
44  * SDL diagram.
45  */
ax25_frames_acked(ax25_cb * ax25,unsigned short nr)46 void ax25_frames_acked(ax25_cb *ax25, unsigned short nr)
47 {
48 	struct sk_buff *skb;
49 
50 	/*
51 	 * Remove all the ack-ed frames from the ack queue.
52 	 */
53 	if (ax25->va != nr) {
54 		while (skb_peek(&ax25->ack_queue) != NULL && ax25->va != nr) {
55 			skb = skb_dequeue(&ax25->ack_queue);
56 			kfree_skb(skb);
57 			ax25->va = (ax25->va + 1) % ax25->modulus;
58 		}
59 	}
60 }
61 
ax25_requeue_frames(ax25_cb * ax25)62 void ax25_requeue_frames(ax25_cb *ax25)
63 {
64 	struct sk_buff *skb;
65 
66 	/*
67 	 * Requeue all the un-ack-ed frames on the output queue to be picked
68 	 * up by ax25_kick called from the timer. This arrangement handles the
69 	 * possibility of an empty output queue.
70 	 */
71 	while ((skb = skb_dequeue_tail(&ax25->ack_queue)) != NULL)
72 		skb_queue_head(&ax25->write_queue, skb);
73 }
74 
75 /*
76  *	Validate that the value of nr is between va and vs. Return true or
77  *	false for testing.
78  */
ax25_validate_nr(ax25_cb * ax25,unsigned short nr)79 int ax25_validate_nr(ax25_cb *ax25, unsigned short nr)
80 {
81 	unsigned short vc = ax25->va;
82 
83 	while (vc != ax25->vs) {
84 		if (nr == vc) return 1;
85 		vc = (vc + 1) % ax25->modulus;
86 	}
87 
88 	if (nr == ax25->vs) return 1;
89 
90 	return 0;
91 }
92 
93 /*
94  *	This routine is the centralised routine for parsing the control
95  *	information for the different frame formats.
96  */
ax25_decode(ax25_cb * ax25,struct sk_buff * skb,int * ns,int * nr,int * pf)97 int ax25_decode(ax25_cb *ax25, struct sk_buff *skb, int *ns, int *nr, int *pf)
98 {
99 	unsigned char *frame;
100 	int frametype = AX25_ILLEGAL;
101 
102 	frame = skb->data;
103 	*ns = *nr = *pf = 0;
104 
105 	if (ax25->modulus == AX25_MODULUS) {
106 		if ((frame[0] & AX25_S) == 0) {
107 			frametype = AX25_I;			/* I frame - carries NR/NS/PF */
108 			*ns = (frame[0] >> 1) & 0x07;
109 			*nr = (frame[0] >> 5) & 0x07;
110 			*pf = frame[0] & AX25_PF;
111 		} else if ((frame[0] & AX25_U) == 1) { 	/* S frame - take out PF/NR */
112 			frametype = frame[0] & 0x0F;
113 			*nr = (frame[0] >> 5) & 0x07;
114 			*pf = frame[0] & AX25_PF;
115 		} else if ((frame[0] & AX25_U) == 3) { 	/* U frame - take out PF */
116 			frametype = frame[0] & ~AX25_PF;
117 			*pf = frame[0] & AX25_PF;
118 		}
119 		skb_pull(skb, 1);
120 	} else {
121 		if ((frame[0] & AX25_S) == 0) {
122 			frametype = AX25_I;			/* I frame - carries NR/NS/PF */
123 			*ns = (frame[0] >> 1) & 0x7F;
124 			*nr = (frame[1] >> 1) & 0x7F;
125 			*pf = frame[1] & AX25_EPF;
126 			skb_pull(skb, 2);
127 		} else if ((frame[0] & AX25_U) == 1) { 	/* S frame - take out PF/NR */
128 			frametype = frame[0] & 0x0F;
129 			*nr = (frame[1] >> 1) & 0x7F;
130 			*pf = frame[1] & AX25_EPF;
131 			skb_pull(skb, 2);
132 		} else if ((frame[0] & AX25_U) == 3) { 	/* U frame - take out PF */
133 			frametype = frame[0] & ~AX25_PF;
134 			*pf = frame[0] & AX25_PF;
135 			skb_pull(skb, 1);
136 		}
137 	}
138 
139 	return frametype;
140 }
141 
142 /*
143  *	This routine is called when the HDLC layer internally  generates a
144  *	command or  response  for  the remote machine ( eg. RR, UA etc. ).
145  *	Only supervisory or unnumbered frames are processed.
146  */
ax25_send_control(ax25_cb * ax25,int frametype,int poll_bit,int type)147 void ax25_send_control(ax25_cb *ax25, int frametype, int poll_bit, int type)
148 {
149 	struct sk_buff *skb;
150 	unsigned char  *dptr;
151 
152 	if ((skb = alloc_skb(ax25->ax25_dev->dev->hard_header_len + 2, GFP_ATOMIC)) == NULL)
153 		return;
154 
155 	skb_reserve(skb, ax25->ax25_dev->dev->hard_header_len);
156 
157 	skb_reset_network_header(skb);
158 
159 	/* Assume a response - address structure for DTE */
160 	if (ax25->modulus == AX25_MODULUS) {
161 		dptr = skb_put(skb, 1);
162 		*dptr = frametype;
163 		*dptr |= (poll_bit) ? AX25_PF : 0;
164 		if ((frametype & AX25_U) == AX25_S)		/* S frames carry NR */
165 			*dptr |= (ax25->vr << 5);
166 	} else {
167 		if ((frametype & AX25_U) == AX25_U) {
168 			dptr = skb_put(skb, 1);
169 			*dptr = frametype;
170 			*dptr |= (poll_bit) ? AX25_PF : 0;
171 		} else {
172 			dptr = skb_put(skb, 2);
173 			dptr[0] = frametype;
174 			dptr[1] = (ax25->vr << 1);
175 			dptr[1] |= (poll_bit) ? AX25_EPF : 0;
176 		}
177 	}
178 
179 	ax25_transmit_buffer(ax25, skb, type);
180 }
181 
182 /*
183  *	Send a 'DM' to an unknown connection attempt, or an invalid caller.
184  *
185  *	Note: src here is the sender, thus it's the target of the DM
186  */
ax25_return_dm(struct net_device * dev,ax25_address * src,ax25_address * dest,ax25_digi * digi)187 void ax25_return_dm(struct net_device *dev, ax25_address *src, ax25_address *dest, ax25_digi *digi)
188 {
189 	struct sk_buff *skb;
190 	char *dptr;
191 	ax25_digi retdigi;
192 
193 	if (dev == NULL)
194 		return;
195 
196 	if ((skb = alloc_skb(dev->hard_header_len + 1, GFP_ATOMIC)) == NULL)
197 		return;	/* Next SABM will get DM'd */
198 
199 	skb_reserve(skb, dev->hard_header_len);
200 	skb_reset_network_header(skb);
201 
202 	ax25_digi_invert(digi, &retdigi);
203 
204 	dptr = skb_put(skb, 1);
205 
206 	*dptr = AX25_DM | AX25_PF;
207 
208 	/*
209 	 *	Do the address ourselves
210 	 */
211 	dptr  = skb_push(skb, ax25_addr_size(digi));
212 	dptr += ax25_addr_build(dptr, dest, src, &retdigi, AX25_RESPONSE, AX25_MODULUS);
213 
214 	ax25_queue_xmit(skb, dev);
215 }
216 
217 /*
218  *	Exponential backoff for AX.25
219  */
ax25_calculate_t1(ax25_cb * ax25)220 void ax25_calculate_t1(ax25_cb *ax25)
221 {
222 	int n, t = 2;
223 
224 	switch (ax25->backoff) {
225 	case 0:
226 		break;
227 
228 	case 1:
229 		t += 2 * ax25->n2count;
230 		break;
231 
232 	case 2:
233 		for (n = 0; n < ax25->n2count; n++)
234 			t *= 2;
235 		if (t > 8) t = 8;
236 		break;
237 	}
238 
239 	ax25->t1 = t * ax25->rtt;
240 }
241 
242 /*
243  *	Calculate the Round Trip Time
244  */
ax25_calculate_rtt(ax25_cb * ax25)245 void ax25_calculate_rtt(ax25_cb *ax25)
246 {
247 	if (ax25->backoff == 0)
248 		return;
249 
250 	if (ax25_t1timer_running(ax25) && ax25->n2count == 0)
251 		ax25->rtt = (9 * ax25->rtt + ax25->t1 - ax25_display_timer(&ax25->t1timer)) / 10;
252 
253 	if (ax25->rtt < AX25_T1CLAMPLO)
254 		ax25->rtt = AX25_T1CLAMPLO;
255 
256 	if (ax25->rtt > AX25_T1CLAMPHI)
257 		ax25->rtt = AX25_T1CLAMPHI;
258 }
259 
ax25_disconnect(ax25_cb * ax25,int reason)260 void ax25_disconnect(ax25_cb *ax25, int reason)
261 {
262 	ax25_clear_queues(ax25);
263 
264 	if (reason == ENETUNREACH) {
265 		del_timer_sync(&ax25->timer);
266 		del_timer_sync(&ax25->t1timer);
267 		del_timer_sync(&ax25->t2timer);
268 		del_timer_sync(&ax25->t3timer);
269 		del_timer_sync(&ax25->idletimer);
270 	} else {
271 		if (ax25->sk && !sock_flag(ax25->sk, SOCK_DESTROY))
272 			ax25_stop_heartbeat(ax25);
273 		ax25_stop_t1timer(ax25);
274 		ax25_stop_t2timer(ax25);
275 		ax25_stop_t3timer(ax25);
276 		ax25_stop_idletimer(ax25);
277 	}
278 
279 	ax25->state = AX25_STATE_0;
280 
281 	ax25_link_failed(ax25, reason);
282 
283 	if (ax25->sk != NULL) {
284 		local_bh_disable();
285 		bh_lock_sock(ax25->sk);
286 		ax25->sk->sk_state     = TCP_CLOSE;
287 		ax25->sk->sk_err       = reason;
288 		ax25->sk->sk_shutdown |= SEND_SHUTDOWN;
289 		if (!sock_flag(ax25->sk, SOCK_DEAD)) {
290 			ax25->sk->sk_state_change(ax25->sk);
291 			sock_set_flag(ax25->sk, SOCK_DEAD);
292 		}
293 		bh_unlock_sock(ax25->sk);
294 		local_bh_enable();
295 	}
296 }
297