1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 *	X.25 Packet Layer release 002
4 *
5 *	This is ALPHA test software. This code may break your machine,
6 *	randomly fail to work with new releases, misbehave and/or generally
7 *	screw up. It might even work.
8 *
9 *	This code REQUIRES 2.1.15 or higher
10 *
11 *	History
12 *	X.25 001	Jonathan Naylor	Started coding.
13 *	X.25 002	Jonathan Naylor	New timer architecture.
14 *	2000-09-04	Henner Eisen	Prevented x25_output() skb leakage.
15 *	2000-10-27	Henner Eisen	MSG_DONTWAIT for fragment allocation.
16 *	2000-11-10	Henner Eisen	x25_send_iframe(): re-queued frames
17 *					needed cleaned seq-number fields.
18 */
19
20#include <linux/slab.h>
21#include <linux/socket.h>
22#include <linux/kernel.h>
23#include <linux/string.h>
24#include <linux/skbuff.h>
25#include <net/sock.h>
26#include <net/x25.h>
27
28static int x25_pacsize_to_bytes(unsigned int pacsize)
29{
30	int bytes = 1;
31
32	if (!pacsize)
33		return 128;
34
35	while (pacsize-- > 0)
36		bytes *= 2;
37
38	return bytes;
39}
40
41/*
42 *	This is where all X.25 information frames pass.
43 *
44 *      Returns the amount of user data bytes sent on success
45 *      or a negative error code on failure.
46 */
47int x25_output(struct sock *sk, struct sk_buff *skb)
48{
49	struct sk_buff *skbn;
50	unsigned char header[X25_EXT_MIN_LEN];
51	int err, frontlen, len;
52	int sent=0, noblock = X25_SKB_CB(skb)->flags & MSG_DONTWAIT;
53	struct x25_sock *x25 = x25_sk(sk);
54	int header_len = x25->neighbour->extended ? X25_EXT_MIN_LEN :
55						    X25_STD_MIN_LEN;
56	int max_len = x25_pacsize_to_bytes(x25->facilities.pacsize_out);
57
58	if (skb->len - header_len > max_len) {
59		/* Save a copy of the Header */
60		skb_copy_from_linear_data(skb, header, header_len);
61		skb_pull(skb, header_len);
62
63		frontlen = skb_headroom(skb);
64
65		while (skb->len > 0) {
66			release_sock(sk);
67			skbn = sock_alloc_send_skb(sk, frontlen + max_len,
68						   noblock, &err);
69			lock_sock(sk);
70			if (!skbn) {
71				if (err == -EWOULDBLOCK && noblock){
72					kfree_skb(skb);
73					return sent;
74				}
75				net_dbg_ratelimited("x25_output: fragment alloc"
76					       " failed, err=%d, %d bytes "
77					       "sent\n", err, sent);
78				return err;
79			}
80
81			skb_reserve(skbn, frontlen);
82
83			len = max_len > skb->len ? skb->len : max_len;
84
85			/* Copy the user data */
86			skb_copy_from_linear_data(skb, skb_put(skbn, len), len);
87			skb_pull(skb, len);
88
89			/* Duplicate the Header */
90			skb_push(skbn, header_len);
91			skb_copy_to_linear_data(skbn, header, header_len);
92
93			if (skb->len > 0) {
94				if (x25->neighbour->extended)
95					skbn->data[3] |= X25_EXT_M_BIT;
96				else
97					skbn->data[2] |= X25_STD_M_BIT;
98			}
99
100			skb_queue_tail(&sk->sk_write_queue, skbn);
101			sent += len;
102		}
103
104		kfree_skb(skb);
105	} else {
106		skb_queue_tail(&sk->sk_write_queue, skb);
107		sent = skb->len - header_len;
108	}
109	return sent;
110}
111
112/*
113 *	This procedure is passed a buffer descriptor for an iframe. It builds
114 *	the rest of the control part of the frame and then writes it out.
115 */
116static void x25_send_iframe(struct sock *sk, struct sk_buff *skb)
117{
118	struct x25_sock *x25 = x25_sk(sk);
119
120	if (!skb)
121		return;
122
123	if (x25->neighbour->extended) {
124		skb->data[2]  = (x25->vs << 1) & 0xFE;
125		skb->data[3] &= X25_EXT_M_BIT;
126		skb->data[3] |= (x25->vr << 1) & 0xFE;
127	} else {
128		skb->data[2] &= X25_STD_M_BIT;
129		skb->data[2] |= (x25->vs << 1) & 0x0E;
130		skb->data[2] |= (x25->vr << 5) & 0xE0;
131	}
132
133	x25_transmit_link(skb, x25->neighbour);
134}
135
136void x25_kick(struct sock *sk)
137{
138	struct sk_buff *skb, *skbn;
139	unsigned short start, end;
140	int modulus;
141	struct x25_sock *x25 = x25_sk(sk);
142
143	if (x25->state != X25_STATE_3)
144		return;
145
146	/*
147	 *	Transmit interrupt data.
148	 */
149	if (skb_peek(&x25->interrupt_out_queue) != NULL &&
150		!test_and_set_bit(X25_INTERRUPT_FLAG, &x25->flags)) {
151
152		skb = skb_dequeue(&x25->interrupt_out_queue);
153		x25_transmit_link(skb, x25->neighbour);
154	}
155
156	if (x25->condition & X25_COND_PEER_RX_BUSY)
157		return;
158
159	if (!skb_peek(&sk->sk_write_queue))
160		return;
161
162	modulus = x25->neighbour->extended ? X25_EMODULUS : X25_SMODULUS;
163
164	start   = skb_peek(&x25->ack_queue) ? x25->vs : x25->va;
165	end     = (x25->va + x25->facilities.winsize_out) % modulus;
166
167	if (start == end)
168		return;
169
170	x25->vs = start;
171
172	/*
173	 * Transmit data until either we're out of data to send or
174	 * the window is full.
175	 */
176
177	skb = skb_dequeue(&sk->sk_write_queue);
178
179	do {
180		if ((skbn = skb_clone(skb, GFP_ATOMIC)) == NULL) {
181			skb_queue_head(&sk->sk_write_queue, skb);
182			break;
183		}
184
185		skb_set_owner_w(skbn, sk);
186
187		/*
188		 * Transmit the frame copy.
189		 */
190		x25_send_iframe(sk, skbn);
191
192		x25->vs = (x25->vs + 1) % modulus;
193
194		/*
195		 * Requeue the original data frame.
196		 */
197		skb_queue_tail(&x25->ack_queue, skb);
198
199	} while (x25->vs != end &&
200		 (skb = skb_dequeue(&sk->sk_write_queue)) != NULL);
201
202	x25->vl         = x25->vr;
203	x25->condition &= ~X25_COND_ACK_PENDING;
204
205	x25_stop_timer(sk);
206}
207
208/*
209 * The following routines are taken from page 170 of the 7th ARRL Computer
210 * Networking Conference paper, as is the whole state machine.
211 */
212
213void x25_enquiry_response(struct sock *sk)
214{
215	struct x25_sock *x25 = x25_sk(sk);
216
217	if (x25->condition & X25_COND_OWN_RX_BUSY)
218		x25_write_internal(sk, X25_RNR);
219	else
220		x25_write_internal(sk, X25_RR);
221
222	x25->vl         = x25->vr;
223	x25->condition &= ~X25_COND_ACK_PENDING;
224
225	x25_stop_timer(sk);
226}
227