summaryrefslogtreecommitdiffstats
path: root/openbsc/src/gprs/gprs_llc_parse.c
blob: b1f1a56dd3daaa5a91bf094567677fbef414c62d (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
/* GPRS LLC protocol implementation as per 3GPP TS 04.64 */

/* (C) 2009-2010 by Harald Welte <laforge@gnumonks.org>
 *
 * All Rights Reserved
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

#include <errno.h>
#include <stdint.h>

#include <osmocom/core/msgb.h>
#include <osmocom/core/linuxlist.h>
#include <osmocom/core/timer.h>
#include <osmocom/core/talloc.h>
#include <osmocom/gprs/gprs_bssgp.h>

#include <openbsc/gsm_data.h>
#include <openbsc/debug.h>
#include <openbsc/gprs_sgsn.h>
#include <openbsc/gprs_gmm.h>
#include <openbsc/gprs_llc.h>
#include <openbsc/crc24.h>

static const struct value_string llc_cmd_strs[] = {
	{ GPRS_LLC_NULL,	"NULL" },
	{ GPRS_LLC_RR,		"RR" },
	{ GPRS_LLC_ACK,		"ACK" },
	{ GPRS_LLC_RNR,		"RNR" },
	{ GPRS_LLC_SACK,	"SACK" },
	{ GPRS_LLC_DM,		"DM" },
	{ GPRS_LLC_DISC,	"DISC" },
	{ GPRS_LLC_UA,		"UA" },
	{ GPRS_LLC_SABM,	"SABM" },
	{ GPRS_LLC_FRMR,	"FRMR" },
	{ GPRS_LLC_XID,		"XID" },
	{ GPRS_LLC_UI,		"UI" },
	{ 0, NULL }
};

#define LLC_ALLOC_SIZE 16384
#define UI_HDR_LEN	3
#define N202		4
#define CRC24_LENGTH	3

int gprs_llc_fcs(uint8_t *data, unsigned int len)
{
	uint32_t fcs_calc;

	fcs_calc = crc24_calc(INIT_CRC24, data, len);
	fcs_calc = ~fcs_calc;
	fcs_calc &= 0xffffff;

	return fcs_calc;
}

void gprs_llc_hdr_dump(struct gprs_llc_hdr_parsed *gph)
{
	DEBUGP(DLLC, "LLC SAPI=%u %c %c FCS=0x%06x",
		gph->sapi, gph->is_cmd ? 'C' : 'R', gph->ack_req ? 'A' : ' ',
		gph->fcs);

	if (gph->cmd)
		DEBUGPC(DLLC, "CMD=%s ", get_value_string(llc_cmd_strs, gph->cmd));

	if (gph->data)
		DEBUGPC(DLLC, "DATA ");

	DEBUGPC(DLLC, "\n");
}

/* parse a GPRS LLC header, also check for invalid frames */
int gprs_llc_hdr_parse(struct gprs_llc_hdr_parsed *ghp,
		       uint8_t *llc_hdr, int len)
{
	uint8_t *ctrl = llc_hdr+1;

	if (len <= CRC24_LENGTH)
		return -EIO;

	ghp->crc_length = len - CRC24_LENGTH;

	ghp->ack_req = 0;

	/* Section 5.5: FCS */
	ghp->fcs = *(llc_hdr + len - 3);
	ghp->fcs |= *(llc_hdr + len - 2) << 8;
	ghp->fcs |= *(llc_hdr + len - 1) << 16;

	/* Section 6.2.1: invalid PD field */
	if (llc_hdr[0] & 0x80)
		return -EIO;

	/* This only works for the MS->SGSN direction */
	if (llc_hdr[0] & 0x40)
		ghp->is_cmd = 0;
	else
		ghp->is_cmd = 1;

	ghp->sapi = llc_hdr[0] & 0xf;

	/* Section 6.2.3: check for reserved SAPI */
	switch (ghp->sapi) {
	case 0:
	case 4:
	case 6:
	case 0xa:
	case 0xc:
	case 0xd:
	case 0xf:
		return -EINVAL;
	}

	if ((ctrl[0] & 0x80) == 0) {
		/* I (Information transfer + Supervisory) format */
		uint8_t k;

		ghp->data = ctrl + 3;

		if (ctrl[0] & 0x40)
			ghp->ack_req = 1;

		ghp->seq_tx  = (ctrl[0] & 0x1f) << 4;
		ghp->seq_tx |= (ctrl[1] >> 4);

		ghp->seq_rx  = (ctrl[1] & 0x7) << 6;
		ghp->seq_rx |= (ctrl[2] >> 2);

		switch (ctrl[2] & 0x03) {
		case 0:
			ghp->cmd = GPRS_LLC_RR;
			break;
		case 1:
			ghp->cmd = GPRS_LLC_ACK;
			break;
		case 2:
			ghp->cmd = GPRS_LLC_RNR;
			break;
		case 3:
			ghp->cmd = GPRS_LLC_SACK;
			k = ctrl[3] & 0x1f;
			ghp->data += 1 + k;
			break;
		}
		ghp->data_len = (llc_hdr + len - 3) - ghp->data;
	} else if ((ctrl[0] & 0xc0) == 0x80) {
		/* S (Supervisory) format */
		ghp->data = NULL;
		ghp->data_len = 0;

		if (ctrl[0] & 0x20)
			ghp->ack_req = 1;
		ghp->seq_rx  = (ctrl[0] & 0x7) << 6;
		ghp->seq_rx |= (ctrl[1] >> 2);

		switch (ctrl[1] & 0x03) {
		case 0:
			ghp->cmd = GPRS_LLC_RR;
			break;
		case 1:
			ghp->cmd = GPRS_LLC_ACK;
			break;
		case 2:
			ghp->cmd = GPRS_LLC_RNR;
			break;
		case 3:
			ghp->cmd = GPRS_LLC_SACK;
			break;
		}
	} else if ((ctrl[0] & 0xe0) == 0xc0) {
		/* UI (Unconfirmed Inforamtion) format */
		ghp->cmd = GPRS_LLC_UI;
		ghp->data = ctrl + 2;
		ghp->data_len = (llc_hdr + len - 3) - ghp->data;

		ghp->seq_tx  = (ctrl[0] & 0x7) << 6;
		ghp->seq_tx |= (ctrl[1] >> 2);
		if (ctrl[1] & 0x02) {
			ghp->is_encrypted = 1;
			/* FIXME: encryption */
		}
		if (ctrl[1] & 0x01) {
			/* FCS over hdr + all inf fields */
		} else {
			/* FCS over hdr + N202 octets (4) */
			if (ghp->crc_length > UI_HDR_LEN + N202)
				ghp->crc_length = UI_HDR_LEN + N202;
		}
	} else {
		/* U (Unnumbered) format: 1 1 1 P/F M4 M3 M2 M1 */
		ghp->data = NULL;
		ghp->data_len = 0;

		switch (ctrl[0] & 0xf) {
		case GPRS_LLC_U_NULL_CMD:
			ghp->cmd = GPRS_LLC_NULL;
			break;
		case GPRS_LLC_U_DM_RESP:
			ghp->cmd = GPRS_LLC_DM;
			break;
		case GPRS_LLC_U_DISC_CMD:
			ghp->cmd = GPRS_LLC_DISC;
			break;
		case GPRS_LLC_U_UA_RESP:
			ghp->cmd = GPRS_LLC_UA;
			break;
		case GPRS_LLC_U_SABM_CMD:
			ghp->cmd = GPRS_LLC_SABM;
			break;
		case GPRS_LLC_U_FRMR_RESP:
			ghp->cmd = GPRS_LLC_FRMR;
			break;
		case GPRS_LLC_U_XID:
			ghp->cmd = GPRS_LLC_XID;
			ghp->data = ctrl + 1;
			ghp->data_len = (llc_hdr + len - 3) - ghp->data;
			break;
		default:
			return -EIO;
		}
	}

	/* FIXME: parse sack frame */
	if (ghp->cmd == GPRS_LLC_SACK) {
		LOGP(DLLC, LOGL_NOTICE, "Unsupported SACK frame\n");
		return -EIO;
	}

	return 0;
}