gsmtap: Support dissection of non CS-1 (E)GPRS data blocks
Work based on current code from epan/dissectors/packet-gsm_abis_pgsl.c, as well as on initial patch from Holger Hans Peter Freyther [1]. Tested with one downlink MCS1 data block generated by osmo-pcu. [1] https://osmocom.org/issues/1542 Change-Id: I01a8bd1cdb78d1c236a451fbee37854eb688fa14 Reviewed-on: https://code.wireshark.org/review/36489 Reviewed-by: Harald Welte <laforge@gnumonks.org> Petri-Dish: Alexis La Goutte <alexis.lagoutte@gmail.com> Tested-by: Petri Dish Buildbot Reviewed-by: Anders Broman <a.broman58@gmail.com>
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Anders Broman
parent
378ecc27df
commit
dcd65a4012
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@ -3,6 +3,7 @@
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*
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* (C) 2008-2013 by Harald Welte <laforge@gnumonks.org>
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* (C) 2011 by Holger Hans Peter Freyther
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* (C) 2020 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
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*
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* Wireshark - Network traffic analyzer
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* By Gerald Combs <gerald@wireshark.org>
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@ -34,6 +35,7 @@
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#include <epan/packet.h>
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#include <epan/conversation.h>
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#include <epan/dissectors/packet-gsm_rlcmac.h>
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#include "packet-gsmtap.h"
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#include "packet-lapdm.h"
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@ -555,6 +557,216 @@ handle_tetra(int channel, tvbuff_t *payload_tvb, packet_info *pinfo, proto_tree
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tetra_dissect_pdu(tetra_chan, TETRA_DOWNLINK, payload_tvb, tree, pinfo);
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}
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/* length of an EGPRS RLC data block for given MCS */
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static const guint data_block_len_by_mcs[] = {
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0, /* MCS0 */
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22, /* MCS1 */
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28,
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37,
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44,
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56,
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74,
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56,
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68,
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74, /* MCS9 */
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0, /* MCS_INVALID */
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};
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/* determine the number of rlc data blocks and their size / offsets */
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static void
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setup_rlc_mac_priv(RlcMacPrivateData_t *rm, gboolean is_uplink,
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guint *n_calls, guint *data_block_bits, guint *data_block_offsets)
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{
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guint nc, dbl = 0, dbo[2] = {0,0};
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dbl = data_block_len_by_mcs[rm->mcs];
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switch (rm->block_format) {
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case RLCMAC_HDR_TYPE_1:
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nc = 3;
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dbo[0] = is_uplink ? 5*8 + 6 : 5*8 + 0;
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dbo[1] = dbo[0] + dbl * 8 + 2;
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break;
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case RLCMAC_HDR_TYPE_2:
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nc = 2;
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dbo[0] = is_uplink ? 4*8 + 5 : 3*8 + 4;
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break;
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case RLCMAC_HDR_TYPE_3:
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nc = 2;
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dbo[0] = 3*8 + 7;
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break;
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default:
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nc = 1;
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break;
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}
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*n_calls = nc;
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*data_block_bits = dbl * 8 + 2;
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data_block_offsets[0] = dbo[0];
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data_block_offsets[1] = dbo[1];
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}
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/* bit-shift the entire 'src' of length 'length_bytes' by 'offset_bits'
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* and store the reuslt to caller-allocated 'buffer'. The shifting is
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* done lsb-first, unlike tvb_new_octet_aligned() */
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static void clone_aligned_buffer_lsbf(guint offset_bits, guint length_bytes,
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const guint8 *src, guint8 *buffer)
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{
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guint hdr_bytes;
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guint extra_bits;
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guint i;
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guint8 c, last_c;
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guint8 *dst;
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hdr_bytes = offset_bits / 8;
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extra_bits = offset_bits % 8;
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if (extra_bits == 0) {
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/* It is aligned already */
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memmove(buffer, src + hdr_bytes, length_bytes);
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return;
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}
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dst = buffer;
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src = src + hdr_bytes;
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last_c = *(src++);
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for (i = 0; i < length_bytes; i++) {
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c = src[i];
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*(dst++) = (last_c >> extra_bits) | (c << (8 - extra_bits));
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last_c = c;
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}
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}
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/* obtain an (aligned) EGPRS data block with given bit-offset and
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* bit-length from the parent TVB */
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static tvbuff_t *get_egprs_data_block(tvbuff_t *tvb, guint offset_bits,
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guint length_bits, packet_info *pinfo)
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{
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tvbuff_t *aligned_tvb;
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const guint initial_spare_bits = 6;
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guint8 *aligned_buf;
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guint min_src_length_bytes = (offset_bits + length_bits + 7) / 8;
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guint length_bytes = (initial_spare_bits + length_bits + 7) / 8;
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tvb_ensure_bytes_exist(tvb, 0, min_src_length_bytes);
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aligned_buf = (guint8 *) wmem_alloc(pinfo->pool, length_bytes);
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/* Copy the data out of the tvb to an aligned buffer */
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clone_aligned_buffer_lsbf(
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offset_bits - initial_spare_bits, length_bytes,
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tvb_get_ptr(tvb, 0, min_src_length_bytes),
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aligned_buf);
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/* clear spare bits and move block header bits to the right */
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aligned_buf[0] = aligned_buf[0] >> initial_spare_bits;
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aligned_tvb = tvb_new_child_real_data(tvb, aligned_buf,
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length_bytes, length_bytes);
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add_new_data_source(pinfo, aligned_tvb, "Aligned EGPRS data bits");
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return aligned_tvb;
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}
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static void tvb_len_get_mcs_and_fmt(guint len, gboolean is_uplink, guint *frm, guint8 *mcs)
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{
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if (len <= 5 && is_uplink) {
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/* Assume random access burst */
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*frm = RLCMAC_PRACH;
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*mcs = 0;
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return;
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}
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switch (len)
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{
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case 23: *frm = RLCMAC_CS1; *mcs = 0; break;
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case 34: *frm = RLCMAC_CS2; *mcs = 0; break;
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case 40: *frm = RLCMAC_CS3; *mcs = 0; break;
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case 54: *frm = RLCMAC_CS4; *mcs = 0; break;
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case 27: *frm = RLCMAC_HDR_TYPE_3; *mcs = 1; break;
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case 33: *frm = RLCMAC_HDR_TYPE_3; *mcs = 2; break;
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case 42: *frm = RLCMAC_HDR_TYPE_3; *mcs = 3; break;
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case 49: *frm = RLCMAC_HDR_TYPE_3; *mcs = 4; break;
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case 60: /* fall through */
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case 61: *frm = RLCMAC_HDR_TYPE_2; *mcs = 5; break;
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case 78: /* fall through */
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case 79: *frm = RLCMAC_HDR_TYPE_2; *mcs = 6; break;
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case 118: /* fall through */
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case 119: *frm = RLCMAC_HDR_TYPE_1; *mcs = 7; break;
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case 142: /* fall through */
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case 143: *frm = RLCMAC_HDR_TYPE_1; *mcs = 8; break;
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case 154: /* fall through */
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case 155: *frm = RLCMAC_HDR_TYPE_1; *mcs = 9; break;
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default: *frm = RLCMAC_CS1; *mcs = 0; break; /* TODO: report error instead */
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}
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}
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static void
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handle_rlcmac(guint32 frame_nr, tvbuff_t *payload_tvb, packet_info *pinfo, proto_tree *tree)
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{
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int sub_handle;
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RlcMacPrivateData_t rlcmac_data = {0};
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tvbuff_t *data_tvb;
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guint data_block_bits, data_block_offsets[2];
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guint num_calls;
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gboolean is_uplink;
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if (pinfo->p2p_dir == P2P_DIR_SENT) {
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is_uplink = 1;
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sub_handle = GSMTAP_SUB_UM_RLC_MAC_UL;
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} else {
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is_uplink = 0;
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sub_handle = GSMTAP_SUB_UM_RLC_MAC_DL;
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}
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rlcmac_data.magic = GSM_RLC_MAC_MAGIC_NUMBER;
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rlcmac_data.frame_number = frame_nr;
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tvb_len_get_mcs_and_fmt(tvb_reported_length(payload_tvb), is_uplink,
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(guint *) &rlcmac_data.block_format,
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(guint8 *) &rlcmac_data.mcs);
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switch (rlcmac_data.block_format) {
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case RLCMAC_HDR_TYPE_1:
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case RLCMAC_HDR_TYPE_2:
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case RLCMAC_HDR_TYPE_3:
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/* First call of RLC/MAC dissector for header */
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call_dissector_with_data(sub_handles[sub_handle], payload_tvb,
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pinfo, tree, (void *) &rlcmac_data);
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/* now determine how to proceed for data */
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setup_rlc_mac_priv(&rlcmac_data, is_uplink,
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&num_calls, &data_block_bits, data_block_offsets);
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/* and call dissector one or two time for the data blocks */
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if (num_calls >= 2) {
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rlcmac_data.flags = GSM_RLC_MAC_EGPRS_BLOCK1;
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data_tvb = get_egprs_data_block(payload_tvb, data_block_offsets[0],
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data_block_bits, pinfo);
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call_dissector_with_data(sub_handles[sub_handle], data_tvb, pinfo, tree,
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(void *) &rlcmac_data);
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}
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if (num_calls == 3) {
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rlcmac_data.flags = GSM_RLC_MAC_EGPRS_BLOCK2;
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data_tvb = get_egprs_data_block(payload_tvb, data_block_offsets[1],
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data_block_bits, pinfo);
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call_dissector_with_data(sub_handles[sub_handle], data_tvb, pinfo, tree,
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(void *) &rlcmac_data);
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}
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break;
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default:
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/* regular GPRS CS doesn't need any
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* shifting/re-alignment or even separate calls for
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* header and data blocks. We simply call the dissector
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* as-is */
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call_dissector_with_data(sub_handles[sub_handle], payload_tvb, pinfo, tree,
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(void *) &rlcmac_data);
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}
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}
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/* dissect a GSMTAP header and hand payload off to respective dissector */
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static int
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dissect_gsmtap(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)
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@ -565,6 +777,7 @@ dissect_gsmtap(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _
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tvbuff_t *payload_tvb, *l1h_tvb = NULL;
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guint8 hdr_len, type, sub_type, timeslot, subslot;
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guint16 arfcn;
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guint32 frame_nr;
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len = tvb_reported_length(tvb);
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@ -572,6 +785,7 @@ dissect_gsmtap(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _
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type = tvb_get_guint8(tvb, offset + 2);
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timeslot = tvb_get_guint8(tvb, offset + 3);
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arfcn = tvb_get_ntohs(tvb, offset + 4);
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frame_nr = tvb_get_ntohl(tvb, offset + 8);
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sub_type = tvb_get_guint8(tvb, offset + 12);
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subslot = tvb_get_guint8(tvb, offset + 14);
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@ -736,7 +950,6 @@ dissect_gsmtap(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _
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handle_lapdm(sub_type, payload_tvb, pinfo, tree);
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return tvb_captured_length(tvb);
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case GSMTAP_CHANNEL_PACCH:
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case GSMTAP_CHANNEL_PDTCH:
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if (pinfo->p2p_dir == P2P_DIR_SENT) {
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sub_handle = GSMTAP_SUB_UM_RLC_MAC_UL;
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}
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@ -745,6 +958,9 @@ dissect_gsmtap(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _
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sub_handle = GSMTAP_SUB_UM_RLC_MAC_DL;
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}
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break;
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case GSMTAP_CHANNEL_PDTCH:
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handle_rlcmac(frame_nr, payload_tvb, pinfo, tree);
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return tvb_captured_length(tvb);
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/* See 3GPP TS 45.003, section 5.2 "Packet control channels" */
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case GSMTAP_CHANNEL_PTCCH:
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/* PTCCH/D carries Timing Advance updates encoded with CS-1 */
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