2020-11-19 05:13:24 +00:00
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/* packet-ssyncp.c
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* Routines for dissecting mosh's State Synchronization Protocol
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* Copyright 2020 Google LLC
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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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* Copyright 1998 Gerald Combs
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*
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* SPDX-License-Identifier: GPL-2.0-or-later
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*/
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/*
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* State Synchronization Protocol is the protocol used by mosh:
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* <https://mosh.org/mosh-paper-draft.pdf>
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*
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* The protocol name is abbreviated as SSyncP to avoid conflict with the
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* "Scripting Service Protocol".
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*
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* The protocol is based on UDP, with a plaintext header followed by an
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* encrypted payload. For now we just support decrypting a single connection at
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* a time, using the MOSH_KEY dumped from the environment variables
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* (`cat /proc/$pid/environ | tr '\0' '\n' | grep MOSH_KEY` on Linux).
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* Note that to display the embedded protobuf properly, you'll have to add
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* src/protobufs/ from mosh's source code to the ProtoBuf search path.
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* For now we stop decoding after reaching the first level of protobufs; in
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* them, a second layer of protobufs is sometimes embedded (e.g. for
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* transmitting screen contents and such). Implementing that is left as an
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* exercise for the reader.
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*/
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#include <config.h>
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#include <epan/packet.h> /* Should be first Wireshark include (other than config.h) */
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#include <epan/conversation.h>
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2021-07-26 00:31:17 +00:00
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#include <epan/wmem_scopes.h>
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2020-11-19 05:13:24 +00:00
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#include <epan/proto_data.h>
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#include <epan/prefs.h>
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#include <epan/expert.h>
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#include <wsutil/report_message.h>
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#include <wsutil/wsgcrypt.h>
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void proto_reg_handoff_ssyncp(void);
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void proto_register_ssyncp(void);
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static int proto_ssyncp = -1;
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static int hf_ssyncp_direction = -1;
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static int hf_ssyncp_seq = -1;
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static int hf_ssyncp_encrypted = -1;
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static int hf_ssyncp_seq_delta = -1;
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static int hf_ssyncp_timestamp = -1;
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static int hf_ssyncp_timestamp_reply = -1;
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static int hf_ssyncp_frag_seq = -1;
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static int hf_ssyncp_frag_final = -1;
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static int hf_ssyncp_frag_idx = -1;
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static int hf_ssyncp_rtt_to_server = -1;
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static int hf_ssyncp_rtt_to_client = -1;
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/* Initialize the subtree pointers */
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static gint ett_ssyncp = -1;
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static gint ett_ssyncp_decrypted = -1;
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static expert_field ei_ssyncp_fragmented = EI_INIT;
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static expert_field ei_ssyncp_bad_key = EI_INIT;
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static const char *pref_ssyncp_key;
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static char ssyncp_raw_aes_key[16];
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static gboolean have_ssyncp_key;
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static dissector_handle_t dissector_protobuf;
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typedef struct _ssyncp_conv_info_t {
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/* last sequence numbers per direction */
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guint64 last_seq[2];
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/* for each direction, have we seen any traffic yet? */
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gboolean seen_packet[2];
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guint16 clock_offset[2];
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gboolean clock_seen[2];
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} ssyncp_conv_info_t;
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typedef struct _ssyncp_packet_info_t {
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gboolean first_packet;
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gint64 seq_delta;
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gboolean have_rtt_estimate;
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gint16 rtt_estimate;
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} ssyncp_packet_info_t;
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#define SSYNCP_IV_PAD 4
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#define SSYNCP_SEQ_LEN 8
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#define SSYNCP_DATAGRAM_HEADER_LEN (SSYNCP_SEQ_LEN + 2 + 2) /* 64-bit IV and two 16-bit timestamps */
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#define SSYNCP_TRANSPORT_HEADER_LEN (8 + 2)
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#define SSYNCP_AUTHTAG_LEN 16 /* 128-bit auth tag */
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/*
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* We only match on 60001, which mosh uses for its first connection.
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* If there are more connections in the range 60002-61000, the user will have to
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* mark those as ssyncp traffic manually - we'd have too many false positives
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* otherwise.
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*/
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#define SSYNCP_UDP_PORT 60001
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static int
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dissect_ssyncp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree,
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void *data _U_)
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{
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/* Check that we have at least a datagram plus an OCB auth tag. */
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if (tvb_reported_length(tvb) < SSYNCP_DATAGRAM_HEADER_LEN + SSYNCP_TRANSPORT_HEADER_LEN + SSYNCP_AUTHTAG_LEN)
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return 0;
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guint64 direction_and_seq = tvb_get_guint64(tvb, 0, ENC_BIG_ENDIAN);
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guint direction = direction_and_seq >> 63;
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guint64 seq = direction_and_seq & ~(1ULL << 63);
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/* Heuristic: The 63-bit sequence number starts from zero and increments
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* from there. Even if you send 1000 packets per second over 10 years, you
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* won't reach 2^35. So check that the sequence number is not outrageously
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* high.
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*/
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if (seq > (1ULL << 35))
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return 0;
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/* On the first pass, track the previous sequence numbers per direction,
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* compute deltas between sequence numbers, and save those deltas.
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* On subsequent passes, use the computed deltas.
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*/
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ssyncp_packet_info_t *ssyncp_pinfo;
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ssyncp_conv_info_t *ssyncp_info = NULL;
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if (pinfo->fd->visited) {
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ssyncp_pinfo = (ssyncp_packet_info_t *)p_get_proto_data(wmem_file_scope(), pinfo, proto_ssyncp, 0);
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} else {
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conversation_t *conversation = find_or_create_conversation(pinfo);
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ssyncp_info = (ssyncp_conv_info_t *)conversation_get_proto_data(conversation, proto_ssyncp);
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if (!ssyncp_info) {
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ssyncp_info = wmem_new(wmem_file_scope(), ssyncp_conv_info_t);
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conversation_add_proto_data(conversation, proto_ssyncp, ssyncp_info);
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ssyncp_info->seen_packet[0] = FALSE;
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ssyncp_info->seen_packet[1] = FALSE;
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ssyncp_info->clock_seen[0] = FALSE;
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ssyncp_info->clock_seen[1] = FALSE;
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}
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ssyncp_pinfo = wmem_new(wmem_file_scope(), ssyncp_packet_info_t);
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ssyncp_pinfo->first_packet = !ssyncp_info->seen_packet[direction];
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if (ssyncp_pinfo->first_packet) {
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ssyncp_info->seen_packet[direction] = TRUE;
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} else {
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ssyncp_pinfo->seq_delta = seq - ssyncp_info->last_seq[direction];
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}
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ssyncp_pinfo->have_rtt_estimate = FALSE;
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p_add_proto_data(wmem_file_scope(), pinfo, proto_ssyncp, 0, ssyncp_pinfo);
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ssyncp_info->last_seq[direction] = seq;
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}
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/*** COLUMN DATA ***/
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col_set_str(pinfo->cinfo, COL_PROTOCOL, "ssyncp");
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col_clear(pinfo->cinfo, COL_INFO);
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char *direction_str = direction ? "Server->Client" : "Client->Server";
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col_set_str(pinfo->cinfo, COL_INFO, direction_str);
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/*** PROTOCOL TREE ***/
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/* create display subtree for the protocol */
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proto_item *ti = proto_tree_add_item(tree, proto_ssyncp, tvb, 0, -1, ENC_NA);
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proto_tree *ssyncp_tree = proto_item_add_subtree(ti, ett_ssyncp);
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/* Add an item to the subtree, see section 1.5 of README.dissector for more
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* information. */
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proto_tree_add_item(ssyncp_tree, hf_ssyncp_direction, tvb,
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0, 1, ENC_BIG_ENDIAN);
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proto_tree_add_item(ssyncp_tree, hf_ssyncp_seq, tvb,
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0, 8, ENC_BIG_ENDIAN);
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2020-12-01 12:42:01 +00:00
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#ifdef GCRY_OCB_BLOCK_LEN
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proto_item *encrypted_item =
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#endif
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proto_tree_add_item(ssyncp_tree, hf_ssyncp_encrypted,
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2020-11-19 05:13:24 +00:00
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tvb, 8, -1, ENC_NA);
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if (!ssyncp_pinfo->first_packet) {
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proto_item *delta_item =
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proto_tree_add_int64(ssyncp_tree, hf_ssyncp_seq_delta, tvb, 0, 0,
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ssyncp_pinfo->seq_delta);
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proto_item_set_generated(delta_item);
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}
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unsigned char *decrypted = NULL;
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guint decrypted_len = 0;
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/* avoid build failure on ancient libgcrypt without OCB support */
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#ifdef GCRY_OCB_BLOCK_LEN
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if (have_ssyncp_key) {
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gcry_error_t gcry_err;
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/* try to decrypt the rest of the packet */
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gcry_cipher_hd_t gcry_hd;
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gcry_err = gcry_cipher_open(&gcry_hd, GCRY_CIPHER_AES128, GCRY_CIPHER_MODE_OCB, 0);
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if (gcry_err_code(gcry_err)) {
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/* this shouldn't happen (even if the packet is garbage) */
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report_failure("ssyncp: unable to initialize cipher???");
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return tvb_captured_length(tvb);
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}
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gcry_err = gcry_cipher_setkey(gcry_hd, ssyncp_raw_aes_key, sizeof(ssyncp_raw_aes_key));
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if (gcry_err_code(gcry_err)) {
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/* this shouldn't happen (even if the packet is garbage) */
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report_failure("ssyncp: unable to set key???");
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gcry_cipher_close(gcry_hd);
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return tvb_captured_length(tvb);
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}
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char nonce[SSYNCP_IV_PAD + SSYNCP_SEQ_LEN];
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memset(nonce, 0, SSYNCP_IV_PAD);
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tvb_memcpy(tvb, nonce + SSYNCP_IV_PAD, 0, SSYNCP_SEQ_LEN);
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gcry_err = gcry_cipher_setiv(gcry_hd, nonce, sizeof(nonce));
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if (gcry_err_code(gcry_err)) {
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/* this shouldn't happen (even if the packet is garbage) */
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report_failure("ssyncp: unable to set iv???");
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gcry_cipher_close(gcry_hd);
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return tvb_captured_length(tvb);
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}
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decrypted_len = tvb_captured_length(tvb) - SSYNCP_SEQ_LEN - SSYNCP_AUTHTAG_LEN;
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decrypted = (unsigned char *)tvb_memdup(pinfo->pool, tvb,
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SSYNCP_SEQ_LEN, decrypted_len);
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gcry_cipher_final(gcry_hd);
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gcry_err = gcry_cipher_decrypt(gcry_hd, decrypted, decrypted_len, NULL, 0);
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if (gcry_err_code(gcry_err)) {
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/* this shouldn't happen (even if the packet is garbage) */
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report_failure("ssyncp: unable to decrypt???");
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gcry_cipher_close(gcry_hd);
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return tvb_captured_length(tvb);
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}
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gcry_err = gcry_cipher_checktag(gcry_hd,
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tvb_get_ptr(tvb, SSYNCP_SEQ_LEN+decrypted_len, SSYNCP_AUTHTAG_LEN),
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SSYNCP_AUTHTAG_LEN);
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if (gcry_err_code(gcry_err) && gcry_err_code(gcry_err) != GPG_ERR_CHECKSUM) {
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/* this shouldn't happen (even if the packet is garbage) */
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report_failure("ssyncp: unable to check auth tag???");
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gcry_cipher_close(gcry_hd);
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return tvb_captured_length(tvb);
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}
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if (gcry_err_code(gcry_err)) {
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/* if the tag is wrong, the key was wrong and the decrypted data is useless */
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decrypted = NULL;
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expert_add_info(pinfo, encrypted_item, &ei_ssyncp_bad_key);
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}
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gcry_cipher_close(gcry_hd);
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}
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#endif
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if (decrypted) {
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tvbuff_t *decrypted_tvb = tvb_new_child_real_data(tvb, decrypted, decrypted_len, decrypted_len);
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add_new_data_source(pinfo, decrypted_tvb, "Decrypted data");
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if (!pinfo->fd->visited) {
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guint16 our_clock16 = ((guint64)pinfo->abs_ts.secs * 1000 + pinfo->abs_ts.nsecs / 1000000) & 0xffff;
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guint16 sender_ts = tvb_get_guint16(decrypted_tvb, 0, ENC_BIG_ENDIAN);
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guint16 reply_ts = tvb_get_guint16(decrypted_tvb, 2, ENC_BIG_ENDIAN);
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ssyncp_info->clock_offset[direction] = sender_ts - our_clock16;
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ssyncp_info->clock_seen[direction] = TRUE;
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if (reply_ts != 0xffff && ssyncp_info->clock_seen[1-direction]) {
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guint16 projected_send_time_our_clock = reply_ts - ssyncp_info->clock_offset[1-direction];
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ssyncp_pinfo->rtt_estimate = our_clock16 - projected_send_time_our_clock;
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ssyncp_pinfo->have_rtt_estimate = TRUE;
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}
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}
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proto_tree *dec_tree = proto_tree_add_subtree(ssyncp_tree, decrypted_tvb,
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0, -1, ett_ssyncp_decrypted, NULL, "Decrypted data");
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proto_tree_add_item(dec_tree, hf_ssyncp_timestamp, decrypted_tvb,
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0, 2, ENC_BIG_ENDIAN);
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proto_tree_add_item(dec_tree, hf_ssyncp_timestamp_reply, decrypted_tvb,
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2, 2, ENC_BIG_ENDIAN);
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if (ssyncp_pinfo->have_rtt_estimate) {
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int rtt_id = direction ? hf_ssyncp_rtt_to_server : hf_ssyncp_rtt_to_client;
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proto_item *rtt_item = proto_tree_add_int(dec_tree, rtt_id, decrypted_tvb, 2, 2, ssyncp_pinfo->rtt_estimate);
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proto_item_set_generated(rtt_item);
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}
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proto_tree_add_item(dec_tree, hf_ssyncp_frag_seq, decrypted_tvb,
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4, 8, ENC_BIG_ENDIAN);
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proto_tree_add_item(dec_tree, hf_ssyncp_frag_final, decrypted_tvb,
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12, 2, ENC_BIG_ENDIAN);
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proto_item *frag_idx_item = proto_tree_add_item(dec_tree,
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hf_ssyncp_frag_idx, decrypted_tvb, 12, 2, ENC_BIG_ENDIAN);
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/* TODO actually handle fragmentation; for now just bail out on fragmentation */
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if (tvb_get_guint16(decrypted_tvb, 12, ENC_BIG_ENDIAN) != 0x8000) {
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expert_add_info(pinfo, frag_idx_item, &ei_ssyncp_fragmented);
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return tvb_captured_length(tvb);
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}
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tvbuff_t *inflated_tvb = tvb_child_uncompress(decrypted_tvb, decrypted_tvb, 14, decrypted_len - 14);
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if (inflated_tvb == NULL)
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return tvb_captured_length(tvb);
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add_new_data_source(pinfo, inflated_tvb, "Inflated data");
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if (dissector_protobuf) {
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call_dissector_with_data(dissector_protobuf, inflated_tvb, pinfo,
|
|
|
|
dec_tree, "message,TransportBuffers.Instruction");
|
|
|
|
}
|
|
|
|
}
|
|
|
|
|
|
|
|
return tvb_captured_length(tvb);
|
|
|
|
}
|
|
|
|
|
|
|
|
/* Register the protocol with Wireshark.
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|
|
|
*
|
|
|
|
* This format is required because a script is used to build the C function that
|
|
|
|
* calls all the protocol registration.
|
|
|
|
*/
|
|
|
|
void
|
|
|
|
proto_register_ssyncp(void)
|
|
|
|
{
|
|
|
|
static const true_false_string direction_name = {
|
|
|
|
"Server->Client",
|
|
|
|
"Client->Server"
|
|
|
|
};
|
|
|
|
|
|
|
|
/* Setup list of header fields See Section 1.5 of README.dissector for
|
|
|
|
* details. */
|
|
|
|
static hf_register_info hf[] = {
|
|
|
|
{ &hf_ssyncp_direction,
|
|
|
|
{ "Direction", "ssyncp.direction",
|
|
|
|
FT_BOOLEAN, 8, TFS(&direction_name), 0x80,
|
|
|
|
"Direction of packet", HFILL }
|
|
|
|
},
|
|
|
|
{ &hf_ssyncp_seq,
|
|
|
|
{ "Sequence number", "ssyncp.seq",
|
|
|
|
FT_UINT64, BASE_HEX, NULL, 0x7fffffffffffffff,
|
|
|
|
"Monotonically incrementing packet sequence number", HFILL }
|
|
|
|
},
|
|
|
|
{ &hf_ssyncp_encrypted,
|
|
|
|
{ "Encrypted data", "ssyncp.enc_data",
|
|
|
|
FT_BYTES, BASE_NONE, NULL, 0,
|
|
|
|
"Encrypted RTT estimation fields and Transport Layer payload, encrypted with AES-128-OCB",
|
|
|
|
HFILL }
|
|
|
|
},
|
|
|
|
{ &hf_ssyncp_seq_delta,
|
|
|
|
{ "Sequence number delta", "ssyncp.seq_delta",
|
|
|
|
FT_INT64, BASE_DEC, NULL, 0,
|
|
|
|
"Delta from last sequence number; 1 is normal, 0 is duplicated packet, <0 is reordering, >1 is reordering or packet loss", HFILL }
|
|
|
|
},
|
|
|
|
{ &hf_ssyncp_timestamp,
|
|
|
|
{ "Truncated timestamp", "ssyncp.timestamp",
|
|
|
|
FT_UINT16, BASE_HEX, NULL, 0,
|
|
|
|
"Low 16 bits of sender's time in milliseconds", HFILL }
|
|
|
|
},
|
|
|
|
{ &hf_ssyncp_timestamp_reply,
|
|
|
|
{ "Last timestamp received", "ssyncp.timestamp_reply",
|
|
|
|
FT_UINT16, BASE_HEX, NULL, 0,
|
|
|
|
"Low 16 bits of timestamp of last received packet plus time since it was received (for RTT estimation)", HFILL }
|
|
|
|
},
|
|
|
|
{ &hf_ssyncp_frag_seq,
|
|
|
|
{ "Fragment ID", "ssyncp.frag_seq",
|
|
|
|
FT_UINT64, BASE_HEX, NULL, 0,
|
|
|
|
"Transport-level sequence number, used for fragment reassembly", HFILL }
|
|
|
|
},
|
|
|
|
{ &hf_ssyncp_frag_final,
|
|
|
|
{ "Final fragment", "ssyncp.frag_final",
|
|
|
|
FT_BOOLEAN, 16, NULL, 0x8000,
|
|
|
|
"Is this the last fragment?", HFILL }
|
|
|
|
},
|
|
|
|
{ &hf_ssyncp_frag_idx,
|
|
|
|
{ "Fragment Index", "ssyncp.frag_idx",
|
|
|
|
FT_UINT16, BASE_HEX, NULL, 0x7fff,
|
|
|
|
"Index of this fragment in the list of fragments of the transport-level message", HFILL }
|
|
|
|
},
|
|
|
|
{ &hf_ssyncp_rtt_to_server,
|
|
|
|
{ "RTT estimate to server (in ms)", "ssyncp.rtt_est_to_server",
|
|
|
|
FT_INT16, BASE_DEC, NULL, 0,
|
|
|
|
"Estimated round trip time from point of capture to server", HFILL }
|
|
|
|
},
|
|
|
|
{ &hf_ssyncp_rtt_to_client,
|
|
|
|
{ "RTT estimate to client (in ms)", "ssyncp.rtt_est_to_client",
|
|
|
|
FT_INT16, BASE_DEC, NULL, 0,
|
|
|
|
"Estimated round trip time from point of capture to client", HFILL }
|
|
|
|
}
|
|
|
|
};
|
|
|
|
|
|
|
|
/* Setup protocol subtree array */
|
|
|
|
static gint *ett[] = {
|
|
|
|
&ett_ssyncp,
|
|
|
|
&ett_ssyncp_decrypted
|
|
|
|
};
|
|
|
|
|
|
|
|
/* Setup protocol expert items */
|
|
|
|
static ei_register_info ei[] = {
|
|
|
|
{ &ei_ssyncp_fragmented,
|
|
|
|
{ "ssyncp.fragmented", PI_REASSEMBLE, PI_WARN,
|
|
|
|
"SSYNCP-level fragmentation, dissector can't handle that", EXPFILL }
|
|
|
|
},
|
|
|
|
{ &ei_ssyncp_bad_key,
|
|
|
|
{ "ssyncp.badkey", PI_DECRYPTION, PI_WARN,
|
|
|
|
"Encrypted data could not be decrypted with the provided key", EXPFILL }
|
|
|
|
}
|
|
|
|
};
|
|
|
|
|
|
|
|
/* Register the protocol name and description */
|
|
|
|
proto_ssyncp = proto_register_protocol("State Synchronization Protocol", "SSyncP", "ssyncp");
|
|
|
|
|
|
|
|
/* Required function calls to register the header fields and subtrees */
|
|
|
|
proto_register_field_array(proto_ssyncp, hf, array_length(hf));
|
|
|
|
proto_register_subtree_array(ett, array_length(ett));
|
|
|
|
|
|
|
|
expert_module_t *expert_ssyncp = expert_register_protocol(proto_ssyncp);
|
|
|
|
expert_register_field_array(expert_ssyncp, ei, array_length(ei));
|
|
|
|
|
|
|
|
module_t *ssyncp_module = prefs_register_protocol(proto_ssyncp, proto_reg_handoff_ssyncp);
|
|
|
|
|
|
|
|
prefs_register_string_preference(ssyncp_module, "key",
|
|
|
|
"ssyncp MOSH_KEY",
|
|
|
|
"MOSH_KEY AES key (from mosh-{client,server} environment variable)",
|
|
|
|
&pref_ssyncp_key);
|
|
|
|
}
|
|
|
|
|
|
|
|
void
|
|
|
|
proto_reg_handoff_ssyncp(void)
|
|
|
|
{
|
|
|
|
static dissector_handle_t ssyncp_handle;
|
|
|
|
static gboolean initialized = FALSE;
|
|
|
|
|
|
|
|
if (!initialized) {
|
|
|
|
ssyncp_handle = create_dissector_handle(dissect_ssyncp, proto_ssyncp);
|
|
|
|
dissector_add_uint("udp.port", SSYNCP_UDP_PORT, ssyncp_handle);
|
|
|
|
initialized = TRUE;
|
|
|
|
}
|
|
|
|
|
|
|
|
dissector_protobuf = find_dissector("protobuf");
|
|
|
|
if (dissector_protobuf == NULL) {
|
|
|
|
report_failure("unable to find protobuf dissector");
|
|
|
|
}
|
|
|
|
|
|
|
|
have_ssyncp_key = FALSE;
|
|
|
|
if (strlen(pref_ssyncp_key) != 0) {
|
|
|
|
if (strlen(pref_ssyncp_key) != 22) {
|
|
|
|
report_failure("ssyncp: invalid key, must be 22 characters long");
|
|
|
|
return;
|
|
|
|
}
|
|
|
|
char base64_key[25];
|
|
|
|
memcpy(base64_key, pref_ssyncp_key, 22);
|
|
|
|
memcpy(base64_key+22, "==\0", 3);
|
|
|
|
gsize out_len;
|
|
|
|
if (g_base64_decode_inplace(base64_key, &out_len) == NULL || out_len != sizeof(ssyncp_raw_aes_key)) {
|
|
|
|
report_failure("ssyncp: invalid key, base64 decoding (with \"==\" appended) failed");
|
|
|
|
return;
|
|
|
|
}
|
|
|
|
memcpy(ssyncp_raw_aes_key, base64_key, sizeof(ssyncp_raw_aes_key));
|
|
|
|
have_ssyncp_key = TRUE;
|
|
|
|
}
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Editor modelines - https://www.wireshark.org/tools/modelines.html
|
|
|
|
*
|
|
|
|
* Local variables:
|
|
|
|
* c-basic-offset: 4
|
|
|
|
* tab-width: 8
|
|
|
|
* indent-tabs-mode: nil
|
|
|
|
* End:
|
|
|
|
*
|
|
|
|
* vi: set shiftwidth=4 tabstop=8 expandtab:
|
|
|
|
* :indentSize=4:tabSize=8:noTabs=true:
|
|
|
|
*/
|