FreeCalypso > hg > gsm-net-reveng

annotate tfo/find-is-hdr.c @ 14:98c0881c2af0

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tfo/find-is-hdr: move here from freecalypso-reveng This little program was developed in freecalypso-reveng Hg repository in 2023-03, when we didn't have a separate repository for network-side reverse eng, but now that we do have separate repositories for FreeCalypso (mobile side) vs network side reverse eng, move TFO RE work to the proper place.
author Mychaela Falconia <falcon@freecalypso.org>
date Fri, 24 May 2024 21:18:22 +0000
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14
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Mychaela Falconia <falcon@freecalypso.org>
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1 /*
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Mychaela Falconia <falcon@freecalypso.org>
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2 * This program reads a binary file containing a G.711 PCM stream capture
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Mychaela Falconia <falcon@freecalypso.org>
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3 * and looks for an IS_Header pattern as defined in ETSI TS 101 504
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Mychaela Falconia <falcon@freecalypso.org>
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4 * (GSM 08.62) section A.1.2. The objective is to analyze PCM streams
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Mychaela Falconia <falcon@freecalypso.org>
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5 * originating from extant commercial GSM network operators and see if
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Mychaela Falconia <falcon@freecalypso.org>
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6 * they implement in-band TFO.
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Mychaela Falconia <falcon@freecalypso.org>
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7 */
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8
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9 #include <sys/types.h>
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Mychaela Falconia <falcon@freecalypso.org>
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10 #include <sys/file.h>
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Mychaela Falconia <falcon@freecalypso.org>
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11 #include <sys/stat.h>
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Mychaela Falconia <falcon@freecalypso.org>
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12 #include <sys/mman.h>
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13 #include <stdio.h>
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14 #include <stdlib.h>
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Mychaela Falconia <falcon@freecalypso.org>
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15 #include <unistd.h>
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Mychaela Falconia <falcon@freecalypso.org>
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16
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Mychaela Falconia <falcon@freecalypso.org>
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17 static char *pcmfile;
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Mychaela Falconia <falcon@freecalypso.org>
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18 static size_t pcm_file_size;
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Mychaela Falconia <falcon@freecalypso.org>
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19 static u_char *filemap;
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20
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21 static const u_char hdr_pattern[20] = {0, 1, 0, 1, 0, 1, 1, 0, 1, 0,
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22 0, 1, 1, 0, 1, 0, 1, 0, 0, 1};
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23
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24 static void
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Mychaela Falconia <falcon@freecalypso.org>
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25 mmap_pcm_file()
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Mychaela Falconia <falcon@freecalypso.org>
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26 {
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Mychaela Falconia <falcon@freecalypso.org>
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27 int fd;
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28 struct stat st;
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29
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30 fd = open(pcmfile, O_RDONLY);
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Mychaela Falconia <falcon@freecalypso.org>
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31 if (fd < 0) {
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Mychaela Falconia <falcon@freecalypso.org>
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32 perror(pcmfile);
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33 exit(1);
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Mychaela Falconia <falcon@freecalypso.org>
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34 }
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Mychaela Falconia <falcon@freecalypso.org>
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35 fstat(fd, &st);
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Mychaela Falconia <falcon@freecalypso.org>
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36 if (!S_ISREG(st.st_mode)) {
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37 fprintf(stderr, "error: %s is not a regular file\n", pcmfile);
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38 exit(1);
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Mychaela Falconia <falcon@freecalypso.org>
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39 }
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Mychaela Falconia <falcon@freecalypso.org>
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40 pcm_file_size = st.st_size;
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Mychaela Falconia <falcon@freecalypso.org>
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41 if (pcm_file_size < 320) {
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Mychaela Falconia <falcon@freecalypso.org>
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42 fprintf(stderr, "error: %s is too short\n", pcmfile);
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Mychaela Falconia <falcon@freecalypso.org>
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43 exit(1);
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44 }
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Mychaela Falconia <falcon@freecalypso.org>
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45 filemap = mmap(NULL, pcm_file_size, PROT_READ, MAP_PRIVATE, fd, 0L);
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Mychaela Falconia <falcon@freecalypso.org>
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46 if (filemap == MAP_FAILED) {
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Mychaela Falconia <falcon@freecalypso.org>
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47 perror("mmap");
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48 exit(1);
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Mychaela Falconia <falcon@freecalypso.org>
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49 }
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Mychaela Falconia <falcon@freecalypso.org>
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50 close(fd);
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Mychaela Falconia <falcon@freecalypso.org>
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51 }
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52
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Mychaela Falconia <falcon@freecalypso.org>
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53 static void
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54 try_offset(offset)
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55 size_t offset;
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56 {
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57 unsigned n;
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58
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59 for (n = 0; n < 20; n++) {
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60 if ((filemap[offset + n * 16] & 1) != hdr_pattern[n])
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61 return;
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62 }
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63 printf("Found IS_Header at offset %lu (0x%lx)\n", (u_long) offset,
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Mychaela Falconia <falcon@freecalypso.org>
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64 (u_long) offset);
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65 }
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66
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67 main(argc, argv)
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68 char **argv;
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69 {
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70 size_t offset, endoff;
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71
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72 if (argc != 2) {
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73 fprintf(stderr, "usage: %s pcm-capture-file\n", argv[0]);
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Mychaela Falconia <falcon@freecalypso.org>
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74 exit(1);
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Mychaela Falconia <falcon@freecalypso.org>
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75 }
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76 pcmfile = argv[1];
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77 mmap_pcm_file();
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Mychaela Falconia <falcon@freecalypso.org>
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78 endoff = pcm_file_size - 320;
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79 for (offset = 0; offset <= endoff; offset++)
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Mychaela Falconia <falcon@freecalypso.org>
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80 try_offset(offset);
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81 exit(0);
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82 }