1 | /* vi: set sw=4 ts=4: */
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2 | /*
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3 | * micro lpd
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4 | *
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5 | * Copyright (C) 2008 by Vladimir Dronnikov <dronnikov@gmail.com>
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6 | *
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7 | * Licensed under GPLv2, see file LICENSE in this source tree.
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8 | */
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9 |
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10 | /*
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11 | * A typical usage of BB lpd looks as follows:
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12 | * # tcpsvd -E 0 515 lpd [SPOOLDIR] [HELPER-PROG [ARGS...]]
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13 | *
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14 | * This starts TCP listener on port 515 (default for LP protocol).
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15 | * When a client connection is made (via lpr) lpd first changes its
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16 | * working directory to SPOOLDIR (current dir is the default).
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17 | *
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18 | * SPOOLDIR is the spool directory which contains printing queues
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19 | * and should have the following structure:
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20 | *
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21 | * SPOOLDIR/
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22 | * <queue1>
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23 | * ...
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24 | * <queueN>
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25 | *
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26 | * <queueX> can be of two types:
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27 | * A. a printer character device, an ordinary file or a link to such;
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28 | * B. a directory.
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29 | *
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30 | * In case A lpd just dumps the data it receives from client (lpr) to the
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31 | * end of queue file/device. This is non-spooling mode.
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32 | *
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33 | * In case B lpd enters spooling mode. It reliably saves client data along
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34 | * with control info in two unique files under the queue directory. These
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35 | * files are named dfAXXXHHHH and cfAXXXHHHH, where XXX is the job number
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36 | * and HHHH is the client hostname. Unless a printing helper application
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37 | * is specified lpd is done at this point.
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38 | *
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39 | * NB: file names are produced by peer! They actually may be anything at all.
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40 | * lpd only sanitizes them (by removing most non-alphanumerics).
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41 | *
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42 | * If HELPER-PROG (with optional arguments) is specified then lpd continues
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43 | * to process client data:
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44 | * 1. it reads and parses control file (cfA...). The parse process
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45 | * results in setting environment variables whose values were passed
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46 | * in control file; when parsing is complete, lpd deletes control file.
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47 | * 2. it spawns specified helper application. It is then
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48 | * the helper application who is responsible for both actual printing
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49 | * and deleting of processed data file.
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50 | *
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51 | * A good lpr passes control files which when parsed provides the following
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52 | * variables:
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53 | * $H = host which issues the job
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54 | * $P = user who prints
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55 | * $C = class of printing (what is printed on banner page)
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56 | * $J = the name of the job
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57 | * $L = print banner page
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58 | * $M = the user to whom a mail should be sent if a problem occurs
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59 | *
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60 | * We specifically filter out and NOT provide:
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61 | * $l = name of datafile ("dfAxxx") - file whose content are to be printed
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62 | *
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63 | * lpd provides $DATAFILE instead - the ACTUAL name
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64 | * of the datafile under which it was saved.
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65 | * $l would be not reliable (you would be at mercy of remote peer).
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66 | *
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67 | * Thus, a typical helper can be something like this:
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68 | * #!/bin/sh
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69 | * cat ./"$DATAFILE" >/dev/lp0
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70 | * mv -f ./"$DATAFILE" save/
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71 | */
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72 | //config:config LPD
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73 | //config: bool "lpd"
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74 | //config: default y
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75 | //config: help
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76 | //config: lpd is a print spooling daemon.
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77 |
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78 | //applet:IF_LPD(APPLET(lpd, BB_DIR_USR_SBIN, BB_SUID_DROP))
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79 |
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80 | //kbuild:lib-$(CONFIG_LPD) += lpd.o
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81 |
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82 | //usage:#define lpd_trivial_usage
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83 | //usage: "SPOOLDIR [HELPER [ARGS]]"
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84 | //usage:#define lpd_full_usage "\n\n"
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85 | //usage: "SPOOLDIR must contain (symlinks to) device nodes or directories"
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86 | //usage: "\nwith names matching print queue names. In the first case, jobs are"
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87 | //usage: "\nsent directly to the device. Otherwise each job is stored in queue"
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88 | //usage: "\ndirectory and HELPER program is called. Name of file to print"
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89 | //usage: "\nis passed in $DATAFILE variable."
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90 | //usage: "\nExample:"
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91 | //usage: "\n tcpsvd -E 0 515 softlimit -m 999999 lpd /var/spool ./print"
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92 |
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93 | #include "libbb.h"
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94 |
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95 | // strip argument of bad chars
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96 | static char *sane(char *str)
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97 | {
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98 | char *s = str;
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99 | char *p = s;
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100 | while (*s) {
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101 | if (isalnum(*s) || '-' == *s || '_' == *s) {
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102 | *p++ = *s;
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103 | }
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104 | s++;
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105 | }
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106 | *p = '\0';
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107 | return str;
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108 | }
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109 |
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110 | static char *xmalloc_read_stdin(void)
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111 | {
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112 | // SECURITY:
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113 | size_t max = 4 * 1024; // more than enough for commands!
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114 | return xmalloc_reads(STDIN_FILENO, &max);
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115 | }
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116 |
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117 | int lpd_main(int argc, char *argv[]) MAIN_EXTERNALLY_VISIBLE;
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118 | int lpd_main(int argc UNUSED_PARAM, char *argv[])
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119 | {
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120 | int spooling = spooling; // for compiler
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121 | char *s, *queue;
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122 | char *filenames[2];
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123 |
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124 | // goto spool directory
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125 | if (*++argv)
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126 | xchdir(*argv++);
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127 |
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128 | // error messages of xfuncs will be sent over network
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129 | xdup2(STDOUT_FILENO, STDERR_FILENO);
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130 |
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131 | // nullify ctrl/data filenames
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132 | memset(filenames, 0, sizeof(filenames));
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133 |
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134 | // read command
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135 | s = queue = xmalloc_read_stdin();
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136 | // we understand only "receive job" command
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137 | if (2 != *queue) {
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138 | unsupported_cmd:
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139 | printf("Command %02x %s\n",
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140 | (unsigned char)s[0], "is not supported");
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141 | goto err_exit;
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142 | }
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143 |
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144 | // parse command: "2 | QUEUE_NAME | '\n'"
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145 | queue++;
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146 | // protect against "/../" attacks
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147 | // *strchrnul(queue, '\n') = '\0'; - redundant, sane() will do
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148 | if (!*sane(queue))
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149 | return EXIT_FAILURE;
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150 |
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151 | // queue is a directory -> chdir to it and enter spooling mode
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152 | spooling = chdir(queue) + 1; // 0: cannot chdir, 1: done
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153 | // we don't free(s), we might need "queue" var later
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154 |
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155 | while (1) {
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156 | char *fname;
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157 | int fd;
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158 | // int is easier than ssize_t: can use xatoi_positive,
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159 | // and can correctly display error returns (-1)
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160 | int expected_len, real_len;
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161 |
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162 | // signal OK
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163 | safe_write(STDOUT_FILENO, "", 1);
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164 |
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165 | // get subcommand
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166 | // valid s must be of form: "SUBCMD | LEN | space | FNAME"
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167 | // N.B. we bail out on any error
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168 | s = xmalloc_read_stdin();
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169 | if (!s) { // (probably) EOF
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170 | char *p, *q, var[2];
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171 |
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172 | // non-spooling mode or no spool helper specified
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173 | if (!spooling || !*argv)
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174 | return EXIT_SUCCESS; // the only non-error exit
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175 | // spooling mode but we didn't see both ctrlfile & datafile
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176 | if (spooling != 7)
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177 | goto err_exit; // reject job
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178 |
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179 | // spooling mode and spool helper specified -> exec spool helper
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180 | // (we exit 127 if helper cannot be executed)
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181 | var[1] = '\0';
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182 | // read and delete ctrlfile
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183 | q = xmalloc_xopen_read_close(filenames[0], NULL);
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184 | unlink(filenames[0]);
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185 | // provide datafile name
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186 | // we can use leaky setenv since we are about to exec or exit
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187 | xsetenv("DATAFILE", filenames[1]);
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188 | // parse control file by "\n"
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189 | while ((p = strchr(q, '\n')) != NULL && isalpha(*q)) {
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190 | *p++ = '\0';
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191 | // q is a line of <SYM><VALUE>,
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192 | // we are setting environment string <SYM>=<VALUE>.
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193 | // Ignoring "l<datafile>", exporting others:
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194 | if (*q != 'l') {
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195 | var[0] = *q++;
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196 | xsetenv(var, q);
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197 | }
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198 | q = p; // next line
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199 | }
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200 | // helper should not talk over network.
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201 | // this call reopens stdio fds to "/dev/null"
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202 | // (no daemonization is done)
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203 | bb_daemonize_or_rexec(DAEMON_DEVNULL_STDIO | DAEMON_ONLY_SANITIZE, NULL);
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204 | BB_EXECVP_or_die(argv);
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205 | }
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206 |
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207 | // validate input.
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208 | // we understand only "control file" or "data file" cmds
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209 | if (2 != s[0] && 3 != s[0])
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210 | goto unsupported_cmd;
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211 | if (spooling & (1 << (s[0]-1))) {
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212 | puts("Duplicated subcommand");
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213 | goto err_exit;
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214 | }
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215 | // get filename
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216 | chomp(s);
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217 | fname = strchr(s, ' ');
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218 | if (!fname) {
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219 | // bad_fname:
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220 | puts("No or bad filename");
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221 | goto err_exit;
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222 | }
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223 | *fname++ = '\0';
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224 | // // s[0]==2: ctrlfile, must start with 'c'
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225 | // // s[0]==3: datafile, must start with 'd'
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226 | // if (fname[0] != s[0] + ('c'-2))
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227 | // goto bad_fname;
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228 | // get length
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229 | expected_len = bb_strtou(s + 1, NULL, 10);
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230 | if (errno || expected_len < 0) {
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231 | puts("Bad length");
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232 | goto err_exit;
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233 | }
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234 | if (2 == s[0] && expected_len > 16 * 1024) {
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235 | // SECURITY:
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236 | // ctrlfile can't be big (we want to read it back later!)
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237 | puts("File is too big");
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238 | goto err_exit;
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239 | }
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240 |
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241 | // open the file
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242 | if (spooling) {
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243 | // spooling mode: dump both files
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244 | // job in flight has mode 0200 "only writable"
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245 | sane(fname);
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246 | fd = open3_or_warn(fname, O_CREAT | O_WRONLY | O_TRUNC | O_EXCL, 0200);
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247 | if (fd < 0)
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248 | goto err_exit;
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249 | filenames[s[0] - 2] = xstrdup(fname);
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250 | } else {
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251 | // non-spooling mode:
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252 | // 2: control file (ignoring), 3: data file
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253 | fd = -1;
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254 | if (3 == s[0])
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255 | fd = xopen(queue, O_RDWR | O_APPEND);
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256 | }
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257 |
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258 | // signal OK
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259 | safe_write(STDOUT_FILENO, "", 1);
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260 |
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261 | // copy the file
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262 | real_len = bb_copyfd_size(STDIN_FILENO, fd, expected_len);
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263 | if (real_len != expected_len) {
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264 | printf("Expected %d but got %d bytes\n",
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265 | expected_len, real_len);
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266 | goto err_exit;
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267 | }
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268 | // get EOF indicator, see whether it is NUL (ok)
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269 | // (and don't trash s[0]!)
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270 | if (safe_read(STDIN_FILENO, &s[1], 1) != 1 || s[1] != 0) {
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271 | // don't send error msg to peer - it obviously
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272 | // doesn't follow the protocol, so probably
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273 | // it can't understand us either
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274 | goto err_exit;
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275 | }
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276 |
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277 | if (spooling) {
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278 | // chmod completely downloaded file as "readable+writable"
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279 | fchmod(fd, 0600);
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280 | // accumulate dump state
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281 | // N.B. after all files are dumped spooling should be 1+2+4==7
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282 | spooling |= (1 << (s[0]-1)); // bit 1: ctrlfile; bit 2: datafile
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283 | }
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284 |
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285 | free(s);
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286 | close(fd); // NB: can do close(-1). Who cares?
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287 |
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288 | // NB: don't do "signal OK" write here, it will be done
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289 | // at the top of the loop
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290 | } // while (1)
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291 |
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292 | err_exit:
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293 | // don't keep corrupted files
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294 | if (spooling) {
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295 | #define i spooling
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296 | for (i = 2; --i >= 0; )
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297 | if (filenames[i])
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298 | unlink(filenames[i]);
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299 | }
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300 | return EXIT_FAILURE;
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301 | }
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