1 | /* vi: set sw=4 ts=4: */
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2 | /*
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3 | * bare bones sendmail
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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 | //kbuild:lib-$(CONFIG_SENDMAIL) += sendmail.o mail.o
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11 |
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12 | //usage:#define sendmail_trivial_usage
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13 | //usage: "[OPTIONS] [RECIPIENT_EMAIL]..."
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14 | //usage:#define sendmail_full_usage "\n\n"
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15 | //usage: "Read email from stdin and send it\n"
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16 | //usage: "\nStandard options:"
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17 | //usage: "\n -t Read additional recipients from message body"
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18 | //usage: "\n -f SENDER Sender (required)"
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19 | //usage: "\n -o OPTIONS Various options. -oi implied, others are ignored"
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20 | //usage: "\n -i -oi synonym. implied and ignored"
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21 | //usage: "\n"
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22 | //usage: "\nBusybox specific options:"
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23 | //usage: "\n -v Verbose"
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24 | //usage: "\n -w SECS Network timeout"
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25 | //usage: "\n -H 'PROG ARGS' Run connection helper"
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26 | //usage: "\n Examples:"
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27 | //usage: "\n -H 'exec openssl s_client -quiet -tls1 -starttls smtp"
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28 | //usage: "\n -connect smtp.gmail.com:25' <email.txt"
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29 | //usage: "\n [4<username_and_passwd.txt | -auUSER -apPASS]"
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30 | //usage: "\n -H 'exec openssl s_client -quiet -tls1"
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31 | //usage: "\n -connect smtp.gmail.com:465' <email.txt"
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32 | //usage: "\n [4<username_and_passwd.txt | -auUSER -apPASS]"
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33 | //usage: "\n -S HOST[:PORT] Server"
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34 | //usage: "\n -auUSER Username for AUTH LOGIN"
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35 | //usage: "\n -apPASS Password for AUTH LOGIN"
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36 | ////usage: "\n -amMETHOD Authentication method. Ignored. LOGIN is implied"
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37 | //usage: "\n"
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38 | //usage: "\nOther options are silently ignored; -oi -t is implied"
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39 | //usage: IF_MAKEMIME(
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40 | //usage: "\nUse makemime to create emails with attachments"
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41 | //usage: )
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42 |
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43 | #include "libbb.h"
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44 | #include "mail.h"
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45 |
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46 | // limit maximum allowed number of headers to prevent overflows.
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47 | // set to 0 to not limit
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48 | #define MAX_HEADERS 256
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49 |
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50 | static void send_r_n(const char *s)
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51 | {
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52 | if (verbose)
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53 | bb_error_msg("send:'%s'", s);
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54 | printf("%s\r\n", s);
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55 | }
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56 |
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57 | static int smtp_checkp(const char *fmt, const char *param, int code)
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58 | {
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59 | char *answer;
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60 | char *msg = send_mail_command(fmt, param);
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61 | // read stdin
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62 | // if the string has a form NNN- -- read next string. E.g. EHLO response
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63 | // parse first bytes to a number
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64 | // if code = -1 then just return this number
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65 | // if code != -1 then checks whether the number equals the code
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66 | // if not equal -> die saying msg
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67 | while ((answer = xmalloc_fgetline(stdin)) != NULL) {
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68 | if (verbose)
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69 | bb_error_msg("recv:'%.*s'", (int)(strchrnul(answer, '\r') - answer), answer);
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70 | if (strlen(answer) <= 3 || '-' != answer[3])
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71 | break;
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72 | free(answer);
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73 | }
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74 | if (answer) {
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75 | int n = atoi(answer);
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76 | if (timeout)
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77 | alarm(0);
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78 | free(answer);
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79 | if (-1 == code || n == code) {
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80 | free(msg);
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81 | return n;
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82 | }
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83 | }
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84 | bb_error_msg_and_die("%s failed", msg);
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85 | }
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86 |
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87 | static int smtp_check(const char *fmt, int code)
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88 | {
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89 | return smtp_checkp(fmt, NULL, code);
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90 | }
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91 |
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92 | // strip argument of bad chars
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93 | static char *sane_address(char *str)
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94 | {
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95 | char *s = str;
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96 | char *p = s;
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97 | while (*s) {
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98 | if (isalnum(*s) || '_' == *s || '-' == *s || '.' == *s || '@' == *s) {
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99 | *p++ = *s;
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100 | }
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101 | s++;
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102 | }
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103 | *p = '\0';
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104 | return str;
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105 | }
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106 |
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107 | static void rcptto(const char *s)
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108 | {
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109 | // N.B. we don't die if recipient is rejected, for the other recipients may be accepted
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110 | if (250 != smtp_checkp("RCPT TO:<%s>", s, -1))
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111 | bb_error_msg("Bad recipient: <%s>", s);
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112 | }
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113 |
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114 | int sendmail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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115 | int sendmail_main(int argc UNUSED_PARAM, char **argv)
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116 | {
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117 | char *opt_connect = opt_connect;
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118 | char *opt_from;
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119 | char *s;
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120 | llist_t *list = NULL;
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121 | char *host = sane_address(safe_gethostname());
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122 | unsigned nheaders = 0;
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123 | int code;
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124 |
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125 | enum {
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126 | //--- standard options
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127 | OPT_t = 1 << 0, // read message for recipients, append them to those on cmdline
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128 | OPT_f = 1 << 1, // sender address
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129 | OPT_o = 1 << 2, // various options. -oi IMPLIED! others are IGNORED!
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130 | OPT_i = 1 << 3, // IMPLIED!
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131 | //--- BB specific options
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132 | OPT_w = 1 << 4, // network timeout
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133 | OPT_H = 1 << 5, // use external connection helper
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134 | OPT_S = 1 << 6, // specify connection string
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135 | OPT_a = 1 << 7, // authentication tokens
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136 | OPT_v = 1 << 8, // verbosity
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137 | };
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138 |
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139 | // init global variables
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140 | INIT_G();
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141 |
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142 | // save initial stdin since body is piped!
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143 | xdup2(STDIN_FILENO, 3);
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144 | G.fp0 = xfdopen_for_read(3);
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145 |
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146 | // parse options
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147 | // -v is a counter, -f is required. -H and -S are mutually exclusive, -a is a list
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148 | opt_complementary = "vv:f:w+:H--S:S--H:a::";
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149 | // N.B. since -H and -S are mutually exclusive they do not interfere in opt_connect
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150 | // -a is for ssmtp (http://downloads.openwrt.org/people/nico/man/man8/ssmtp.8.html) compatibility,
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151 | // it is still under development.
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152 | opts = getopt32(argv, "tf:o:iw:H:S:a::v", &opt_from, NULL,
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153 | &timeout, &opt_connect, &opt_connect, &list, &verbose);
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154 | //argc -= optind;
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155 | argv += optind;
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156 |
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157 | // process -a[upm]<token> options
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158 | if ((opts & OPT_a) && !list)
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159 | bb_show_usage();
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160 | while (list) {
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161 | char *a = (char *) llist_pop(&list);
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162 | if ('u' == a[0])
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163 | G.user = xstrdup(a+1);
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164 | if ('p' == a[0])
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165 | G.pass = xstrdup(a+1);
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166 | // N.B. we support only AUTH LOGIN so far
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167 | //if ('m' == a[0])
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168 | // G.method = xstrdup(a+1);
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169 | }
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170 | // N.B. list == NULL here
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171 | //bb_info_msg("OPT[%x] AU[%s], AP[%s], AM[%s], ARGV[%s]", opts, au, ap, am, *argv);
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172 |
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173 | // connect to server
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174 |
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175 | // connection helper ordered? ->
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176 | if (opts & OPT_H) {
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177 | const char *args[] = { "sh", "-c", opt_connect, NULL };
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178 | // plug it in
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179 | launch_helper(args);
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180 | // Now:
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181 | // our stdout will go to helper's stdin,
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182 | // helper's stdout will be available on our stdin.
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183 |
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184 | // Wait for initial server message.
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185 | // If helper (such as openssl) invokes STARTTLS, the initial 220
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186 | // is swallowed by helper (and not repeated after TLS is initiated).
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187 | // We will send NOOP cmd to server and check the response.
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188 | // We should get 220+250 on plain connection, 250 on STARTTLSed session.
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189 | //
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190 | // The problem here is some servers delay initial 220 message,
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191 | // and consider client to be a spammer if it starts sending cmds
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192 | // before 220 reached it. The code below is unsafe in this regard:
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193 | // in non-STARTTLSed case, we potentially send NOOP before 220
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194 | // is sent by server.
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195 | // Ideas? (--delay SECS opt? --assume-starttls-helper opt?)
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196 | code = smtp_check("NOOP", -1);
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197 | if (code == 220)
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198 | // we got 220 - this is not STARTTLSed connection,
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199 | // eat 250 response to our NOOP
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200 | smtp_check(NULL, 250);
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201 | else
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202 | if (code != 250)
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203 | bb_error_msg_and_die("SMTP init failed");
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204 | } else {
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205 | // vanilla connection
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206 | int fd;
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207 | // host[:port] not explicitly specified? -> use $SMTPHOST
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208 | // no $SMTPHOST? -> use localhost
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209 | if (!(opts & OPT_S)) {
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210 | opt_connect = getenv("SMTPHOST");
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211 | if (!opt_connect)
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212 | opt_connect = (char *)"127.0.0.1";
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213 | }
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214 | // do connect
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215 | fd = create_and_connect_stream_or_die(opt_connect, 25);
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216 | // and make ourselves a simple IO filter
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217 | xmove_fd(fd, STDIN_FILENO);
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218 | xdup2(STDIN_FILENO, STDOUT_FILENO);
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219 |
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220 | // Wait for initial server 220 message
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221 | smtp_check(NULL, 220);
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222 | }
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223 |
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224 | // we should start with modern EHLO
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225 | if (250 != smtp_checkp("EHLO %s", host, -1))
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226 | smtp_checkp("HELO %s", host, 250);
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227 | free(host);
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228 |
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229 | // perform authentication
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230 | if (opts & OPT_a) {
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231 | smtp_check("AUTH LOGIN", 334);
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232 | // we must read credentials unless they are given via -a[up] options
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233 | if (!G.user || !G.pass)
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234 | get_cred_or_die(4);
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235 | encode_base64(NULL, G.user, NULL);
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236 | smtp_check("", 334);
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237 | encode_base64(NULL, G.pass, NULL);
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238 | smtp_check("", 235);
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239 | }
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240 |
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241 | // set sender
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242 | // N.B. we have here a very loosely defined algorythm
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243 | // since sendmail historically offers no means to specify secrets on cmdline.
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244 | // 1) server can require no authentication ->
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245 | // we must just provide a (possibly fake) reply address.
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246 | // 2) server can require AUTH ->
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247 | // we must provide valid username and password along with a (possibly fake) reply address.
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248 | // For the sake of security username and password are to be read either from console or from a secured file.
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249 | // Since reading from console may defeat usability, the solution is either to read from a predefined
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250 | // file descriptor (e.g. 4), or again from a secured file.
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251 |
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252 | // got no sender address? -> use system username as a resort
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253 | // N.B. we marked -f as required option!
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254 | //if (!G.user) {
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255 | // // N.B. IMHO getenv("USER") can be way easily spoofed!
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256 | // G.user = xuid2uname(getuid());
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257 | // opt_from = xasprintf("%s@%s", G.user, domain);
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258 | //}
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259 | smtp_checkp("MAIL FROM:<%s>", opt_from, 250);
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260 |
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261 | // process message
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262 |
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263 | // read recipients from message and add them to those given on cmdline.
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264 | // this means we scan stdin for To:, Cc:, Bcc: lines until an empty line
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265 | // and then use the rest of stdin as message body
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266 | code = 0; // set "analyze headers" mode
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267 | while ((s = xmalloc_fgetline(G.fp0)) != NULL) {
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268 | dump:
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269 | // put message lines doubling leading dots
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270 | if (code) {
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271 | // escape leading dots
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272 | // N.B. this feature is implied even if no -i (-oi) switch given
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273 | // N.B. we need to escape the leading dot regardless of
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274 | // whether it is single or not character on the line
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275 | if ('.' == s[0] /*&& '\0' == s[1] */)
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276 | printf(".");
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277 | // dump read line
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278 | send_r_n(s);
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279 | free(s);
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280 | continue;
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281 | }
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282 |
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283 | // analyze headers
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284 | // To: or Cc: headers add recipients
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285 | if (opts & OPT_t) {
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286 | if (0 == strncasecmp("To:", s, 3) || 0 == strncasecmp("Bcc:" + 1, s, 3)) {
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287 | rcptto(sane_address(s+3));
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288 | goto addheader;
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289 | }
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290 | // Bcc: header adds blind copy (hidden) recipient
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291 | if (0 == strncasecmp("Bcc:", s, 4)) {
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292 | rcptto(sane_address(s+4));
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293 | free(s);
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294 | continue; // N.B. Bcc: vanishes from headers!
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295 | }
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296 | }
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297 | if (strchr(s, ':') || (list && isspace(s[0]))) {
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298 | // other headers go verbatim
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299 | // N.B. RFC2822 2.2.3 "Long Header Fields" allows for headers to occupy several lines.
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300 | // Continuation is denoted by prefixing additional lines with whitespace(s).
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301 | // Thanks (stefan.seyfried at googlemail.com) for pointing this out.
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302 | addheader:
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303 | // N.B. we allow MAX_HEADERS generic headers at most to prevent attacks
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304 | if (MAX_HEADERS && ++nheaders >= MAX_HEADERS)
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305 | goto bail;
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306 | llist_add_to_end(&list, s);
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307 | } else {
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308 | // a line without ":" (an empty line too, by definition) doesn't look like a valid header
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309 | // so stop "analyze headers" mode
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310 | reenter:
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311 | // put recipients specified on cmdline
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312 | while (*argv) {
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313 | char *t = sane_address(*argv);
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314 | rcptto(t);
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315 | //if (MAX_HEADERS && ++nheaders >= MAX_HEADERS)
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316 | // goto bail;
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317 | llist_add_to_end(&list, xasprintf("To: %s", t));
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318 | argv++;
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319 | }
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320 | // enter "put message" mode
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321 | // N.B. DATA fails iff no recipients were accepted (or even provided)
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322 | // in this case just bail out gracefully
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323 | if (354 != smtp_check("DATA", -1))
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324 | goto bail;
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325 | // dump the headers
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326 | while (list) {
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327 | send_r_n((char *) llist_pop(&list));
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328 | }
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329 | // stop analyzing headers
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330 | code++;
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331 | // N.B. !s means: we read nothing, and nothing to be read in the future.
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332 | // just dump empty line and break the loop
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333 | if (!s) {
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334 | send_r_n("");
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335 | break;
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336 | }
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337 | // go dump message body
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338 | // N.B. "s" already contains the first non-header line, so pretend we read it from input
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339 | goto dump;
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340 | }
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341 | }
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342 | // odd case: we didn't stop "analyze headers" mode -> message body is empty. Reenter the loop
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343 | // N.B. after reenter code will be > 0
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344 | if (!code)
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345 | goto reenter;
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346 |
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347 | // finalize the message
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348 | smtp_check(".", 250);
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349 | bail:
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350 | // ... and say goodbye
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351 | smtp_check("QUIT", 221);
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352 | // cleanup
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353 | if (ENABLE_FEATURE_CLEAN_UP)
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354 | fclose(G.fp0);
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355 |
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356 | return EXIT_SUCCESS;
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357 | }
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