1/* vi: set sw=4 ts=4: */ 2/* 3 * bare bones sendmail 4 * 5 * Copyright (C) 2008 by Vladimir Dronnikov <dronnikov@gmail.com> 6 * 7 * Licensed under GPLv2, see file LICENSE in this source tree. 8 */ 9//config:config SENDMAIL 10//config: bool "sendmail (14 kb)" 11//config: default y 12//config: help 13//config: Barebones sendmail. 14 15//applet:IF_SENDMAIL(APPLET(sendmail, BB_DIR_USR_SBIN, BB_SUID_DROP)) 16 17//kbuild:lib-$(CONFIG_SENDMAIL) += sendmail.o mail.o 18 19//usage:#define sendmail_trivial_usage 20//usage: "[-tv] [-f SENDER] [-amLOGIN 4<user_pass.txt | -auUSER -apPASS]" 21//usage: "\n [-w SECS] [-H 'PROG ARGS' | -S HOST] [RECIPIENT_EMAIL]..." 22//usage:#define sendmail_full_usage "\n\n" 23//usage: "Read email from stdin and send it\n" 24//usage: "\nStandard options:" 25//usage: "\n -t Read additional recipients from message body" 26//usage: "\n -f SENDER For use in MAIL FROM:<sender>. Can be empty string" 27//usage: "\n Default: -auUSER, or username of current UID" 28//usage: "\n -o OPTIONS Various options. -oi implied, others are ignored" 29//usage: "\n -i -oi synonym, implied and ignored" 30//usage: "\n" 31//usage: "\nBusybox specific options:" 32//usage: "\n -v Verbose" 33//usage: "\n -w SECS Network timeout" 34//usage: "\n -H 'PROG ARGS' Run connection helper. Examples:" 35//usage: "\n openssl s_client -quiet -tls1 -starttls smtp -connect smtp.gmail.com:25" 36//usage: "\n openssl s_client -quiet -tls1 -connect smtp.gmail.com:465" 37//usage: "\n $SMTP_ANTISPAM_DELAY: seconds to wait after helper connect" 38//usage: "\n -S HOST[:PORT] Server (default $SMTPHOST or 127.0.0.1)" 39//usage: "\n -amLOGIN Log in using AUTH LOGIN (-amCRAM-MD5 not supported)" 40//usage: "\n -auUSER Username for AUTH" 41//usage: "\n -apPASS Password for AUTH" 42//usage: "\n" 43//usage: "\nIf no -a options are given, authentication is not done." 44//usage: "\nIf -amLOGIN is given but no -au/-ap, user/password is read from fd #4." 45//usage: "\nOther options are silently ignored; -oi is implied." 46//usage: IF_MAKEMIME( 47//usage: "\nUse makemime to create emails with attachments." 48//usage: ) 49 50/* Currently we don't sanitize or escape user-supplied SENDER and RECIPIENT_EMAILs. 51 * We may need to do so. For one, '.' in usernames seems to require escaping! 52 * 53 * From http://cr.yp.to/smtp/address.html: 54 * 55 * SMTP offers three ways to encode a character inside an address: 56 * 57 * "safe": the character, if it is not <>()[].,;:@, backslash, 58 * double-quote, space, or an ASCII control character; 59 * "quoted": the character, if it is not \012, \015, backslash, 60 * or double-quote; or 61 * "slashed": backslash followed by the character. 62 * 63 * An encoded box part is either (1) a sequence of one or more slashed 64 * or safe characters or (2) a double quote, a sequence of zero or more 65 * slashed or quoted characters, and a double quote. It represents 66 * the concatenation of the characters encoded inside it. 67 * 68 * For example, the encoded box parts 69 * angels 70 * \a\n\g\e\l\s 71 * "\a\n\g\e\l\s" 72 * "angels" 73 * "ang\els" 74 * all represent the 6-byte string "angels", and the encoded box parts 75 * a\,comma 76 * \a\,\c\o\m\m\a 77 * "a,comma" 78 * all represent the 7-byte string "a,comma". 79 * 80 * An encoded address contains 81 * the byte <; 82 * optionally, a route followed by a colon; 83 * an encoded box part, the byte @, and a domain; and 84 * the byte >. 85 * 86 * It represents an Internet mail address, given by concatenating 87 * the string represented by the encoded box part, the byte @, 88 * and the domain. For example, the encoded addresses 89 * <God@heaven.af.mil> 90 * <\God@heaven.af.mil> 91 * <"God"@heaven.af.mil> 92 * <@gateway.af.mil,@uucp.local:"\G\o\d"@heaven.af.mil> 93 * all represent the Internet mail address "God@heaven.af.mil". 94 */ 95 96#include "libbb.h" 97#include "mail.h" 98 99// limit maximum allowed number of headers to prevent overflows. 100// set to 0 to not limit 101#define MAX_HEADERS 256 102 103static void send_r_n(const char *s) 104{ 105 if (verbose) 106 bb_error_msg("send:'%s'", s); 107 printf("%s\r\n", s); 108} 109 110static int smtp_checkp(const char *fmt, const char *param, int code) 111{ 112 char *answer; 113 char *msg = send_mail_command(fmt, param); 114 // read stdin 115 // if the string has a form NNN- -- read next string. E.g. EHLO response 116 // parse first bytes to a number 117 // if code = -1 then just return this number 118 // if code != -1 then checks whether the number equals the code 119 // if not equal -> die saying msg 120 while ((answer = xmalloc_fgetline(stdin)) != NULL) { 121 if (verbose) 122 bb_error_msg("recv:'%.*s'", (int)(strchrnul(answer, '\r') - answer), answer); 123 if (strlen(answer) <= 3 || '-' != answer[3]) 124 break; 125 free(answer); 126 } 127 if (answer) { 128 int n = atoi(answer); 129 if (timeout) 130 alarm(0); 131 free(answer); 132 if (-1 == code || n == code) { 133 free(msg); 134 return n; 135 } 136 } 137 bb_error_msg_and_die("%s failed", msg); 138} 139 140static int smtp_check(const char *fmt, int code) 141{ 142 return smtp_checkp(fmt, NULL, code); 143} 144 145// strip argument of bad chars 146static char *sane_address(char *str) 147{ 148 char *s; 149 150 trim(str); 151 s = str; 152 while (*s) { 153 /* Standard allows these chars in username without quoting: 154 * /!#$%&'*+-=?^_`{|}~ 155 * and allows dot (.) with some restrictions. 156 * I chose to only allow a saner subset. 157 * I propose to expand it only on user's request. 158 */ 159 if (!isalnum(*s) && !strchr("=+_-.@", *s)) { 160 bb_error_msg("bad address '%s'", str); 161 /* returning "": */ 162 str[0] = '\0'; 163 return str; 164 } 165 s++; 166 } 167 return str; 168} 169 170// check for an address inside angle brackets, if not found fall back to normal 171static char *angle_address(char *str) 172{ 173 char *s, *e; 174 175 e = trim(str); 176 if (e != str && *--e == '>') { 177 s = strrchr(str, '<'); 178 if (s) { 179 *e = '\0'; 180 str = s + 1; 181 } 182 } 183 return sane_address(str); 184} 185 186static void rcptto(const char *s) 187{ 188 if (!*s) 189 return; 190 // N.B. we don't die if recipient is rejected, for the other recipients may be accepted 191 if (250 != smtp_checkp("RCPT TO:<%s>", s, -1)) 192 bb_error_msg("Bad recipient: <%s>", s); 193} 194 195// send to a list of comma separated addresses 196static void rcptto_list(const char *list) 197{ 198 char *free_me = xstrdup(list); 199 char *str = free_me; 200 char *s = free_me; 201 char prev = 0; 202 int in_quote = 0; 203 204 while (*s) { 205 char ch = *s++; 206 207 if (ch == '"' && prev != '\\') { 208 in_quote = !in_quote; 209 } else if (!in_quote && ch == ',') { 210 s[-1] = '\0'; 211 rcptto(angle_address(str)); 212 str = s; 213 } 214 prev = ch; 215 } 216 if (prev != ',') 217 rcptto(angle_address(str)); 218 free(free_me); 219} 220 221int sendmail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; 222int sendmail_main(int argc UNUSED_PARAM, char **argv) 223{ 224 char *opt_connect; 225 char *opt_from = NULL; 226 char *s; 227 llist_t *list = NULL; 228 char *host = sane_address(safe_gethostname()); 229 unsigned nheaders = 0; 230 int code; 231 enum { 232 HDR_OTHER = 0, 233 HDR_TOCC, 234 HDR_BCC, 235 } last_hdr = 0; 236 int check_hdr; 237 int has_to = 0; 238 239 enum { 240 //--- standard options 241 OPT_t = 1 << 0, // read message for recipients, append them to those on cmdline 242 OPT_f = 1 << 1, // sender address 243 OPT_o = 1 << 2, // various options. -oi IMPLIED! others are IGNORED! 244 OPT_i = 1 << 3, // IMPLIED! 245 //--- BB specific options 246 OPT_w = 1 << 4, // network timeout 247 OPT_H = 1 << 5, // use external connection helper 248 OPT_S = 1 << 6, // specify connection string 249 OPT_a = 1 << 7, // authentication tokens 250 OPT_v = 1 << 8, // verbosity 251 }; 252 253 // init global variables 254 INIT_G(); 255 256 // default HOST[:PORT] is $SMTPHOST, or localhost 257 opt_connect = getenv("SMTPHOST"); 258 if (!opt_connect) 259 opt_connect = (char *)"127.0.0.1"; 260 261 // save initial stdin since body is piped! 262 xdup2(STDIN_FILENO, 3); 263 G.fp0 = xfdopen_for_read(3); 264 265 // parse options 266 // N.B. since -H and -S are mutually exclusive they do not interfere in opt_connect 267 // -a is for ssmtp (http://downloads.openwrt.org/people/nico/man/man8/ssmtp.8.html) compatibility, 268 // it is still under development. 269 opts = getopt32(argv, "^" 270 "tf:o:iw:+H:S:a:*:v" 271 "\0" 272 // -v is a counter, -H and -S are mutually exclusive, -a is a list 273 "vv:H--S:S--H", 274 &opt_from, NULL, 275 &timeout, &opt_connect, &opt_connect, &list, &verbose 276 ); 277 //argc -= optind; 278 argv += optind; 279 280 // process -a[upm]<token> options 281 if ((opts & OPT_a) && !list) 282 bb_show_usage(); 283 while (list) { 284 char *a = (char *) llist_pop(&list); 285 if ('u' == a[0]) 286 G.user = xstrdup(a+1); 287 if ('p' == a[0]) 288 G.pass = xstrdup(a+1); 289 // N.B. we support only AUTH LOGIN so far 290 //if ('m' == a[0]) 291 // G.method = xstrdup(a+1); 292 } 293 // N.B. list == NULL here 294 //bb_error_msg("OPT[%x] AU[%s], AP[%s], AM[%s], ARGV[%s]", opts, au, ap, am, *argv); 295 296 // connect to server 297 298 // connection helper ordered? -> 299 if (opts & OPT_H) { 300 const char *delay; 301 const char *args[] = { "sh", "-c", opt_connect, NULL }; 302 // plug it in 303 launch_helper(args); 304 // Now: 305 // our stdout will go to helper's stdin, 306 // helper's stdout will be available on our stdin. 307 308 // Wait for initial server message. 309 // If helper (such as openssl) invokes STARTTLS, the initial 220 310 // is swallowed by helper (and not repeated after TLS is initiated). 311 // We will send NOOP cmd to server and check the response. 312 // We should get 220+250 on plain connection, 250 on STARTTLSed session. 313 // 314 // The problem here is some servers delay initial 220 message, 315 // and consider client to be a spammer if it starts sending cmds 316 // before 220 reached it. The code below is unsafe in this regard: 317 // in non-STARTTLSed case, we potentially send NOOP before 220 318 // is sent by server. 319 // 320 // If $SMTP_ANTISPAM_DELAY is set, we pause before sending NOOP. 321 // 322 delay = getenv("SMTP_ANTISPAM_DELAY"); 323 if (delay) 324 sleep(atoi(delay)); 325 code = smtp_check("NOOP", -1); 326 if (code == 220) 327 // we got 220 - this is not STARTTLSed connection, 328 // eat 250 response to our NOOP 329 smtp_check(NULL, 250); 330 else 331 if (code != 250) 332 bb_error_msg_and_die("SMTP init failed"); 333 } else { 334 // vanilla connection 335 int fd; 336 fd = create_and_connect_stream_or_die(opt_connect, 25); 337 // and make ourselves a simple IO filter 338 xmove_fd(fd, STDIN_FILENO); 339 xdup2(STDIN_FILENO, STDOUT_FILENO); 340 341 // Wait for initial server 220 message 342 smtp_check(NULL, 220); 343 } 344 345 // we should start with modern EHLO 346 if (250 != smtp_checkp("EHLO %s", host, -1)) 347 smtp_checkp("HELO %s", host, 250); 348 349 // perform authentication 350 if (opts & OPT_a) { 351 smtp_check("AUTH LOGIN", 334); 352 // we must read credentials unless they are given via -a[up] options 353 if (!G.user || !G.pass) 354 get_cred_or_die(4); 355 encode_base64(NULL, G.user, NULL); 356 smtp_check("", 334); 357 encode_base64(NULL, G.pass, NULL); 358 smtp_check("", 235); 359 } 360 361 // set sender 362 // N.B. we have here a very loosely defined algorythm 363 // since sendmail historically offers no means to specify secrets on cmdline. 364 // 1) server can require no authentication -> 365 // we must just provide a (possibly fake) reply address. 366 // 2) server can require AUTH -> 367 // we must provide valid username and password along with a (possibly fake) reply address. 368 // For the sake of security username and password are to be read either from console or from a secured file. 369 // Since reading from console may defeat usability, the solution is either to read from a predefined 370 // file descriptor (e.g. 4), or again from a secured file. 371 372 // got no sender address? use auth name, then UID username as a last resort 373 if (!opt_from) { 374 opt_from = xasprintf("%s@%s", 375 G.user ? G.user : xuid2uname(getuid()), 376 xgethostbyname(host)->h_name); 377 } 378 free(host); 379 380 smtp_checkp("MAIL FROM:<%s>", opt_from, 250); 381 382 // process message 383 384 // read recipients from message and add them to those given on cmdline. 385 // this means we scan stdin for To:, Cc:, Bcc: lines until an empty line 386 // and then use the rest of stdin as message body 387 code = 0; // set "analyze headers" mode 388 while ((s = xmalloc_fgetline(G.fp0)) != NULL) { 389 dump: 390 // put message lines doubling leading dots 391 if (code) { 392 // escape leading dots 393 // N.B. this feature is implied even if no -i (-oi) switch given 394 // N.B. we need to escape the leading dot regardless of 395 // whether it is single or not character on the line 396 if ('.' == s[0] /*&& '\0' == s[1] */) 397 bb_putchar('.'); 398 // dump read line 399 send_r_n(s); 400 free(s); 401 continue; 402 } 403 404 // analyze headers 405 // To: or Cc: headers add recipients 406 check_hdr = (0 == strncasecmp("To:", s, 3)); 407 has_to |= check_hdr; 408 if (opts & OPT_t) { 409 if (check_hdr || 0 == strncasecmp("Bcc:" + 1, s, 3)) { 410 rcptto_list(s+3); 411 last_hdr = HDR_TOCC; 412 goto addheader; 413 } 414 // Bcc: header adds blind copy (hidden) recipient 415 if (0 == strncasecmp("Bcc:", s, 4)) { 416 rcptto_list(s+4); 417 free(s); 418 last_hdr = HDR_BCC; 419 continue; // N.B. Bcc: vanishes from headers! 420 } 421 } 422 check_hdr = (list && isspace(s[0])); 423 if (strchr(s, ':') || check_hdr) { 424 // other headers go verbatim 425 // N.B. RFC2822 2.2.3 "Long Header Fields" allows for headers to occupy several lines. 426 // Continuation is denoted by prefixing additional lines with whitespace(s). 427 // Thanks (stefan.seyfried at googlemail.com) for pointing this out. 428 if (check_hdr && last_hdr != HDR_OTHER) { 429 rcptto_list(s+1); 430 if (last_hdr == HDR_BCC) 431 continue; 432 // N.B. Bcc: vanishes from headers! 433 } else { 434 last_hdr = HDR_OTHER; 435 } 436 addheader: 437 // N.B. we allow MAX_HEADERS generic headers at most to prevent attacks 438 if (MAX_HEADERS && ++nheaders >= MAX_HEADERS) 439 goto bail; 440 llist_add_to_end(&list, s); 441 } else { 442 // a line without ":" (an empty line too, by definition) doesn't look like a valid header 443 // so stop "analyze headers" mode 444 reenter: 445 // put recipients specified on cmdline 446 check_hdr = 1; 447 while (*argv) { 448 char *t = sane_address(*argv); 449 rcptto(t); 450 //if (MAX_HEADERS && ++nheaders >= MAX_HEADERS) 451 // goto bail; 452 if (!has_to) { 453 const char *hdr; 454 455 if (check_hdr && argv[1]) 456 hdr = "To: %s,"; 457 else if (check_hdr) 458 hdr = "To: %s"; 459 else if (argv[1]) 460 hdr = "To: %s," + 3; 461 else 462 hdr = "To: %s" + 3; 463 llist_add_to_end(&list, 464 xasprintf(hdr, t)); 465 check_hdr = 0; 466 } 467 argv++; 468 } 469 // enter "put message" mode 470 // N.B. DATA fails iff no recipients were accepted (or even provided) 471 // in this case just bail out gracefully 472 if (354 != smtp_check("DATA", -1)) 473 goto bail; 474 // dump the headers 475 while (list) { 476 send_r_n((char *) llist_pop(&list)); 477 } 478 // stop analyzing headers 479 code++; 480 // N.B. !s means: we read nothing, and nothing to be read in the future. 481 // just dump empty line and break the loop 482 if (!s) { 483 send_r_n(""); 484 break; 485 } 486 // go dump message body 487 // N.B. "s" already contains the first non-header line, so pretend we read it from input 488 goto dump; 489 } 490 } 491 // odd case: we didn't stop "analyze headers" mode -> message body is empty. Reenter the loop 492 // N.B. after reenter code will be > 0 493 if (!code) 494 goto reenter; 495 496 // finalize the message 497 smtp_check(".", 250); 498 bail: 499 // ... and say goodbye 500 smtp_check("QUIT", 221); 501 // cleanup 502 if (ENABLE_FEATURE_CLEAN_UP) 503 fclose(G.fp0); 504 505 return EXIT_SUCCESS; 506} 507