1 /* vi: set sw=4 ts=4: */
5 * Copyright (C) 2008 by Vladimir Dronnikov <dronnikov@gmail.com>
7 * Licensed under GPLv2, see file LICENSE in this source tree.
9 //config:config SENDMAIL
10 //config: bool "sendmail (14 kb)"
13 //config: Barebones sendmail.
15 //applet:IF_SENDMAIL(APPLET(sendmail, BB_DIR_USR_SBIN, BB_SUID_DROP))
17 //kbuild:lib-$(CONFIG_SENDMAIL) += sendmail.o mail.o
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"
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"
40 //usage: "\n -amPLAIN or AUTH PLAIN"
41 //usage: "\n (-amCRAM-MD5 not supported)"
42 //usage: "\n -auUSER Username for AUTH"
43 //usage: "\n -apPASS Password for AUTH"
45 //usage: "\nIf no -a options are given, authentication is not done."
46 //usage: "\nIf -amLOGIN is given but no -au/-ap, user/password is read from fd #4."
47 //usage: "\nOther options are silently ignored; -oi is implied."
49 //usage: "\nUse makemime to create emails with attachments."
52 /* Currently we don't sanitize or escape user-supplied SENDER and RECIPIENT_EMAILs.
53 * We may need to do so. For one, '.' in usernames seems to require escaping!
55 * From http://cr.yp.to/smtp/address.html:
57 * SMTP offers three ways to encode a character inside an address:
59 * "safe": the character, if it is not <>()[].,;:@, backslash,
60 * double-quote, space, or an ASCII control character;
61 * "quoted": the character, if it is not \012, \015, backslash,
63 * "slashed": backslash followed by the character.
65 * An encoded box part is either (1) a sequence of one or more slashed
66 * or safe characters or (2) a double quote, a sequence of zero or more
67 * slashed or quoted characters, and a double quote. It represents
68 * the concatenation of the characters encoded inside it.
70 * For example, the encoded box parts
76 * all represent the 6-byte string "angels", and the encoded box parts
80 * all represent the 7-byte string "a,comma".
82 * An encoded address contains
84 * optionally, a route followed by a colon;
85 * an encoded box part, the byte @, and a domain; and
88 * It represents an Internet mail address, given by concatenating
89 * the string represented by the encoded box part, the byte @,
90 * and the domain. For example, the encoded addresses
92 * <\God@heaven.af.mil>
93 * <"God"@heaven.af.mil>
94 * <@gateway.af.mil,@uucp.local:"\G\o\d"@heaven.af.mil>
95 * all represent the Internet mail address "God@heaven.af.mil".
101 // limit maximum allowed number of headers to prevent overflows.
102 // set to 0 to not limit
103 #define MAX_HEADERS 256
105 static void send_r_n(const char *s)
108 bb_error_msg("send:'%s'", s);
112 static int smtp_checkp(const char *fmt, const char *param, int code)
115 char *msg = send_mail_command(fmt, param);
117 // if the string has a form NNN- -- read next string. E.g. EHLO response
118 // parse first bytes to a number
119 // if code = -1 then just return this number
120 // if code != -1 then checks whether the number equals the code
121 // if not equal -> die saying msg
122 while ((answer = xmalloc_fgetline(stdin)) != NULL) {
124 bb_error_msg("recv:'%.*s'", (int)(strchrnul(answer, '\r') - answer), answer);
125 if (strlen(answer) <= 3 || '-' != answer[3])
130 int n = atoi(answer);
134 if (-1 == code || n == code) {
139 bb_error_msg_and_die("%s failed", msg);
142 static int smtp_check(const char *fmt, int code)
144 return smtp_checkp(fmt, NULL, code);
147 // strip argument of bad chars
148 static char *sane_address(char *str)
155 /* Standard allows these chars in username without quoting:
156 * /!#$%&'*+-=?^_`{|}~
157 * and allows dot (.) with some restrictions.
158 * I chose to only allow a saner subset.
159 * I propose to expand it only on user's request.
161 if (!isalnum(*s) && !strchr("=+_-.@", *s)) {
162 bb_error_msg("bad address '%s'", str);
172 // check for an address inside angle brackets, if not found fall back to normal
173 static char *angle_address(char *str)
178 if (e != str && *--e == '>') {
179 s = strrchr(str, '<');
185 return sane_address(str);
188 static void rcptto(const char *s)
192 // N.B. we don't die if recipient is rejected, for the other recipients may be accepted
193 if (250 != smtp_checkp("RCPT TO:<%s>", s, -1))
194 bb_error_msg("Bad recipient: <%s>", s);
197 // send to a list of comma separated addresses
198 static void rcptto_list(const char *list)
200 char *free_me = xstrdup(list);
209 if (ch == '"' && prev != '\\') {
210 in_quote = !in_quote;
211 } else if (!in_quote && ch == ',') {
213 rcptto(angle_address(str));
219 rcptto(angle_address(str));
223 int sendmail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
224 int sendmail_main(int argc UNUSED_PARAM, char **argv)
227 char *opt_from = NULL;
229 llist_t *list = NULL;
230 char *host = sane_address(safe_gethostname());
231 unsigned nheaders = 0;
242 //--- standard options
243 OPT_t = 1 << 0, // read message for recipients, append them to those on cmdline
244 OPT_f = 1 << 1, // sender address
245 OPT_o = 1 << 2, // various options. -oi IMPLIED! others are IGNORED!
246 OPT_i = 1 << 3, // IMPLIED!
247 //--- BB specific options
248 OPT_w = 1 << 4, // network timeout
249 OPT_H = 1 << 5, // use external connection helper
250 OPT_S = 1 << 6, // specify connection string
251 OPT_a = 1 << 7, // authentication tokens
252 OPT_v = 1 << 8, // verbosity
254 OPT_am_plain = 1 << 9, // AUTH PLAIN
257 // init global variables
260 // default HOST[:PORT] is $SMTPHOST, or localhost
261 opt_connect = getenv("SMTPHOST");
263 opt_connect = (char *)"127.0.0.1";
265 // save initial stdin since body is piped!
266 xdup2(STDIN_FILENO, 3);
267 G.fp0 = xfdopen_for_read(3);
270 // N.B. since -H and -S are mutually exclusive they do not interfere in opt_connect
271 // -a is for ssmtp (http://downloads.openwrt.org/people/nico/man/man8/ssmtp.8.html) compatibility,
272 // it is still under development.
273 opts = getopt32(argv, "^"
276 // -v is a counter, -H and -S are mutually exclusive, -a is a list
279 &timeout, &opt_connect, &opt_connect, &list, &verbose
284 // process -a[upm]<token> options
285 if ((opts & OPT_a) && !list)
288 char *a = (char *) llist_pop(&list);
290 G.user = xstrdup(a+1);
292 G.pass = xstrdup(a+1);
294 if ((a[1] | 0x20) == 'p') // PLAIN
295 opts |= OPT_am_plain;
296 else if ((a[1] | 0x20) == 'l') // LOGIN
297 ; /* do nothing (this is the default) */
299 bb_error_msg_and_die("unsupported AUTH method %s", a+1);
302 // N.B. list == NULL here
303 //bb_error_msg("OPT[%x] AU[%s], AP[%s], AM[%s], ARGV[%s]", opts, au, ap, am, *argv);
307 // connection helper ordered? ->
310 const char *args[] = { "sh", "-c", opt_connect, NULL };
314 // our stdout will go to helper's stdin,
315 // helper's stdout will be available on our stdin.
317 // Wait for initial server message.
318 // If helper (such as openssl) invokes STARTTLS, the initial 220
319 // is swallowed by helper (and not repeated after TLS is initiated).
320 // We will send NOOP cmd to server and check the response.
321 // We should get 220+250 on plain connection, 250 on STARTTLSed session.
323 // The problem here is some servers delay initial 220 message,
324 // and consider client to be a spammer if it starts sending cmds
325 // before 220 reached it. The code below is unsafe in this regard:
326 // in non-STARTTLSed case, we potentially send NOOP before 220
327 // is sent by server.
329 // If $SMTP_ANTISPAM_DELAY is set, we pause before sending NOOP.
331 delay = getenv("SMTP_ANTISPAM_DELAY");
334 code = smtp_check("NOOP", -1);
336 // we got 220 - this is not STARTTLSed connection,
337 // eat 250 response to our NOOP
338 smtp_check(NULL, 250);
341 bb_error_msg_and_die("SMTP init failed");
343 // vanilla connection
345 fd = create_and_connect_stream_or_die(opt_connect, 25);
346 // and make ourselves a simple IO filter
347 xmove_fd(fd, STDIN_FILENO);
348 xdup2(STDIN_FILENO, STDOUT_FILENO);
350 // Wait for initial server 220 message
351 smtp_check(NULL, 220);
354 // we should start with modern EHLO
355 if (250 != smtp_checkp("EHLO %s", host, -1))
356 smtp_checkp("HELO %s", host, 250);
358 // perform authentication
360 // read credentials unless they are given via -a[up] options
361 if (!G.user || !G.pass)
363 if (opts & OPT_am_plain) {
366 // C: base64encoded(auth<NUL>user<NUL>pass)
367 // S: 235 2.7.0 Authentication successful
368 //Note: a shorter format is allowed:
369 // C: AUTH PLAIN base64encoded(auth<NUL>user<NUL>pass)
370 // S: 235 2.7.0 Authentication successful
371 smtp_check("AUTH PLAIN", 334);
373 unsigned user_len = strlen(G.user);
374 unsigned pass_len = strlen(G.pass);
375 unsigned sz = 1 + user_len + 1 + pass_len;
376 char plain_auth[sz + 1];
378 // "authorization identity<NUL>username<NUL>password"
379 // authorization identity is empty.
380 plain_auth[0] = '\0';
381 strcpy(stpcpy(plain_auth + 1, G.user) + 1, G.pass);
382 printbuf_base64(plain_auth, sz);
386 // S: 334 VXNlcm5hbWU6
387 // ^^^^^^^^^^^^ server says "Username:"
388 // C: base64encoded(user)
389 // S: 334 UGFzc3dvcmQ6
390 // ^^^^^^^^^^^^ server says "Password:"
391 // C: base64encoded(pass)
392 // S: 235 2.7.0 Authentication successful
393 smtp_check("AUTH LOGIN", 334);
394 printstr_base64(G.user);
396 printstr_base64(G.pass);
402 // N.B. we have here a very loosely defined algorythm
403 // since sendmail historically offers no means to specify secrets on cmdline.
404 // 1) server can require no authentication ->
405 // we must just provide a (possibly fake) reply address.
406 // 2) server can require AUTH ->
407 // we must provide valid username and password along with a (possibly fake) reply address.
408 // For the sake of security username and password are to be read either from console or from a secured file.
409 // Since reading from console may defeat usability, the solution is either to read from a predefined
410 // file descriptor (e.g. 4), or again from a secured file.
412 // got no sender address? use auth name, then UID username as a last resort
414 opt_from = xasprintf("%s@%s",
415 G.user ? G.user : xuid2uname(getuid()),
416 xgethostbyname(host)->h_name);
420 smtp_checkp("MAIL FROM:<%s>", opt_from, 250);
424 // read recipients from message and add them to those given on cmdline.
425 // this means we scan stdin for To:, Cc:, Bcc: lines until an empty line
426 // and then use the rest of stdin as message body
427 code = 0; // set "analyze headers" mode
428 while ((s = xmalloc_fgetline(G.fp0)) != NULL) {
430 // put message lines doubling leading dots
432 // escape leading dots
433 // N.B. this feature is implied even if no -i (-oi) switch given
434 // N.B. we need to escape the leading dot regardless of
435 // whether it is single or not character on the line
436 if ('.' == s[0] /*&& '\0' == s[1] */)
445 // To: or Cc: headers add recipients
446 check_hdr = (0 == strncasecmp("To:", s, 3));
449 if (check_hdr || 0 == strncasecmp("Bcc:" + 1, s, 3)) {
454 // Bcc: header adds blind copy (hidden) recipient
455 if (0 == strncasecmp("Bcc:", s, 4)) {
459 continue; // N.B. Bcc: vanishes from headers!
462 check_hdr = (list && isspace(s[0]));
463 if (strchr(s, ':') || check_hdr) {
464 // other headers go verbatim
465 // N.B. RFC2822 2.2.3 "Long Header Fields" allows for headers to occupy several lines.
466 // Continuation is denoted by prefixing additional lines with whitespace(s).
467 // Thanks (stefan.seyfried at googlemail.com) for pointing this out.
468 if (check_hdr && last_hdr != HDR_OTHER) {
470 if (last_hdr == HDR_BCC)
472 // N.B. Bcc: vanishes from headers!
474 last_hdr = HDR_OTHER;
477 // N.B. we allow MAX_HEADERS generic headers at most to prevent attacks
478 if (MAX_HEADERS && ++nheaders >= MAX_HEADERS)
480 llist_add_to_end(&list, s);
482 // a line without ":" (an empty line too, by definition) doesn't look like a valid header
483 // so stop "analyze headers" mode
485 // put recipients specified on cmdline
488 char *t = sane_address(*argv);
490 //if (MAX_HEADERS && ++nheaders >= MAX_HEADERS)
495 if (check_hdr && argv[1])
503 llist_add_to_end(&list,
509 // enter "put message" mode
510 // N.B. DATA fails iff no recipients were accepted (or even provided)
511 // in this case just bail out gracefully
512 if (354 != smtp_check("DATA", -1))
516 send_r_n((char *) llist_pop(&list));
518 // stop analyzing headers
520 // N.B. !s means: we read nothing, and nothing to be read in the future.
521 // just dump empty line and break the loop
526 // go dump message body
527 // N.B. "s" already contains the first non-header line, so pretend we read it from input
531 // odd case: we didn't stop "analyze headers" mode -> message body is empty. Reenter the loop
532 // N.B. after reenter code will be > 0
536 // finalize the message
537 smtp_check(".", 250);
539 // ... and say goodbye
540 smtp_check("QUIT", 221);
542 if (ENABLE_FEATURE_CLEAN_UP)