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 (-amCRAM-MD5 not supported)"
40 //usage: "\n -auUSER Username for AUTH"
41 //usage: "\n -apPASS Password for AUTH"
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."
47 //usage: "\nUse makemime to create emails with attachments."
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!
53 * From http://cr.yp.to/smtp/address.html:
55 * SMTP offers three ways to encode a character inside an address:
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,
61 * "slashed": backslash followed by the character.
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.
68 * For example, the encoded box parts
74 * all represent the 6-byte string "angels", and the encoded box parts
78 * all represent the 7-byte string "a,comma".
80 * An encoded address contains
82 * optionally, a route followed by a colon;
83 * an encoded box part, the byte @, and a domain; and
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
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".
99 // limit maximum allowed number of headers to prevent overflows.
100 // set to 0 to not limit
101 #define MAX_HEADERS 256
103 static void send_r_n(const char *s)
106 bb_error_msg("send:'%s'", s);
110 static int smtp_checkp(const char *fmt, const char *param, int code)
113 char *msg = send_mail_command(fmt, param);
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) {
122 bb_error_msg("recv:'%.*s'", (int)(strchrnul(answer, '\r') - answer), answer);
123 if (strlen(answer) <= 3 || '-' != answer[3])
128 int n = atoi(answer);
132 if (-1 == code || n == code) {
137 bb_error_msg_and_die("%s failed", msg);
140 static int smtp_check(const char *fmt, int code)
142 return smtp_checkp(fmt, NULL, code);
145 // strip argument of bad chars
146 static char *sane_address(char *str)
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.
159 if (!isalnum(*s) && !strchr("=+_-.@", *s)) {
160 bb_error_msg("bad address '%s'", str);
170 // check for an address inside angle brackets, if not found fall back to normal
171 static char *angle_address(char *str)
176 if (e != str && e[-1] == '>') {
177 s = strrchr(str, '<');
183 return sane_address(str);
186 static void rcptto(const char *s)
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);
195 // send to a list of comma separated addresses
196 static void rcptto_list(const char *list)
198 char *free_me = xstrdup(list);
207 if (ch == '"' && prev != '\\') {
208 in_quote = !in_quote;
209 } else if (!in_quote && ch == ',') {
211 rcptto(angle_address(str));
217 rcptto(angle_address(str));
221 int sendmail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
222 int sendmail_main(int argc UNUSED_PARAM, char **argv)
225 char *opt_from = NULL;
227 llist_t *list = NULL;
228 char *host = sane_address(safe_gethostname());
229 unsigned nheaders = 0;
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
253 // init global variables
256 // default HOST[:PORT] is $SMTPHOST, or localhost
257 opt_connect = getenv("SMTPHOST");
259 opt_connect = (char *)"127.0.0.1";
261 // save initial stdin since body is piped!
262 xdup2(STDIN_FILENO, 3);
263 G.fp0 = xfdopen_for_read(3);
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, "^"
272 // -v is a counter, -H and -S are mutually exclusive, -a is a list
275 &timeout, &opt_connect, &opt_connect, &list, &verbose
280 // process -a[upm]<token> options
281 if ((opts & OPT_a) && !list)
284 char *a = (char *) llist_pop(&list);
286 G.user = xstrdup(a+1);
288 G.pass = xstrdup(a+1);
289 // N.B. we support only AUTH LOGIN so far
291 // G.method = xstrdup(a+1);
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);
298 // connection helper ordered? ->
301 const char *args[] = { "sh", "-c", opt_connect, NULL };
305 // our stdout will go to helper's stdin,
306 // helper's stdout will be available on our stdin.
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.
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.
320 // If $SMTP_ANTISPAM_DELAY is set, we pause before sending NOOP.
322 delay = getenv("SMTP_ANTISPAM_DELAY");
325 code = smtp_check("NOOP", -1);
327 // we got 220 - this is not STARTTLSed connection,
328 // eat 250 response to our NOOP
329 smtp_check(NULL, 250);
332 bb_error_msg_and_die("SMTP init failed");
334 // vanilla connection
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);
341 // Wait for initial server 220 message
342 smtp_check(NULL, 220);
345 // we should start with modern EHLO
346 if (250 != smtp_checkp("EHLO %s", host, -1))
347 smtp_checkp("HELO %s", host, 250);
349 // perform authentication
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)
355 encode_base64(NULL, G.user, NULL);
357 encode_base64(NULL, G.pass, NULL);
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.
372 // got no sender address? use auth name, then UID username as a last resort
374 opt_from = xasprintf("%s@%s",
375 G.user ? G.user : xuid2uname(getuid()),
376 xgethostbyname(host)->h_name);
380 smtp_checkp("MAIL FROM:<%s>", opt_from, 250);
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) {
390 // put message lines doubling leading dots
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] */)
405 // To: or Cc: headers add recipients
406 check_hdr = (0 == strncasecmp("To:", s, 3));
409 if (check_hdr || 0 == strncasecmp("Bcc:" + 1, s, 3)) {
414 // Bcc: header adds blind copy (hidden) recipient
415 if (0 == strncasecmp("Bcc:", s, 4)) {
419 continue; // N.B. Bcc: vanishes from headers!
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) {
430 if (last_hdr == HDR_BCC)
432 // N.B. Bcc: vanishes from headers!
434 last_hdr = HDR_OTHER;
437 // N.B. we allow MAX_HEADERS generic headers at most to prevent attacks
438 if (MAX_HEADERS && ++nheaders >= MAX_HEADERS)
440 llist_add_to_end(&list, s);
442 // a line without ":" (an empty line too, by definition) doesn't look like a valid header
443 // so stop "analyze headers" mode
445 // put recipients specified on cmdline
448 char *t = sane_address(*argv);
450 //if (MAX_HEADERS && ++nheaders >= MAX_HEADERS)
455 if (check_hdr && argv[1])
463 llist_add_to_end(&list,
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))
476 send_r_n((char *) llist_pop(&list));
478 // stop analyzing headers
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
486 // go dump message body
487 // N.B. "s" already contains the first non-header line, so pretend we read it from input
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
496 // finalize the message
497 smtp_check(".", 250);
499 // ... and say goodbye
500 smtp_check("QUIT", 221);
502 if (ENABLE_FEATURE_CLEAN_UP)