aboutsummaryrefslogtreecommitdiff
path: root/mailutils/sendmail.c
blob: c70d062638b89f1c028d82104707fc35d9a7eb64 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
/* vi: set sw=4 ts=4: */
/*
 * bare bones sendmail
 *
 * Copyright (C) 2008 by Vladimir Dronnikov <dronnikov@gmail.com>
 *
 * Licensed under GPLv2, see file LICENSE in this source tree.
 */
//config:config SENDMAIL
//config:	bool "sendmail (14 kb)"
//config:	default y
//config:	help
//config:	  Barebones sendmail.

//applet:IF_SENDMAIL(APPLET(sendmail, BB_DIR_USR_SBIN, BB_SUID_DROP))

//kbuild:lib-$(CONFIG_SENDMAIL) += sendmail.o mail.o

//usage:#define sendmail_trivial_usage
//usage:       "[-tv] [-f SENDER] [-amLOGIN 4<user_pass.txt | -auUSER -apPASS]"
//usage:     "\n		[-w SECS] [-H 'PROG ARGS' | -S HOST] [RECIPIENT_EMAIL]..."
//usage:#define sendmail_full_usage "\n\n"
//usage:       "Read email from stdin and send it\n"
//usage:     "\nStandard options:"
//usage:     "\n	-t		Read additional recipients from message body"
//usage:     "\n	-f SENDER	For use in MAIL FROM:<sender>. Can be empty string"
//usage:     "\n			Default: -auUSER, or username of current UID"
//usage:     "\n	-o OPTIONS	Various options. -oi implied, others are ignored"
//usage:     "\n	-i		-oi synonym, implied and ignored"
//usage:     "\n"
//usage:     "\nBusybox specific options:"
//usage:     "\n	-v		Verbose"
//usage:     "\n	-w SECS		Network timeout"
//usage:     "\n	-H 'PROG ARGS'	Run connection helper. Examples:"
//usage:     "\n		openssl s_client -quiet -tls1 -starttls smtp -connect smtp.gmail.com:25"
//usage:     "\n		openssl s_client -quiet -tls1 -connect smtp.gmail.com:465"
//usage:     "\n			$SMTP_ANTISPAM_DELAY: seconds to wait after helper connect"
//usage:     "\n	-S HOST[:PORT]	Server (default $SMTPHOST or 127.0.0.1)"
//usage:     "\n	-amLOGIN	Log in using AUTH LOGIN (-amCRAM-MD5 not supported)"
//usage:     "\n	-auUSER		Username for AUTH"
//usage:     "\n	-apPASS 	Password for AUTH"
//usage:     "\n"
//usage:     "\nIf no -a options are given, authentication is not done."
//usage:     "\nIf -amLOGIN is given but no -au/-ap, user/password is read from fd #4."
//usage:     "\nOther options are silently ignored; -oi is implied."
//usage:	IF_MAKEMIME(
//usage:     "\nUse makemime to create emails with attachments."
//usage:	)

/* Currently we don't sanitize or escape user-supplied SENDER and RECIPIENT_EMAILs.
 * We may need to do so. For one, '.' in usernames seems to require escaping!
 *
 * From http://cr.yp.to/smtp/address.html:
 *
 * SMTP offers three ways to encode a character inside an address:
 *
 * "safe": the character, if it is not <>()[].,;:@, backslash,
 *  double-quote, space, or an ASCII control character;
 * "quoted": the character, if it is not \012, \015, backslash,
 *   or double-quote; or
 * "slashed": backslash followed by the character.
 *
 * An encoded box part is either (1) a sequence of one or more slashed
 * or safe characters or (2) a double quote, a sequence of zero or more
 * slashed or quoted characters, and a double quote. It represents
 * the concatenation of the characters encoded inside it.
 *
 * For example, the encoded box parts
 *	angels
 *	\a\n\g\e\l\s
 *	"\a\n\g\e\l\s"
 *	"angels"
 *	"ang\els"
 * all represent the 6-byte string "angels", and the encoded box parts
 *	a\,comma
 *	\a\,\c\o\m\m\a
 *	"a,comma"
 * all represent the 7-byte string "a,comma".
 *
 * An encoded address contains
 *	the byte <;
 *	optionally, a route followed by a colon;
 *	an encoded box part, the byte @, and a domain; and
 *	the byte >.
 *
 * It represents an Internet mail address, given by concatenating
 * the string represented by the encoded box part, the byte @,
 * and the domain. For example, the encoded addresses
 *     <God@heaven.af.mil>
 *     <\God@heaven.af.mil>
 *     <"God"@heaven.af.mil>
 *     <@gateway.af.mil,@uucp.local:"\G\o\d"@heaven.af.mil>
 * all represent the Internet mail address "God@heaven.af.mil".
 */

#include "libbb.h"
#include "mail.h"

// limit maximum allowed number of headers to prevent overflows.
// set to 0 to not limit
#define MAX_HEADERS 256

static void send_r_n(const char *s)
{
	if (verbose)
		bb_error_msg("send:'%s'", s);
	printf("%s\r\n", s);
}

static int smtp_checkp(const char *fmt, const char *param, int code)
{
	char *answer;
	char *msg = send_mail_command(fmt, param);
	// read stdin
	// if the string has a form NNN- -- read next string. E.g. EHLO response
	// parse first bytes to a number
	// if code = -1 then just return this number
	// if code != -1 then checks whether the number equals the code
	// if not equal -> die saying msg
	while ((answer = xmalloc_fgetline(stdin)) != NULL) {
		if (verbose)
			bb_error_msg("recv:'%.*s'", (int)(strchrnul(answer, '\r') - answer), answer);
		if (strlen(answer) <= 3 || '-' != answer[3])
			break;
		free(answer);
	}
	if (answer) {
		int n = atoi(answer);
		if (timeout)
			alarm(0);
		free(answer);
		if (-1 == code || n == code) {
			free(msg);
			return n;
		}
	}
	bb_error_msg_and_die("%s failed", msg);
}

static int smtp_check(const char *fmt, int code)
{
	return smtp_checkp(fmt, NULL, code);
}

// strip argument of bad chars
static char *sane_address(char *str)
{
	char *s;

	trim(str);
	s = str;
	while (*s) {
		if (!isalnum(*s) && !strchr("+_-.@", *s)) {
			bb_error_msg("bad address '%s'", str);
			/* returning "": */
			str[0] = '\0';
			return str;
		}
		s++;
	}
	return str;
}

// check for an address inside angle brackets, if not found fall back to normal
static char *angle_address(char *str)
{
	char *s, *e;

	trim(str);
	e = last_char_is(str, '>');
	if (e) {
		s = strrchr(str, '<');
		if (s) {
			*e = '\0';
			str = s + 1;
		}
	}
	return sane_address(str);
}

static void rcptto(const char *s)
{
	if (!*s)
		return;
	// N.B. we don't die if recipient is rejected, for the other recipients may be accepted
	if (250 != smtp_checkp("RCPT TO:<%s>", s, -1))
		bb_error_msg("Bad recipient: <%s>", s);
}

// send to a list of comma separated addresses
static void rcptto_list(const char *list)
{
	char *str = xstrdup(list);
	char *s = str;
	char prev = 0;
	int in_quote = 0;

	while (*s) {
		char ch = *s++;

		if (ch == '"' && prev != '\\') {
			in_quote = !in_quote;
		} else if (!in_quote && ch == ',') {
			s[-1] = '\0';
			rcptto(angle_address(str));
			str = s;
		}
		prev = ch;
	}
	if (prev != ',')
		rcptto(angle_address(str));
	free(str);
}

int sendmail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int sendmail_main(int argc UNUSED_PARAM, char **argv)
{
	char *opt_connect;
	char *opt_from = NULL;
	char *s;
	llist_t *list = NULL;
	char *host = sane_address(safe_gethostname());
	unsigned nheaders = 0;
	int code;
	enum {
		HDR_OTHER = 0,
		HDR_TOCC,
		HDR_BCC,
	} last_hdr = 0;
	int check_hdr;
	int has_to = 0;

	enum {
	//--- standard options
		OPT_t = 1 << 0,         // read message for recipients, append them to those on cmdline
		OPT_f = 1 << 1,         // sender address
		OPT_o = 1 << 2,         // various options. -oi IMPLIED! others are IGNORED!
		OPT_i = 1 << 3,         // IMPLIED!
	//--- BB specific options
		OPT_w = 1 << 4,         // network timeout
		OPT_H = 1 << 5,         // use external connection helper
		OPT_S = 1 << 6,         // specify connection string
		OPT_a = 1 << 7,         // authentication tokens
		OPT_v = 1 << 8,         // verbosity
	};

	// init global variables
	INIT_G();

	// default HOST[:PORT] is $SMTPHOST, or localhost
	opt_connect = getenv("SMTPHOST");
	if (!opt_connect)
		opt_connect = (char *)"127.0.0.1";

	// save initial stdin since body is piped!
	xdup2(STDIN_FILENO, 3);
	G.fp0 = xfdopen_for_read(3);

	// parse options
	// -v is a counter, -H and -S are mutually exclusive, -a is a list
	opt_complementary = "vv:H--S:S--H";
	// N.B. since -H and -S are mutually exclusive they do not interfere in opt_connect
	// -a is for ssmtp (http://downloads.openwrt.org/people/nico/man/man8/ssmtp.8.html) compatibility,
	// it is still under development.
	opts = getopt32(argv, "tf:o:iw:+H:S:a:*:v", &opt_from, NULL,
			&timeout, &opt_connect, &opt_connect, &list, &verbose);
	//argc -= optind;
	argv += optind;

	// process -a[upm]<token> options
	if ((opts & OPT_a) && !list)
		bb_show_usage();
	while (list) {
		char *a = (char *) llist_pop(&list);
		if ('u' == a[0])
			G.user = xstrdup(a+1);
		if ('p' == a[0])
			G.pass = xstrdup(a+1);
		// N.B. we support only AUTH LOGIN so far
		//if ('m' == a[0])
		//	G.method = xstrdup(a+1);
	}
	// N.B. list == NULL here
	//bb_error_msg("OPT[%x] AU[%s], AP[%s], AM[%s], ARGV[%s]", opts, au, ap, am, *argv);

	// connect to server

	// connection helper ordered? ->
	if (opts & OPT_H) {
		const char *delay;
		const char *args[] = { "sh", "-c", opt_connect, NULL };
		// plug it in
		launch_helper(args);
		// Now:
		// our stdout will go to helper's stdin,
		// helper's stdout will be available on our stdin.

		// Wait for initial server message.
		// If helper (such as openssl) invokes STARTTLS, the initial 220
		// is swallowed by helper (and not repeated after TLS is initiated).
		// We will send NOOP cmd to server and check the response.
		// We should get 220+250 on plain connection, 250 on STARTTLSed session.
		//
		// The problem here is some servers delay initial 220 message,
		// and consider client to be a spammer if it starts sending cmds
		// before 220 reached it. The code below is unsafe in this regard:
		// in non-STARTTLSed case, we potentially send NOOP before 220
		// is sent by server.
		//
		// If $SMTP_ANTISPAM_DELAY is set, we pause before sending NOOP.
		//
		delay = getenv("SMTP_ANTISPAM_DELAY");
		if (delay)
			sleep(atoi(delay));
		code = smtp_check("NOOP", -1);
		if (code == 220)
			// we got 220 - this is not STARTTLSed connection,
			// eat 250 response to our NOOP
			smtp_check(NULL, 250);
		else
		if (code != 250)
			bb_error_msg_and_die("SMTP init failed");
	} else {
		// vanilla connection
		int fd;
		fd = create_and_connect_stream_or_die(opt_connect, 25);
		// and make ourselves a simple IO filter
		xmove_fd(fd, STDIN_FILENO);
		xdup2(STDIN_FILENO, STDOUT_FILENO);

		// Wait for initial server 220 message
		smtp_check(NULL, 220);
	}

	// we should start with modern EHLO
	if (250 != smtp_checkp("EHLO %s", host, -1))
		smtp_checkp("HELO %s", host, 250);

	// perform authentication
	if (opts & OPT_a) {
		smtp_check("AUTH LOGIN", 334);
		// we must read credentials unless they are given via -a[up] options
		if (!G.user || !G.pass)
			get_cred_or_die(4);
		encode_base64(NULL, G.user, NULL);
		smtp_check("", 334);
		encode_base64(NULL, G.pass, NULL);
		smtp_check("", 235);
	}

	// set sender
	// N.B. we have here a very loosely defined algorythm
	// since sendmail historically offers no means to specify secrets on cmdline.
	// 1) server can require no authentication ->
	//	we must just provide a (possibly fake) reply address.
	// 2) server can require AUTH ->
	//	we must provide valid username and password along with a (possibly fake) reply address.
	//	For the sake of security username and password are to be read either from console or from a secured file.
	//	Since reading from console may defeat usability, the solution is either to read from a predefined
	//	file descriptor (e.g. 4), or again from a secured file.

	// got no sender address? use auth name, then UID username as a last resort
	if (!opt_from) {
		opt_from = xasprintf("%s@%s",
		                     G.user ? G.user : xuid2uname(getuid()),
		                     xgethostbyname(host)->h_name);
	}
	free(host);

	smtp_checkp("MAIL FROM:<%s>", opt_from, 250);

	// process message

	// read recipients from message and add them to those given on cmdline.
	// this means we scan stdin for To:, Cc:, Bcc: lines until an empty line
	// and then use the rest of stdin as message body
	code = 0; // set "analyze headers" mode
	while ((s = xmalloc_fgetline(G.fp0)) != NULL) {
 dump:
		// put message lines doubling leading dots
		if (code) {
			// escape leading dots
			// N.B. this feature is implied even if no -i (-oi) switch given
			// N.B. we need to escape the leading dot regardless of
			// whether it is single or not character on the line
			if ('.' == s[0] /*&& '\0' == s[1] */)
				bb_putchar('.');
			// dump read line
			send_r_n(s);
			free(s);
			continue;
		}

		// analyze headers
		// To: or Cc: headers add recipients
		check_hdr = (0 == strncasecmp("To:", s, 3));
		has_to |= check_hdr;
		if (opts & OPT_t) {
			if (check_hdr || 0 == strncasecmp("Bcc:" + 1, s, 3)) {
				rcptto_list(s+3);
				last_hdr = HDR_TOCC;
				goto addheader;
			}
			// Bcc: header adds blind copy (hidden) recipient
			if (0 == strncasecmp("Bcc:", s, 4)) {
				rcptto_list(s+4);
				free(s);
				last_hdr = HDR_BCC;
				continue; // N.B. Bcc: vanishes from headers!
			}
		}
		check_hdr = (list && isspace(s[0]));
		if (strchr(s, ':') || check_hdr) {
			// other headers go verbatim
			// N.B. RFC2822 2.2.3 "Long Header Fields" allows for headers to occupy several lines.
			// Continuation is denoted by prefixing additional lines with whitespace(s).
			// Thanks (stefan.seyfried at googlemail.com) for pointing this out.
			if (check_hdr && last_hdr != HDR_OTHER) {
				rcptto_list(s+1);
				if (last_hdr == HDR_BCC)
					continue;
					// N.B. Bcc: vanishes from headers!
			} else {
				last_hdr = HDR_OTHER;
			}
 addheader:
			// N.B. we allow MAX_HEADERS generic headers at most to prevent attacks
			if (MAX_HEADERS && ++nheaders >= MAX_HEADERS)
				goto bail;
			llist_add_to_end(&list, s);
		} else {
			// a line without ":" (an empty line too, by definition) doesn't look like a valid header
			// so stop "analyze headers" mode
 reenter:
			// put recipients specified on cmdline
			check_hdr = 1;
			while (*argv) {
				char *t = sane_address(*argv);
				rcptto(t);
				//if (MAX_HEADERS && ++nheaders >= MAX_HEADERS)
				//	goto bail;
				if (!has_to) {
					const char *hdr;

					if (check_hdr && argv[1])
						hdr = "To: %s,";
					else if (check_hdr)
						hdr = "To: %s";
					else if (argv[1])
						hdr = "To: %s," + 3;
					else
						hdr = "To: %s" + 3;
					llist_add_to_end(&list,
							xasprintf(hdr, t));
					check_hdr = 0;
				}
				argv++;
			}
			// enter "put message" mode
			// N.B. DATA fails iff no recipients were accepted (or even provided)
			// in this case just bail out gracefully
			if (354 != smtp_check("DATA", -1))
				goto bail;
			// dump the headers
			while (list) {
				send_r_n((char *) llist_pop(&list));
			}
			// stop analyzing headers
			code++;
			// N.B. !s means: we read nothing, and nothing to be read in the future.
			// just dump empty line and break the loop
			if (!s) {
				send_r_n("");
				break;
			}
			// go dump message body
			// N.B. "s" already contains the first non-header line, so pretend we read it from input
			goto dump;
		}
	}
	// odd case: we didn't stop "analyze headers" mode -> message body is empty. Reenter the loop
	// N.B. after reenter code will be > 0
	if (!code)
		goto reenter;

	// finalize the message
	smtp_check(".", 250);
 bail:
	// ... and say goodbye
	smtp_check("QUIT", 221);
	// cleanup
	if (ENABLE_FEATURE_CLEAN_UP)
		fclose(G.fp0);

	return EXIT_SUCCESS;
}