busybox/mailutils/sendmail.c

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/* 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 tarball for details.
*/
#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
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static int smtp_checkp(const char *fmt, const char *param, int code)
{
char *answer;
const char *msg = command(fmt, param);
// read stdin
// if the string has a form \d\d\d- -- 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 (strlen(answer) <= 3 || '-' != answer[3])
break;
if (answer) {
int n = atoi(answer);
if (timeout)
alarm(0);
free(answer);
if (-1 == code || n == code)
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 = str;
char *p = s;
while (*s) {
if (isalnum(*s) || '_' == *s || '-' == *s || '.' == *s || '@' == *s) {
*p++ = *s;
}
s++;
}
*p = '\0';
return str;
}
static void rcptto(const char *s)
{
// 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);
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}
int sendmail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int sendmail_main(int argc UNUSED_PARAM, char **argv)
{
char *opt_connect = opt_connect;
char *opt_from;
char *s;
llist_t *list = NULL;
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char *domain = sane_address(safe_getdomainname());
unsigned nheaders = 0;
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int code;
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
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};
// init global variables
INIT_G();
// save initial stdin since body is piped!
xdup2(STDIN_FILENO, 3);
G.fp0 = xfdopen_for_read(3);
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// parse options
// -f is required. -H and -S are mutually exclusive
opt_complementary = "f:w+:H--S:S--H:a::";
// 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::", &opt_from, NULL, &timeout, &opt_connect, &opt_connect, &list);
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//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_info_msg("OPT[%x] AU[%s], AP[%s], AM[%s], ARGV[%s]", opts, au, ap, am, *argv);
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// connect to server
// connection helper ordered? ->
if (opts & OPT_H) {
const char *args[] = { "sh", "-c", opt_connect, NULL };
// plug it in
launch_helper(args);
// vanilla connection
} else {
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int fd;
// host[:port] not explicitly specified? -> use $SMTPHOST
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// no $SMTPHOST ? -> use localhost
if (!(opts & OPT_S)) {
opt_connect = getenv("SMTPHOST");
if (!opt_connect)
opt_connect = (char *)"127.0.0.1";
}
// do connect
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);
}
// N.B. from now we know nothing about network :)
// wait for initial server OK
// N.B. if we used openssl the initial 220 answer is already swallowed during openssl TLS init procedure
// so we need to kick the server to see whether we are ok
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code = smtp_check("NOOP", -1);
// 220 on plain connection, 250 on openssl-helped TLS session
if (220 == code)
smtp_check(NULL, 250); // reread the code to stay in sync
else if (250 != code)
bb_error_msg_and_die("INIT failed");
// we should start with modern EHLO
if (250 != smtp_checkp("EHLO %s", domain, -1)) {
smtp_checkp("HELO %s", domain, 250);
}
if (ENABLE_FEATURE_CLEAN_UP)
free(domain);
// 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);
}
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// set sender
// N.B. we have here a very loosely defined algotythm
// 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 system username as a resort
// N.B. we marked -f as required option!
//if (!G.user) {
// // N.B. IMHO getenv("USER") can be way easily spoofed!
// G.user = xuid2uname(getuid());
// opt_from = xasprintf("%s@%s", G.user, domain);
//}
//if (ENABLE_FEATURE_CLEAN_UP)
// free(domain);
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) {
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// 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] */)
printf(".");
// dump read line
printf("%s\r\n", s);
free(s);
continue;
}
// analyze headers
// To: or Cc: headers add recipients
if (0 == strncasecmp("To: ", s, 4) || 0 == strncasecmp("Bcc: " + 1, s, 4)) {
rcptto(sane_address(s+4));
goto addheader;
// Bcc: header adds blind copy (hidden) recipient
} else if (0 == strncasecmp("Bcc: ", s, 5)) {
rcptto(sane_address(s+5));
free(s);
// N.B. Bcc: vanishes from headers!
// 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.
} else if (strchr(s, ':') || (list && skip_whitespace(s) != s)) {
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);
// a line without ":" (an empty line too, by definition) doesn't look like a valid header
// so stop "analyze headers" mode
} else {
reenter:
// put recipients specified on cmdline
while (*argv) {
char *t = sane_address(*argv);
rcptto(t);
//if (MAX_HEADERS && ++nheaders >= MAX_HEADERS)
// goto bail;
llist_add_to_end(&list, xasprintf("To: %s", t));
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) {
printf("%s\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) {
puts("\r");
break;
}
// go dump message body
// N.B. "s" already contains the first non-header line, so pretend we read it from input
goto dump;
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}
}
// 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;
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// finalize the message
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smtp_check(".", 250);
bail:
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// ... and say goodbye
smtp_check("QUIT", 221);
// cleanup
if (ENABLE_FEATURE_CLEAN_UP)
fclose(G.fp0);
return EXIT_SUCCESS;
}