/* vi: set sw=4 ts=4: */ /* * bare bones sendmail * * Copyright (C) 2008 by Vladimir Dronnikov * * 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. 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" //usage: "\n -amPLAIN or AUTH PLAIN" //usage: "\n (-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> * <@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) { /* Standard allows these chars in username without quoting: * /!#$%&'*+-=?^_`{|}~ * and allows dot (.) with some restrictions. * I chose to only allow a saner subset. * I propose to expand it only on user's request. */ 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; e = trim(str); if (e != str && *--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 *free_me = xstrdup(list); char *str = free_me; char *s = free_me; 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(free_me); } 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 //--- for -amMETHOD OPT_am_plain = 1 << 9, // AUTH PLAIN }; // 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 // 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" "\0" // -v is a counter, -H and -S are mutually exclusive, -a is a list "vv:H--S:S--H", &opt_from, NULL, &timeout, &opt_connect, &opt_connect, &list, &verbose ); //argc -= optind; argv += optind; // process -a[upm] 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); if ('m' == a[0]) { if ((a[1] | 0x20) == 'p') // PLAIN opts |= OPT_am_plain; else if ((a[1] | 0x20) == 'l') // LOGIN ; /* do nothing (this is the default) */ else bb_error_msg_and_die("unsupported AUTH method %s", 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) { // read credentials unless they are given via -a[up] options if (!G.user || !G.pass) get_cred_or_die(4); if (opts & OPT_am_plain) { char *plain_auth; size_t user_len, pass_len; user_len = strlen(G.user); pass_len = strlen(G.pass); smtp_check("AUTH PLAIN", 334); // use \1 as placeholders for \0 (format string is NUL-terminated) plain_auth = xasprintf("\1%s\1%s", G.user, G.pass); // substitute placeholders plain_auth[0] = '\0'; plain_auth[1 + user_len] = '\0'; printbuf_base64(plain_auth, 1 + user_len + 1 + pass_len); free(plain_auth); } else { smtp_check("AUTH LOGIN", 334); printstr_base64(G.user); smtp_check("", 334); printstr_base64(G.pass); } 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; }