net.c

/*
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 2008-2014, Simon Schubert <2@0x2c.org>.
 * Copyright (c) 2008 The DragonFly Project.  All rights reserved.
 *
 * This code is derived from software contributed to The DragonFly Project
 * by Matthias Schmidt <matthias@dragonflybsd.org>, University of Marburg,
 * Germany.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name of The DragonFly Project nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific, prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include "dfcompat.h"

#include <sys/param.h>
#include <sys/queue.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#include <openssl/ssl.h>
#include <openssl/err.h>

#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <netdb.h>
#include <setjmp.h>
#include <signal.h>
#include <strings.h>
#include <string.h>
#include <syslog.h>
#include <unistd.h>

#include "dma.h"

char neterr[ERRMSG_SIZE];

char *
ssl_errstr(void)
{
	long oerr, nerr;

	oerr = 0;
	while ((nerr = ERR_get_error()) != 0)
		oerr = nerr;

	return (ERR_error_string(oerr, NULL));
}

ssize_t
send_remote_command(int fd, const char* fmt, ...)
{
	va_list va;
	char cmd[4096];
	size_t len, pos;
	int s;
	ssize_t n;

	va_start(va, fmt);
	s = vsnprintf(cmd, sizeof(cmd) - 2, fmt, va);
	va_end(va);
	if (s < 0 || (size_t)s >= sizeof(cmd) - 2) {
		strcpy(neterr, "Internal error: oversized command string");
		return (-1);
	}

	/* We *know* there are at least two more bytes available */
	strcat(cmd, "\r\n");
	len = strlen(cmd);

	pos = 0;
	while (pos < len) {
		if (((config.features & SECURETRANSFER) != 0) &&
		    ((config.features & NOSSL) == 0)) {
			if ((n = SSL_write(config.ssl, (const char*)(cmd + pos), len - pos)) <= 0) {
				s = SSL_get_error(config.ssl, n);
				if (s == SSL_ERROR_ZERO_RETURN ||
				    s == SSL_ERROR_SYSCALL ||
				    s == SSL_ERROR_SSL) {
					strlcpy(neterr, ssl_errstr(), sizeof(neterr));
					return (-1);
				}
				n = 0;
			}
		} else {
			n = write(fd, cmd + pos, len - pos);
			if (n < 0) {
				if ((errno != EAGAIN) && (errno != EINTR))
					return (-1);
				n = 0;
			}
		}
		pos += n;
	}

	return (len);
}

int
read_remote(int fd, int extbufsize, char *extbuf)
{
	ssize_t rlen = 0;
	size_t pos, len, copysize;
	char buff[BUF_SIZE];
	int done = 0, status = 0, status_running = 0, extbufpos = 0;
	enum { parse_status, parse_spacedash, parse_rest } parsestate;

	if (do_timeout(CON_TIMEOUT, 1) != 0) {
		snprintf(neterr, sizeof(neterr), "Timeout reached");
		return (-1);
	}

	/*
	 * Remote reading code from femail.c written by Henning Brauer of
	 * OpenBSD and released under a BSD style license.
	 */
	len = 0;
	pos = 0;
	parsestate = parse_status;
	neterr[0] = 0;
	while (!(done && parsestate == parse_status)) {
		rlen = 0;
		if (pos == 0 ||
		    (pos > 0 && memchr(buff + pos, '\n', len - pos) == NULL)) {
			memmove(buff, buff + pos, len - pos);
			len -= pos;
			pos = 0;
			if (((config.features & SECURETRANSFER) != 0) &&
			    (config.features & NOSSL) == 0) {
				if ((rlen = SSL_read(config.ssl, buff + len, sizeof(buff) - len)) <= 0) {
					switch (SSL_get_error(config.ssl, rlen)) {
					case SSL_ERROR_ZERO_RETURN:
					case SSL_ERROR_SYSCALL:
					case SSL_ERROR_SSL:
						strlcpy(neterr, ssl_errstr(), sizeof(neterr));
						goto error;
					default:
						/* in case of recoverable error, retry after short sleep */
						usleep(10000);
						continue;
					}
				}
			} else {
				if ((rlen = read(fd, buff + len, sizeof(buff) - len)) == -1) {
					strlcpy(neterr, strerror(errno), sizeof(neterr));
					goto error;
				}
			}
			len += rlen;

			copysize = sizeof(neterr) - strlen(neterr) - 1;
			if (copysize > len)
				copysize = len;
			strncat(neterr, buff, copysize);
		}
		/*
		 * If there is an external buffer with a size bigger than zero
		 * and as long as there is space in the external buffer and
		 * there are new characters read from the mailserver
		 * copy them to the external buffer
		 */
		if (extbufpos <= (extbufsize - 1) && rlen > 0 && extbufsize > 0 && extbuf != NULL) {
			/* do not write over the bounds of the buffer */
			if(extbufpos + rlen > (extbufsize - 1)) {
				rlen = extbufsize - extbufpos;
			}
			memcpy(extbuf + extbufpos, buff + len - rlen, rlen);
			extbufpos += rlen;
		}

		if (pos == len)
			continue;

		switch (parsestate) {
		case parse_status:
			for (; pos < len; pos++) {
				if (isdigit((unsigned char)buff[pos])) {
					status_running = status_running * 10 + (buff[pos] - '0');
				} else {
					status = status_running;
					status_running = 0;
					parsestate = parse_spacedash;
					break;
				}
			}
			continue;

		case parse_spacedash:
			switch (buff[pos]) {
			case ' ':
				done = 1;
				break;

			case '-':
				/* ignore */
				/* XXX read capabilities */
				break;

			default:
				strcpy(neterr, "invalid syntax in reply from server");
				goto error;
			}

			pos++;
			parsestate = parse_rest;
			continue;

		case parse_rest:
			/* skip up to \n */
			for (; pos < len; pos++) {
				if (buff[pos] == '\n') {
					pos++;
					parsestate = parse_status;
					break;
				}
			}
		}

	}

	do_timeout(0, 0);

	/* chop off trailing newlines */
	while (neterr[0] != 0 && strchr("\r\n", neterr[strlen(neterr) - 1]) != 0)
		neterr[strlen(neterr) - 1] = 0;

	return (status/100);

error:
	do_timeout(0, 0);
	return (-1);
}

static int
smtp_auth_login(int fd, char *login, char* password)
{
	char *temp;
	int len, res = 0;

	/* Send AUTH command according to RFC 2554 */
	send_remote_command(fd, "AUTH LOGIN");
	if (read_remote(fd, 0, NULL) != 3) {
		syslog(LOG_NOTICE, "remote delivery deferred:"
		    " AUTH login not available: %s",
		    neterr);
		return (1);
	}

	len = base64_encode(login, strlen(login), &temp);
	if (len < 0) {
encerr:
		syslog(LOG_ERR, "can not encode auth reply: %m");
		return (1);
	}

	send_remote_command(fd, "%s", temp);
	free(temp);
	res = read_remote(fd, 0, NULL);
	if (res != 3) {
		syslog(LOG_NOTICE, "remote delivery %s: AUTH login failed: %s",
		    res == 5 ? "failed" : "deferred", neterr);
		return (res == 5 ? -1 : 1);
	}

	len = base64_encode(password, strlen(password), &temp);
	if (len < 0)
		goto encerr;

	send_remote_command(fd, "%s", temp);
	free(temp);
	res = read_remote(fd, 0, NULL);
	if (res != 2) {
		syslog(LOG_NOTICE, "remote delivery %s: Authentication failed: %s",
		    res == 5 ? "failed" : "deferred", neterr);
		return (res == 5 ? -1 : 1);
	}

	return (0);
}

static int
smtp_auth_plain(int fd, char *login, char* password)
{
	char *temp, *authdata;
	int len, res;

	len = asprintf(&authdata, "%c%s%c%s", '\0', login, '\0', password);
	if (len < 0) {
		syslog(LOG_ERR, "can not format auth reply: %m");
		return (1);
	}
	
	len = base64_encode(authdata, len, &temp);
	free(authdata);
	if (len < 0) {
		syslog(LOG_ERR, "can not encode auth reply: %m");
		return (1);
	}

	/* Send AUTH command according to RFC 2554 */
	send_remote_command(fd, "AUTH PLAIN %s", temp);
	free(temp);
	res = read_remote(fd, 0, NULL);
	if (res != 2) {
		syslog(LOG_NOTICE, "remote delivery %s: Authentication failed: %s",
		    res == 5 ? "failed" : "deferred", neterr);
		return (res == 5 ? -1 : 1);
	}

	return (0);
}

/*
 * Handle SMTP authentication
 */
static int
smtp_auth(int fd, char *login, char* password, const struct smtp_features* features)
{
	int res = 1;

	// CRAM-MD5
	if (features->auth.cram_md5) {
		res = smtp_auth_md5(fd, login, password);
		if (res != 1) {
			return (res);
		}
	}

	if ((config.features & INSECURE) != 0 ||
		    (config.features & SECURETRANSFER) != 0) {

		// LOGIN
		if (features->auth.login) {
			res = smtp_auth_login(fd, login, password);
			if (res != 1) {
				return (res);
			}
		}

		// PLAIN
		if (features->auth.plain) {
			res = smtp_auth_plain(fd, login, password);
			if (res != 1) {
				return (res);
			}
		}	
	} else if (features->auth.login || features->auth.plain) {
		syslog(LOG_WARNING, "non-encrypted SMTP authentication is disabled in config, so skipping it.");
		return (1);
	}

	return (res);
}

static int
open_connection(struct mx_hostentry *h)
{
	int fd;

	syslog(LOG_INFO, "trying remote delivery to %s [%s] pref %d",
	       h->host, h->addr, h->pref);

	fd = socket(h->ai.ai_family, h->ai.ai_socktype, h->ai.ai_protocol);
	if (fd < 0) {
		syslog(LOG_INFO, "socket for %s [%s] failed: %m",
		       h->host, h->addr);
		return (-1);
	}

	if (connect(fd, (struct sockaddr *)&h->sa, h->ai.ai_addrlen) < 0) {
		syslog(LOG_INFO, "connect to %s [%s] failed: %m",
		       h->host, h->addr);
		close(fd);
		return (-1);
	}

	return (fd);
}

static void
close_connection(int fd)
{
	if (config.ssl != NULL) {
		if (((config.features & SECURETRANSFER) != 0) &&
		    ((config.features & NOSSL) == 0))
			SSL_shutdown(config.ssl);
		SSL_free(config.ssl);
	}

	close(fd);
}

static void parse_auth_line(char* line, struct smtp_auth_mechanisms* auth) {
	// Skip the auth prefix
	line += strlen("AUTH ");

	char* method = strtok(line, " ");
	while (method) {
		if (strcmp(method, "CRAM-MD5") == 0)
			auth->cram_md5 = 1;

		else if (strcmp(method, "LOGIN") == 0)
			auth->login = 1;

		else if (strcmp(method, "PLAIN") == 0)
			auth->plain = 1;

		method = strtok(NULL, " ");
	}
}

int perform_server_greeting(int fd, struct smtp_features* features) {
	send_remote_command(fd, "%s %s", config.features & LMTP ? "LHLO" : "EHLO", hostname());

	char buffer[EHLO_RESPONSE_SIZE];
	memset(buffer, 0, sizeof(buffer));

	int res = read_remote(fd, sizeof(buffer) - 1, buffer);

	if (res == 5 && (config.features & LMTP) == 0) {
		syslog(LOG_DEBUG, "EHLO rejected, falling back to HELO");
		send_remote_command(fd, "HELO %s", hostname());
		memset(buffer, 0, sizeof(buffer));
		res = read_remote(fd, sizeof(buffer) - 1, buffer);
	}

	// Got an unexpected response
	if (res != 2)
		return -1;

	// Reset all features
	memset(features, 0, sizeof(*features));

	// Run through the buffer line by line
	char linebuffer[EHLO_RESPONSE_SIZE];
	char* p = buffer;

	while (*p) {
		char* line = linebuffer;
		while (*p && *p != '\n') {
			*line++ = *p++;
		}

		// p should never point to NULL after the loop
		// above unless we reached the end of the buffer.
		// In that case we will raise an error.
		if (!*p) {
			return -1;
		}

		// Otherwise p points to the newline character which
		// we will skip.
		p++;

		// Terminte the string (and remove the carriage-return character)
		*--line = '\0';
		line = linebuffer;

		// End main loop for empty lines
		if (*line == '\0')
			break;

		// Process the line
		// - Must start with 250, followed by dash or space
		// - We won't check for the correct usage of space and dash because
		//    that is already done in read_remote().
		if ((strncmp(line, "250-", 4) != 0) && (strncmp(line, "250 ", 4) != 0)) {
			syslog(LOG_ERR, "Invalid line: %s\n", line);
			return -1;
		}

		// Skip the prefix
		line += 4;

		// Check for STARTTLS
		if (strcmp(line, "STARTTLS") == 0)
			features->starttls = 1;

		// Parse authentication mechanisms
		else if (strncmp(line, "AUTH ", 5) == 0)
			parse_auth_line(line, &features->auth);
	}

	syslog(LOG_DEBUG, "Server greeting successfully completed");

	// STARTTLS
	if (features->starttls)
		syslog(LOG_DEBUG, "  Server supports STARTTLS");
	else
		syslog(LOG_DEBUG, "  Server does not support STARTTLS");

	// Authentication
	if (features->auth.cram_md5) {
		syslog(LOG_DEBUG, "  Server supports CRAM-MD5 authentication");
	}
	if (features->auth.login) {
		syslog(LOG_DEBUG, "  Server supports LOGIN authentication");
	}
	if (features->auth.plain) {
		syslog(LOG_DEBUG, "  Server supports PLAIN authentication");
	}

	return 0;
}

static int
deliver_to_host(struct qitem *it, struct mx_hostentry *host)
{
	struct authuser *a;
	struct smtp_features features;
	char line[1000], *addrtmp = NULL, *to_addr;
	size_t linelen;
	int fd, error = 0, do_auth = 0, res = 0, complete = 0;

	if (fseek(it->mailf, 0, SEEK_SET) != 0) {
		snprintf(errmsg, sizeof(errmsg), "can not seek: %s", strerror(errno));
		return (-1);
	}

	fd = open_connection(host);
	if (fd < 0)
		return (1);

#define READ_REMOTE_CHECK(c, exp)                                       \
        do {                                                            \
                res = read_remote(fd, 0, NULL);                         \
                if (res == 5) {                                         \
                        syslog(LOG_ERR, "remote delivery to %s [%s] failed after %s: %s", \
                               host->host, host->addr, c, neterr);      \
                        snprintf(errmsg, sizeof(errmsg), "%s [%s] did not like our %s:\n%s", \
                                 host->host, host->addr, c, neterr);    \
                        error = -1;                                     \
                        goto out;                                       \
                } else if (res != exp) {                                \
                        syslog(LOG_NOTICE, "remote delivery deferred: %s [%s] failed after %s: %s", \
                               host->host, host->addr, c, neterr);      \
                        error = 1;                                      \
                        goto out;                                       \
                }                                                       \
        } while (0)

	/* Check first reply from remote host */
	if ((config.features & SECURETRANSFER) == 0 ||
	    (config.features & STARTTLS) != 0) {
		config.features |= NOSSL;
		READ_REMOTE_CHECK("connect", 2);

		config.features &= ~NOSSL;
	}

	if ((config.features & SECURETRANSFER) != 0) {
		error = smtp_init_crypto(fd, config.features, &features, host->host);
		if (error == 0)
			syslog(LOG_DEBUG, "SSL initialization successful");
		else
			goto out;

		if ((config.features & STARTTLS) == 0)
			READ_REMOTE_CHECK("connect", 2);
	}

	// Say EHLO
	if (perform_server_greeting(fd, &features) != 0) {
		syslog(LOG_ERR, "Could not perform server greeting at %s [%s]: %s",
			host->host, host->addr, neterr);
		return -1;
	}

	/*
	 * Use SMTP authentication if the user defined an entry for the remote
	 * or smarthost
	 */
	SLIST_FOREACH(a, &authusers, next) {
		if (strcmp(a->host, host->host) == 0) {
			do_auth = 1;
			break;
		}
	}

	if (do_auth == 1) {
		/*
		 * Check if the user wants plain text login without using
		 * encryption.
		 */
		if (features.auth.cram_md5 || features.auth.login || features.auth.plain) {
			syslog(LOG_INFO, "using SMTP authentication for user %s", a->login);
			error = smtp_auth(fd, a->login, a->password, &features);
			if (error < 0) {
				snprintf(errmsg, sizeof(errmsg), "SMTP auth to %s failed", host->host);
				error = -1;
				goto out;
			}
			/* SMTP authentication is not available, so try without */
			else if (error > 0) {
				syslog(LOG_WARNING, "SMTP authentication not available. Trying without.");
			}
		} else {
			syslog(LOG_ERR, "No supported AUTH mechanisms in common with server."
					" Skipping authentication.");
		}
	}

	/* XXX send ESMTP ENVID, RET (FULL/HDRS) and 8BITMIME */
	send_remote_command(fd, "MAIL FROM:<%s>", it->sender);
	READ_REMOTE_CHECK("MAIL FROM", 2);

	/* XXX send ESMTP ORCPT */
	if ((addrtmp = strdup(it->addr)) == NULL) {
		syslog(LOG_CRIT, "remote delivery deferred: unable to allocate memory");
		error = 1;
		goto out;
	}
	to_addr = strtok(addrtmp, ",");
	while (to_addr != NULL) {
		send_remote_command(fd, "RCPT TO:<%s>", to_addr);
		READ_REMOTE_CHECK("RCPT TO", 2);
		to_addr = strtok(NULL, ",");
	}

	send_remote_command(fd, "DATA");
	READ_REMOTE_CHECK("DATA", 3);

	error = 0;
	while (!feof(it->mailf)) {
		if (fgets(line, sizeof(line), it->mailf) == NULL)
			break;
		linelen = strlen(line);
		if (linelen == 0 || line[linelen - 1] != '\n') {
			syslog(LOG_CRIT, "remote delivery failed: corrupted queue file");
			snprintf(errmsg, sizeof(errmsg), "corrupted queue file");
			error = -1;
			goto out;
		}

		/* Remove trailing \n's and escape leading dots */
		trim_line(line);

		/*
		 * If the first character is a dot, we escape it so the line
		 * length increases
		*/
		if (line[0] == '.')
			linelen++;

		if (send_remote_command(fd, "%s", line) != (ssize_t)linelen+1) {
			syslog(LOG_NOTICE, "remote delivery deferred: write error");
			error = 1;
			goto out;
		}
	}

	send_remote_command(fd, ".");
	READ_REMOTE_CHECK("final DATA", 2);
	complete = 1;

out:
	send_remote_command(fd, "QUIT");
	if (read_remote(fd, 0, NULL) != 2)
		syslog(LOG_INFO, "%sQUIT failed: %s", complete ? "remote delivery succeeded but " : "",neterr);

	free(addrtmp);
	close_connection(fd);
	return (error);
}

int
deliver_remote(struct qitem *it)
{
	struct mx_hostentry *hosts, *h;
	const char *host;
	int port;
	int error = 1, smarthost = 0;

	port = SMTP_PORT;

	/* Smarthost support? */
	if (config.smarthost != NULL) {
		host = config.smarthost;
		port = config.port;
		syslog(LOG_INFO, "using smarthost (%s:%i)", host, port);
		smarthost = 1;
	} else {
		host = strrchr(it->addr, '@');
		/* Should not happen */
		if (host == NULL) {
			snprintf(errmsg, sizeof(errmsg), "Internal error: badly formed address %s",
				 it->addr);
			return(-1);
		} else {
			/* Step over the @ */
			host++;
		}
	}

	error = dns_get_mx_list(host, port, &hosts, smarthost);
	if (error) {
		snprintf(errmsg, sizeof(errmsg), "DNS lookup failure: host %s not found", host);
		syslog(LOG_NOTICE, "remote delivery %s: DNS lookup failure: host %s not found",
		       error < 0 ? "failed" : "deferred",
		       host);
		return (error);
	}

	for (h = hosts; *h->host != 0; h++) {
		switch (deliver_to_host(it, h)) {
		case 0:
			/* success */
			error = 0;
			goto out;
		case 1:
			/* temp failure */
			error = 1;
			break;
		default:
			/* perm failure */
			error = -1;
			goto out;
		}
	}
out:
	free(hosts);

	return (error);
}