export

CMakeLists.txt

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+cmake_minimum_required(VERSION 2.9)
+
+project(MilterFrom C)
+
+set(CMAKE_CXX_STANDARD 11)
+
+list(APPEND CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR})
+
+find_package(Threads REQUIRED)
+find_package(Milter REQUIRED)
+
+include_directories(${Milter_INCLUDE_DIRS})
+add_executable(milterfrom milterfrom.c)
+target_link_libraries(milterfrom ${Milter_LIBRARY})

FindMilter.cmake

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+# - Try to find Milter lib
+#
+# The following variables are defined
+#
+#  Milter_FOUND - system has Milter lib
+#  Milter_INCLUDE_DIR - the Milter include directory
+#  Milter_LIBRARY - the Milter library
+
+find_path(Milter_INCLUDE_DIR libmilter/mfapi.h
+	/usr/local/include
+	/usr/include
+	/opt/local/include
+	/sw/local/include
+	/sw/include
+	NO_DEFAULT_PATH
+)
+find_library(Milter_LIBRARY
+	NAMES "milter"
+	PATHS
+	~/Library/Frameworks
+	/Library/Frameworks
+	/usr/local/lib
+	/usr/local/lib64
+	/usr/lib
+	/usr/lib64
+	/opt/local/lib
+	/sw/local/lib
+	/sw/lib
+)
+
+SET(Milter_FOUND FALSE)
+IF(Milter_INCLUDE_DIR AND Milter_LIBRARY)
+	SET(Milter_FOUND TRUE)
+ENDIF(Milter_INCLUDE_DIR AND Milter_LIBRARY)

README.md

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+# MilterFrom
+This milter is used to compare the envelope sender with the sender specified in the mail header for authenticated users.
+
+It aims to resolve the problem that OpenDKIM signs ALL mails with domains listed in its databases. If you have a multi user setup user A "a@example.invalid" can send mails with the from field "From: b@example.invalid" and OpenDKIM signs it although user A should not be allowed to send authenticated mails from b@example.invalid.
+
+The postconf option "reject_authenticated_sender_login_mismatch" doesn't solve the problem at all, because it only enforces the envelope sender to be correct. This milter furhter ensures that the sender specified in the header matches the envelope sender.
+
+## Beta
+This code is beta. Someone who has more experience in using libmilter should look over the code and send me some feedback. The code is really short (one file with 209 lines) and based on the libmilter example. 
+
+## Build
+As always:
+```bash
+mkdir build
+cd $_
+cmake ..
+make
+```
+
+## Run
+```bash
+./milterfrom -d -p pidfile.pid -s /var/spool/postfix/themilter
+```
+
+## License
+Licensed under the 3-Clause BSD License.

milterfrom.c

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+/* 
+ * Argument parser
+ * 
+ * Copyright (c) 2017, Max von Buelow
+ * All rights reserved.
+ * Contact: https://maxvonbuelow.de
+ * 
+ * This file is part of the MilterFrom project.
+ * https://github.com/magcks/milterfrom
+ * 
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * 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.
+ *     * Neither the name of the copyright holder 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 <COPYRIGHT HOLDER> 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 <sys/types.h>
+#include <sys/stat.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sysexits.h>
+#include <unistd.h>
+#include <errno.h>
+
+#include "libmilter/mfapi.h"
+#include "libmilter/mfdef.h"
+
+struct mlfiPriv
+{
+	int is_auth;
+	char *env_from;
+	int env_from_len;
+	int reject;
+};
+
+#define MLFIPRIV ((struct mlfiPriv*)smfi_getpriv(ctx))
+
+static unsigned long mta_caps = 0;
+
+// Function to extract addresses from the header/envelope fields.
+// If the field contains a < with a subsequent >, the inner part is used. If not, the whole header field is used. This allows matching "Max Mustermann <max.mustermann@example.invalid>" matching.
+const char *parse_address(const char *address, int *len)
+{
+	int inlen = strlen(address);
+	int pos_open = -1, pos_close = -1;
+	int i;
+	for (i = 0; i < inlen; ++i) {
+		if (address[i] == '<') pos_open = i;
+		else if (address[i] == '>') pos_close = i;
+	}
+
+	if (pos_open != -1 && pos_close != -1 && pos_open < pos_close) {
+		*len = pos_close - pos_open - 1;
+		return address + pos_open + 1;
+	} else {
+		*len = inlen;
+		return address;
+	}
+}
+
+void mlfi_cleanup(SMFICTX *ctx)
+{
+	struct mlfiPriv *priv = MLFIPRIV;
+
+	if (priv == NULL) return;
+
+	free(priv->env_from);
+	free(priv);
+	smfi_setpriv(ctx, NULL);
+}
+
+sfsistat mlfi_envfrom(SMFICTX *ctx, char **envfrom)
+{
+	struct mlfiPriv *priv;
+
+	// Allocate some private memory.
+	priv = malloc(sizeof *priv);
+	if (priv == NULL) return SMFIS_TEMPFAIL;
+	memset(priv, '\0', sizeof *priv);
+
+	// Parse envelope from.
+	int len;
+	const char *from = parse_address(*envfrom, &len);
+	char *fromcp = strndup(from, len);
+	if (fromcp == NULL) return SMFIS_TEMPFAIL;
+
+	// Set private values.
+	priv->is_auth = smfi_getsymval(ctx, "{auth_type}") ? 1 : 0;
+	priv->env_from = fromcp;
+	priv->env_from_len = len;
+	priv->reject = 0;
+
+	smfi_setpriv(ctx, priv);
+
+	return SMFIS_CONTINUE;
+}
+
+sfsistat mlfi_header(SMFICTX *ctx, char *headerf, char *headerv)
+{
+	struct mlfiPriv *priv = MLFIPRIV;
+
+	// Perform checks if the sender is authenticated and the message is not rejected yet (the mail may contain multiple from tags, all have to match!).
+	if (priv->is_auth && !priv->reject) {
+		if (strcasecmp(headerf, "from") == 0) {
+			int len;
+			const char *from = parse_address(headerv, &len);
+
+			// Check whether header from matches envelope from and reject if not.
+			if (len != priv->env_from_len || strncasecmp(from, priv->env_from, len) != 0) priv->reject = 1;
+		}
+	}
+
+	return ((mta_caps & SMFIP_NR_HDR) != 0) ? SMFIS_NOREPLY : SMFIS_CONTINUE;
+}
+
+sfsistat
+mlfi_eom(SMFICTX *ctx)
+{
+	struct mlfiPriv *priv = MLFIPRIV;
+	if (priv->reject) {
+		smfi_setreply(ctx, "550", "5.7.1", "Rejected due to unmatching envelope and header sender.");
+		mlfi_cleanup(ctx);
+		return SMFIS_REJECT;
+	}
+	mlfi_cleanup(ctx);
+	return SMFIS_CONTINUE;
+}
+
+
+sfsistat
+mlfi_abort(SMFICTX *ctx)
+{
+	mlfi_cleanup(ctx);
+	return SMFIS_CONTINUE;
+}
+
+sfsistat
+mlfi_negotiate(SMFICTX *ctx, unsigned long f0, unsigned long f1, unsigned long f2, unsigned long f3, unsigned long *pf0, unsigned long *pf1, unsigned long *pf2, unsigned long *pf3)
+{
+	*pf0 = 0;
+	/* milter protocol steps: all but connect, HELO, RCPT */
+	*pf1 = SMFIP_NOCONNECT|SMFIP_NOHELO|SMFIP_NORCPT;
+	mta_caps = f1;
+	if ((mta_caps & SMFIP_NR_HDR) != 0) *pf1 |= SMFIP_NR_HDR;
+	*pf2 = 0;
+	*pf3 = 0;
+	return SMFIS_CONTINUE;
+}
+
+struct smfiDesc smfilter =
+{
+	"Header from check", /* filter name */
+	SMFI_VERSION,        /* version code -- do not change */
+	0,                   /* flags */
+	NULL,                /* connection info filter */
+	NULL,                /* SMTP HELO command filter */
+	mlfi_envfrom,        /* envelope sender filter */
+	NULL,                /* envelope recipient filter */
+	mlfi_header,         /* header filter */
+	NULL,                /* end of header */
+	NULL,                /* body block filter */
+	mlfi_eom,            /* end of message */
+	mlfi_abort,          /* message aborted */
+	NULL,                /* connection cleanup */
+	NULL,                /* unknown/unimplemented SMTP commands */
+	NULL,                /* DATA command filter */
+	mlfi_negotiate       /* option negotiation at connection startup */
+};
+
+int main(int argc, char **argv)
+{
+	int c, daemonize = 0;
+	char *pidfilename = NULL, *sockname = NULL;
+	FILE *pidfile = NULL;
+
+	while ((c = getopt(argc, argv, "ds:p:")) != -1) {
+		switch (c) {
+		case 's':
+			sockname = strdup(optarg);
+			break;
+		case 'p':
+			pidfilename = strdup(optarg);
+			break;
+		case 'd':
+			daemonize = 1;
+			break;
+		}
+	}
+	if (!sockname) {
+		fprintf(stderr, "%s: Missing required -s argument\n", argv[0]);
+		exit(EX_USAGE);
+	}
+	if (pidfilename) {
+		unlink(pidfilename);
+		pidfile = fopen(pidfilename, "w");
+		if (!pidfile)
+		{
+			fprintf(stderr, "Could not open pidfile: %s\n", strerror(errno));
+			exit(1);
+		}
+		free(pidfilename);
+	}
+	if (daemonize) {
+		if (daemon(0, 0) == -1) {
+			fprintf(stderr, "daemon() failed: %s\n", strerror(errno));
+			exit(EXIT_FAILURE);
+		}
+	}
+	if (pidfile) {
+		fprintf(pidfile, "%ld\n", (long)getpid());
+		fclose(pidfile);
+	}
+
+	struct stat junk;
+	if (stat(sockname, &junk) == 0) unlink(sockname);
+	smfi_setconn(sockname);
+	free(sockname);
+
+	if (smfi_register(smfilter) == MI_FAILURE) {
+		fprintf(stderr, "smfi_register failed\n");
+		exit(EX_UNAVAILABLE);
+	}
+	return smfi_main();
+}