Added dkim detection

Signed-off-by: tyrolyean <tyrolyean@tyrolyean.net>

README

@@ -1,5 +1,37 @@
 MAILATTACH
 
-This program starts a process which listens on a unix socket for incoming
+This program starts a process which listens on the LOOPBACKv4 address for
-milter connections. Incoming mail is scanned for large files and files above a
+incoming connections from postfix. The postfix master should view this as an
-certain threshold are replaced with links which the user may specify.
+advanced filter as explained in their documentation for post queue filtering:
+
+http://www.postfix.org/FILTER_README.html
+
+The original attempt was to implement this as a pre queue filter, but this
+required the milter protocol and postfix currently does not implement the
+replace body function from libmilter.
+
+You can specify the following command line options:
+
+--abort-pgp --noabort-pgp
+	To either abort the attachment process if PGP encryption or signatures 
+	have been detected or not. If true, the mail will not be modified.
+
+--abort-dkim --noabort-dkim
+	To either abort the attachment process if DKIM signatures have been
+	detected or not. If true, the mail will not be modified.
+
+--in-port -i
+	The incoming smtp port/the port from which mail is received.
+
+--out-port -o
+	The outgoing smtp port/the port to which mail ist passed through.
+
+HOWTO
+
+We essentially are MITM sniffing your email traffic and playing proxy from your
+postfix to your postfix. That's how this is intended to work according to the
+postfix website.
+
+This program needs to be started via it's own systemd service on system boot.
+You need to add the in and oputput ports to your postfix queue as described in
+the link above. More documentation is to a TODO

include/config.h

@@ -22,6 +22,8 @@
 
 extern uint16_t listen_port, forward_port;
 
-extern bool abort_on_pgp, abort_on_dkim;
+/* Used as booleans, but integers for getops sake... */
+
+extern int abort_on_pgp, abort_on_dkim;
 
 #endif /* CONFIG_H */

include/detect.h

@@ -23,6 +23,7 @@
 #include "attach.h"
 
 bool detect_pgp(struct email_t* mail);
+bool detect_dkim(struct email_t* mail);
 char* detect_start_of_body(char* message);
 char* detect_end_of_body(char* message);
 #endif /* DETECT_H */

include/tools.h

@@ -23,4 +23,5 @@
 const char* insert_string(char * destination, const char* source, 
 	size_t dest_orig_len, size_t offset);
 
+
 #endif /* TOOLS_H */

src/attach.c

@@ -83,17 +83,16 @@ char* attach_files(char* message, size_t len){
 
 	struct email_t email = mail_from_text(message,len);
 	
-	printf("Received message header: [%.*s]\n", email.header_len, 
-		email.message);
-	printf("Received message body: [%.*s]\n", 
-		email.message_length-email.body_offset,
-		email.message + email.body_offset);
-
 	/* Check if mails are signed/encrypted, and abort if nescessary */
 	if(abort_on_pgp && detect_pgp(&email)){
 		printf("PGP detected, aborting...");
 		return email.message;
 	}
+	/* Check if mails are signed/encrypted, and abort if nescessary */
+	if(abort_on_dkim && detect_dkim(&email)){
+		printf("DKIM signature detected, aborting...");
+		return email.message;
+	}
 
 	return email.message;
 }

src/config.c

@@ -17,4 +17,4 @@
 #include "config.h"
 
 uint16_t listen_port = 4269, forward_port = 4270;
-bool abort_on_pgp = true, abort_on_dkim = true;
+int abort_on_pgp = true, abort_on_dkim = true;

src/detect.c

@@ -29,6 +29,11 @@ char* pgp_signatures[] =
 	"-----BEGIN PGP MESSAGE-----"
 };
 
+char* dkim_signatures[] = 
+{
+	"DKIM-Signature:"
+};
+
 bool detect_pgp(struct email_t* mail){
 		
 	size_t points = 0;
@@ -45,6 +50,23 @@ bool detect_pgp(struct email_t* mail){
 	return points >= 2;
 }
 
+bool detect_dkim(struct email_t* mail){
+		
+	size_t points = 0;
+	
+	for(size_t i = 0; i < (sizeof(dkim_signatures)/sizeof(char*));i++){
+		if(strcasestr(mail->message, dkim_signatures[i]) != NULL
+				&& strcasestr(mail->message, dkim_signatures[i])
+				<= (mail->message+mail->header_len)){
+			points++;
+		}
+		
+	}
+	
+
+	return points >= 1;
+}
+
 /* If body hasn't started yet, it returns NULL, if it has started, it returns
  * the pointer to the beginning of the newline.
  */

src/main.c

@@ -6,7 +6,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
-
+#include <getopt.h>
 
 #include "network.h"
 #include "config.h"
@@ -15,11 +15,66 @@
 int main(int argc, char* argv[]){
 	
 	printf("INIT\n");
-	
+
+	int c;
+
+	while (1){
+		static struct option long_options[] =
+		{
+			{"abort-pgp",	no_argument, &abort_on_pgp, 1},
+			{"abort-dkim",	no_argument, &abort_on_dkim,1},
+			{"noabort-pgp",	no_argument, &abort_on_pgp, 0},
+			{"noabort-dkim",no_argument, &abort_on_dkim,0},
+			{"in-port",	required_argument, 0, 'i'},
+			{"out-port",	required_argument, 0, 'o'},
+			{0, 0, 0, 0}
+		};
+		/* getopt_long stores the option index here. */
+		int option_index = 0;
+
+		c = getopt_long (argc, argv, "i:o:pd",
+			       long_options, &option_index);
+
+		/* Detect the end of the options. */
+		if (c == -1){
+			break;
+		}
+
+		switch (c){
+		case 0:
+			break;
+		case 'i':
+			listen_port = atoi(optarg);
+			break;
+
+		case 'o':
+			forward_port = atoi(optarg);
+			break;
+
+		case '?':
+			/* getopt_long already printed an error message. */
+			return EXIT_FAILURE;
+			break;
+
+		default:
+			abort ();
+		}
+	}
+
+	printf("Incoming port: %u outgoing port: %u on loopback interface\n",
+		 listen_port, forward_port);
+
+	printf("Ignoring PGP signed/encrypted messages: %s\n",
+		abort_on_pgp ? "true":false);
+
+	printf("Ignoring DKIM signed messages: %s\n",
+		abort_on_dkim ? "true" : "false");
+
 	if(init_net() < 0){
 		return EXIT_FAILURE;
 	}
 
-
+	loop_clients();
+	return EXIT_SUCCESS;
 
 }

src/network.c

@@ -273,9 +273,6 @@ void loop_clients(){
 	
 	while (1) {
 
-		/*
-		* accept: wait for a connection request
-		*/
 		childfd = accept(parentfd, (struct sockaddr *) &clientaddr, &clientlen);
 		if (childfd < 0){
 			perror("accept failed");