From 764203ea99ce1f2f92b1700479527b1c9e5a784d Mon Sep 17 00:00:00 2001
From: maride <maride@darknebu.la>
Date: Thu, 28 Sep 2017 14:41:07 +0200
Subject: [PATCH] Add blacklist functionality

---
 knockr.go | 50 +++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 45 insertions(+), 5 deletions(-)

diff --git a/knockr.go b/knockr.go
index 496299b..7780f29 100644
--- a/knockr.go
+++ b/knockr.go
@@ -12,12 +12,16 @@ type knockArguments struct {
 	cli.Helper
 	WhitelistPort int `cli:'wp' usage:'The port to launch the whitelist server on'`
 	GatewayPort int `cli:'gp' usage:'The port to protect'`
+	BlacklistPort int `cli:'wp' usage:'If set: The port to blacklist the connected host'`
 	Destination string `cli:'d' usage:'The destination to relay traffic to'`
 	Timeout int64 `cli:'t' usage:'Time in seconds after which a whitelist entry will be removed'`
 }
 
-var whitelist = make(map[string]int64)
-var arguments *knockArguments
+var (
+	whitelist = make(map[string]int64)
+	blacklist []string
+	arguments *knockArguments
+)
 
 func main() {
 	// Parse command line arguments
@@ -28,6 +32,7 @@ func main() {
 
 	// Launch listeners
 	go listener(arguments.WhitelistPort, whitelist_handler)
+	go listener(arguments.BlacklistPort, blacklist_handler)
 	listener(arguments.GatewayPort, gateway_handler)
 }
 
@@ -55,8 +60,26 @@ func whitelist_handler(c net.Conn) {
 	// Handler function for whitelist socket connections, whitelisting the connecting host
 	host, _, _ := net.SplitHostPort(c.RemoteAddr().String())
 
-	io.WriteString(c, fmt.Sprintf("Knock Knock, %s.", host))
-	add_to_whitelist(host)
+	if is_blacklisted(host) {
+		fmt.Println("[BLK] Denying blacklisted host ", host)
+	} else {
+		io.WriteString(c, fmt.Sprintf("Knock Knock, %s.", host))
+		add_to_whitelist(host)
+	}
+	c.Close()
+}
+
+func blacklist_handler(c net.Conn) {
+	// Handler which blocks every host connecting to it.
+	// Useful to place it on port (whitelistPort-1) to crash port scanners.
+	host, _, _ := net.SplitHostPort(c.RemoteAddr().String())
+
+	if ! is_whitelisted(host) {
+		fmt.Println("[BLK] Blacklisting ", host)
+		add_to_blacklist(host)
+	} else {
+		fmt.Println("[ERR] Whitelisted host ", host, " connected to blacklist port. Ignoring.")
+	}
 	c.Close()
 }
 
@@ -64,7 +87,9 @@ func gateway_handler(c net.Conn) {
 	// Filter connections whether or not the connecting host is whitelisted
 	host, _, _ := net.SplitHostPort(c.RemoteAddr().String())
 
-	if is_whitelisted(host) {
+	if is_blacklisted(host) {
+		fmt.Println("[BLK] Blacklisted host ", host, ", ignoring")
+	} else if is_whitelisted(host) {
 		fmt.Println("[OK ] Whitelisted host ", host, " connected")
 		update_whitelist_time(host)
 		proxy(c)
@@ -111,6 +136,21 @@ func is_whitelisted(addr string) bool {
 	return false
 }
 
+func add_to_blacklist(addr string) {
+	// Add specified address to blacklist
+	blacklist = append(blacklist, addr)
+}
+
+func is_blacklisted(addr string) bool {
+	// Check whether or not the specified address is blacklisted
+	for i:=0; i<len(blacklist); i++ {
+		if blacklist[i] == addr {
+			return true
+		}
+	}
+	return false
+}
+
 func update_whitelist_time(addr string) {
 	// Update whitelist - prevent timeout of connection
 	whitelist[addr] = time.Now().Unix()