feat: add SCREEGO_TURN_DENY_PEERS

Deny/ban peers within specific CIDRs to prevent TURN server users from accessing machines reachable by the TURN server but not from the internet, useful when the server is behind a NAT. By default denies local addresses.
screego · Sep 28, 2024 · 5fda00e · 5fda00e
1 parent e5864f3
commit 5fda00e
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Showing 4 changed files with 43 additions and 2 deletions.
diff --git a/config/config.go b/config/config.go
@@ -4,6 +4,7 @@ import (
 	"crypto/rand"
 	"errors"
 	"fmt"
+	"net"
 	"os"
 	"path/filepath"
 	"regexp"
@@ -63,6 +64,9 @@ type Config struct {
 	TurnIPProvider ipdns.Provider    `ignored:"true"`
 	TurnPort       string            `ignored:"true"`
 
+	TurnDenyPeers       []string     `default:"0.0.0.0/8,127.0.0.1/8,::/128,::1/128,fe80::/10" split_words:"true"`
+	TurnDenyPeersParsed []*net.IPNet `ignored:"true"`
+
 	CloseRoomWhenOwnerLeaves bool `default:"true" split_words:"true"`
 }
 
@@ -218,6 +222,22 @@ func Get() (Config, []FutureLog) {
 	}
 	logs = append(logs, logDeprecated()...)
 
+	for _, cidrString := range config.TurnDenyPeers {
+		_, cidr, err := net.ParseCIDR(cidrString)
+		if err != nil {
+			logs = append(logs, FutureLog{
+				Level: zerolog.FatalLevel,
+				Msg:   fmt.Sprintf("Invalid SCREEGO_TURN_DENY_PEERS %q: %s", cidrString, err),
+			})
+		} else {
+			config.TurnDenyPeersParsed = append(config.TurnDenyPeersParsed, cidr)
+		}
+	}
+	logs = append(logs, FutureLog{
+		Level: zerolog.InfoLevel,
+		Msg:   fmt.Sprintf("Deny turn peers within %q", config.TurnDenyPeersParsed),
+	})
+
 	return config, logs
 }
 

diff --git a/screego.config.development b/screego.config.development
@@ -2,3 +2,4 @@ SCREEGO_SECRET=secure
 SCREEGO_LOG_LEVEL=debug
 SCREEGO_CORS_ALLOWED_ORIGINS=http://localhost:3000
 SCREEGO_USERS_FILE=./users
+SCREEGO_TURN_DENY_PEERS=
diff --git a/screego.config.example b/screego.config.example
@@ -60,6 +60,16 @@ SCREEGO_TURN_EXTERNAL_PORT=3478
 # Authentication secret for the external TURN server.
 SCREEGO_TURN_EXTERNAL_SECRET=
 
+# Deny/ban peers within specific CIDRs to prevent TURN server users from
+# accessing machines reachable by the TURN server but not from the internet,
+# useful when the server is behind a NAT.
+#
+# Disallow internal ip addresses: https://en.wikipedia.org/wiki/Reserved_IP_addresses
+# SCREEGO_TURN_DENY_PEERS=0.0.0.0/8,10.0.0.0/8,100.64.0.0/10,127.0.0.1/8,169.254.0.0/16,172.16.0.0/12,192.0.0.0/24,192.0.2.0/24,192.88.99.0/24,192.168.0.0/16,198.18.0.0/15,198.51.100.0/24,203.0.113.0/24,224.0.0.0/4,239.0.0.0/8,255.255.255.255/32,::/128,::1/128,64:ff9b:1::/48,100::/64,2001::/32,2002::/16,fc00::/7,fe80::/10
+#
+# By default denies local addresses.
+SCREEGO_TURN_DENY_PEERS=0.0.0.0/8,127.0.0.1/8,::/128,::1/128,fe80::/10
+
 # If reverse proxy headers should be trusted.
 # Screego uses ip whitelisting for authentication
 # of TURN connections. When behind a proxy the ip is always the proxy server.

diff --git a/turn/server.go b/turn/server.go
@@ -98,14 +98,24 @@ func newInternalServer(conf config.Config) (Server, error) {
 		IPProvider:            conf.TurnIPProvider,
 	}
 
+	var permissions turn.PermissionHandler = func(clientAddr net.Addr, peerIP net.IP) bool {
+		for _, cidr := range conf.TurnDenyPeersParsed {
+			if cidr.Contains(peerIP) {
+				return false
+			}
+		}
+
+		return true
+	}
+
 	_, err = turn.NewServer(turn.ServerConfig{
 		Realm:       Realm,
 		AuthHandler: svr.authenticate,
 		ListenerConfigs: []turn.ListenerConfig{
-			{Listener: tcpListener, RelayAddressGenerator: gen},
+			{Listener: tcpListener, RelayAddressGenerator: gen, PermissionHandler: permissions},
 		},
 		PacketConnConfigs: []turn.PacketConnConfig{
-			{PacketConn: udpListener, RelayAddressGenerator: gen},
+			{PacketConn: udpListener, RelayAddressGenerator: gen, PermissionHandler: permissions},
 		},
 	})
 	if err != nil {