ssh-tarpit/ssh-tarpit.go

package main

import (
	"context"
	"crypto/rand"
	"database/sql"
	"fmt"
	"log"
	"net"
	"os"
	"os/signal"
	"strconv"
	"strings"
	"sync"
	"syscall"
	"time"

	// MySQL driver registration
	_ "github.com/go-sql-driver/mysql"
	// Pure-Go SQLite driver
	_ "modernc.org/sqlite"
	"github.com/oschwald/geoip2-golang"
)

// Config holds all configuration sourced from environment variables.
type Config struct {
	Port             int
	Tarpit           bool
	TarpitDelay      time.Duration
	TarpitMaxDur     time.Duration // 0 = unlimited
	DBPath           string
	GeoIPPath        string
	MySQLUser        string
	MySQLPass        string
	MySQLHost        string
	MySQLPort        string
	MySQLDB          string
	Banner           string
	MaxConns         int
	ShutdownTimeout  time.Duration
}

const charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"

func loadConfig() Config {
	return Config{
		Port:             getEnvInt("SSH_TARPIT_PORT", 2222),
		Tarpit:           getEnvBool("SSH_TARPIT_TARPIT", false),
		TarpitDelay:      getEnvDuration("SSH_TARPIT_TARPIT_DELAY", 1*time.Second),
		TarpitMaxDur:     getEnvDuration("SSH_TARPIT_TARPIT_MAX_DURATION", 0),
		DBPath:           getEnv("SSH_TARPIT_DB_PATH", "./logs.db"),
		GeoIPPath:        getEnv("SSH_TARPIT_GEOIP_PATH", ""),
		MySQLUser:        getEnv("SSH_TARPIT_MYSQL_USER", ""),
		MySQLPass:        getEnv("SSH_TARPIT_MYSQL_PASS", ""),
		MySQLHost:        getEnv("SSH_TARPIT_MYSQL_HOST", "localhost"),
		MySQLPort:        getEnv("SSH_TARPIT_MYSQL_PORT", "3306"),
		MySQLDB:          getEnv("SSH_TARPIT_MYSQL_DB", "sshtarpit"),
		Banner:           getEnv("SSH_TARPIT_BANNER", "SSH-2.0-OpenSSH_9.1p1 Debian-1"),
		MaxConns:         getEnvInt("SSH_TARPIT_MAX_CONNS", 100),
		ShutdownTimeout:  getEnvDuration("SSH_TARPIT_SHUTDOWN_TIMEOUT", 30*time.Second),
	}
}

// Env helpers
func getEnv(key, defaultVal string) string {
	if v := os.Getenv(key); v != "" {
		return v
	}
	return defaultVal
}

func getEnvBool(key string, defaultVal bool) bool {
	v := os.Getenv(key)
	if v == "" {
		return defaultVal
	}
	switch strings.ToLower(v) {
	case "true", "1", "yes", "on":
		return true
	default:
		return false
	}
}

func getEnvInt(key string, defaultVal int) int {
	v := os.Getenv(key)
	if v == "" {
		return defaultVal
	}
	i, err := strconv.Atoi(v)
	if err != nil {
		log.Printf("Invalid value for %s=%q, using default %d: %v", key, v, defaultVal, err)
		return defaultVal
	}
	return i
}

func getEnvDuration(key string, defaultVal time.Duration) time.Duration {
	v := os.Getenv(key)
	if v == "" {
		return defaultVal
	}
	d, err := time.ParseDuration(v)
	if err != nil {
		log.Printf("Invalid duration for %s=%q, using default %s: %v", key, v, defaultVal, err)
		return defaultVal
	}
	return d
}

// ConnectionLogger persists connection records.
type ConnectionLogger interface {
	LogConnection(ip, country, city string, latitude, longitude float64, isp string) error
	Close() error
}

// dbLogger implements ConnectionLogger with a *sql.DB connection pool.
type dbLogger struct {
	db *sql.DB
}

func (l *dbLogger) LogConnection(ip, country, city string, latitude, longitude float64, isp string) error {
	_, err := l.db.Exec(
		"INSERT INTO connections (ip, country, city, latitude, longitude, isp) VALUES (?, ?, ?, ?, ?, ?)",
		ip, country, city, latitude, longitude, isp,
	)
	return err
}

func (l *dbLogger) Close() error {
	return l.db.Close()
}

func newLogger(cfg Config) (ConnectionLogger, error) {
	var driverName, dsn string

	if cfg.MySQLUser != "" {
		driverName = "mysql"
		dsn = fmt.Sprintf("%s:%s@tcp(%s:%s)/%s?parseTime=true",
			cfg.MySQLUser, cfg.MySQLPass, cfg.MySQLHost, cfg.MySQLPort, cfg.MySQLDB)
	} else {
		driverName = "sqlite"
		dsn = cfg.DBPath
	}

	db, err := sql.Open(driverName, dsn)
	if err != nil {
		return nil, fmt.Errorf("sql.Open: %w", err)
	}

	// Connection pool tuning
	db.SetMaxOpenConns(25)
	db.SetMaxIdleConns(5)
	db.SetConnMaxLifetime(5 * time.Minute)

	// SQLite-specific pragmas for better concurrent write performance
	if driverName == "sqlite" {
		if _, err := db.Exec("PRAGMA journal_mode=WAL"); err != nil {
			log.Printf("Warning: could not set WAL mode: %v", err)
		}
		if _, err := db.Exec("PRAGMA busy_timeout=5000"); err != nil {
			log.Printf("Warning: could not set busy_timeout: %v", err)
		}
	}

	// Create table once at startup
	createSQL := `CREATE TABLE IF NOT EXISTS connections (
		ip TEXT,
		country TEXT,
		city TEXT,
		latitude REAL,
		longitude REAL,
		isp TEXT,
		timestamp TIMESTAMP DEFAULT CURRENT_TIMESTAMP
	)`
	if _, err := db.Exec(createSQL); err != nil {
		db.Close()
		return nil, fmt.Errorf("create table: %w", err)
	}

	log.Printf("Database ready (driver=%s)", driverName)
	return &dbLogger{db: db}, nil
}

// GeoIP helpers
type geoipReaders struct {
	city *geoip2.Reader
	asn  *geoip2.Reader
}

func newGeoIPReaders(geoipPath string) (*geoipReaders, error) {
	city, err := geoip2.Open(geoipPath + "/GeoLite2-City.mmdb")
	if err != nil {
		return nil, fmt.Errorf("open City DB: %w", err)
	}
	asn, err := geoip2.Open(geoipPath + "/GeoLite2-ASN.mmdb")
	if err != nil {
		city.Close()
		return nil, fmt.Errorf("open ASN DB: %w", err)
	}
	return &geoipReaders{city: city, asn: asn}, nil
}

func (g *geoipReaders) Close() {
	if g.city != nil {
		g.city.Close()
	}
	if g.asn != nil {
		g.asn.Close()
	}
}

func (g *geoipReaders) lookup(ip string) (country, city string, latitude, longitude float64, isp string, err error) {
	parsedIP := net.ParseIP(ip)
	if parsedIP == nil {
		return "", "", 0, 0, "", fmt.Errorf("invalid IP: %s", ip)
	}

	record, err := g.city.City(parsedIP)
	if err != nil {
		return "", "", 0, 0, "", fmt.Errorf("city lookup: %w", err)
	}
	latitude, longitude = record.Location.Latitude, record.Location.Longitude
	country = record.Country.Names["en"]
	city = record.City.Names["en"]

	asnRecord, err := g.asn.ASN(parsedIP)
	if err != nil {
		return "", "", 0, 0, "", fmt.Errorf("ASN lookup: %w", err)
	}
	isp = asnRecord.AutonomousSystemOrganization

	return country, city, latitude, longitude, isp, nil
}

// Main
func main() {
	log.SetFlags(log.LstdFlags | log.Lmsgprefix)
	log.SetPrefix("[ssh-tarpit] ")

	cfg := loadConfig()

	// Initialise database connection pool once
	logger, err := newLogger(cfg)
	if err != nil {
		log.Fatalf("Failed to initialise database: %v", err)
	}
	defer logger.Close()

	// Initialise GeoIP readers once (if configured)
	var geoReaders *geoipReaders
	if cfg.GeoIPPath != "" {
		geoReaders, err = newGeoIPReaders(cfg.GeoIPPath)
		if err != nil {
			log.Printf("Warning: GeoIP initialisation failed, falling back to IP-only logging: %v", err)
			geoReaders = nil
		} else {
			defer geoReaders.Close()
		}
	}

	addr := fmt.Sprintf(":%d", cfg.Port)
	ln, err := net.Listen("tcp", addr)
	if err != nil {
		log.Fatalf("Failed to listen on %s: %v", addr, err)
	}
	log.Printf("Listening on %s", addr)

	// Signal handling for graceful shutdown
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()

	sigCh := make(chan os.Signal, 1)
	signal.Notify(sigCh, syscall.SIGINT, syscall.SIGTERM)
	go func() {
		sig := <-sigCh
		log.Printf("Received %v, shutting down...", sig)
		cancel()
		ln.Close() // unblock Accept
	}()

	// Semaphore to limit concurrent connections
	sem := make(chan struct{}, cfg.MaxConns)
	var wg sync.WaitGroup

	acceptLoop:
	for {
		conn, err := ln.Accept()
		if err != nil {
			select {
			case <-ctx.Done():
				break acceptLoop
			default:
				log.Printf("Accept error: %v", err)
				continue
			}
		}

		select {
		case sem <- struct{}{}:
			wg.Add(1)
			go func() {
				defer wg.Done()
				defer func() { <-sem }()
				handleConnection(ctx, conn, logger, geoReaders, cfg)
			}()
		default:
			log.Printf("Connection limit reached (%d), rejecting %s", cfg.MaxConns, conn.RemoteAddr())
			conn.Close()
		}
	}

	// Wait for active connections to drain
	log.Println("Waiting for active connections to finish...")
	done := make(chan struct{})
	go func() {
		wg.Wait()
		close(done)
	}()
	select {
	case <-done:
		log.Println("All connections finished cleanly")
	case <-time.After(cfg.ShutdownTimeout):
		log.Printf("Timed out after %s waiting for connections", cfg.ShutdownTimeout)
	}
}

// Connection handler
func handleConnection(ctx context.Context, conn net.Conn, logger ConnectionLogger, geoReaders *geoipReaders, cfg Config) {
	defer conn.Close()

	// Parse remote IP properly
	remoteAddr := conn.RemoteAddr().String()
	ip, _, err := net.SplitHostPort(remoteAddr)
	if err != nil {
		log.Printf("Failed to parse remote address %q: %v", remoteAddr, err)
		return
	}

	// Set a deadline for GeoIP / DB operations
	conn.SetDeadline(time.Now().Add(30 * time.Second))

	// Look up GeoIP data if available, otherwise just log the IP
	country, city, isp := "", "", ""
	var latitude, longitude float64

	if geoReaders != nil {
		country, city, latitude, longitude, isp, err = geoReaders.lookup(ip)
		if err != nil {
			log.Printf("GeoIP lookup failed for %s: %v", ip, err)
			// Fall back to IP-only logging
			country, city, latitude, longitude, isp = "", "", 0, 0, ""
		}
	}

	if err := logger.LogConnection(ip, country, city, latitude, longitude, isp); err != nil {
		log.Printf("Failed to log connection from %s: %v", ip, err)
	}

	if geoReaders != nil {
		log.Printf("Connection from %s (%s, %s, %s)", ip, country, city, isp)
	} else {
		log.Printf("Connection from %s", ip)
	}

	// Reset deadline for the remainder of the connection
	conn.SetDeadline(time.Time{})

	if !cfg.Tarpit {
		// Send banner and hold briefly
		conn.Write([]byte(cfg.Banner + "\r\n"))
		select {
		case <-time.After(2 * time.Second):
		case <-ctx.Done():
		}
		return
	}

	// Tarpit mode: drip random bytes periodically
	tarpitCtx, tarpitCancel := context.WithCancel(ctx)
	defer tarpitCancel()
	if cfg.TarpitMaxDur > 0 {
		tarpitCtx, tarpitCancel = context.WithTimeout(ctx, cfg.TarpitMaxDur)
		defer tarpitCancel()
	}

	b := make([]byte, 1)
	for {
		select {
		case <-tarpitCtx.Done():
			return
		default:
		}
		if _, err := rand.Read(b); err != nil {
			log.Printf("rand.Read error: %v", err)
			return
		}
		if _, err := conn.Write([]byte{charset[int(b[0])%len(charset)]}); err != nil {
			return
		}
		time.Sleep(cfg.TarpitDelay)
	}
}