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utils.go
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utils.go
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// Package utils implements utilities used across different
// areas of the sish application. There are utility functions
// that help with overall state management and are core to the application.
package utils
import (
"bytes"
"crypto/ed25519"
"crypto/rand"
"encoding/pem"
"fmt"
"io"
"io/ioutil"
"log"
mathrand "math/rand"
"net"
"os"
"os/signal"
"path/filepath"
"strconv"
"strings"
"sync"
"time"
"github.com/ScaleFT/sshkeys"
"github.com/antoniomika/go-proxyproto"
"github.com/fsnotify/fsnotify"
"github.com/jpillora/ipfilter"
"github.com/logrusorgru/aurora"
"github.com/mikesmitty/edkey"
"github.com/spf13/viper"
"golang.org/x/crypto/ssh"
)
const (
// sishDNSPrefix is the prefix used for DNS TXT records.
sishDNSPrefix = "sish="
)
var (
// Filter is the IPFilter used to block connections.
Filter *ipfilter.IPFilter
// certHolder is a slice of publickeys for auth.
certHolder = make([]ssh.PublicKey, 0)
// holderLock is the mutex used to update the certHolder slice.
holderLock = sync.Mutex{}
// bannedSubdomainList is a list of subdomains that cannot be bound.
bannedSubdomainList = []string{""}
// bannedAliasList is a list of aliases that cannot be bound.
bannedAliasList = []string{""}
// multiWriter is the writer that can be used for writing to multiple locations.
multiWriter io.Writer
)
// Setup main utils. This initializes, whitelists, blacklists,
// and log writers.
func Setup(logWriter io.Writer) {
multiWriter = logWriter
upperList := func(stringList string) []string {
list := strings.FieldsFunc(stringList, CommaSplitFields)
for k, v := range list {
list[k] = strings.ToUpper(v)
}
return list
}
whitelistedCountriesList := upperList(viper.GetString("whitelisted-countries"))
whitelistedIPList := strings.FieldsFunc(viper.GetString("whitelisted-ips"), CommaSplitFields)
ipfilterOpts := ipfilter.Options{
BlockedCountries: upperList(viper.GetString("banned-countries")),
AllowedCountries: whitelistedCountriesList,
BlockedIPs: strings.FieldsFunc(viper.GetString("banned-ips"), CommaSplitFields),
AllowedIPs: whitelistedIPList,
BlockByDefault: len(whitelistedIPList) > 0 || len(whitelistedCountriesList) > 0,
}
if viper.GetBool("geodb") {
Filter = ipfilter.NewLazy(ipfilterOpts)
} else {
Filter = ipfilter.NewNoDB(ipfilterOpts)
}
bannedSubdomainList = append(bannedSubdomainList, strings.FieldsFunc(viper.GetString("banned-subdomains"), CommaSplitFields)...)
for k, v := range bannedSubdomainList {
bannedSubdomainList[k] = strings.ToLower(strings.TrimSpace(v) + "." + viper.GetString("domain"))
}
bannedAliasList = append(bannedAliasList, strings.FieldsFunc(viper.GetString("banned-aliases"), CommaSplitFields)...)
for k, v := range bannedAliasList {
bannedAliasList[k] = strings.ToLower(strings.TrimSpace(v))
}
}
// CommaSplitFields is a function used by strings.FieldsFunc to split around commas.
func CommaSplitFields(c rune) bool {
return c == ','
}
// LoadProxyProtoConfig will load the timeouts and policies for the proxy protocol.
func LoadProxyProtoConfig(l *proxyproto.Listener) {
if viper.GetBool("proxy-protocol-use-timeout") {
l.UseTimeout = true
l.Timeout = viper.GetDuration("proxy-protocol-timeout")
l.Policy = func(upstream net.Addr) (proxyproto.Policy, error) {
switch viper.GetString("proxy-protocol-policy") {
case "ignore":
return proxyproto.IGNORE, nil
case "reject":
return proxyproto.REJECT, nil
case "require":
return proxyproto.REQUIRE, nil
}
return proxyproto.USE, nil
}
}
}
// GetRandomPortInRange returns a random port in the provided range.
// The port range is a comma separated list of ranges or ports.
func GetRandomPortInRange(portRange string) uint32 {
var bindPort uint32
ranges := strings.Split(strings.TrimSpace(portRange), ",")
possible := [][]uint64{}
for _, r := range ranges {
ends := strings.Split(strings.TrimSpace(r), "-")
if len(ends) == 1 {
ui, err := strconv.ParseUint(ends[0], 0, 64)
if err != nil {
return 0
}
possible = append(possible, []uint64{uint64(ui)})
} else if len(ends) == 2 {
ui1, err := strconv.ParseUint(ends[0], 0, 64)
if err != nil {
return 0
}
ui2, err := strconv.ParseUint(ends[1], 0, 64)
if err != nil {
return 0
}
possible = append(possible, []uint64{uint64(ui1), uint64(ui2)})
}
}
mathrand.Seed(time.Now().UnixNano())
locHolder := mathrand.Intn(len(possible))
if len(possible[locHolder]) == 1 {
bindPort = uint32(possible[locHolder][0])
} else if len(possible[locHolder]) == 2 {
bindPort = uint32(mathrand.Intn(int(possible[locHolder][1]-possible[locHolder][0])) + int(possible[locHolder][0]))
}
ln, err := net.Listen("tcp", fmt.Sprintf(":%d", bindPort))
if err != nil {
return GetRandomPortInRange(portRange)
}
ln.Close()
return bindPort
}
// CheckPort verifies if a port exists within the port range.
// It will return 0 and an error if not (0 allows the kernel to select)
// the port.
func CheckPort(port uint32, portRanges string) (uint32, error) {
ranges := strings.Split(strings.TrimSpace(portRanges), ",")
checks := false
for _, r := range ranges {
ends := strings.Split(strings.TrimSpace(r), "-")
if len(ends) == 1 {
ui, err := strconv.ParseUint(ends[0], 0, 64)
if err != nil {
return 0, err
}
if uint64(ui) == uint64(port) {
checks = true
continue
}
} else if len(ends) == 2 {
ui1, err := strconv.ParseUint(ends[0], 0, 64)
if err != nil {
return 0, err
}
ui2, err := strconv.ParseUint(ends[1], 0, 64)
if err != nil {
return 0, err
}
if uint64(port) >= ui1 && uint64(port) <= ui2 {
checks = true
continue
}
}
}
if checks {
return port, nil
}
return 0, fmt.Errorf("not a safe port")
}
// WatchCerts watches ssh keys for changes and will load them.
func WatchCerts() {
loadCerts()
watcher, err := fsnotify.NewWatcher()
if err != nil {
log.Fatal(err)
}
go func() {
c := make(chan os.Signal, 1)
signal.Notify(c, os.Interrupt)
go func() {
for range c {
watcher.Close()
os.Exit(0)
}
}()
for {
select {
case _, ok := <-watcher.Events:
if !ok {
return
}
loadCerts()
case _, ok := <-watcher.Errors:
if !ok {
return
}
}
}
}()
err = watcher.Add(viper.GetString("authentication-keys-directory"))
if err != nil {
log.Fatal(err)
}
}
// loadCerts loads public keys from the keys directory into a slice that is used
// authenticating a user.
func loadCerts() {
tmpCertHolder := make([]ssh.PublicKey, 0)
files, err := ioutil.ReadDir(viper.GetString("authentication-keys-directory"))
if err != nil {
log.Fatal(err)
}
parseKey := func(keyBytes []byte, fileInfo os.FileInfo) {
keyHandle := func(keyBytes []byte, fileInfo os.FileInfo) []byte {
key, _, _, rest, e := ssh.ParseAuthorizedKey(keyBytes)
if e != nil {
log.Printf("Can't load file %s as public key: %s\n", fileInfo.Name(), e)
}
if key != nil {
tmpCertHolder = append(tmpCertHolder, key)
}
return rest
}
for ok := true; ok; ok = len(keyBytes) > 0 {
keyBytes = keyHandle(keyBytes, fileInfo)
}
}
for _, f := range files {
i, e := ioutil.ReadFile(filepath.Join(viper.GetString("authentication-keys-directory"), f.Name()))
if e == nil && len(i) > 0 {
parseKey(i, f)
}
}
holderLock.Lock()
defer holderLock.Unlock()
certHolder = tmpCertHolder
}
// GetSSHConfig Returns an SSH config for the ssh muxer.
// It handles auth and storing user connection information.
func GetSSHConfig() *ssh.ServerConfig {
sshConfig := &ssh.ServerConfig{
NoClientAuth: !viper.GetBool("authentication"),
PasswordCallback: func(c ssh.ConnMetadata, password []byte) (*ssh.Permissions, error) {
log.Printf("Login attempt: %s, user %s", c.RemoteAddr(), c.User())
if string(password) == viper.GetString("authentication-password") && viper.GetString("authentication-password") != "" {
return nil, nil
}
return nil, fmt.Errorf("password doesn't match")
},
PublicKeyCallback: func(c ssh.ConnMetadata, key ssh.PublicKey) (*ssh.Permissions, error) {
log.Printf("Login attempt: %s, user %s key: %s", c.RemoteAddr(), c.User(), string(ssh.MarshalAuthorizedKey(key)))
holderLock.Lock()
defer holderLock.Unlock()
for _, i := range certHolder {
if bytes.Equal(key.Marshal(), i.Marshal()) {
permssionsData := &ssh.Permissions{
Extensions: map[string]string{
"pubKey": string(key.Marshal()),
"pubKeyFingerprint": ssh.FingerprintSHA256(key),
},
}
return permssionsData, nil
}
}
return nil, fmt.Errorf("public key doesn't match")
},
}
sshConfig.AddHostKey(loadPrivateKey(viper.GetString("private-key-passphrase")))
return sshConfig
}
// generatePrivateKey creates a new ed25519 private key to be used by the
// the SSH server as the host key.
func generatePrivateKey(passphrase string) []byte {
_, pk, err := ed25519.GenerateKey(rand.Reader)
if err != nil {
log.Fatal(err)
}
log.Println("Generated ED25519 Keypair")
// In an effort to guarantee that keys can still be loaded by OpenSSH
// we adopt branching logic here for passphrase encrypted keys.
// I wrote a module that handled both, but ultimately decided this
// is likely cleaner and less specialized.
var pemData []byte
if passphrase != "" {
pemData, err = sshkeys.Marshal(pk, &sshkeys.MarshalOptions{
Passphrase: []byte(passphrase),
Format: sshkeys.FormatOpenSSHv1,
})
if err != nil {
log.Fatal(err)
}
} else {
pemBlock := &pem.Block{
Type: "OPENSSH PRIVATE KEY",
Bytes: edkey.MarshalED25519PrivateKey(pk),
}
pemData = pem.EncodeToMemory(pemBlock)
}
err = ioutil.WriteFile(viper.GetString("private-key-location"), pemData, 0600)
if err != nil {
log.Println("Error writing to file:", err)
}
return pemData
}
// ParsePrivateKey parses the PrivateKey into a ssh.Signer and
// let's it be used by the SSH server.
func loadPrivateKey(passphrase string) ssh.Signer {
var signer ssh.Signer
pk, err := ioutil.ReadFile(viper.GetString("private-key-location"))
if err != nil {
log.Println("Error loading private key, generating a new one:", err)
pk = generatePrivateKey(passphrase)
}
if passphrase != "" {
signer, err = ssh.ParsePrivateKeyWithPassphrase(pk, []byte(passphrase))
if err != nil {
log.Fatal(err)
}
} else {
signer, err = ssh.ParsePrivateKey(pk)
if err != nil {
log.Fatal(err)
}
}
return signer
}
// inList is used to scan whether or not something exists
// in a slice of data.
func inList(host string, bannedList []string) bool {
for _, v := range bannedList {
if strings.TrimSpace(v) == host {
return true
}
}
return false
}
// verifyDNS will verify that a specific domain/subdomain combo matches
// the specific TXT entry that exists for the domain. It will check that the
// publickey used for auth is at least included in the TXT records for the domain.
func verifyDNS(addr string, sshConn *SSHConnection) (bool, string, error) {
if !viper.GetBool("verify-dns") || sshConn.SSHConn.Permissions == nil {
return false, "", nil
}
if _, ok := sshConn.SSHConn.Permissions.Extensions["pubKeyFingerprint"]; !ok {
return false, "", nil
}
records, err := net.LookupTXT(addr)
for _, v := range records {
if strings.HasPrefix(v, sishDNSPrefix) {
dnsPubKeyFingerprint := strings.TrimSpace(strings.TrimPrefix(v, sishDNSPrefix))
match := sshConn.SSHConn.Permissions.Extensions["pubKeyFingerprint"] == dnsPubKeyFingerprint
if match {
return match, dnsPubKeyFingerprint, err
}
}
}
return false, "", nil
}
// GetOpenPort returns open ports that can be bound. It verifies the host to
// bind the port to and attempts to listen to the port to ensure it is open.
// If load balancing is enabled, it will return the port if used.
func GetOpenPort(addr string, port uint32, state *State, sshConn *SSHConnection) (string, uint32, *TCPHolder) {
getUnusedPort := func() (string, uint32, *TCPHolder) {
var tH *TCPHolder
first := true
bindPort := port
bindAddr := addr
listenAddr := ""
if bindAddr == "localhost" && viper.GetBool("localhost-as-all") {
bindAddr = ""
}
reportUnavailable := func(unavailable bool) {
if first && unavailable {
extra := " Assigning a random port."
if viper.GetBool("force-requested-ports") {
extra = ""
}
sshConn.SendMessage(aurora.Sprintf("The TCP port %s is unavailable.%s", aurora.Red(listenAddr), extra), true)
}
}
checkPort := func(checkerAddr string, checkerPort uint32) bool {
listenAddr = fmt.Sprintf("%s:%d", bindAddr, bindPort)
checkedPort, err := CheckPort(checkerPort, viper.GetString("port-bind-range"))
_, ok := state.TCPListeners.Load(listenAddr)
if err == nil && (!viper.GetBool("tcp-load-balancer") || (viper.GetBool("tcp-load-balancer") && !ok)) {
ln, listenErr := net.Listen("tcp", fmt.Sprintf(":%d", port))
if listenErr != nil {
err = listenErr
} else {
ln.Close()
}
}
if viper.GetBool("bind-random-ports") || !first || err != nil {
reportUnavailable(true)
if viper.GetString("port-bind-range") != "" {
bindPort = GetRandomPortInRange(viper.GetString("port-bind-range"))
} else {
bindPort = 0
}
} else {
bindPort = checkedPort
}
listenAddr = fmt.Sprintf("%s:%d", bindAddr, bindPort)
holder, ok := state.TCPListeners.Load(listenAddr)
if ok && viper.GetBool("tcp-load-balancer") {
tH = holder.(*TCPHolder)
ok = false
}
reportUnavailable(ok)
first = false
return ok
}
for checkPort(bindAddr, bindPort) {
}
return listenAddr, bindPort, tH
}
return getUnusedPort()
}
// GetOpenHost returns an open host or a random host if that one is unavailable.
// If load balancing is enabled, it will return the requested domain.
func GetOpenHost(addr string, state *State, sshConn *SSHConnection) (string, *HTTPHolder) {
dnsMatch, _, err := verifyDNS(addr, sshConn)
if err != nil && viper.GetBool("debug") {
log.Println("Error looking up txt records for domain:", addr)
}
getUnusedHost := func() (string, *HTTPHolder) {
var pH *HTTPHolder
first := true
hostExtension := ""
if viper.GetBool("append-user-to-subdomain") {
hostExtension = viper.GetString("append-user-to-subdomain-separator") + sshConn.SSHConn.User()
}
proposedHost := addr + hostExtension + "." + viper.GetString("domain")
domainParts := strings.Join(strings.Split(addr, ".")[1:], ".")
if dnsMatch || (viper.GetBool("bind-any-host") && strings.Contains(addr, ".")) || inList(domainParts, strings.FieldsFunc(viper.GetString("bind-hosts"), CommaSplitFields)) {
proposedHost = addr
}
host := strings.ToLower(proposedHost)
getRandomHost := func() string {
return strings.ToLower(RandStringBytesMaskImprSrc(viper.GetInt("bind-random-subdomains-length")) + "." + viper.GetString("domain"))
}
reportUnavailable := func(unavailable bool) {
if first && unavailable {
extra := " Assigning a random subdomain."
if viper.GetBool("force-requested-subdomains") {
extra = ""
}
sshConn.SendMessage(aurora.Sprintf("The subdomain %s is unavailable.%s", aurora.Red(host), extra), true)
}
}
checkHost := func(checkHost string) bool {
if viper.GetBool("bind-random-subdomains") || !first || inList(host, bannedSubdomainList) {
reportUnavailable(true)
host = getRandomHost()
}
holder, ok := state.HTTPListeners.Load(host)
if ok && viper.GetBool("http-load-balancer") {
pH = holder.(*HTTPHolder)
ok = false
}
reportUnavailable(ok)
first = false
return ok
}
for checkHost(host) {
}
return host, pH
}
return getUnusedHost()
}
// GetOpenAlias returns open aliases or a random one if it is not enabled.
// If load balancing is enabled, it will return the requested alias.
func GetOpenAlias(addr string, port string, state *State, sshConn *SSHConnection) (string, *AliasHolder) {
getUnusedAlias := func() (string, *AliasHolder) {
var aH *AliasHolder
first := true
alias := fmt.Sprintf("%s:%s", strings.ToLower(addr), port)
getRandomAlias := func() string {
return fmt.Sprintf("%s:%s", strings.ToLower(RandStringBytesMaskImprSrc(viper.GetInt("bind-random-aliases-length"))), port)
}
reportUnavailable := func(unavailable bool) {
if first && unavailable {
extra := " Assigning a random alias."
if viper.GetBool("force-requested-aliases") {
extra = ""
}
sshConn.SendMessage(aurora.Sprintf("The alias %s is unavailable.%s", aurora.Red(alias), extra), true)
}
}
checkAlias := func(checkAlias string) bool {
if viper.GetBool("bind-random-aliases") || !first || inList(alias, bannedAliasList) {
reportUnavailable(true)
alias = getRandomAlias()
}
holder, ok := state.AliasListeners.Load(alias)
if ok && viper.GetBool("alias-load-balancer") {
aH = holder.(*AliasHolder)
ok = false
}
reportUnavailable(ok)
first = false
return ok
}
for checkAlias(alias) {
}
return alias, aH
}
return getUnusedAlias()
}
// RandStringBytesMaskImprSrc creates a random string of length n
// https://stackoverflow.com/questions/22892120/how-to-generate-a-random-string-of-a-fixed-length-in-golang
func RandStringBytesMaskImprSrc(n int) string {
const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
const (
letterIdxBits = 6 // 6 bits to represent a letter index
letterIdxMask = 1<<letterIdxBits - 1 // All 1-bits, as many as letterIdxBits
letterIdxMax = 63 / letterIdxBits // # of letter indices fitting in 63 bits
)
var src = mathrand.NewSource(time.Now().UnixNano())
b := make([]byte, n)
// A src.Int63() generates 63 random bits, enough for letterIdxMax characters!
for i, cache, remain := n-1, src.Int63(), letterIdxMax; i >= 0; {
if remain == 0 {
cache, remain = src.Int63(), letterIdxMax
}
if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
b[i] = letterBytes[idx]
i--
}
cache >>= letterIdxBits
remain--
}
return string(b)
}