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geoip.go
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geoip.go
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/*
* Copyright (c) 2016, Psiphon Inc.
* All rights reserved.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*/
package server
import (
"crypto/hmac"
"crypto/sha256"
"net"
"time"
"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common"
maxminddb "github.com/oschwald/maxminddb-golang"
cache "github.com/patrickmn/go-cache"
)
const (
GEOIP_SESSION_CACHE_TTL = 60 * time.Minute
GEOIP_UNKNOWN_VALUE = "None"
)
// GeoIPData is GeoIP data for a client session. Individual client
// IP addresses are neither logged nor explicitly referenced during a session.
// The GeoIP country, city, and ISP corresponding to a client IP address are
// resolved and then logged along with usage stats. The DiscoveryValue is
// a special value derived from the client IP that's used to compartmentalize
// discoverable servers (see calculateDiscoveryValue for details).
type GeoIPData struct {
Country string
City string
ISP string
DiscoveryValue int
}
// NewGeoIPData returns a GeoIPData initialized with the expected
// GEOIP_UNKNOWN_VALUE values to be used when GeoIP lookup fails.
func NewGeoIPData() GeoIPData {
return GeoIPData{
Country: GEOIP_UNKNOWN_VALUE,
City: GEOIP_UNKNOWN_VALUE,
ISP: GEOIP_UNKNOWN_VALUE,
}
}
// GeoIPService implements GeoIP lookup and session/GeoIP caching.
// Lookup is via a MaxMind database; the ReloadDatabase function
// supports hot reloading of MaxMind data while the server is
// running.
type GeoIPService struct {
databases []*geoIPDatabase
sessionCache *cache.Cache
discoveryValueHMACKey string
}
type geoIPDatabase struct {
common.ReloadableFile
maxMindReader *maxminddb.Reader
}
// NewGeoIPService initializes a new GeoIPService.
func NewGeoIPService(
databaseFilenames []string,
discoveryValueHMACKey string) (*GeoIPService, error) {
geoIP := &GeoIPService{
databases: make([]*geoIPDatabase, len(databaseFilenames)),
sessionCache: cache.New(GEOIP_SESSION_CACHE_TTL, 1*time.Minute),
discoveryValueHMACKey: discoveryValueHMACKey,
}
for i, filename := range databaseFilenames {
database := &geoIPDatabase{}
database.ReloadableFile = common.NewReloadableFile(
filename,
func(fileContent []byte) error {
maxMindReader, err := maxminddb.FromBytes(fileContent)
if err != nil {
// On error, database state remains the same
return common.ContextError(err)
}
if database.maxMindReader != nil {
database.maxMindReader.Close()
}
database.maxMindReader = maxMindReader
return nil
})
_, err := database.Reload()
if err != nil {
return nil, common.ContextError(err)
}
geoIP.databases[i] = database
}
return geoIP, nil
}
// Reloaders gets the list of reloadable databases in use
// by the GeoIPService. This list is used to hot reload
// these databases.
func (geoIP *GeoIPService) Reloaders() []common.Reloader {
reloaders := make([]common.Reloader, len(geoIP.databases))
for i, database := range geoIP.databases {
reloaders[i] = database
}
return reloaders
}
// Lookup determines a GeoIPData for a given client IP address.
func (geoIP *GeoIPService) Lookup(ipAddress string) GeoIPData {
result := NewGeoIPData()
ip := net.ParseIP(ipAddress)
if ip == nil || len(geoIP.databases) == 0 {
return result
}
var geoIPFields struct {
Country struct {
ISOCode string `maxminddb:"iso_code"`
} `maxminddb:"country"`
City struct {
Names map[string]string `maxminddb:"names"`
} `maxminddb:"city"`
ISP string `maxminddb:"isp"`
}
// Each database will populate geoIPFields with the values it contains. In the
// current MaxMind deployment, the City database populates Country and City and
// the separate ISP database populates ISP.
for _, database := range geoIP.databases {
database.ReloadableFile.RLock()
err := database.maxMindReader.Lookup(ip, &geoIPFields)
database.ReloadableFile.RUnlock()
if err != nil {
log.WithContextFields(LogFields{"error": err}).Warning("GeoIP lookup failed")
}
}
if geoIPFields.Country.ISOCode != "" {
result.Country = geoIPFields.Country.ISOCode
}
name, ok := geoIPFields.City.Names["en"]
if ok && name != "" {
result.City = name
}
if geoIPFields.ISP != "" {
result.ISP = geoIPFields.ISP
}
result.DiscoveryValue = calculateDiscoveryValue(
geoIP.discoveryValueHMACKey, ipAddress)
return result
}
// SetSessionCache adds the sessionID/geoIPData pair to the
// session cache. This value will not expire; the caller must
// call MarkSessionCacheToExpire to initiate expiry.
// Calling SetSessionCache for an existing sessionID will
// replace the previous value and reset any expiry.
func (geoIP *GeoIPService) SetSessionCache(sessionID string, geoIPData GeoIPData) {
geoIP.sessionCache.Set(sessionID, geoIPData, cache.NoExpiration)
}
// MarkSessionCacheToExpire initiates expiry for an existing
// session cache entry, if the session ID is found in the cache.
// Concurrency note: SetSessionCache and MarkSessionCacheToExpire
// should not be called concurrently for a single session ID.
func (geoIP *GeoIPService) MarkSessionCacheToExpire(sessionID string) {
geoIPData, found := geoIP.sessionCache.Get(sessionID)
// Note: potential race condition between Get and Set. In practice,
// the tunnel server won't clobber a SetSessionCache value by calling
// MarkSessionCacheToExpire concurrently.
if found {
geoIP.sessionCache.Set(sessionID, geoIPData, cache.DefaultExpiration)
}
}
// GetSessionCache returns the cached GeoIPData for the
// specified session ID; a blank GeoIPData is returned
// if the session ID is not found in the cache.
func (geoIP *GeoIPService) GetSessionCache(sessionID string) GeoIPData {
geoIPData, found := geoIP.sessionCache.Get(sessionID)
if !found {
return NewGeoIPData()
}
return geoIPData.(GeoIPData)
}
// InSessionCache returns whether the session ID is present
// in the session cache.
func (geoIP *GeoIPService) InSessionCache(sessionID string) bool {
_, found := geoIP.sessionCache.Get(sessionID)
return found
}
// calculateDiscoveryValue derives a value from the client IP address to be
// used as input in the server discovery algorithm. Since we do not explicitly
// store the client IP address, we must derive the value here and store it for
// later use by the discovery algorithm.
// See https://bitbucket.org/psiphon/psiphon-circumvention-system/src/tip/Automation/psi_ops_discovery.py
// for full details.
func calculateDiscoveryValue(discoveryValueHMACKey, ipAddress string) int {
// From: psi_ops_discovery.calculate_ip_address_strategy_value:
// # Mix bits from all octets of the client IP address to determine the
// # bucket. An HMAC is used to prevent pre-calculation of buckets for IPs.
// return ord(hmac.new(HMAC_KEY, ip_address, hashlib.sha256).digest()[0])
// TODO: use 3-octet algorithm?
hash := hmac.New(sha256.New, []byte(discoveryValueHMACKey))
hash.Write([]byte(ipAddress))
return int(hash.Sum(nil)[0])
}