Initial commit

2018-08-30 17:25:33 +03:00
commit ed4077a969
91 changed files with 48004 additions and 0 deletions
--- a/dnsfilter/dnsfilter.go
+++ b/dnsfilter/dnsfilter.go
@@ -0,0 +1,798 @@
+package dnsfilter
+
+import (
+	"bufio"
+	"bytes"
+	"crypto/sha256"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"regexp"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"github.com/bluele/gcache"
+	"golang.org/x/net/publicsuffix"
+)
+
+const defaultCacheSize = 64 * 1024 // in number of elements
+const defaultCacheTime time.Duration = 30 * time.Minute
+
+const defaultHTTPTimeout time.Duration = 5 * time.Minute
+const defaultHTTPMaxIdleConnections = 100
+
+const defaultSafebrowsingServer = "sb.adtidy.org"
+const defaultSafebrowsingURL = "http://%s/safebrowsing-lookup-hash.html?prefixes=%s"
+const defaultParentalURL = "http://pctrl.adguard.com/check-parental-control-hash?prefixes=%s&sensitivity=%d"
+
+var ErrInvalidSyntax = errors.New("dnsfilter: invalid rule syntax")
+var ErrInvalidParental = errors.New("dnsfilter: invalid parental sensitivity, must be either 3, 10, 13 or 17")
+
+const shortcutLength = 6 // used for rule search optimization, 6 hits the sweet spot
+
+const enableFastLookup = true         // flag for debugging, must be true in production for faster performance
+const enableDelayedCompilation = true // flag for debugging, must be true in production for faster performance
+
+type Config struct {
+	safeSearchEnabled   bool
+	safeBrowsingEnabled bool
+	safeBrowsingServer  string
+	parentalEnabled     bool
+	parentalSensitivity int // must be either 3, 10, 13 or 17
+}
+
+type Rule struct {
+	text         string // text without @@ decorators or $ options
+	shortcut     string // for speeding up lookup
+	originalText string // original text for reporting back to applications
+
+	// options
+	options []string // optional options after $
+
+	// parsed options
+	isWhitelist bool
+	isImportant bool
+	apps        []string
+
+	// user-supplied data
+	listID uint32
+
+	// compiled regexp
+	compiled *regexp.Regexp
+
+	sync.RWMutex
+}
+
+type LookupStats struct {
+	Requests   uint64 // number of HTTP requests that were sent
+	CacheHits  uint64 // number of lookups that didn't need HTTP requests
+	Pending    int64  // number of currently pending HTTP requests
+	PendingMax int64  // maximum number of pending HTTP requests
+}
+
+type Stats struct {
+	Safebrowsing LookupStats
+	Parental     LookupStats
+}
+
+// Dnsfilter holds added rules and performs hostname matches against the rules
+type Dnsfilter struct {
+	storage      map[string]*Rule // rule storage, not used for matching, needs to be key->value
+	storageMutex sync.RWMutex
+
+	// rules are checked against these lists in the order defined here
+	important *rulesTable // more important than whitelist and is checked first
+	whiteList *rulesTable // more important than blacklist
+	blackList *rulesTable
+
+	// HTTP lookups for safebrowsing and parental
+	client    http.Client     // handle for http client -- single instance as recommended by docs
+	transport *http.Transport // handle for http transport used by http client
+
+	config Config
+}
+
+//go:generate stringer -type=Reason
+
+// filtered/notfiltered reason
+type Reason int
+
+const (
+	// reasons for not filtering
+	NotFilteredNotFound  Reason = iota // host was not find in any checks, default value for result
+	NotFilteredWhiteList               // the host is explicitly whitelisted
+	NotFilteredError                   // there was a transitive error during check
+
+	// reasons for filtering
+	FilteredBlackList    // the host was matched to be advertising host
+	FilteredSafeBrowsing // the host was matched to be malicious/phishing
+	FilteredParental     // the host was matched to be outside of parental control settings
+	FilteredInvalid      // the request was invalid and was not processed
+	FilteredSafeSearch   // the host was replaced with safesearch variant
+)
+
+// these variables need to survive coredns reload
+var (
+	stats             Stats
+	safebrowsingCache = gcache.New(defaultCacheSize).LRU().Expiration(defaultCacheTime).Build()
+	parentalCache     = gcache.New(defaultCacheSize).LRU().Expiration(defaultCacheTime).Build()
+)
+
+// search result
+type Result struct {
+	IsFiltered bool
+	Reason     Reason
+	Rule       string
+}
+
+func (r Reason) Matched() bool {
+	return r != NotFilteredNotFound
+}
+
+// CheckHost tries to match host against rules, then safebrowsing and parental if they are enabled
+func (d *Dnsfilter) CheckHost(host string) (Result, error) {
+	// sometimes DNS clients will try to resolve ".", which in turns transforms into "" when it reaches here
+	if host == "" {
+		return Result{Reason: FilteredInvalid}, nil
+	}
+
+	// try filter lists first
+	result, err := d.matchHost(host)
+	if err != nil {
+		return result, err
+	}
+	if result.Reason.Matched() {
+		return result, nil
+	}
+
+	// check safebrowsing if no match
+	if d.config.safeBrowsingEnabled {
+		result, err = d.checkSafeBrowsing(host)
+		if err != nil {
+			// failed to do HTTP lookup -- treat it as if we got empty response, but don't save cache
+			log.Printf("Failed to do safebrowsing HTTP lookup, ignoring check: %v", err)
+			return Result{}, nil
+		}
+		if result.Reason.Matched() {
+			return result, nil
+		}
+	}
+
+	// check parental if no match
+	if d.config.parentalEnabled {
+		result, err = d.checkParental(host)
+		if err != nil {
+			// failed to do HTTP lookup -- treat it as if we got empty response, but don't save cache
+			log.Printf("Failed to do parental HTTP lookup, ignoring check: %v", err)
+			return Result{}, nil
+		}
+		if result.Reason.Matched() {
+			return result, nil
+		}
+	}
+
+	// nothing matched, return nothing
+	return Result{}, nil
+}
+
+//
+// rules table
+//
+
+type rulesTable struct {
+	rulesByShortcut map[string][]*Rule
+	rulesLeftovers  []*Rule
+	sync.RWMutex
+}
+
+func newRulesTable() *rulesTable {
+	return &rulesTable{
+		rulesByShortcut: make(map[string][]*Rule),
+		rulesLeftovers:  make([]*Rule, 0),
+	}
+}
+
+func (r *rulesTable) Add(rule *Rule) {
+	r.Lock()
+	if len(rule.shortcut) == shortcutLength && enableFastLookup {
+		r.rulesByShortcut[rule.shortcut] = append(r.rulesByShortcut[rule.shortcut], rule)
+	} else {
+		r.rulesLeftovers = append(r.rulesLeftovers, rule)
+	}
+	r.Unlock()
+}
+
+func (r *rulesTable) matchByHost(host string) (Result, error) {
+	res, err := r.searchShortcuts(host)
+	if err != nil {
+		return res, err
+	}
+	if res.Reason.Matched() {
+		return res, nil
+	}
+
+	res, err = r.searchLeftovers(host)
+	if err != nil {
+		return res, err
+	}
+	if res.Reason.Matched() {
+		return res, nil
+	}
+
+	return Result{}, nil
+}
+
+func (r *rulesTable) searchShortcuts(host string) (Result, error) {
+	// check in shortcuts first
+	for i := 0; i < len(host); i++ {
+		shortcut := host[i:]
+		if len(shortcut) > shortcutLength {
+			shortcut = shortcut[:shortcutLength]
+		}
+		if len(shortcut) != shortcutLength {
+			continue
+		}
+		rules, ok := r.rulesByShortcut[shortcut]
+		if !ok {
+			continue
+		}
+		for _, rule := range rules {
+			res, err := rule.match(host)
+			// error? stop search
+			if err != nil {
+				return res, err
+			}
+			// matched? stop search
+			if res.Reason.Matched() {
+				return res, err
+			}
+			// continue otherwise
+		}
+	}
+	return Result{}, nil
+}
+
+func (r *rulesTable) searchLeftovers(host string) (Result, error) {
+	for _, rule := range r.rulesLeftovers {
+		res, err := rule.match(host)
+		// error? stop search
+		if err != nil {
+			return res, err
+		}
+		// matched? stop search
+		if res.Reason.Matched() {
+			return res, err
+		}
+		// continue otherwise
+	}
+	return Result{}, nil
+}
+
+func findOptionIndex(text string) int {
+	for i, r := range text {
+		// ignore non-$
+		if r != '$' {
+			continue
+		}
+		// ignore `\$`
+		if i > 0 && text[i-1] == '\\' {
+			continue
+		}
+		// ignore `$/`
+		if i > len(text) && text[i+1] == '/' {
+			continue
+		}
+		return i + 1
+	}
+	return -1
+}
+
+func (rule *Rule) extractOptions() error {
+	optIndex := findOptionIndex(rule.text)
+	if optIndex == 0 { // starts with $
+		return ErrInvalidSyntax
+	}
+	if optIndex == len(rule.text) { // ends with $
+		return ErrInvalidSyntax
+	}
+	if optIndex < 0 {
+		return nil
+	}
+
+	optionsStr := rule.text[optIndex:]
+	rule.text = rule.text[:optIndex-1] // remove options from text
+
+	begin := 0
+	i := 0
+	for i = 0; i < len(optionsStr); i++ {
+		switch optionsStr[i] {
+		case ',':
+			if i > 0 {
+				// it might be escaped, if so, ignore
+				if optionsStr[i-1] == '\\' {
+					break // from switch, not for loop
+				}
+			}
+			rule.options = append(rule.options, optionsStr[begin:i])
+			begin = i + 1
+		}
+	}
+	if begin != i {
+		// there's still an option remaining
+		rule.options = append(rule.options, optionsStr[begin:])
+	}
+
+	return nil
+}
+
+func (rule *Rule) parseOptions() error {
+	err := rule.extractOptions()
+	if err != nil {
+		return err
+	}
+
+	for _, option := range rule.options {
+		switch {
+		case option == "important":
+			rule.isImportant = true
+		case strings.HasPrefix(option, "app="):
+			option = strings.TrimPrefix(option, "app=")
+			rule.apps = strings.Split(option, "|")
+		default:
+			return ErrInvalidSyntax
+		}
+	}
+
+	return nil
+}
+
+func (rule *Rule) extractShortcut() {
+	// regex rules have no shortcuts
+	if rule.text[0] == '/' && rule.text[len(rule.text)-1] == '/' {
+		return
+	}
+
+	fields := strings.FieldsFunc(rule.text, func(r rune) bool {
+		switch r {
+		case '*', '^', '|':
+			return true
+		}
+		return false
+	})
+	longestField := ""
+	for _, field := range fields {
+		if len(field) > len(longestField) {
+			longestField = field
+		}
+	}
+	if len(longestField) > shortcutLength {
+		longestField = longestField[:shortcutLength]
+	}
+	rule.shortcut = strings.ToLower(longestField)
+}
+
+func (rule *Rule) compile() error {
+	rule.RLock()
+	isCompiled := rule.compiled != nil
+	rule.RUnlock()
+	if isCompiled {
+		return nil
+	}
+
+	expr, err := ruleToRegexp(rule.text)
+	if err != nil {
+		return err
+	}
+
+	compiled, err := regexp.Compile(expr)
+	if err != nil {
+		return err
+	}
+
+	rule.Lock()
+	rule.compiled = compiled
+	rule.Unlock()
+
+	return nil
+}
+
+func (rule *Rule) match(host string) (Result, error) {
+	res := Result{}
+	err := rule.compile()
+	if err != nil {
+		return res, err
+	}
+	rule.RLock()
+	matched := rule.compiled.MatchString(host)
+	rule.RUnlock()
+	if matched {
+		res.Reason = FilteredBlackList
+		res.IsFiltered = true
+		if rule.isWhitelist {
+			res.Reason = NotFilteredWhiteList
+			res.IsFiltered = false
+		}
+		res.Rule = rule.text
+	}
+	return res, nil
+}
+
+func getCachedReason(cache gcache.Cache, host string) (result Result, isFound bool, err error) {
+	isFound = false // not found yet
+
+	// get raw value
+	rawValue, err := cache.Get(host)
+	if err == gcache.KeyNotFoundError {
+		// not a real error, just not found
+		err = nil
+		return
+	}
+	if err != nil {
+		// real error
+		return
+	}
+
+	// since it can be something else, validate that it belongs to proper type
+	cachedValue, ok := rawValue.(Result)
+	if ok == false {
+		// this is not our type -- error
+		text := "SHOULD NOT HAPPEN: entry with invalid type was found in lookup cache"
+		log.Println(text)
+		err = errors.New(text)
+		return
+	}
+	isFound = ok
+	return cachedValue, isFound, err
+}
+
+// for each dot, hash it and add it to string
+func hostnameToHashParam(host string, addslash bool) (string, map[string]bool) {
+	var hashparam bytes.Buffer
+	hashes := map[string]bool{}
+	tld, icann := publicsuffix.PublicSuffix(host)
+	if icann == false {
+		// private suffixes like cloudfront.net
+		tld = ""
+	}
+	curhost := host
+	for {
+		if curhost == "" {
+			// we've reached end of string
+			break
+		}
+		if tld != "" && curhost == tld {
+			// we've reached the TLD, don't hash it
+			break
+		}
+		tohash := []byte(curhost)
+		if addslash {
+			tohash = append(tohash, '/')
+		}
+		sum := sha256.Sum256(tohash)
+		hexhash := fmt.Sprintf("%X", sum)
+		hashes[hexhash] = true
+		hashparam.WriteString(fmt.Sprintf("%02X%02X%02X%02X/", sum[0], sum[1], sum[2], sum[3]))
+		pos := strings.IndexByte(curhost, byte('.'))
+		if pos < 0 {
+			break
+		}
+		curhost = curhost[pos+1:]
+	}
+	return hashparam.String(), hashes
+}
+
+func (d *Dnsfilter) checkSafeBrowsing(host string) (Result, error) {
+	format := func(hashparam string) string {
+		url := fmt.Sprintf(defaultSafebrowsingURL, d.config.safeBrowsingServer, hashparam)
+		return url
+	}
+	handleBody := func(body []byte, hashes map[string]bool) (Result, error) {
+		result := Result{}
+		scanner := bufio.NewScanner(strings.NewReader(string(body)))
+		for scanner.Scan() {
+			line := scanner.Text()
+			splitted := strings.Split(line, ":")
+			if len(splitted) < 3 {
+				continue
+			}
+			hash := splitted[2]
+			if _, ok := hashes[hash]; ok {
+				// it's in the hash
+				result.IsFiltered = true
+				result.Reason = FilteredSafeBrowsing
+				result.Rule = splitted[0]
+				break
+			}
+		}
+
+		if err := scanner.Err(); err != nil {
+			// error, don't save cache
+			return Result{}, err
+		}
+		return result, nil
+	}
+	result, err := d.lookupCommon(host, &stats.Safebrowsing, safebrowsingCache, true, format, handleBody)
+	return result, err
+}
+
+func (d *Dnsfilter) checkParental(host string) (Result, error) {
+	format2 := func(hashparam string) string {
+		url := fmt.Sprintf(defaultParentalURL, hashparam, d.config.parentalSensitivity)
+		return url
+	}
+	handleBody2 := func(body []byte, hashes map[string]bool) (Result, error) {
+		// parse json
+		var m []struct {
+			Blocked   bool   `json:"blocked"`
+			ClientTTL int    `json:"clientTtl"`
+			Reason    string `json:"reason"`
+		}
+		err := json.Unmarshal(body, &m)
+		if err != nil {
+			// error, don't save cache
+			log.Printf("Couldn't parse json '%s': %s", body, err)
+			return Result{}, err
+		}
+
+		result := Result{}
+
+		for i := range m {
+			if m[i].Blocked {
+				result.IsFiltered = true
+				result.Reason = FilteredParental
+				result.Rule = fmt.Sprintf("parental %s", m[i].Reason)
+				break
+			}
+		}
+		return result, nil
+	}
+	result, err := d.lookupCommon(host, &stats.Parental, parentalCache, false, format2, handleBody2)
+	return result, err
+}
+
+// real implementation of lookup/check
+func (d *Dnsfilter) lookupCommon(host string, lookupstats *LookupStats, cache gcache.Cache, hashparamNeedSlash bool, format func(hashparam string) string, handleBody func(body []byte, hashes map[string]bool) (Result, error)) (Result, error) {
+	// if host ends with a dot, trim it
+	host = strings.ToLower(strings.Trim(host, "."))
+
+	// check cache
+	cachedValue, isFound, err := getCachedReason(cache, host)
+	if isFound {
+		atomic.AddUint64(&stats.Safebrowsing.CacheHits, 1)
+		return cachedValue, nil
+	}
+	if err != nil {
+		return Result{}, err
+	}
+
+	// convert hostname to hash parameters
+	hashparam, hashes := hostnameToHashParam(host, hashparamNeedSlash)
+
+	// format URL with our hashes
+	url := format(hashparam)
+
+	// do HTTP request
+	atomic.AddUint64(&lookupstats.Requests, 1)
+	atomic.AddInt64(&lookupstats.Pending, 1)
+	updateMax(&lookupstats.Pending, &lookupstats.PendingMax)
+	resp, err := d.client.Get(url)
+	atomic.AddInt64(&lookupstats.Pending, -1)
+	if resp != nil && resp.Body != nil {
+		defer resp.Body.Close()
+	}
+	if err != nil {
+		// error, don't save cache
+		return Result{}, err
+	}
+
+	// get body text
+	body, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		// error, don't save cache
+		return Result{}, err
+	}
+
+	// handle status code
+	switch {
+	case resp.StatusCode == 204:
+		// empty result, save cache
+		cache.Set(host, Result{})
+		return Result{}, nil
+	case resp.StatusCode != 200:
+		// error, don't save cache
+		return Result{}, nil
+	}
+
+	result, err := handleBody(body, hashes)
+	if err != nil {
+		// error, don't save cache
+		return Result{}, err
+	}
+
+	cache.Set(host, result)
+	return result, nil
+}
+
+//
+// Adding rule and matching against the rules
+//
+
+// AddRule adds a rule, checking if it is a valid rule first and if it wasn't added already
+func (d *Dnsfilter) AddRule(input string, filterListID uint32) error {
+	input = strings.TrimSpace(input)
+	d.storageMutex.RLock()
+	_, exists := d.storage[input]
+	d.storageMutex.RUnlock()
+	if exists {
+		// already added
+		return ErrInvalidSyntax
+	}
+
+	if !isValidRule(input) {
+		return ErrInvalidSyntax
+	}
+
+	rule := Rule{
+		text:         input, // will be modified
+		originalText: input,
+		listID:       filterListID,
+	}
+
+	// mark rule as whitelist if it starts with @@
+	if strings.HasPrefix(rule.text, "@@") {
+		rule.isWhitelist = true
+		rule.text = rule.text[2:]
+	}
+
+	err := rule.parseOptions()
+	if err != nil {
+		return err
+	}
+
+	rule.extractShortcut()
+
+	if !enableDelayedCompilation {
+		err := rule.compile()
+		if err != nil {
+			return err
+		}
+	}
+
+	destination := d.blackList
+	if rule.isImportant {
+		destination = d.important
+	} else if rule.isWhitelist {
+		destination = d.whiteList
+	}
+
+	d.storageMutex.Lock()
+	d.storage[input] = &rule
+	d.storageMutex.Unlock()
+	destination.Add(&rule)
+	return nil
+}
+
+// matchHost is a low-level way to check only if hostname is filtered by rules, skipping expensive safebrowsing and parental lookups
+func (d *Dnsfilter) matchHost(host string) (Result, error) {
+	lists := []*rulesTable{
+		d.important,
+		d.whiteList,
+		d.blackList,
+	}
+
+	for _, table := range lists {
+		res, err := table.matchByHost(host)
+		if err != nil {
+			return res, err
+		}
+		if res.Reason.Matched() {
+			return res, nil
+		}
+	}
+	return Result{}, nil
+}
+
+//
+// lifecycle helper functions
+//
+
+func New() *Dnsfilter {
+	d := new(Dnsfilter)
+
+	d.storage = make(map[string]*Rule)
+	d.important = newRulesTable()
+	d.whiteList = newRulesTable()
+	d.blackList = newRulesTable()
+
+	// Customize the Transport to have larger connection pool
+	defaultRoundTripper := http.DefaultTransport
+	defaultTransportPointer, ok := defaultRoundTripper.(*http.Transport)
+	if !ok {
+		panic(fmt.Sprintf("defaultRoundTripper not an *http.Transport"))
+	}
+	d.transport = defaultTransportPointer                           // dereference it to get a copy of the struct that the pointer points to
+	d.transport.MaxIdleConns = defaultHTTPMaxIdleConnections        // default 100
+	d.transport.MaxIdleConnsPerHost = defaultHTTPMaxIdleConnections // default 2
+	d.client = http.Client{
+		Transport: d.transport,
+		Timeout:   defaultHTTPTimeout,
+	}
+	d.config.safeBrowsingServer = defaultSafebrowsingServer
+	return d
+}
+
+func (d *Dnsfilter) Destroy() {
+	d.transport.CloseIdleConnections()
+}
+
+//
+// config manipulation helpers
+//
+
+func (d *Dnsfilter) EnableSafeBrowsing() {
+	d.config.safeBrowsingEnabled = true
+}
+
+func (d *Dnsfilter) EnableParental(sensitivity int) error {
+	switch sensitivity {
+	case 3, 10, 13, 17:
+		d.config.parentalSensitivity = sensitivity
+		d.config.parentalEnabled = true
+		return nil
+	default:
+		return ErrInvalidParental
+	}
+}
+
+func (d *Dnsfilter) EnableSafeSearch() {
+	d.config.safeSearchEnabled = true
+}
+
+func (d *Dnsfilter) SetSafeBrowsingServer(host string) {
+	if len(host) == 0 {
+		d.config.safeBrowsingServer = defaultSafebrowsingServer
+	} else {
+		d.config.safeBrowsingServer = host
+	}
+}
+
+func (d *Dnsfilter) SetHTTPTimeout(t time.Duration) {
+	d.client.Timeout = t
+}
+
+func (d *Dnsfilter) ResetHTTPTimeout() {
+	d.client.Timeout = defaultHTTPTimeout
+}
+
+func (d *Dnsfilter) SafeSearchDomain(host string) (string, bool) {
+	if d.config.safeSearchEnabled == false {
+		return "", false
+	}
+	val, ok := safeSearchDomains[host]
+	return val, ok
+}
+
+//
+// stats
+//
+
+func (d *Dnsfilter) GetStats() Stats {
+	return stats
+}
+
+func (d *Dnsfilter) Count() int {
+	return len(d.storage)
+}
+
+//
+// cache control, right now needed only for tests
+//
+func purgeCaches() {
+	safebrowsingCache.Purge()
+	parentalCache.Purge()
+}