package aghnet import ( "bufio" "fmt" "io" "io/fs" "net" "path" "strings" "sync" "github.com/AdguardTeam/AdGuardHome/internal/aghos" "github.com/AdguardTeam/golibs/errors" "github.com/AdguardTeam/golibs/log" "github.com/AdguardTeam/golibs/netutil" "github.com/AdguardTeam/golibs/stringutil" "github.com/AdguardTeam/urlfilter" "github.com/AdguardTeam/urlfilter/filterlist" "github.com/AdguardTeam/urlfilter/rules" "github.com/miekg/dns" ) // DefaultHostsPaths returns the slice of paths default for the operating system // to files and directories which are containing the hosts database. The result // is intended to be used within fs.FS so the initial slash is omitted. func DefaultHostsPaths() (paths []string) { return defaultHostsPaths() } // requestMatcher combines the logic for matching requests and translating the // appropriate rules. type requestMatcher struct { // stateLock protects all the fields of requestMatcher. stateLock *sync.RWMutex // rulesStrg stores the rules obtained from the hosts' file. rulesStrg *filterlist.RuleStorage // engine serves rulesStrg. engine *urlfilter.DNSEngine // translator maps generated $dnsrewrite rules into hosts-syntax rules. // // TODO(e.burkov): Store the filename from which the rule was parsed. translator map[string]string } // MatchRequest processes the request rewriting hostnames and addresses read // from the operating system's hosts files. // // res is nil for any request having not an A/AAAA or PTR type. Results // containing CNAME information may be queried again with the same question type // and the returned CNAME for Host field of request. Results are guaranteed to // be direct, i.e. any returned CNAME resolves into actual address like an alias // in hosts does, see man hosts (5). // // It's safe for concurrent use. func (rm *requestMatcher) MatchRequest( req urlfilter.DNSRequest, ) (res *urlfilter.DNSResult, ok bool) { switch req.DNSType { case dns.TypeA, dns.TypeAAAA, dns.TypePTR: log.Debug("%s: handling the request", hostsContainerPref) default: return nil, false } rm.stateLock.RLock() defer rm.stateLock.RUnlock() return rm.engine.MatchRequest(req) } // Translate returns the source hosts-syntax rule for the generated dnsrewrite // rule or an empty string if the last doesn't exist. func (rm *requestMatcher) Translate(rule string) (hostRule string) { rm.stateLock.RLock() defer rm.stateLock.RUnlock() return rm.translator[rule] } // resetEng updates container's engine and the translation map. func (rm *requestMatcher) resetEng(rulesStrg *filterlist.RuleStorage, tr map[string]string) { rm.stateLock.Lock() defer rm.stateLock.Unlock() rm.rulesStrg = rulesStrg rm.engine = urlfilter.NewDNSEngine(rm.rulesStrg) rm.translator = tr } // hostsContainerPref is a prefix for logging and wrapping errors in // HostsContainer's methods. const hostsContainerPref = "hosts container" // HostsContainer stores the relevant hosts database provided by the OS and // processes both A/AAAA and PTR DNS requests for those. type HostsContainer struct { // requestMatcher matches the requests and translates the rules. It's // embedded to implement MatchRequest and Translate for *HostsContainer. requestMatcher // listID is the identifier for the list of generated rules. listID int // done is the channel to sign closing the container. done chan struct{} // updates is the channel for receiving updated hosts. updates chan *netutil.IPMap // last is the set of hosts that was cached within last detected change. last *netutil.IPMap // fsys is the working file system to read hosts files from. fsys fs.FS // w tracks the changes in specified files and directories. w aghos.FSWatcher // patterns stores specified paths in the fs.Glob-compatible form. patterns []string } // ErrNoHostsPaths is returned when there are no valid paths to watch passed to // the HostsContainer. const ErrNoHostsPaths errors.Error = "no valid paths to hosts files provided" // NewHostsContainer creates a container of hosts, that watches the paths with // w. listID is used as an identifier of the underlying rules list. paths // shouldn't be empty and each of paths should locate either a file or a // directory in fsys. fsys and w must be non-nil. func NewHostsContainer( listID int, fsys fs.FS, w aghos.FSWatcher, paths ...string, ) (hc *HostsContainer, err error) { defer func() { err = errors.Annotate(err, "%s: %w", hostsContainerPref) }() if len(paths) == 0 { return nil, ErrNoHostsPaths } var patterns []string patterns, err = pathsToPatterns(fsys, paths) if err != nil { return nil, err } else if len(patterns) == 0 { return nil, ErrNoHostsPaths } hc = &HostsContainer{ requestMatcher: requestMatcher{ stateLock: &sync.RWMutex{}, }, listID: listID, done: make(chan struct{}, 1), updates: make(chan *netutil.IPMap, 1), fsys: fsys, w: w, patterns: patterns, } log.Debug("%s: starting", hostsContainerPref) // Load initially. if err = hc.refresh(); err != nil { return nil, err } for _, p := range paths { if err = w.Add(p); err != nil { if !errors.Is(err, fs.ErrNotExist) { return nil, fmt.Errorf("adding path: %w", err) } log.Debug("%s: file %q expected to exist but doesn't", hostsContainerPref, p) } } go hc.handleEvents() return hc, nil } // Close implements the io.Closer interface for *HostsContainer. Close must // only be called once. The returned err is always nil. func (hc *HostsContainer) Close() (err error) { log.Debug("%s: closing", hostsContainerPref) close(hc.done) return nil } // Upd returns the channel into which the updates are sent. The receivable // map's values are guaranteed to be of type of *stringutil.Set. func (hc *HostsContainer) Upd() (updates <-chan *netutil.IPMap) { return hc.updates } // pathsToPatterns converts paths into patterns compatible with fs.Glob. func pathsToPatterns(fsys fs.FS, paths []string) (patterns []string, err error) { for i, p := range paths { var fi fs.FileInfo fi, err = fs.Stat(fsys, p) if err != nil { if errors.Is(err, fs.ErrNotExist) { continue } // Don't put a filename here since it's already added by fs.Stat. return nil, fmt.Errorf("path at index %d: %w", i, err) } if fi.IsDir() { p = path.Join(p, "*") } patterns = append(patterns, p) } return patterns, nil } // handleEvents concurrently handles the events. It closes the update channel // of HostsContainer when finishes. Used to be called within a goroutine. func (hc *HostsContainer) handleEvents() { defer log.OnPanic(fmt.Sprintf("%s: handling events", hostsContainerPref)) defer close(hc.updates) ok, eventsCh := true, hc.w.Events() for ok { select { case _, ok = <-eventsCh: if !ok { log.Debug("%s: watcher closed the events channel", hostsContainerPref) continue } if err := hc.refresh(); err != nil { log.Error("%s: %s", hostsContainerPref, err) } case _, ok = <-hc.done: // Go on. } } } // hostsParser is a helper type to parse rules from the operating system's hosts // file. It exists for only a single refreshing session. type hostsParser struct { // rulesBuilder builds the resulting rulesBuilder list content. rulesBuilder *strings.Builder // translations maps generated $dnsrewrite rules to the hosts-translations // rules. translations map[string]string // cnameSet prevents duplicating cname rules. cnameSet *stringutil.Set // table stores only the unique IP-hostname pairs. It's also sent to the // updates channel afterwards. table *netutil.IPMap } func (hc *HostsContainer) newHostsParser() (hp *hostsParser) { return &hostsParser{ rulesBuilder: &strings.Builder{}, // For A/AAAA and PTRs. translations: make(map[string]string, hc.last.Len()*2), cnameSet: stringutil.NewSet(), table: netutil.NewIPMap(hc.last.Len()), } } // parseFile is a aghos.FileWalker for parsing the files with hosts syntax. It // never signs to stop walking and never returns any additional patterns. // // See man hosts(5). func (hp *hostsParser) parseFile( r io.Reader, ) (patterns []string, cont bool, err error) { s := bufio.NewScanner(r) for s.Scan() { ip, hosts := hp.parseLine(s.Text()) if ip == nil { continue } hp.addPairs(ip, hosts) } return nil, true, s.Err() } // parseLine parses the line having the hosts syntax ignoring invalid ones. func (hp *hostsParser) parseLine(line string) (ip net.IP, hosts []string) { fields := strings.Fields(line) if len(fields) < 2 { return nil, nil } if ip = net.ParseIP(fields[0]); ip == nil { return nil, nil } for _, f := range fields[1:] { switch hashIdx := strings.IndexByte(f, '#'); hashIdx { case -1: hosts = append(hosts, f) continue case 0: // Go on. default: // Only a part of the field is a comment. hosts = append(hosts, f[:hashIdx]) } // The rest of the fields are a part of the comment so skip // immediately. break } return ip, hosts } // Simple types of hosts in hosts database. Zero value isn't used to be able // quizzaciously emulate nil with 0. const ( _ = iota hostAlias hostMain ) // add tries to add the ip-host pair. It returns: // // hostAlias if the host is not the first one added for the ip. // hostMain if the host is the first one added for the ip. // 0 if the ip-host pair has already been added. // func (hp *hostsParser) add(ip net.IP, host string) (hostType int) { v, ok := hp.table.Get(ip) switch hosts, _ := v.(*stringutil.Set); { case ok && hosts.Has(host): return 0 case hosts == nil: hosts = stringutil.NewSet(host) hp.table.Set(ip, hosts) return hostMain default: hosts.Add(host) return hostAlias } } // addPair puts the pair of ip and host to the rules builder if needed. For // each ip the first member of hosts will become the main one. func (hp *hostsParser) addPairs(ip net.IP, hosts []string) { // Put the rule in a preproccesed format like: // // ip host1 host2 ... // hostsLine := strings.Join(append([]string{ip.String()}, hosts...), " ") var mainHost string for _, host := range hosts { switch hp.add(ip, host) { case 0: continue case hostMain: mainHost = host added, addedPtr := hp.writeMainHostRule(host, ip) hp.translations[added], hp.translations[addedPtr] = hostsLine, hostsLine case hostAlias: pair := fmt.Sprint(host, " ", mainHost) if hp.cnameSet.Has(pair) { continue } // Since the hostAlias couldn't be returned from add before the // hostMain the mainHost shouldn't appear empty. hp.writeAliasHostRule(host, mainHost) hp.cnameSet.Add(pair) } log.Debug("%s: added ip-host pair %q-%q", hostsContainerPref, ip, host) } } // writeAliasHostRule writes the CNAME rule for the alias-host pair into // internal builders. func (hp *hostsParser) writeAliasHostRule(alias, host string) { const ( nl = "\n" sc = ";" rwSuccess = rules.MaskSeparator + "$dnsrewrite=NOERROR" + sc + "CNAME" + sc constLen = len(rules.MaskStartURL) + len(rwSuccess) + len(nl) ) hp.rulesBuilder.Grow(constLen + len(host) + len(alias)) stringutil.WriteToBuilder(hp.rulesBuilder, rules.MaskStartURL, alias, rwSuccess, host, nl) } // writeMainHostRule writes the actual rule for the qtype and the PTR for the // host-ip pair into internal builders. func (hp *hostsParser) writeMainHostRule(host string, ip net.IP) (added, addedPtr string) { arpa, err := netutil.IPToReversedAddr(ip) if err != nil { return } const ( nl = "\n" rwSuccess = "^$dnsrewrite=NOERROR;" rwSuccessPTR = "^$dnsrewrite=NOERROR;PTR;" modLen = len("||") + len(rwSuccess) modLenPTR = len("||") + len(rwSuccessPTR) ) var qtype string // The validation of the IP address has been performed earlier so it is // guaranteed to be either an IPv4 or an IPv6. if ip.To4() != nil { qtype = "A" } else { qtype = "AAAA" } ipStr := ip.String() fqdn := dns.Fqdn(host) ruleBuilder := &strings.Builder{} ruleBuilder.Grow(modLen + len(host) + len(qtype) + len(ipStr)) stringutil.WriteToBuilder( ruleBuilder, "||", host, rwSuccess, qtype, ";", ipStr, ) added = ruleBuilder.String() ruleBuilder.Reset() ruleBuilder.Grow(modLenPTR + len(arpa) + len(fqdn)) stringutil.WriteToBuilder( ruleBuilder, "||", arpa, rwSuccessPTR, fqdn, ) addedPtr = ruleBuilder.String() hp.rulesBuilder.Grow(len(added) + len(addedPtr) + 2*len(nl)) stringutil.WriteToBuilder(hp.rulesBuilder, added, nl, addedPtr, nl) return added, addedPtr } // equalSet returns true if the internal hosts table just parsed equals target. func (hp *hostsParser) equalSet(target *netutil.IPMap) (ok bool) { if target == nil { // hp.table shouldn't appear nil since it's initialized on each refresh. return target == hp.table } if hp.table.Len() != target.Len() { return false } hp.table.Range(func(ip net.IP, val interface{}) (cont bool) { v, hasIP := target.Get(ip) // ok is set to true if the target doesn't contain ip or if the // appropriate hosts set isn't equal to the checked one, i.e. the maps // have at least one disperancy. ok = !hasIP || !v.(*stringutil.Set).Equal(val.(*stringutil.Set)) // Continue only if maps has no discrepancies. return !ok }) // Return true if every value from the IP map has no disperancies with the // appropriate one from the target. return !ok } // sendUpd tries to send the parsed data to the ch. func (hp *hostsParser) sendUpd(ch chan *netutil.IPMap) { log.Debug("%s: sending upd", hostsContainerPref) upd := hp.table select { case ch <- upd: // Updates are delivered. Go on. case <-ch: ch <- upd log.Debug("%s: replaced the last update", hostsContainerPref) case ch <- upd: // The previous update was just read and the next one pushed. Go on. default: log.Error("%s: the updates channel is broken", hostsContainerPref) } } // newStrg creates a new rules storage from parsed data. func (hp *hostsParser) newStrg(id int) (s *filterlist.RuleStorage, err error) { return filterlist.NewRuleStorage([]filterlist.RuleList{&filterlist.StringRuleList{ ID: id, RulesText: hp.rulesBuilder.String(), IgnoreCosmetic: true, }}) } // refresh gets the data from specified files and propagates the updates if // needed. // // TODO(e.burkov): Accept a parameter to specify the files to refresh. func (hc *HostsContainer) refresh() (err error) { log.Debug("%s: refreshing", hostsContainerPref) hp := hc.newHostsParser() if _, err = aghos.FileWalker(hp.parseFile).Walk(hc.fsys, hc.patterns...); err != nil { return fmt.Errorf("refreshing : %w", err) } if hp.equalSet(hc.last) { log.Debug("%s: no updates detected", hostsContainerPref) return nil } defer hp.sendUpd(hc.updates) hc.last = hp.table.ShallowClone() var rulesStrg *filterlist.RuleStorage if rulesStrg, err = hp.newStrg(hc.listID); err != nil { return fmt.Errorf("initializing rules storage: %w", err) } hc.resetEng(rulesStrg, hp.translations) return nil }