package aghnet import ( "bufio" "net" "os" "path/filepath" "runtime" "strings" "sync" "github.com/AdguardTeam/AdGuardHome/internal/aghos" "github.com/AdguardTeam/golibs/errors" "github.com/AdguardTeam/golibs/log" "github.com/fsnotify/fsnotify" "github.com/miekg/dns" ) type onChangedT func() // EtcHostsContainer - automatic DNS records // // TODO(e.burkov): Move the logic under interface. Refactor. Probably remove // the resolving logic. type EtcHostsContainer struct { // lock protects table and tableReverse. lock sync.RWMutex // table is the host-to-IPs map. table map[string][]net.IP // tableReverse is the IP-to-hosts map. // // TODO(a.garipov): Make better use of newtypes. Perhaps a custom map. tableReverse map[string][]string hostsFn string // path to the main hosts-file hostsDirs []string // paths to OS-specific directories with hosts-files watcher *fsnotify.Watcher // file and directory watcher object // onlyWritesChan used to contain only writing events from watcher. onlyWritesChan chan fsnotify.Event onChanged onChangedT // notification to other modules } // SetOnChanged - set callback function that will be called when the data is changed func (ehc *EtcHostsContainer) SetOnChanged(onChanged onChangedT) { ehc.onChanged = onChanged } // Notify other modules func (ehc *EtcHostsContainer) notify() { if ehc.onChanged == nil { return } ehc.onChanged() } // Init - initialize // hostsFn: Override default name for the hosts-file (optional) func (ehc *EtcHostsContainer) Init(hostsFn string) { ehc.table = make(map[string][]net.IP) ehc.onlyWritesChan = make(chan fsnotify.Event, 2) ehc.hostsFn = "/etc/hosts" if runtime.GOOS == "windows" { ehc.hostsFn = os.ExpandEnv("$SystemRoot\\system32\\drivers\\etc\\hosts") } if len(hostsFn) != 0 { ehc.hostsFn = hostsFn } if aghos.IsOpenWrt() { // OpenWrt: "/tmp/hosts/dhcp.cfg01411c". ehc.hostsDirs = append(ehc.hostsDirs, "/tmp/hosts") } // Load hosts initially ehc.updateHosts() var err error ehc.watcher, err = fsnotify.NewWatcher() if err != nil { log.Error("etchostscontainer: %s", err) } } // Start - start module func (ehc *EtcHostsContainer) Start() { if ehc == nil { return } log.Debug("Start etchostscontainer module") ehc.updateHosts() if ehc.watcher != nil { go ehc.watcherLoop() err := ehc.watcher.Add(ehc.hostsFn) if err != nil { log.Error("Error while initializing watcher for a file %s: %s", ehc.hostsFn, err) } for _, dir := range ehc.hostsDirs { err = ehc.watcher.Add(dir) if err != nil { log.Error("Error while initializing watcher for a directory %s: %s", dir, err) } } } } // Close - close module func (ehc *EtcHostsContainer) Close() { if ehc == nil { return } if ehc.watcher != nil { _ = ehc.watcher.Close() } // Don't close onlyWritesChan here and let onlyWrites close it after // watcher.Events is closed to prevent close races. } // Process returns the list of IP addresses for the hostname or nil if nothing // found. func (ehc *EtcHostsContainer) Process(host string, qtype uint16) []net.IP { if qtype == dns.TypePTR { return nil } var ipsCopy []net.IP ehc.lock.RLock() defer ehc.lock.RUnlock() if ips, ok := ehc.table[host]; ok { ipsCopy = make([]net.IP, len(ips)) copy(ipsCopy, ips) } log.Debug("etchostscontainer: answer: %s -> %v", host, ipsCopy) return ipsCopy } // ProcessReverse processes a PTR request. It returns nil if nothing is found. func (ehc *EtcHostsContainer) ProcessReverse(addr string, qtype uint16) (hosts []string) { if qtype != dns.TypePTR { return nil } ipReal := UnreverseAddr(addr) if ipReal == nil { return nil } ipStr := ipReal.String() ehc.lock.RLock() defer ehc.lock.RUnlock() hosts = ehc.tableReverse[ipStr] if len(hosts) == 0 { return nil // not found } log.Debug("etchostscontainer: reverse-lookup: %s -> %s", addr, hosts) return hosts } // List returns an IP-to-hostnames table. It is safe for concurrent use. func (ehc *EtcHostsContainer) List() (ipToHosts map[string][]string) { ehc.lock.RLock() defer ehc.lock.RUnlock() ipToHosts = make(map[string][]string, len(ehc.tableReverse)) for k, v := range ehc.tableReverse { ipToHosts[k] = v } return ipToHosts } // update table func (ehc *EtcHostsContainer) updateTable(table map[string][]net.IP, host string, ipAddr net.IP) { ips, ok := table[host] if ok { for _, ip := range ips { if ip.Equal(ipAddr) { // IP already exists: don't add duplicates ok = false break } } if !ok { ips = append(ips, ipAddr) table[host] = ips } } else { table[host] = []net.IP{ipAddr} ok = true } if ok { log.Debug("etchostscontainer: added %s -> %s", ipAddr, host) } } // updateTableRev updates the reverse address table. func (ehc *EtcHostsContainer) updateTableRev(tableRev map[string][]string, newHost string, ipAddr net.IP) { ipStr := ipAddr.String() hosts, ok := tableRev[ipStr] if !ok { tableRev[ipStr] = []string{newHost} log.Debug("etchostscontainer: added reverse-address %s -> %s", ipStr, newHost) return } for _, host := range hosts { if host == newHost { return } } tableRev[ipStr] = append(tableRev[ipStr], newHost) log.Debug("etchostscontainer: added reverse-address %s -> %s", ipStr, newHost) } // parseHostsLine parses hosts from the fields. func parseHostsLine(fields []string) (hosts []string) { for _, f := range fields { hashIdx := strings.IndexByte(f, '#') if hashIdx == 0 { // The rest of the fields are a part of the comment. // Skip immediately. return } else if hashIdx > 0 { // Only a part of the field is a comment. hosts = append(hosts, f[:hashIdx]) return hosts } hosts = append(hosts, f) } return hosts } // load reads IP-hostname pairs from the hosts file. Multiple hostnames per // line for one IP are supported. func (ehc *EtcHostsContainer) load( table map[string][]net.IP, tableRev map[string][]string, fn string, ) { f, err := os.Open(fn) if err != nil { log.Error("etchostscontainer: %s", err) return } defer func() { derr := f.Close() if derr != nil { log.Error("etchostscontainer: closing file: %s", err) } }() log.Debug("etchostscontainer: loading hosts from file %s", fn) s := bufio.NewScanner(f) for s.Scan() { line := strings.TrimSpace(s.Text()) fields := strings.Fields(line) if len(fields) < 2 { continue } ip := net.ParseIP(fields[0]) if ip == nil { continue } hosts := parseHostsLine(fields[1:]) for _, host := range hosts { ehc.updateTable(table, host, ip) ehc.updateTableRev(tableRev, host, ip) } } err = s.Err() if err != nil { log.Error("etchostscontainer: %s", err) } } // onlyWrites is a filter for (*fsnotify.Watcher).Events. func (ehc *EtcHostsContainer) onlyWrites() { for event := range ehc.watcher.Events { if event.Op&fsnotify.Write == fsnotify.Write { ehc.onlyWritesChan <- event } } close(ehc.onlyWritesChan) } // Receive notifications from fsnotify package func (ehc *EtcHostsContainer) watcherLoop() { go ehc.onlyWrites() for { select { case event, ok := <-ehc.onlyWritesChan: if !ok { return } // Assume that we sometimes have the same event occurred // several times. repeat := true for repeat { select { case _, ok = <-ehc.onlyWritesChan: repeat = ok default: repeat = false } } if event.Op&fsnotify.Write == fsnotify.Write { log.Debug("etchostscontainer: modified: %s", event.Name) ehc.updateHosts() } case err, ok := <-ehc.watcher.Errors: if !ok { return } log.Error("etchostscontainer: %s", err) } } } // updateHosts - loads system hosts func (ehc *EtcHostsContainer) updateHosts() { table := make(map[string][]net.IP) tableRev := make(map[string][]string) ehc.load(table, tableRev, ehc.hostsFn) for _, dir := range ehc.hostsDirs { des, err := os.ReadDir(dir) if err != nil { if !errors.Is(err, os.ErrNotExist) { log.Error("etchostscontainer: Opening directory: %q: %s", dir, err) } continue } for _, de := range des { ehc.load(table, tableRev, filepath.Join(dir, de.Name())) } } func() { ehc.lock.Lock() defer ehc.lock.Unlock() ehc.table = table ehc.tableReverse = tableRev }() ehc.notify() }