badguardhome/home/rdns.go

142 lines
3.0 KiB
Go

package home
import (
"fmt"
"strings"
"sync"
"time"
"github.com/AdguardTeam/dnsproxy/upstream"
"github.com/AdguardTeam/golibs/log"
"github.com/miekg/dns"
)
const (
rdnsTimeout = 3 * time.Second // max time to wait for rDNS response
)
// RDNS - module context
type RDNS struct {
clients *clientsContainer
ipChannel chan string // pass data from DNS request handling thread to rDNS thread
// contains IP addresses of clients to be resolved by rDNS
// if IP address couldn't be resolved, it stays here forever to prevent further attempts to resolve the same IP
ips map[string]bool
lock sync.Mutex // synchronize access to 'ips'
upstream upstream.Upstream // Upstream object for our own DNS server
}
// InitRDNS - create module context
func InitRDNS(clients *clientsContainer) *RDNS {
r := RDNS{}
r.clients = clients
var err error
bindhost := config.DNS.BindHost
if config.DNS.BindHost == "0.0.0.0" {
bindhost = "127.0.0.1"
}
resolverAddress := fmt.Sprintf("%s:%d", bindhost, config.DNS.Port)
opts := upstream.Options{
Timeout: rdnsTimeout,
}
r.upstream, err = upstream.AddressToUpstream(resolverAddress, opts)
if err != nil {
log.Error("upstream.AddressToUpstream: %s", err)
return nil
}
r.ips = make(map[string]bool)
r.ipChannel = make(chan string, 256)
go r.workerLoop()
return &r
}
// Begin - add IP address to rDNS queue
func (r *RDNS) Begin(ip string) {
if r.clients.Exists(ip, ClientSourceRDNS) {
return
}
// add IP to ips, if not exists
r.lock.Lock()
defer r.lock.Unlock()
_, ok := r.ips[ip]
if ok {
return
}
r.ips[ip] = true
log.Tracef("Adding %s for rDNS resolve", ip)
select {
case r.ipChannel <- ip:
//
default:
log.Tracef("rDNS queue is full")
}
}
// Use rDNS to get hostname by IP address
func (r *RDNS) resolve(ip string) string {
log.Tracef("Resolving host for %s", ip)
req := dns.Msg{}
req.Id = dns.Id()
req.RecursionDesired = true
req.Question = []dns.Question{
{
Qtype: dns.TypePTR,
Qclass: dns.ClassINET,
},
}
var err error
req.Question[0].Name, err = dns.ReverseAddr(ip)
if err != nil {
log.Debug("Error while calling dns.ReverseAddr(%s): %s", ip, err)
return ""
}
resp, err := r.upstream.Exchange(&req)
if err != nil {
log.Debug("Error while making an rDNS lookup for %s: %s", ip, err)
return ""
}
if len(resp.Answer) != 1 {
log.Debug("No answer for rDNS lookup of %s", ip)
return ""
}
ptr, ok := resp.Answer[0].(*dns.PTR)
if !ok {
log.Debug("not a PTR response for %s", ip)
return ""
}
log.Tracef("PTR response for %s: %s", ip, ptr.String())
if strings.HasSuffix(ptr.Ptr, ".") {
ptr.Ptr = ptr.Ptr[:len(ptr.Ptr)-1]
}
return ptr.Ptr
}
// Wait for a signal and then synchronously resolve hostname by IP address
// Add the hostname:IP pair to "Clients" array
func (r *RDNS) workerLoop() {
for {
var ip string
ip = <-r.ipChannel
host := r.resolve(ip)
if len(host) == 0 {
continue
}
r.lock.Lock()
delete(r.ips, ip)
r.lock.Unlock()
_, _ = config.clients.AddHost(ip, host, ClientSourceRDNS)
}
}