From 8d0c8ad4381cbf23e1e6653561f7f14a26544d34 Mon Sep 17 00:00:00 2001
From: Simon Zolin <s.zolin@adguard.com>
Date: Tue, 18 Aug 2020 12:36:52 +0300
Subject: [PATCH] + DNS: resolve host names to IP addresses leased by AGH DHCP
server
Close #1956
Squashed commit of the following:
commit 21f11632c871e9c17faa77f9cd6a7aa836559779
Author: Simon Zolin <s.zolin@adguard.com>
Date: Mon Aug 17 19:54:24 2020 +0300
+ DNS: resolve host names to IP addresses leased by AGH DHCP server
---
dnsforward/dnsforward.go | 3 ++
dnsforward/handle_dns.go | 65 +++++++++++++++++++++++++++++++++++++++-
2 files changed, 67 insertions(+), 1 deletion(-)
diff --git a/dnsforward/dnsforward.go b/dnsforward/dnsforward.go
index 95db8967..e73824b0 100644
--- a/dnsforward/dnsforward.go
+++ b/dnsforward/dnsforward.go
@@ -51,6 +51,9 @@ type Server struct {
stats stats.Stats
access *accessCtx
+ tableHostToIP map[string]net.IP // "hostname -> IP" table for internal addresses (DHCP)
+ tableHostToIPLock sync.Mutex
+
tablePTR map[string]string // "IP -> hostname" table for reverse lookup
tablePTRLock sync.Mutex
diff --git a/dnsforward/handle_dns.go b/dnsforward/handle_dns.go
index 462f3750..6860dcf3 100644
--- a/dnsforward/handle_dns.go
+++ b/dnsforward/handle_dns.go
@@ -1,6 +1,7 @@
package dnsforward
import (
+ "net"
"strings"
"time"
@@ -42,6 +43,7 @@ func (s *Server) handleDNSRequest(_ *proxy.Proxy, d *proxy.DNSContext) error {
type modProcessFunc func(ctx *dnsContext) int
mods := []modProcessFunc{
processInitial,
+ processInternalHosts,
processInternalIPAddrs,
processFilteringBeforeRequest,
processUpstream,
@@ -102,20 +104,81 @@ func (s *Server) onDHCPLeaseChanged(flags int) {
return
}
+ hostToIP := make(map[string]net.IP)
m := make(map[string]string)
+
ll := s.dhcpServer.Leases(dhcpd.LeasesAll)
+
for _, l := range ll {
if len(l.Hostname) == 0 {
continue
}
+
m[l.IP.String()] = l.Hostname
+
+ ip := make(net.IP, 4)
+ copy(ip, l.IP.To4())
+ hostToIP[l.Hostname] = ip
}
- log.Debug("DNS: added %d PTR entries from DHCP", len(m))
+
+ log.Debug("DNS: added %d A/PTR entries from DHCP", len(m))
+
+ s.tableHostToIPLock.Lock()
+ s.tableHostToIP = hostToIP
+ s.tableHostToIPLock.Unlock()
+
s.tablePTRLock.Lock()
s.tablePTR = m
s.tablePTRLock.Unlock()
}
+// Respond to A requests if the target host name is associated with a lease from our DHCP server
+func processInternalHosts(ctx *dnsContext) int {
+ s := ctx.srv
+ req := ctx.proxyCtx.Req
+ if !(req.Question[0].Qtype == dns.TypeA || req.Question[0].Qtype == dns.TypeAAAA) {
+ return resultDone
+ }
+
+ host := req.Question[0].Name
+ host = strings.ToLower(host)
+ if !strings.HasSuffix(host, ".lan.") {
+ return resultDone
+ }
+ host = strings.TrimSuffix(host, ".lan.")
+
+ s.tableHostToIPLock.Lock()
+ if s.tableHostToIP == nil {
+ s.tableHostToIPLock.Unlock()
+ return resultDone
+ }
+ ip, ok := s.tableHostToIP[host]
+ s.tableHostToIPLock.Unlock()
+ if !ok {
+ return resultDone
+ }
+
+ log.Debug("DNS: internal record: %s -> %s", req.Question[0].Name, ip.String())
+
+ resp := s.makeResponse(req)
+
+ if req.Question[0].Qtype == dns.TypeA {
+ a := &dns.A{}
+ a.Hdr = dns.RR_Header{
+ Name: req.Question[0].Name,
+ Rrtype: dns.TypeA,
+ Ttl: s.conf.BlockedResponseTTL,
+ Class: dns.ClassINET,
+ }
+ a.A = make([]byte, 4)
+ copy(a.A, ip)
+ resp.Answer = append(resp.Answer, a)
+ }
+
+ ctx.proxyCtx.Res = resp
+ return resultDone
+}
+
// Respond to PTR requests if the target IP address is leased by our DHCP server
func processInternalIPAddrs(ctx *dnsContext) int {
s := ctx.srv