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net: don't crash on unexpected DNS SRV responses
Fixes #1350 R=rsc, bradfitzwork CC=golang-dev https://golang.org/cl/4432089
This commit is contained in:
Brad Fitzpatrick
parent
2c92fe0b4f
commit
8ef56f7e92
@ -121,15 +121,19 @@ func answer(name, server string, dns *dnsMsg, qtype uint16) (cname string, addrs
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Cname:
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for cnameloop := 0; cnameloop < 10; cnameloop++ {
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addrs = addrs[0:0]
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for i := 0; i < len(dns.answer); i++ {
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rr := dns.answer[i]
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for _, rr := range dns.answer {
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if _, justHeader := rr.(*dnsRR_Header); justHeader {
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// Corrupt record: we only have a
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// header. That header might say it's
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// of type qtype, but we don't
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// actually have it. Skip.
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continue
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}
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h := rr.Header()
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if h.Class == dnsClassINET && h.Name == name {
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switch h.Rrtype {
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case qtype:
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n := len(addrs)
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addrs = addrs[0 : n+1]
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addrs[n] = rr
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addrs = append(addrs, rr)
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case dnsTypeCNAME:
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// redirect to cname
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name = rr.(*dnsRR_CNAME).Cname
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@ -181,8 +185,7 @@ func tryOneName(cfg *dnsConfig, name string, qtype uint16) (cname string, addrs
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func convertRR_A(records []dnsRR) []IP {
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addrs := make([]IP, len(records))
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for i := 0; i < len(records); i++ {
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rr := records[i]
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for i, rr := range records {
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a := rr.(*dnsRR_A).A
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addrs[i] = IPv4(byte(a>>24), byte(a>>16), byte(a>>8), byte(a))
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}
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@ -191,8 +194,7 @@ func convertRR_A(records []dnsRR) []IP {
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func convertRR_AAAA(records []dnsRR) []IP {
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addrs := make([]IP, len(records))
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for i := 0; i < len(records); i++ {
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rr := records[i]
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for i, rr := range records {
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a := make(IP, 16)
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copy(a, rr.(*dnsRR_AAAA).AAAA[:])
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addrs[i] = a
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@ -384,9 +386,7 @@ func goLookupCNAME(name string) (cname string, err os.Error) {
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if err != nil {
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return
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}
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if len(rr) >= 0 {
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cname = rr[0].(*dnsRR_CNAME).Cname
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}
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return
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}
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@ -410,8 +410,8 @@ func LookupSRV(service, proto, name string) (cname string, addrs []*SRV, err os.
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return
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}
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addrs = make([]*SRV, len(records))
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for i := 0; i < len(records); i++ {
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r := records[i].(*dnsRR_SRV)
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for i, rr := range records {
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r := rr.(*dnsRR_SRV)
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addrs[i] = &SRV{r.Target, r.Port, r.Priority, r.Weight}
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}
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return
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@ -715,25 +715,36 @@ func (dns *dnsMsg) Unpack(msg []byte) bool {
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// Arrays.
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dns.question = make([]dnsQuestion, dh.Qdcount)
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dns.answer = make([]dnsRR, dh.Ancount)
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dns.ns = make([]dnsRR, dh.Nscount)
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dns.extra = make([]dnsRR, dh.Arcount)
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dns.answer = make([]dnsRR, 0, dh.Ancount)
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dns.ns = make([]dnsRR, 0, dh.Nscount)
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dns.extra = make([]dnsRR, 0, dh.Arcount)
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var rec dnsRR
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for i := 0; i < len(dns.question); i++ {
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off, ok = unpackStruct(&dns.question[i], msg, off)
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}
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for i := 0; i < len(dns.answer); i++ {
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dns.answer[i], off, ok = unpackRR(msg, off)
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}
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for i := 0; i < len(dns.ns); i++ {
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dns.ns[i], off, ok = unpackRR(msg, off)
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}
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for i := 0; i < len(dns.extra); i++ {
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dns.extra[i], off, ok = unpackRR(msg, off)
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}
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for i := 0; i < int(dh.Ancount); i++ {
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rec, off, ok = unpackRR(msg, off)
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if !ok {
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return false
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}
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dns.answer = append(dns.answer, rec)
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}
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for i := 0; i < int(dh.Nscount); i++ {
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rec, off, ok = unpackRR(msg, off)
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if !ok {
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return false
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}
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dns.ns = append(dns.ns, rec)
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}
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for i := 0; i < int(dh.Arcount); i++ {
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rec, off, ok = unpackRR(msg, off)
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if !ok {
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return false
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}
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dns.extra = append(dns.extra, rec)
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}
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// if off != len(msg) {
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// println("extra bytes in dns packet", off, "<", len(msg));
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// }
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100
src/pkg/net/dnsmsg_test.go
Normal file
100
src/pkg/net/dnsmsg_test.go
Normal file
@ -0,0 +1,100 @@
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// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package net
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import (
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"encoding/hex"
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"testing"
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)
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func TestDNSParseSRVReply(t *testing.T) {
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data, err := hex.DecodeString(dnsSRVReply)
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if err != nil {
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t.Fatal(err)
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}
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msg := new(dnsMsg)
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ok := msg.Unpack(data)
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if !ok {
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t.Fatalf("unpacking packet failed")
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}
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if g, e := len(msg.answer), 5; g != e {
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t.Errorf("len(msg.answer) = %d; want %d", g, e)
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}
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for idx, rr := range msg.answer {
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if g, e := rr.Header().Rrtype, uint16(dnsTypeSRV); g != e {
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t.Errorf("rr[%d].Header().Rrtype = %d; want %d", idx, g, e)
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}
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if _, ok := rr.(*dnsRR_SRV); !ok {
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t.Errorf("answer[%d] = %T; want *dnsRR_SRV", idx, rr)
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}
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}
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_, addrs, err := answer("_xmpp-server._tcp.google.com.", "foo:53", msg, uint16(dnsTypeSRV))
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if err != nil {
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t.Fatalf("answer: %v", err)
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}
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if g, e := len(addrs), 5; g != e {
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t.Errorf("len(addrs) = %d; want %d", g, e)
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t.Logf("addrs = %#v", addrs)
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}
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}
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func TestDNSParseCorruptSRVReply(t *testing.T) {
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data, err := hex.DecodeString(dnsSRVCorruptReply)
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if err != nil {
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t.Fatal(err)
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}
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msg := new(dnsMsg)
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ok := msg.Unpack(data)
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if !ok {
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t.Fatalf("unpacking packet failed")
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}
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if g, e := len(msg.answer), 5; g != e {
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t.Errorf("len(msg.answer) = %d; want %d", g, e)
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}
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for idx, rr := range msg.answer {
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if g, e := rr.Header().Rrtype, uint16(dnsTypeSRV); g != e {
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t.Errorf("rr[%d].Header().Rrtype = %d; want %d", idx, g, e)
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}
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if idx == 4 {
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if _, ok := rr.(*dnsRR_Header); !ok {
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t.Errorf("answer[%d] = %T; want *dnsRR_Header", idx, rr)
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}
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} else {
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if _, ok := rr.(*dnsRR_SRV); !ok {
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t.Errorf("answer[%d] = %T; want *dnsRR_SRV", idx, rr)
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}
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}
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}
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_, addrs, err := answer("_xmpp-server._tcp.google.com.", "foo:53", msg, uint16(dnsTypeSRV))
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if err != nil {
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t.Fatalf("answer: %v", err)
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}
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if g, e := len(addrs), 4; g != e {
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t.Errorf("len(addrs) = %d; want %d", g, e)
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t.Logf("addrs = %#v", addrs)
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}
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}
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// Valid DNS SRV reply
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const dnsSRVReply = "0901818000010005000000000c5f786d70702d736572766572045f74637006676f6f67" +
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"6c6503636f6d0000210001c00c002100010000012c00210014000014950c786d70702d" +
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"73657276657234016c06676f6f676c6503636f6d00c00c002100010000012c00210014" +
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"000014950c786d70702d73657276657232016c06676f6f676c6503636f6d00c00c0021" +
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"00010000012c00210014000014950c786d70702d73657276657233016c06676f6f676c" +
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"6503636f6d00c00c002100010000012c00200005000014950b786d70702d7365727665" +
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"72016c06676f6f676c6503636f6d00c00c002100010000012c00210014000014950c78" +
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"6d70702d73657276657231016c06676f6f676c6503636f6d00"
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// Corrupt DNS SRV reply, with its final RR having a bogus length
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// (perhaps it was truncated, or it's malicious) The mutation is the
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// capital "FF" below, instead of the proper "21".
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const dnsSRVCorruptReply = "0901818000010005000000000c5f786d70702d736572766572045f74637006676f6f67" +
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"6c6503636f6d0000210001c00c002100010000012c00210014000014950c786d70702d" +
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"73657276657234016c06676f6f676c6503636f6d00c00c002100010000012c00210014" +
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"000014950c786d70702d73657276657232016c06676f6f676c6503636f6d00c00c0021" +
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"00010000012c00210014000014950c786d70702d73657276657233016c06676f6f676c" +
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"6503636f6d00c00c002100010000012c00200005000014950b786d70702d7365727665" +
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"72016c06676f6f676c6503636f6d00c00c002100010000012c00FF0014000014950c78" +
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"6d70702d73657276657231016c06676f6f676c6503636f6d00"
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