From d3c9ef57ce5a887f6eb3d87a22adf38ef4e651ee Mon Sep 17 00:00:00 2001 From: Ian Lance Taylor Date: Tue, 15 Feb 2022 13:38:57 -0800 Subject: [PATCH] Revert "net: send EDNS(0) packet length in DNS query" This reverts https://go.dev/cl/385035. For 1.18 we will use a simple change to increase the accepted DNS packet size, to handle what appear to be broken resolvers that don't honor the 512 byte limit. For 1.19 we will restore CL 385035 to make a proper EDNS request, so that it has more testing time before it goes out in a release. For #6464 For #21160 For #44135 For #51127 For #51153 Change-Id: Ie4a0eb85ca0a6a73bee5cd4cfc6b7d2a15ef259f Reviewed-on: https://go-review.googlesource.com/c/go/+/386014 Trust: Ian Lance Taylor Reviewed-by: Matthew Dempsky Reviewed-by: Damien Neil --- src/net/dnsclient_unix.go | 19 +----------- src/net/dnsclient_unix_test.go | 57 +--------------------------------- 2 files changed, 2 insertions(+), 74 deletions(-) diff --git a/src/net/dnsclient_unix.go b/src/net/dnsclient_unix.go index fae78ae1b1..21aa91f665 100644 --- a/src/net/dnsclient_unix.go +++ b/src/net/dnsclient_unix.go @@ -30,10 +30,6 @@ const ( // to be used as a useTCP parameter to exchange useTCPOnly = true useUDPOrTCP = false - - // Requested DNS packet size. - // Value taken from https://dnsflagday.net/2020/. - maxDNSPacketSize = 1232 ) var ( @@ -60,19 +56,6 @@ func newRequest(q dnsmessage.Question) (id uint16, udpReq, tcpReq []byte, err er if err := b.Question(q); err != nil { return 0, nil, nil, err } - - // Accept packets up to maxDNSPacketSize. RFC 6891. - if err := b.StartAdditionals(); err != nil { - return 0, nil, nil, err - } - var rh dnsmessage.ResourceHeader - if err := rh.SetEDNS0(maxDNSPacketSize, dnsmessage.RCodeSuccess, false); err != nil { - return 0, nil, nil, err - } - if err := b.OPTResource(rh, dnsmessage.OPTResource{}); err != nil { - return 0, nil, nil, err - } - tcpReq, err = b.Finish() udpReq = tcpReq[2:] l := len(tcpReq) - 2 @@ -99,7 +82,7 @@ func dnsPacketRoundTrip(c Conn, id uint16, query dnsmessage.Question, b []byte) return dnsmessage.Parser{}, dnsmessage.Header{}, err } - b = make([]byte, maxDNSPacketSize) + b = make([]byte, 512) // see RFC 1035 for { n, err := c.Read(b) if err != nil { diff --git a/src/net/dnsclient_unix_test.go b/src/net/dnsclient_unix_test.go index e5f01dba2a..14366eca8c 100644 --- a/src/net/dnsclient_unix_test.go +++ b/src/net/dnsclient_unix_test.go @@ -881,7 +881,7 @@ func (f *fakeDNSPacketConn) Close() error { func TestIgnoreDNSForgeries(t *testing.T) { c, s := Pipe() go func() { - b := make([]byte, maxDNSPacketSize) + b := make([]byte, 512) n, err := s.Read(b) if err != nil { t.Error(err) @@ -2161,58 +2161,3 @@ func TestRootNS(t *testing.T) { t.Errorf("records = [%v]; want [%v]", strings.Join(records, " "), want[0]) } } - -// Test that we advertise support for a larger DNS packet size. -// This isn't a great test as it just tests the dnsmessage package -// against itself. -func TestDNSPacketSize(t *testing.T) { - fake := fakeDNSServer{ - rh: func(_, _ string, q dnsmessage.Message, _ time.Time) (dnsmessage.Message, error) { - if len(q.Additionals) == 0 { - t.Error("missing EDNS record") - } else if opt, ok := q.Additionals[0].Body.(*dnsmessage.OPTResource); !ok { - t.Errorf("additional record type %T, expected OPTResource", q.Additionals[0]) - } else if len(opt.Options) != 0 { - t.Errorf("found %d Options, expected none", len(opt.Options)) - } else { - got := int(q.Additionals[0].Header.Class) - t.Logf("EDNS packet size == %d", got) - if got != maxDNSPacketSize { - t.Errorf("EDNS packet size == %d, want %d", got, maxDNSPacketSize) - } - } - - // Hand back a dummy answer to verify that - // LookupIPAddr completes. - r := dnsmessage.Message{ - Header: dnsmessage.Header{ - ID: q.Header.ID, - Response: true, - RCode: dnsmessage.RCodeSuccess, - }, - Questions: q.Questions, - } - if q.Questions[0].Type == dnsmessage.TypeA { - r.Answers = []dnsmessage.Resource{ - { - Header: dnsmessage.ResourceHeader{ - Name: q.Questions[0].Name, - Type: dnsmessage.TypeA, - Class: dnsmessage.ClassINET, - Length: 4, - }, - Body: &dnsmessage.AResource{ - A: TestAddr, - }, - }, - } - } - return r, nil - }, - } - - r := &Resolver{PreferGo: true, Dial: fake.DialContext} - if _, err := r.LookupIPAddr(context.Background(), "go.dev"); err != nil { - t.Errorf("lookup failed: %v", err) - } -} -- 2.48.1