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net: prevent unintended retries upon receiving an empty answer response from the DNS server.

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CL https://golang.org/cl/37879 migrates DNS message parsing to the golang.org/x/net/dns/dnsmessage package. However, during the modification of the "lame referral" error check introduced by CL https://golang.org/cl/22428, a condition was overlooked. This omission results in unexpected retries when a DNS server returns an empty response (not an invalid response, but one that includes an additional section).

Fixes #57697
Fixes #64783

Change-Id: I203896aa2902c305569005c1712fd2f9f13a9b6b
Reviewed-on: https://go-review.googlesource.com/c/go/+/550435
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Commit-Queue: Ian Lance Taylor <iant@golang.org>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Dexter Ouyang <kkhaike@gmail.com>
This commit is contained in:
kkhaike 2023-12-16 18:08:16 +08:00 committed by Gopher Robot
parent e5f4c68c44
commit aaf8e844ed
2 changed files with 30 additions and 6 deletions
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13
src/net/dnsclient_unix.go
View File

@ -211,7 +211,7 @@ func (r *Resolver) exchange(ctx context.Context, server string, q dnsmessage.Que
// checkHeader performs basic sanity checks on the header.
func checkHeader(p *dnsmessage.Parser, h dnsmessage.Header) error {
rcode := extractExtendedRCode(*p, h)
rcode, hasAdd := extractExtendedRCode(*p, h)
if rcode == dnsmessage.RCodeNameError {
return errNoSuchHost
@ -224,7 +224,7 @@ func checkHeader(p *dnsmessage.Parser, h dnsmessage.Header) error {
// libresolv continues to the next server when it receives
// an invalid referral response. See golang.org/issue/15434.
if rcode == dnsmessage.RCodeSuccess && !h.Authoritative && !h.RecursionAvailable && err == dnsmessage.ErrSectionDone {
if rcode == dnsmessage.RCodeSuccess && !h.Authoritative && !h.RecursionAvailable && err == dnsmessage.ErrSectionDone && !hasAdd {
return errLameReferral
}
@ -263,16 +263,19 @@ func skipToAnswer(p *dnsmessage.Parser, qtype dnsmessage.Type) error {
// extractExtendedRCode extracts the extended RCode from the OPT resource (EDNS(0))
// If an OPT record is not found, the RCode from the hdr is returned.
func extractExtendedRCode(p dnsmessage.Parser, hdr dnsmessage.Header) dnsmessage.RCode {
// Another return value indicates whether an additional resource was found.
func extractExtendedRCode(p dnsmessage.Parser, hdr dnsmessage.Header) (dnsmessage.RCode, bool) {
p.SkipAllAnswers()
p.SkipAllAuthorities()
hasAdd := false
for {
ahdr, err := p.AdditionalHeader()
hasAdd = hasAdd || err != dnsmessage.ErrSectionDone
if err != nil {
return hdr.RCode
return hdr.RCode, hasAdd
}
if ahdr.Type == dnsmessage.TypeOPT {
return ahdr.ExtendedRCode(hdr.RCode)
return ahdr.ExtendedRCode(hdr.RCode), hasAdd
}
p.SkipAdditional()
}

23
src/net/dnsclient_unix_test.go
View File

@ -803,13 +803,25 @@ func TestIgnoreLameReferrals(t *testing.T) {
},
}
}
} else if s == "192.0.2.1:53" {
if q.Questions[0].Type == dnsmessage.TypeA && strings.HasPrefix(q.Questions[0].Name.String(), "empty.com.") {
var edns0Hdr dnsmessage.ResourceHeader
edns0Hdr.SetEDNS0(maxDNSPacketSize, dnsmessage.RCodeSuccess, false)
r.Additionals = []dnsmessage.Resource{
{
Header: edns0Hdr,
Body: &dnsmessage.OPTResource{},
},
}
}
}
return r, nil
}}
r := Resolver{PreferGo: true, Dial: fake.DialContext}
addrs, err := r.LookupIPAddr(context.Background(), "www.golang.org")
addrs, err := r.LookupIP(context.Background(), "ip4", "www.golang.org")
if err != nil {
t.Fatal(err)
}
@ -821,6 +833,15 @@ func TestIgnoreLameReferrals(t *testing.T) {
if got, want := addrs[0].String(), "192.0.2.1"; got != want {
t.Fatalf("got address %v, want %v", got, want)
}
_, err = r.LookupIP(context.Background(), "ip4", "empty.com")
de, ok := err.(*DNSError)
if !ok {
t.Fatalf("err = %#v; wanted a *net.DNSError", err)
}
if de.Err != errNoSuchHost.Error() {
t.Fatalf("Err = %#v; wanted %q", de.Err, errNoSuchHost.Error())
}
}
func BenchmarkGoLookupIP(b *testing.B) {