diff --git a/src/net/dnsclient_unix.go b/src/net/dnsclient_unix.go index 4e7462b66fac48..7ed4ea8708c2c2 100644 --- a/src/net/dnsclient_unix.go +++ b/src/net/dnsclient_unix.go @@ -26,6 +26,12 @@ import ( "golang.org/x/net/dns/dnsmessage" ) +const ( + // to be used as a useTCP parameter to exchange + useTCPOnly = true + useUDPOrTCP = false +) + var ( errLameReferral = errors.New("lame referral") errCannotUnmarshalDNSMessage = errors.New("cannot unmarshal DNS message") @@ -131,13 +137,19 @@ func dnsStreamRoundTrip(c Conn, id uint16, query dnsmessage.Question, b []byte) } // exchange sends a query on the connection and hopes for a response. -func (r *Resolver) exchange(ctx context.Context, server string, q dnsmessage.Question, timeout time.Duration) (dnsmessage.Parser, dnsmessage.Header, error) { +func (r *Resolver) exchange(ctx context.Context, server string, q dnsmessage.Question, timeout time.Duration, useTCP bool) (dnsmessage.Parser, dnsmessage.Header, error) { q.Class = dnsmessage.ClassINET id, udpReq, tcpReq, err := newRequest(q) if err != nil { return dnsmessage.Parser{}, dnsmessage.Header{}, errCannotMarshalDNSMessage } - for _, network := range []string{"udp", "tcp"} { + var networks []string + if useTCP { + networks = []string{"tcp"} + } else { + networks = []string{"udp", "tcp"} + } + for _, network := range networks { ctx, cancel := context.WithDeadline(ctx, time.Now().Add(timeout)) defer cancel() @@ -241,7 +253,7 @@ func (r *Resolver) tryOneName(ctx context.Context, cfg *dnsConfig, name string, for j := uint32(0); j < sLen; j++ { server := cfg.servers[(serverOffset+j)%sLen] - p, h, err := r.exchange(ctx, server, q, cfg.timeout) + p, h, err := r.exchange(ctx, server, q, cfg.timeout, cfg.useTCP) if err != nil { dnsErr := &DNSError{ Err: err.Error(), diff --git a/src/net/dnsclient_unix_test.go b/src/net/dnsclient_unix_test.go index 51d54a4ccadf22..f1ed58c837d856 100644 --- a/src/net/dnsclient_unix_test.go +++ b/src/net/dnsclient_unix_test.go @@ -81,7 +81,7 @@ func TestDNSTransportFallback(t *testing.T) { for _, tt := range dnsTransportFallbackTests { ctx, cancel := context.WithCancel(context.Background()) defer cancel() - _, h, err := r.exchange(ctx, tt.server, tt.question, time.Second) + _, h, err := r.exchange(ctx, tt.server, tt.question, time.Second, useUDPOrTCP) if err != nil { t.Error(err) continue @@ -137,7 +137,7 @@ func TestSpecialDomainName(t *testing.T) { for _, tt := range specialDomainNameTests { ctx, cancel := context.WithCancel(context.Background()) defer cancel() - _, h, err := r.exchange(ctx, server, tt.question, 3*time.Second) + _, h, err := r.exchange(ctx, server, tt.question, 3*time.Second, useUDPOrTCP) if err != nil { t.Error(err) continue @@ -1564,7 +1564,7 @@ func TestDNSDialTCP(t *testing.T) { } r := Resolver{PreferGo: true, Dial: fake.DialContext} ctx := context.Background() - _, _, err := r.exchange(ctx, "0.0.0.0", mustQuestion("com.", dnsmessage.TypeALL, dnsmessage.ClassINET), time.Second) + _, _, err := r.exchange(ctx, "0.0.0.0", mustQuestion("com.", dnsmessage.TypeALL, dnsmessage.ClassINET), time.Second, useUDPOrTCP) if err != nil { t.Fatal("exhange failed:", err) } @@ -1695,3 +1695,30 @@ func TestSingleRequestLookup(t *testing.T) { } } } + +// Issue 29358. Add configuration knob to force TCP-only DNS requests in the pure Go resolver. +func TestDNSUseTCP(t *testing.T) { + fake := fakeDNSServer{ + rh: func(n, _ string, q dnsmessage.Message, _ time.Time) (dnsmessage.Message, error) { + r := dnsmessage.Message{ + Header: dnsmessage.Header{ + ID: q.Header.ID, + Response: true, + RCode: dnsmessage.RCodeSuccess, + }, + Questions: q.Questions, + } + if n == "udp" { + t.Fatal("udp protocol was used instead of tcp") + } + return r, nil + }, + } + r := Resolver{PreferGo: true, Dial: fake.DialContext} + ctx, cancel := context.WithCancel(context.Background()) + defer cancel() + _, _, err := r.exchange(ctx, "0.0.0.0", mustQuestion("com.", dnsmessage.TypeALL, dnsmessage.ClassINET), time.Second, useTCPOnly) + if err != nil { + t.Fatal("exchange failed:", err) + } +} diff --git a/src/net/dnsconfig_unix.go b/src/net/dnsconfig_unix.go index 3ca8d71f5f9f2e..877e77c0493d26 100644 --- a/src/net/dnsconfig_unix.go +++ b/src/net/dnsconfig_unix.go @@ -33,6 +33,7 @@ type dnsConfig struct { mtime time.Time // time of resolv.conf modification soffset uint32 // used by serverOffset singleRequest bool // use sequential A and AAAA queries instead of parallel queries + useTCP bool // force usage of TCP for DNS resolutions } // See resolv.conf(5) on a Linux machine. @@ -123,6 +124,14 @@ func dnsReadConfig(filename string) *dnsConfig { // This option disables the behavior and makes glibc // perform the IPv6 and IPv4 requests sequentially." conf.singleRequest = true + case s == "use-vc" || s == "usevc" || s == "tcp": + // Linux (use-vc), FreeBSD (usevc) and OpenBSD (tcp) option: + // http://man7.org/linux/man-pages/man5/resolv.conf.5.html + // "Sets RES_USEVC in _res.options. + // This option forces the use of TCP for DNS resolutions." + // https://www.freebsd.org/cgi/man.cgi?query=resolv.conf&sektion=5&manpath=freebsd-release-ports + // https://man.openbsd.org/resolv.conf.5 + conf.useTCP = true default: conf.unknownOpt = true } diff --git a/src/net/dnsconfig_unix_test.go b/src/net/dnsconfig_unix_test.go index f16f90ad505309..42880123c52d2f 100644 --- a/src/net/dnsconfig_unix_test.go +++ b/src/net/dnsconfig_unix_test.go @@ -124,6 +124,39 @@ var dnsReadConfigTests = []struct { search: []string{"domain.local."}, }, }, + { + name: "testdata/linux-use-vc-resolv.conf", + want: &dnsConfig{ + servers: defaultNS, + ndots: 1, + useTCP: true, + timeout: 5 * time.Second, + attempts: 2, + search: []string{"domain.local."}, + }, + }, + { + name: "testdata/freebsd-usevc-resolv.conf", + want: &dnsConfig{ + servers: defaultNS, + ndots: 1, + useTCP: true, + timeout: 5 * time.Second, + attempts: 2, + search: []string{"domain.local."}, + }, + }, + { + name: "testdata/openbsd-tcp-resolv.conf", + want: &dnsConfig{ + servers: defaultNS, + ndots: 1, + useTCP: true, + timeout: 5 * time.Second, + attempts: 2, + search: []string{"domain.local."}, + }, + }, } func TestDNSReadConfig(t *testing.T) { diff --git a/src/net/testdata/freebsd-usevc-resolv.conf b/src/net/testdata/freebsd-usevc-resolv.conf new file mode 100644 index 00000000000000..4afb281c5bbf22 --- /dev/null +++ b/src/net/testdata/freebsd-usevc-resolv.conf @@ -0,0 +1 @@ +options usevc \ No newline at end of file diff --git a/src/net/testdata/linux-use-vc-resolv.conf b/src/net/testdata/linux-use-vc-resolv.conf new file mode 100644 index 00000000000000..4e4a58b7a7e0e8 --- /dev/null +++ b/src/net/testdata/linux-use-vc-resolv.conf @@ -0,0 +1 @@ +options use-vc \ No newline at end of file diff --git a/src/net/testdata/openbsd-tcp-resolv.conf b/src/net/testdata/openbsd-tcp-resolv.conf new file mode 100644 index 00000000000000..7929e50e8df037 --- /dev/null +++ b/src/net/testdata/openbsd-tcp-resolv.conf @@ -0,0 +1 @@ +options tcp \ No newline at end of file