net: ensure that malformed domain names report a consistent error

Previously it depended on whether we were using the Go resolver or the Cgo resolver.

Fixes #12421.

Change-Id: Ib162e336f30f736d7244e29d96651c3be11fc3cd
Reviewed-on: https://go-review.googlesource.com/18383
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

2 files changed, 66 insertions, 0 deletions

diff --git a/src/net/ip_test.go b/src/net/ip_test.go
index 3d95a73c09..69ef5a1ae5 100644
--- a/src/net/ip_test.go
+++ b/src/net/ip_test.go
@@ -540,3 +540,48 @@ func TestIPAddrScope(t *testing.T) {
 		}
 	}
 }
+
+func TestLookupBadName(t *testing.T) {
+	// Check that we get the same error for invalid names regardless of lookup algorithm.
+
+	mode := ""
+	check := func(fn string, err error) {
+		if e, ok := err.(*DNSError); !ok || e.Err != "invalid domain name" {
+			t.Errorf("%s: %s(\"!!!.local\") = %T(%v), want DNSError(invalid domain name)", mode, fn, err, err)
+		}
+	}
+
+	for i, fn := range []func() func(){forceGoDNS, forceCgoDNS} {
+		fixup := fn()
+		if fixup == nil {
+			continue
+		}
+		mode = "netgo"
+		if i == 1 {
+			mode = "netcgo"
+		}
+
+		_, err := LookupHost("!!!.local")
+		check("LookupHost", err)
+
+		_, err = LookupIP("!!!.local")
+		check("LookupIP", err)
+
+		_, err = LookupCNAME("!!!.local")
+		check("LookupCNAME", err)
+
+		_, _, err = LookupSRV("x", "tcp", "!!!.local")
+		check("LookupSRV", err)
+
+		_, err = LookupMX("!!!.local")
+		check("LookupMX", err)
+
+		_, err = LookupNS("!!!.local")
+		check("LookupNS", err)
+
+		_, err = LookupTXT("!!!.local")
+		check("LookupTXT", err)
+
+		fixup()
+	}
+}
diff --git a/src/net/lookup.go b/src/net/lookup.go
index 7aa111ba92..b5d77e02ea 100644
--- a/src/net/lookup.go
+++ b/src/net/lookup.go
@@ -33,6 +33,9 @@ func LookupHost(host string) (addrs []string, err error) {
 	if ip := ParseIP(host); ip != nil {
 		return []string{host}, nil
 	}
+	if !isDomainName(host) {
+		return nil, &DNSError{Err: "invalid domain name", Name: host}
+	}
 	return lookupHost(host)
 }
 
@@ -47,6 +50,9 @@ func LookupIP(host string) (ips []IP, err error) {
 	if ip := ParseIP(host); ip != nil {
 		return []IP{ip}, nil
 	}
+	if !isDomainName(host) {
+		return nil, &DNSError{Err: "invalid domain name", Name: host}
+	}
 	addrs, err := lookupIPMerge(host)
 	if err != nil {
 		return
@@ -146,6 +152,9 @@ func LookupPort(network, service string) (port int, err error) {
 // LookupHost or LookupIP directly; both take care of resolving
 // the canonical name as part of the lookup.
 func LookupCNAME(name string) (cname string, err error) {
+	if !isDomainName(name) {
+		return "", &DNSError{Err: "invalid domain name", Name: name}
+	}
 	return lookupCNAME(name)
 }
 
@@ -159,21 +168,33 @@ func LookupCNAME(name string) (cname string, err error) {
 // publishing SRV records under non-standard names, if both service
 // and proto are empty strings, LookupSRV looks up name directly.
 func LookupSRV(service, proto, name string) (cname string, addrs []*SRV, err error) {
+	if !isDomainName(name) {
+		return "", nil, &DNSError{Err: "invalid domain name", Name: name}
+	}
 	return lookupSRV(service, proto, name)
 }
 
 // LookupMX returns the DNS MX records for the given domain name sorted by preference.
 func LookupMX(name string) (mxs []*MX, err error) {
+	if !isDomainName(name) {
+		return nil, &DNSError{Err: "invalid domain name", Name: name}
+	}
 	return lookupMX(name)
 }
 
 // LookupNS returns the DNS NS records for the given domain name.
 func LookupNS(name string) (nss []*NS, err error) {
+	if !isDomainName(name) {
+		return nil, &DNSError{Err: "invalid domain name", Name: name}
+	}
 	return lookupNS(name)
 }
 
 // LookupTXT returns the DNS TXT records for the given domain name.
 func LookupTXT(name string) (txts []string, err error) {
+	if !isDomainName(name) {
+		return nil, &DNSError{Err: "invalid domain name", Name: name}
+	}
 	return lookupTXT(name)
 }