1 files changed, 65 insertions, 19 deletions
diff --git a/src/net/lookup.go b/src/net/lookup.go
index 0660268249b..4135122d60d 100644
--- a/src/net/lookup.go
+++ b/src/net/lookup.go
@@ -415,7 +415,7 @@ func (r *Resolver) LookupCNAME(ctx context.Context, host string) (string, error)
 		return "", err
 	}
 	if !isDomainName(cname) {
-		return "", &DNSError{Err: "CNAME target is invalid", Name: host}
+		return "", &DNSError{Err: errMalformedDNSRecordsDetail, Name: host}
 	}
 	return cname, nil
 }
@@ -431,7 +431,9 @@ func (r *Resolver) LookupCNAME(ctx context.Context, host string) (string, error)
 // and proto are empty strings, LookupSRV looks up name directly.
 //
 // The returned service names are validated to be properly
-// formatted presentation-format domain names.
+// formatted presentation-format domain names. If the response contains
+// invalid names, those records are filtered out and an error
+// will be returned alongside the the remaining results, if any.
 func LookupSRV(service, proto, name string) (cname string, addrs []*SRV, err error) {
 	return DefaultResolver.LookupSRV(context.Background(), service, proto, name)
 }
@@ -447,7 +449,9 @@ func LookupSRV(service, proto, name string) (cname string, addrs []*SRV, err err
 // and proto are empty strings, LookupSRV looks up name directly.
 //
 // The returned service names are validated to be properly
-// formatted presentation-format domain names.
+// formatted presentation-format domain names. If the response contains
+// invalid names, those records are filtered out and an error
+// will be returned alongside the the remaining results, if any.
 func (r *Resolver) LookupSRV(ctx context.Context, service, proto, name string) (string, []*SRV, error) {
 	cname, addrs, err := r.lookupSRV(ctx, service, proto, name)
 	if err != nil {
@@ -456,21 +460,31 @@ func (r *Resolver) LookupSRV(ctx context.Context, service, proto, name string) (
 	if cname != "" && !isDomainName(cname) {
 		return "", nil, &DNSError{Err: "SRV header name is invalid", Name: name}
 	}
+	filteredAddrs := make([]*SRV, 0, len(addrs))
 	for _, addr := range addrs {
 		if addr == nil {
 			continue
 		}
 		if !isDomainName(addr.Target) {
-			return "", nil, &DNSError{Err: "SRV target is invalid", Name: name}
+			continue
 		}
+		filteredAddrs = append(filteredAddrs, addr)
+	}
+	if len(addrs) != len(filteredAddrs) {
+		return cname, filteredAddrs, &DNSError{Err: errMalformedDNSRecordsDetail, Name: name}
 	}
-	return cname, addrs, nil
+	return cname, filteredAddrs, nil
 }
 
 // LookupMX returns the DNS MX records for the given domain name sorted by preference.
 //
 // The returned mail server names are validated to be properly
-// formatted presentation-format domain names.
+// formatted presentation-format domain names. If the response contains
+// invalid names, those records are filtered out and an error
+// will be returned alongside the the remaining results, if any.
+//
+// LookupMX uses context.Background internally; to specify the context, use
+// Resolver.LookupMX.
 func LookupMX(name string) ([]*MX, error) {
 	return DefaultResolver.LookupMX(context.Background(), name)
 }
@@ -478,27 +492,41 @@ func LookupMX(name string) ([]*MX, error) {
 // LookupMX returns the DNS MX records for the given domain name sorted by preference.
 //
 // The returned mail server names are validated to be properly
-// formatted presentation-format domain names.
+// formatted presentation-format domain names. If the response contains
+// invalid names, those records are filtered out and an error
+// will be returned alongside the the remaining results, if any.
 func (r *Resolver) LookupMX(ctx context.Context, name string) ([]*MX, error) {
 	records, err := r.lookupMX(ctx, name)
 	if err != nil {
 		return nil, err
 	}
+	filteredMX := make([]*MX, 0, len(records))
 	for _, mx := range records {
 		if mx == nil {
 			continue
 		}
-		if !isDomainName(mx.Host) {
-			return nil, &DNSError{Err: "MX target is invalid", Name: name}
+		// Bypass the hostname validity check for targets which contain only a dot,
+		// as this is used to represent a 'Null' MX record.
+		if mx.Host != "." && !isDomainName(mx.Host) {
+			continue
 		}
+		filteredMX = append(filteredMX, mx)
+	}
+	if len(records) != len(filteredMX) {
+		return filteredMX, &DNSError{Err: errMalformedDNSRecordsDetail, Name: name}
 	}
-	return records, nil
+	return filteredMX, nil
 }
 
 // LookupNS returns the DNS NS records for the given domain name.
 //
 // The returned name server names are validated to be properly
-// formatted presentation-format domain names.
+// formatted presentation-format domain names. If the response contains
+// invalid names, those records are filtered out and an error
+// will be returned alongside the the remaining results, if any.
+//
+// LookupNS uses context.Background internally; to specify the context, use
+// Resolver.LookupNS.
 func LookupNS(name string) ([]*NS, error) {
 	return DefaultResolver.LookupNS(context.Background(), name)
 }
@@ -506,21 +534,28 @@ func LookupNS(name string) ([]*NS, error) {
 // LookupNS returns the DNS NS records for the given domain name.
 //
 // The returned name server names are validated to be properly
-// formatted presentation-format domain names.
+// formatted presentation-format domain names. If the response contains
+// invalid names, those records are filtered out and an error
+// will be returned alongside the the remaining results, if any.
 func (r *Resolver) LookupNS(ctx context.Context, name string) ([]*NS, error) {
 	records, err := r.lookupNS(ctx, name)
 	if err != nil {
 		return nil, err
 	}
+	filteredNS := make([]*NS, 0, len(records))
 	for _, ns := range records {
 		if ns == nil {
 			continue
 		}
 		if !isDomainName(ns.Host) {
-			return nil, &DNSError{Err: "NS target is invalid", Name: name}
+			continue
 		}
+		filteredNS = append(filteredNS, ns)
+	}
+	if len(records) != len(filteredNS) {
+		return filteredNS, &DNSError{Err: errMalformedDNSRecordsDetail, Name: name}
 	}
-	return records, nil
+	return filteredNS, nil
 }
 
 // LookupTXT returns the DNS TXT records for the given domain name.
@@ -537,7 +572,8 @@ func (r *Resolver) LookupTXT(ctx context.Context, name string) ([]string, error)
 // of names mapping to that address.
 //
 // The returned names are validated to be properly formatted presentation-format
-// domain names.
+// domain names. If the response contains invalid names, those records are filtered
+// out and an error will be returned alongside the the remaining results, if any.
 //
 // When using the host C library resolver, at most one result will be
 // returned. To bypass the host resolver, use a custom Resolver.
@@ -549,16 +585,26 @@ func LookupAddr(addr string) (names []string, err error) {
 // of names mapping to that address.
 //
 // The returned names are validated to be properly formatted presentation-format
-// domain names.
+// domain names. If the response contains invalid names, those records are filtered
+// out and an error will be returned alongside the the remaining results, if any.
 func (r *Resolver) LookupAddr(ctx context.Context, addr string) ([]string, error) {
 	names, err := r.lookupAddr(ctx, addr)
 	if err != nil {
 		return nil, err
 	}
+	filteredNames := make([]string, 0, len(names))
 	for _, name := range names {
-		if !isDomainName(name) {
-			return nil, &DNSError{Err: "PTR target is invalid", Name: addr}
+		if isDomainName(name) {
+			filteredNames = append(filteredNames, name)
 		}
 	}
-	return names, nil
+	if len(names) != len(filteredNames) {
+		return filteredNames, &DNSError{Err: errMalformedDNSRecordsDetail, Name: addr}
+	}
+	return filteredNames, nil
 }
+
+// errMalformedDNSRecordsDetail is the DNSError detail which is returned when a Resolver.Lookup...
+// method recieves DNS records which contain invalid DNS names. This may be returned alongside
+// results which have had the malformed records filtered out.
+var errMalformedDNSRecordsDetail = "DNS response contained records which contain invalid names"