[v17] kube: prevent init failure when proxy listener addr host is unspecified

lib/kube/grpc/utils.go

@@ -22,6 +22,7 @@ import (
 	"crypto/tls"
 	"net"
 	"net/http"
+	"strconv"
 	"time"
 
 	"github.com/gravitational/trace"
@@ -42,15 +43,25 @@ import (
 // multiplexing mode, the Kube proxy is always reachable on the same address as
 // the web server using the SNI.
 func getWebAddrAndKubeSNI(proxyAddr string) (string, string, error) {
-	addr, port, err := utils.SplitHostPort(proxyAddr)
+	// we avoid using utils.SplitHostPort because
+	// we allow the host to be empty
+	addr, port, err := net.SplitHostPort(proxyAddr)
 	if err != nil {
 		return "", "", trace.Wrap(err)
 	}
-	sni := client.GetKubeTLSServerName(addr)
+
+	// validate the port
+	if _, err := strconv.Atoi(port); err != nil {
+		return "", "", trace.Wrap(err, "invalid port")
+	}
+
 	// if the proxy is an unspecified address (0.0.0.0, ::), use localhost.
-	if ip := net.ParseIP(addr); ip != nil && ip.IsUnspecified() {
+	if ip := net.ParseIP(addr); ip != nil && ip.IsUnspecified() || addr == "" {
 		addr = string(teleport.PrincipalLocalhost)
 	}
+
+	sni := client.GetKubeTLSServerName(addr)
+
 	return sni, "https://" + net.JoinHostPort(addr, port), nil
 }
 

lib/kube/grpc/utils_test.go

@@ -0,0 +1,119 @@
+/*
+ * Teleport
+ * Copyright (C) 2025  Gravitational, Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package kubev1
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestGetWebAddrAndkubeSNI(t *testing.T) {
+	const localKubeSNI = "kube-teleport-proxy-alpn.teleport.cluster.local"
+	tests := []struct {
+		name      string
+		proxyAddr string
+		sni       string
+		host      string
+		assertErr require.ErrorAssertionFunc
+	}{
+		{
+			name:      "empty proxy address",
+			proxyAddr: "",
+			assertErr: require.Error,
+		},
+		{
+			name:      "invalid address format",
+			proxyAddr: "not-a-valid-addr",
+			assertErr: require.Error,
+		},
+		{
+			name:      "invalid port format",
+			proxyAddr: ":not-a-valid-port",
+			assertErr: require.Error,
+		},
+		{
+			name:      "valid localhost address",
+			proxyAddr: "localhost:3000",
+			sni:       localKubeSNI,
+			host:      "https://localhost:3000",
+			assertErr: require.NoError,
+		},
+		{
+			name:      "valid ip address",
+			proxyAddr: "1.2.3.4:3000",
+			sni:       localKubeSNI,
+			host:      "https://1.2.3.4:3000",
+			assertErr: require.NoError,
+		},
+		{
+			name:      "valid wildcard address",
+			proxyAddr: "0.0.0.0:3000",
+			sni:       localKubeSNI,
+			host:      "https://localhost:3000",
+			assertErr: require.NoError,
+		},
+		{
+			name:      "specify port only",
+			proxyAddr: ":3000",
+			sni:       localKubeSNI,
+			host:      "https://localhost:3000",
+			assertErr: require.NoError,
+		},
+		{
+			name:      "double colons in address",
+			proxyAddr: "::3000",
+			assertErr: require.Error,
+		},
+		{
+			name:      "valid ipv6 address",
+			proxyAddr: "[::1]:3000",
+			sni:       localKubeSNI,
+			host:      "https://[::1]:3000",
+			assertErr: require.NoError,
+		},
+		{
+			name:      "unspecified ipv6 address",
+			proxyAddr: "[::]:3000",
+			sni:       localKubeSNI,
+			host:      "https://localhost:3000",
+			assertErr: require.NoError,
+		},
+		{
+			name:      "ipv6 address without port",
+			proxyAddr: "[::1]",
+			assertErr: require.Error,
+		},
+		{
+			name:      "valid domain address",
+			proxyAddr: "ci.goteleport.com:3000",
+			sni:       "kube-teleport-proxy-alpn.ci.goteleport.com",
+			host:      "https://ci.goteleport.com:3000",
+			assertErr: require.NoError,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotSNI, gotHost, err := getWebAddrAndKubeSNI(tt.proxyAddr)
+			tt.assertErr(t, err)
+			require.Equal(t, tt.sni, gotSNI)
+			require.Equal(t, tt.host, gotHost)
+		})
+	}
+}