kube,ipn/store/kubestore: allow patching empty state Secrets

Allow users to pre-create empty state Secrets

Signed-off-by: Irbe Krumina <irbe@tailscale.com>

cmd/containerboot/kube.go

@@ -81,46 +81,47 @@ var kc kube.Client
 // ensure that tailscale state storage and authentication mechanism will work on
 // Kubernetes.
 func (cfg *settings) setupKube(ctx context.Context) error {
-	if cfg.KubeSecret != "" {
-		canPatch, canCreate, err := kc.CheckSecretPermissions(ctx, cfg.KubeSecret)
-		if err != nil {
-			return fmt.Errorf("Some Kubernetes permissions are missing, please check your RBAC configuration: %v", err)
+	if cfg.KubeSecret == "" {
+		return nil
+	}
+	canPatch, canCreate, err := kc.CheckSecretPermissions(ctx, cfg.KubeSecret)
+	if err != nil {
+		return fmt.Errorf("Some Kubernetes permissions are missing, please check your RBAC configuration: %v", err)
+	}
+	cfg.KubernetesCanPatch = canPatch
+
+	s, err := kc.GetSecret(ctx, cfg.KubeSecret)
+	if err != nil && kube.IsNotFoundErr(err) && !canCreate {
+		return fmt.Errorf("Tailscale state Secret %s does not exist and we don't have permissions to create it. "+
+			"If you intend to store tailscale state elsewhere than a Kubernetes Secret, "+
+			"you can explicitly set TS_KUBE_SECRET env var to an empty string. "+
+			"Else ensure that RBAC is set up that allows the service account associated with this installation to create Secrets.", cfg.KubeSecret)
+	} else if err != nil && !kube.IsNotFoundErr(err) {
+		return fmt.Errorf("Getting Tailscale state Secret %s: %v", cfg.KubeSecret, err)
+	}
+
+	if cfg.AuthKey == "" && !isOneStepConfig(cfg) {
+		if s == nil {
+			log.Print("TS_AUTHKEY not provided and kube secret does not exist, login will be interactive if needed.")
+			return nil
 		}
-		cfg.KubernetesCanPatch = canPatch
+		keyBytes, _ := s.Data["authkey"]
+		key := string(keyBytes)
 
-		s, err := kc.GetSecret(ctx, cfg.KubeSecret)
-		if err != nil && kube.IsNotFoundErr(err) && !canCreate {
-			return fmt.Errorf("Tailscale state Secret %s does not exist and we don't have permissions to create it. "+
-				"If you intend to store tailscale state elsewhere than a Kubernetes Secret, "+
-				"you can explicitly set TS_KUBE_SECRET env var to an empty string. "+
-				"Else ensure that RBAC is set up that allows the service account associated with this installation to create Secrets.", cfg.KubeSecret)
-		} else if err != nil && !kube.IsNotFoundErr(err) {
-			return fmt.Errorf("Getting Tailscale state Secret %s: %v", cfg.KubeSecret, err)
-		}
-
-		if cfg.AuthKey == "" && !isOneStepConfig(cfg) {
-			if s == nil {
-				log.Print("TS_AUTHKEY not provided and kube secret does not exist, login will be interactive if needed.")
-				return nil
-			}
-			keyBytes, _ := s.Data["authkey"]
-			key := string(keyBytes)
-
-			if key != "" {
-				// This behavior of pulling authkeys from kube secrets was added
-				// at the same time as the patch permission, so we can enforce
-				// that we must be able to patch out the authkey after
-				// authenticating if you want to use this feature. This avoids
-				// us having to deal with the case where we might leave behind
-				// an unnecessary reusable authkey in a secret, like a rake in
-				// the grass.
-				if !cfg.KubernetesCanPatch {
-					return errors.New("authkey found in TS_KUBE_SECRET, but the pod doesn't have patch permissions on the secret to manage the authkey.")
-				}
-				cfg.AuthKey = key
-			} else {
-				log.Print("No authkey found in kube secret and TS_AUTHKEY not provided, login will be interactive if needed.")
+		if key != "" {
+			// This behavior of pulling authkeys from kube secrets was added
+			// at the same time as the patch permission, so we can enforce
+			// that we must be able to patch out the authkey after
+			// authenticating if you want to use this feature. This avoids
+			// us having to deal with the case where we might leave behind
+			// an unnecessary reusable authkey in a secret, like a rake in
+			// the grass.
+			if !cfg.KubernetesCanPatch {
+				return errors.New("authkey found in TS_KUBE_SECRET, but the pod doesn't have patch permissions on the secret to manage the authkey.")
 			}
+			cfg.AuthKey = key
+		} else {
+			log.Print("No authkey found in kube secret and TS_AUTHKEY not provided, login will be interactive if needed.")
 		}
 	}
 	return nil

ipn/store/kubestore/store_kube.go

@@ -7,6 +7,7 @@ package kubestore
 
 import (
 	"context"
+	"fmt"
 	"net"
 	"strings"
 	"time"
@@ -100,6 +101,19 @@ func (s *Store) WriteState(id ipn.StateKey, bs []byte) error {
 		return err
 	}
 	if s.canPatch {
+		if len(secret.Data) == 0 { // if user has pre-created a blank Secret
+			m := []kube.JSONPatch{
+				{
+					Op:    "add",
+					Path:  "/data",
+					Value: map[string][]byte{sanitizeKey(id): bs},
+				},
+			}
+			if err := s.client.JSONPatchSecret(ctx, s.secretName, m); err != nil {
+				return fmt.Errorf("error patching Secret %s with a /data field: %v", s.secretName, err)
+			}
+			return nil
+		}
 		m := []kube.JSONPatch{
 			{
 				Op:    "add",
@@ -108,7 +122,7 @@ func (s *Store) WriteState(id ipn.StateKey, bs []byte) error {
 			},
 		}
 		if err := s.client.JSONPatchSecret(ctx, s.secretName, m); err != nil {
-			return err
+			return fmt.Errorf("error patching Secret %s with /data/%s field", s.secretName, sanitizeKey(id))
 		}
 		return nil
 	}

kube/client.go

@@ -240,7 +240,7 @@ func (c *client) UpdateSecret(ctx context.Context, s *Secret) error {
 }
 
 // JSONPatch is a JSON patch operation.
-// It currently (2023-03-02) only supports the "remove" operation.
+// It currently (2023-03-02) only supports "add" and "remove" operations.
 //
 // https://tools.ietf.org/html/rfc6902
 type JSONPatch struct {
@@ -278,7 +278,7 @@ func (c *client) StrategicMergePatchSecret(ctx context.Context, name string, s *
 
 // CheckSecretPermissions checks the secret access permissions of the current
 // pod. It returns an error if the basic permissions tailscale needs are
-// missing, and reports whether the patch permission is additionally present.
+// missing, and reports whether the patch and create permissions are additionally present.
 //
 // Errors encountered during the access checking process are logged, but ignored
 // so that the pod tries to fail alive if the permissions exist and there's just