ipn/store/kubestore: handle "/" in ipn.StateKeys

Kubernetes doesn't allow slashes as keys in secrets, replace them with "__".

This shows up in the kubernetes-operator now that tsnet sets resets the ServeConfig
at startup.

Fixes #7662

Signed-off-by: Maisem Ali <maisem@tailscale.com>

ipn/store/kubestore/store_kube.go

@@ -7,6 +7,7 @@ package kubestore
 
 import (
 	"context"
+	"strings"
 	"time"
 
 	"tailscale.com/ipn"
@@ -46,13 +47,24 @@ func (s *Store) ReadState(id ipn.StateKey) ([]byte, error) {
 		}
 		return nil, err
 	}
-	b, ok := secret.Data[string(id)]
+	b, ok := secret.Data[sanitizeKey(id)]
 	if !ok {
 		return nil, ipn.ErrStateNotExist
 	}
 	return b, nil
 }
 
+func sanitizeKey(k ipn.StateKey) string {
+	// The only valid characters in a Kubernetes secret key are alphanumeric, -,
+	// _, and .
+	return strings.Map(func(r rune) rune {
+		if r >= 'a' && r <= 'z' || r >= 'A' && r <= 'Z' || r >= '0' && r <= '9' || r == '-' || r == '_' || r == '.' {
+			return r
+		}
+		return '_'
+	}, string(k))
+}
+
 // WriteState implements the StateStore interface.
 func (s *Store) WriteState(id ipn.StateKey, bs []byte) error {
 	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
@@ -70,13 +82,13 @@ func (s *Store) WriteState(id ipn.StateKey, bs []byte) error {
 					Name: s.secretName,
 				},
 				Data: map[string][]byte{
-					string(id): bs,
+					sanitizeKey(id): bs,
 				},
 			})
 		}
 		return err
 	}
-	secret.Data[string(id)] = bs
+	secret.Data[sanitizeKey(id)] = bs
 	if err := s.client.UpdateSecret(ctx, secret); err != nil {
 		return err
 	}