smb: fix Kerberos credentials being reloaded for every connection - fixes #9674

A new KerberosFactory was constructed for every dial, so the client,
error and ccache modification time caches it holds were discarded
after a single use. Every new SMB connection re-read the Kerberos
config, re-parsed the ccache and did a fresh KDC exchange.

Share a single factory so clients are cached across connections as
intended, and refreshed when the ccache file changes.

backend/smb/connpool.go

@@ -38,7 +38,7 @@ func (f *Fs) dial(ctx context.Context, network, addr string) (*conn, error) {
 
 	d := &smb2.Dialer{}
 	if f.opt.UseKerberos {
-		cl, err := NewKerberosFactory().GetClient(f.opt.KerberosCCache)
+		cl, err := kerberosFactory.GetClient(f.opt.KerberosCCache)
 		if err != nil {
 			return nil, err
 		}

backend/smb/kerberos.go

@@ -33,6 +33,9 @@ type KerberosFactory struct {
 	loadConfig func() (*config.Config, error)
 }
 
+// kerberosFactory is the shared KerberosFactory used to cache all connections
+var kerberosFactory = NewKerberosFactory()
+
 // NewKerberosFactory creates a new instance of KerberosFactory with default dependencies.
 func NewKerberosFactory() *KerberosFactory {
 	return &KerberosFactory{