cifs: fix double free on failed kerberos auth

If session setup failed with kerberos auth, we ended up freeing
cifs_ses::auth_key.response twice in SMB2_auth_kerberos() and
sesInfoFree().

Fix this by zeroing out cifs_ses::auth_key.response after freeing it
in SMB2_auth_kerberos().

Fixes: a4e430c ("cifs: replace kfree() with kfree_sensitive() for sensitive data")
Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Acked-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2pdu.c

@@ -1482,8 +1482,11 @@ SMB2_auth_kerberos(struct SMB2_sess_data *sess_data)
 out_put_spnego_key:
 	key_invalidate(spnego_key);
 	key_put(spnego_key);
-	if (rc)
+	if (rc) {
 		kfree_sensitive(ses->auth_key.response);
+		ses->auth_key.response = NULL;
+		ses->auth_key.len = 0;
+	}
 out:
 	sess_data->result = rc;
 	sess_data->func = NULL;