cifs: release auth_key.response for reconnect.

There is a race that cause cifs reconnect in cifs_mount,
- cifs_mount
  - cifs_get_tcp_session
    - [ start thread cifs_demultiplex_thread
      - cifs_read_from_socket: -ECONNABORTED
        - DELAY_WORK smb2_reconnect_server ]
  - cifs_setup_session
  - [ smb2_reconnect_server ]

auth_key.response was allocated in cifs_setup_session, and
will release when the session destoried. So when session re-
connect, auth_key.response should be check and released.

Tested with my system:
CIFS VFS: Free previous auth_key.response = ffff8800320bbf80

A simple auth_key.response allocation call trace:
- cifs_setup_session
- SMB2_sess_setup
- SMB2_sess_auth_rawntlmssp_authenticate
- build_ntlmssp_auth_blob
- setup_ntlmv2_rsp

Signed-off-by: Shu Wang <shuwang@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>
CC: Stable <stable@vger.kernel.org>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>

fs/cifs/connect.c

@@ -4154,6 +4154,14 @@ cifs_setup_session(const unsigned int xid, struct cifs_ses *ses,
 	cifs_dbg(FYI, "Security Mode: 0x%x Capabilities: 0x%x TimeAdjust: %d\n",
 		 server->sec_mode, server->capabilities, server->timeAdj);
 
+	if (ses->auth_key.response) {
+		cifs_dbg(VFS, "Free previous auth_key.response = %p\n",
+			 ses->auth_key.response);
+		kfree(ses->auth_key.response);
+		ses->auth_key.response = NULL;
+		ses->auth_key.len = 0;
+	}
+
 	if (server->ops->sess_setup)
 		rc = server->ops->sess_setup(xid, ses, nls_info);