fs/cifs: correctly to anonymous authentication for the NTLM(v2) authentication

Only server which map unknown users to guest will allow
access using a non-null NTLMv2_Response.

For Samba it's the "map to guest = bad user" option.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11913

Signed-off-by: Stefan Metzmacher <metze@samba.org>
CC: Stable <stable@vger.kernel.org>
Signed-off-by: Steve French <smfrench@gmail.com>

fs/cifs/sess.c

@@ -895,22 +895,26 @@ sess_auth_ntlmv2(struct sess_data *sess_data)
 	/* LM2 password would be here if we supported it */
 	pSMB->req_no_secext.CaseInsensitivePasswordLength = 0;
 
-	/* calculate nlmv2 response and session key */
-	rc = setup_ntlmv2_rsp(ses, sess_data->nls_cp);
-	if (rc) {
-		cifs_dbg(VFS, "Error %d during NTLMv2 authentication\n", rc);
-		goto out;
-	}
+	if (ses->user_name != NULL) {
+		/* calculate nlmv2 response and session key */
+		rc = setup_ntlmv2_rsp(ses, sess_data->nls_cp);
+		if (rc) {
+			cifs_dbg(VFS, "Error %d during NTLMv2 authentication\n", rc);
+			goto out;
+		}
 
-	memcpy(bcc_ptr, ses->auth_key.response + CIFS_SESS_KEY_SIZE,
-			ses->auth_key.len - CIFS_SESS_KEY_SIZE);
-	bcc_ptr += ses->auth_key.len - CIFS_SESS_KEY_SIZE;
+		memcpy(bcc_ptr, ses->auth_key.response + CIFS_SESS_KEY_SIZE,
+				ses->auth_key.len - CIFS_SESS_KEY_SIZE);
+		bcc_ptr += ses->auth_key.len - CIFS_SESS_KEY_SIZE;
 
-	/* set case sensitive password length after tilen may get
-	 * assigned, tilen is 0 otherwise.
-	 */
-	pSMB->req_no_secext.CaseSensitivePasswordLength =
-		cpu_to_le16(ses->auth_key.len - CIFS_SESS_KEY_SIZE);
+		/* set case sensitive password length after tilen may get
+		 * assigned, tilen is 0 otherwise.
+		 */
+		pSMB->req_no_secext.CaseSensitivePasswordLength =
+			cpu_to_le16(ses->auth_key.len - CIFS_SESS_KEY_SIZE);
+	} else {
+		pSMB->req_no_secext.CaseSensitivePasswordLength = 0;
+	}
 
 	if (ses->capabilities & CAP_UNICODE) {
 		if (sess_data->iov[0].iov_len % 2) {