cifs: Add minor debug message during negprot

Check for unknown security mode flags during negotiate protocol
if debugging enabled.
Signed-off-by: Steve French <smfrench@gmail.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>

fs/cifs/smb2pdu.c

@@ -584,8 +584,10 @@ SMB2_negotiate(const unsigned int xid, struct cifs_ses *ses)
 			       SMB2_MAX_BUFFER_SIZE);
 	server->max_read = le32_to_cpu(rsp->MaxReadSize);
 	server->max_write = le32_to_cpu(rsp->MaxWriteSize);
-	/* BB Do we need to validate the SecurityMode? */
 	server->sec_mode = le16_to_cpu(rsp->SecurityMode);
+	if ((server->sec_mode & SMB2_SEC_MODE_FLAGS_ALL) != server->sec_mode)
+		cifs_dbg(FYI, "Server returned unexpected security mode 0x%x\n",
+				server->sec_mode);
 	server->capabilities = le32_to_cpu(rsp->Capabilities);
 	/* Internal types */
 	server->capabilities |= SMB2_NT_FIND | SMB2_LARGE_FILES;

fs/cifs/smb2pdu.h

@@ -249,6 +249,8 @@ struct smb2_negotiate_req {
 /* SecurityMode flags */
 #define	SMB2_NEGOTIATE_SIGNING_ENABLED	0x0001
 #define SMB2_NEGOTIATE_SIGNING_REQUIRED	0x0002
+#define SMB2_SEC_MODE_FLAGS_ALL		0x0003
+
 /* Capabilities flags */
 #define SMB2_GLOBAL_CAP_DFS		0x00000001
 #define SMB2_GLOBAL_CAP_LEASING		0x00000002 /* Resp only New to SMB2.1 */