Add timeout for rexec's get_password (sonic-net#3484)

### What I did

I added a timeout setting for the get_password function in rexec module so that automatic pipelines that does not expect password input will not get blocked. The current timeout setting is 10 sec.

#### How I did it

Add a SIGALRM signal before waiting for password input. 

#### How to verify it

Run a "show ip bgp summary" on SONiC Chassis Supversior and does not input password until it times out.

#### Previous command output (if the output of a command-line utility has changed)

Before adding such a mechanism, if you do not input password when run "rexec -c <cmd>" you will be blocked at the following output:
```
Since the current device is a chassis supervisor, this command will be executed remotely on all linecards
Password for username 'XXX':
```

#### New command output (if the output of a command-line utility has changed)
After adding such a mechanism, if you do not input password when run "rexec -c <cmd>" you will see a timeout message after 10 seconds.
```
Since the current device is a chassis supervisor, this command will be executed remotely on all linecards
Password for username 'XXX': 
Aborted! Timeout when waiting for password input.
```

rcli/utils.py

@@ -1,7 +1,7 @@
 import click
-from getpass import getpass
+import getpass
 import os
-import sys
+import signal
 
 from swsscommon.swsscommon import SonicV2Connector
 
@@ -19,6 +19,8 @@
 CHASSIS_MODULE_HOSTNAME_TABLE = 'CHASSIS_MODULE_HOSTNAME_TABLE'
 CHASSIS_MODULE_HOSTNAME = 'module_hostname'
 
+GET_PASSWORD_TIMEOUT = 10
+
 def connect_to_chassis_state_db():
     chassis_state_db = SonicV2Connector(host="127.0.0.1")
     chassis_state_db.connect(chassis_state_db.CHASSIS_STATE_DB)
@@ -151,8 +153,17 @@ def get_password(username=None):
     if username is None:
         username = os.getlogin()
 
-    return getpass(
+    def get_password_timeout(*args):
+        print("\nAborted! Timeout when waiting for password input.")
+        exit(1)
+
+    signal.signal(signal.SIGALRM, get_password_timeout)
+    signal.alarm(GET_PASSWORD_TIMEOUT)  # Set a timeout of 60 seconds
+    password = getpass.getpass(
         "Password for username '{}': ".format(username),
         # Pass in click stdout stream - this is similar to using click.echo
         stream=click.get_text_stream('stdout')
     )
+    signal.alarm(0)  # Cancel the alarm
+
+    return password

tests/remote_cli_test.py

@@ -11,6 +11,7 @@
 import select
 import socket
 import termios
+import getpass
 
 MULTI_LC_REXEC_OUTPUT = '''======== LINE-CARD0|sonic-lc1 output: ========
 hello world
@@ -75,17 +76,27 @@ def mock_paramiko_connection(channel):
     return conn
 
 
+def mock_getpass(prompt="Password:", stream=None):
+    return "dummy"
+
+
 class TestRemoteExec(object):
+    __getpass = getpass.getpass
+
     @classmethod
     def setup_class(cls):
         print("SETUP")
         from .mock_tables import dbconnector
         dbconnector.load_database_config()
+        getpass.getpass = mock_getpass
+
+    @classmethod
+    def teardown_class(cls):
+        print("TEARDOWN")
+        getpass.getpass = TestRemoteExec.__getpass
 
     @mock.patch("sonic_py_common.device_info.is_chassis", mock.MagicMock(return_value=True))
     @mock.patch("os.getlogin", mock.MagicMock(return_value="admin"))
-    @mock.patch("rcli.utils.get_password", mock.MagicMock(return_value="dummy"))
-    # @mock.patch.object(linecard.Linecard, '_get_password', mock.MagicMock(return_value='dummmy'))
     @mock.patch.object(paramiko.SSHClient, 'connect', mock.MagicMock())
     @mock.patch.object(paramiko.SSHClient, 'exec_command', mock.MagicMock(return_value=mock_exec_command()))
     def test_rexec_with_module_name(self):
@@ -98,7 +109,6 @@ def test_rexec_with_module_name(self):
 
     @mock.patch("sonic_py_common.device_info.is_chassis", mock.MagicMock(return_value=True))
     @mock.patch("os.getlogin", mock.MagicMock(return_value="admin"))
-    @mock.patch("rcli.utils.get_password", mock.MagicMock(return_value="dummy"))
     @mock.patch.object(paramiko.SSHClient, 'connect', mock.MagicMock())
     @mock.patch.object(paramiko.SSHClient, 'exec_command', mock.MagicMock(return_value=mock_exec_command()))
     def test_rexec_with_hostname(self):
@@ -111,7 +121,6 @@ def test_rexec_with_hostname(self):
 
     @mock.patch("sonic_py_common.device_info.is_chassis", mock.MagicMock(return_value=True))
     @mock.patch("os.getlogin", mock.MagicMock(return_value="admin"))
-    @mock.patch("rcli.utils.get_password", mock.MagicMock(return_value="dummy"))
     @mock.patch.object(paramiko.SSHClient, 'connect', mock.MagicMock())
     @mock.patch.object(paramiko.SSHClient, 'exec_command', mock.MagicMock(return_value=mock_exec_error_cmd()))
     def test_rexec_error_with_module_name(self):
@@ -133,7 +142,6 @@ def test_rexec_error(self):
 
     @mock.patch("sonic_py_common.device_info.is_chassis", mock.MagicMock(return_value=True))
     @mock.patch("os.getlogin", mock.MagicMock(return_value="admin"))
-    @mock.patch("rcli.utils.get_password", mock.MagicMock(return_value="dummy"))
     @mock.patch.object(paramiko.SSHClient, 'connect', mock.MagicMock())
     @mock.patch.object(linecard.Linecard, 'execute_cmd', mock.MagicMock(return_value="hello world"))
     def test_rexec_all(self):
@@ -147,7 +155,6 @@ def test_rexec_all(self):
 
     @mock.patch("sonic_py_common.device_info.is_chassis", mock.MagicMock(return_value=True))
     @mock.patch("os.getlogin", mock.MagicMock(return_value="admin"))
-    @mock.patch("rcli.utils.get_password", mock.MagicMock(return_value="dummy"))
     @mock.patch.object(paramiko.SSHClient, 'connect', mock.MagicMock())
     @mock.patch.object(linecard.Linecard, 'execute_cmd', mock.MagicMock(return_value="hello world"))
     def test_rexec_invalid_lc(self):
@@ -161,7 +168,6 @@ def test_rexec_invalid_lc(self):
 
     @mock.patch("sonic_py_common.device_info.is_chassis", mock.MagicMock(return_value=True))
     @mock.patch("os.getlogin", mock.MagicMock(return_value="admin"))
-    @mock.patch("rcli.utils.get_password", mock.MagicMock(return_value="dummy"))
     @mock.patch.object(paramiko.SSHClient, 'connect', mock.MagicMock())
     @mock.patch.object(linecard.Linecard, 'execute_cmd', mock.MagicMock(return_value="hello world"))
     def test_rexec_unreachable_lc(self):
@@ -175,7 +181,6 @@ def test_rexec_unreachable_lc(self):
 
     @mock.patch("sonic_py_common.device_info.is_chassis", mock.MagicMock(return_value=True))
     @mock.patch("os.getlogin", mock.MagicMock(return_value="admin"))
-    @mock.patch("rcli.utils.get_password", mock.MagicMock(return_value="dummy"))
     @mock.patch.object(paramiko.SSHClient, 'connect', mock.MagicMock())
     @mock.patch.object(linecard.Linecard, 'execute_cmd', mock.MagicMock(return_value="hello world"))
     def test_rexec_help(self):
@@ -188,7 +193,6 @@ def test_rexec_help(self):
 
     @mock.patch("sonic_py_common.device_info.is_chassis", mock.MagicMock(return_value=True))
     @mock.patch("os.getlogin", mock.MagicMock(return_value="admin"))
-    @mock.patch("rcli.utils.get_password", mock.MagicMock(return_value="dummy"))
     @mock.patch.object(paramiko.SSHClient, 'connect', mock.MagicMock(side_effect=paramiko.ssh_exception.NoValidConnectionsError({('192.168.0.1',
                                                                                                                                   22): "None"})))
     @mock.patch.object(linecard.Linecard, 'execute_cmd', mock.MagicMock(return_value="hello world"))
@@ -202,7 +206,6 @@ def test_rexec_exception(self):
         assert "Failed to connect to sonic-lc1 with username admin\n" == result.output
 
     @mock.patch("sonic_py_common.device_info.is_chassis", mock.MagicMock(return_value=True))
-    @mock.patch("rcli.utils.get_password", mock.MagicMock(return_value="dummy"))
     @mock.patch.object(paramiko.SSHClient, 'connect', mock.MagicMock(side_effect=paramiko.ssh_exception.NoValidConnectionsError({('192.168.0.1',
                                                                                                                                   22): "None"})))
     def test_rexec_with_user_param(self):
@@ -214,6 +217,19 @@ def test_rexec_with_user_param(self):
         assert result.exit_code == 1, result.output
         assert "Failed to connect to sonic-lc1 with username testuser\n" == result.output
 
+    @mock.patch("sonic_py_common.device_info.is_chassis", mock.MagicMock(return_value=True))
+    @mock.patch("os.getlogin", mock.MagicMock(return_value="admin"))
+    def test_rexec_without_password_input(self):
+        runner = CliRunner()
+        getpass.getpass = TestRemoteExec.__getpass
+        LINECARD_NAME = "all"
+        result = runner.invoke(
+            rexec.cli, [LINECARD_NAME, "-c", "show version"])
+        getpass.getpass = mock_getpass
+        print(result.output)
+        assert result.exit_code == 1, result.output
+        assert "Aborted" in result.output
+
 
 class TestRemoteCLI(object):
     @classmethod