NAME

Arc::Connection::Server - Class to handle one connection on the server side

DESCRIPTION

ARC allows non-privileged users to run privileged commands on the server. The server decides if the user is allowed to run this command through ACL.

This file is a part of the Perl ARCv2 module suite. ARCv2 is a rewrite of ARC by R.Toebbicke, CERN, Switzerland in Perl.

ABSTRACT

From ARC by R. Toebbicke, modified by me: User requests are shipped from a client machine to a server using a SASL-authenticated socket connection. The purpose is to convey requests such as privileged commands (e.g. AFS, Crontab) to be executed on the server under appropriate privileges. Given that all privileges are confined to the server and the server can be programmed as to filter and check the command to be executed, the client machine can be less trusted than the server.

Because ARC-v1-Commands are written in perl anyway, implementing the client/server in perl makes sense. Platform-independence and "easy-to-read" source code are welcome too. This package provides two perl command line scripts (arcx, arcxd). They can be used for working with the ARC server from the command line, resp. to start the server.

SYNOPSIS

Arc::Connection::Server - Server handle for ARCv2. This class is called by Arc::Server for each incoming connection.

Class VARIABLES

PUBLIC MEMBERS

commands

Description: hash of assignment between Command Name and Command Class. See Arc::Command

Default value: undef

logfileprefix reimplemented from Arc

Default value: "server"

sasl_cb_checkpass

Description: Callback for SASL (if PLAIN (or equal) mechanisms are used). See Authen::SASL(::Cyrus).

sasl_cb_getsecret

Description: Callback for SASL (if PLAIN (or equal) mechanisms are used). See Authen::SASL(::Cyrus).

Default value: ""

sasl_mechanisms

Description: array of allowed SASL mechanisms

Default value: undef

protocol inherited from Arc::Connection

Description: Which protocol is used (0 = ARC/2.0, 1 = ARC/2.1)

Default value: undef

service inherited from Arc::Connection

Description: name of the server (for SASL)

Default value: undef

timeout inherited from Arc::Connection

Description: timeout for all connections (ARCv2 and command) in seconds

Default value: undef

logdestination inherited from Arc

Description: Where should all the log output go to ('stderr','syslog')

Default value: 'syslog'

loglevel inherited from Arc

Description: loglevel is combination of bits (1=AUTH,2=USER,4=ERR,8=CMDDEBUG,16=VERBSIDE,32=DEBUG) see _Log method

Default value: 7

PROTECTED MEMBERS

_realm

Description: Name of the SASL realm, if the user is from the default realm, this is empty

Default value: ""

_authenticated inherited from Arc::Connection

Description: Are we authenticated

_cmdclientsock inherited from Arc::Connection

Description: IO::Socket for the command connection (encrypted)

Default value: undef

_cmdparameter inherited from Arc::Connection

Description: parameter after the command

Default value: undef

_connected inherited from Arc::Connection

Description: are we connected

_connection inherited from Arc::Connection

Description: IO::Socket for the ARCv2 Connection

Default value: undef

_expectedcmds inherited from Arc::Connection

Description: array, which ARCv2 protocol commands are allowed to come next

Default value: undef

_select inherited from Arc::Connection

Description: IO::Select for the ARCv2 Connection

Default value: undef

_username inherited from Arc::Connection

Description: username extracted from SASL

Default value: "anonymous"

_error inherited from Arc

Description: contains the error message

Default value: undef

_syslog inherited from Arc

Description: log to syslog or to STDERR

Default value: 1

PRIVATE MEMBERS

Class METHODS

PUBLIC METHODS

HandleClient ( $clientsock (IO::Socket) )

Description: Public function, gets the clientsocket (from Arc::Server) and handles it. Handles a connection (main loop).

Returns: true on success, otherwise false

Example:

$arc->HandleClient(sock);

Quit ( )

Description: Ends the connection. Do some cleanup.

Returns: always true

Example:

$arc->Quit();

tonne ( )

Description: See source code for this method. /dev/null for unwanted output.

clean ( ) inherited from Arc::Connection

IsConnected ( ) inherited from Arc::Connection

Description: are we connected?

Returns: true, if the ARCv2 control connection is connected, otherwise false

Example:

last unless $arc->IsConnected;

DESTROY ( ) inherited from Arc

Description: Destructor

IsError ( ) inherited from Arc

Description: User function to get the error msg.

Returns: the error message if any otherwise undef

Example:

unless (my $err = $arc->IsError()) { .. } else { print STDERR $err; }

Log ( $facility, ... (message) ) inherited from Arc

Description: Log function. Logs messages to 'logdestination' if 'loglevel' is is set appropriatly. loglevel behaviour has changed in the 1.0 release of ARCv2, the "Arc"-class can export LOG_AUTH (authentication information), LOG_USER (connection information), LOG_ERR (errors), LOG_CMD (ARCv2 addition internal command information), LOG_SIDE (verbose client/server-specific information), LOG_DEBUG (verbose debug information). It possible to combine the levels with or (resp. +) to allow a message to appear when not all loglevels are requested by the user. Commonly used for logging errors from application level.

Returns: always false

Example:

return $arc->Log(LOG_ERR,"Message");

new ( %hash, key => val, ... ) inherited from Arc

Description: Constructor. Initializes the object and returns it blessed. For all sub classes, please override _Init to check the parameter which are passed to the new function. This is necessary because you are not able to call the the new method of a parent class, when having a class name (new $class::SUPER::new, does not work.).

Returns: blessed object of the class

Example:

my $this = new Arc::Class ( key => value, key2 => value2 );

PROTECTED METHODS

_Auth ( )

Description: send the available SASL mechanisms. Protocol command: AUTH <comma-seperated list of SASL mechansims>\r\n

Returns: true when succesful, otherwise false

Example:

$this->_Auth();

_Authtype ( )

Description: tell the client, which SASL mechanism is used. Protocol command: AUTHTYPE <SASL mechansism>\r\n

Returns: true when succesful, otherwise false

Example:

$this->_Authtype();

_CBCanonUser ( )

Description: Callback function to canonicalize the username (SASL) see Authen::SASL(::Cyrus) for parameter list and how to use.

_CheckCmd ( )

_CmdError ( )

Description: send a command error msg to client. Protocol command: CMDERR <msg>\r\n

Returns: true when succesful, otherwise false

Example:

$this->_CmdError("failure.");

_Done ( )

Description: command is ready. When the ARCv2 command is ready with its work, the server sends the DONE command on the control connection. Protocol command: DONE\r\n

Returns: true when succesful, otherwise false

Example:

$this->_Done();

_Error ( )

Description: send an error msg to client (Server error). Protocol command: ERR <msg>\r\n

Returns: true when succesful, otherwise false

Example:

$this->_Error("failure.");

_Init ( ) reimplemented from Arc::Connection

_RAUTHENTICATE ( )

Description: parses the AUTHENTICATE[ <SASL mech>]\r\n, sent by the client. Checks if the demanded SASL mechanism is allowed and returns the selected mechanism.

_RCMD ( )

Description: parses the CMD <cmd>\r\n, sent by the client. check if the command exists, prepares the command connection, executes the command and does cleanups after execution.

_RQUIT ( )

Description: does nothing, placeholder for QUIT\r\n command, sent by the client.

_RSASL ( )

Description: parses the SASL <base64 encoded SASL string>\r\n, sent by the client. Sasl challenge/response from the client

_RunCmd ( )

_SplitCmdArgs ( )

_StartAuthentication ( )

Description: Creates the sasl object (server_new) and sends the first sasl challenge/response. Protocol command: SASL <base64 encoded SASL output>\r\n

Returns: true when succesful, otherwise false

Example:

$this->_StartAuthentication();

_StepAuthentication ( bool $first_step )

Description: Another SASL step Response of a SASL command from the client Protocol command: SASL <base64 encoded SASL outout>\r\n

Returns: true when succesful, otherwise false

Example:

$this->_StepAuthentication(1);

_CommandConnection ( ) inherited from Arc::Connection

Description: initializes command connection. (protocol) Starts listen on the Command socket and sends the CMDPASV command.

Returns: true if everything went like expected, otherwise false.

Example:

$this->_CommandConnection();

_PrepareAuthentication ( ) inherited from Arc::Connection

Description: initialize sasl. This function initializes the __sasl member with an object of Authen::SASL.

Returns: true if successful, otherwise false

Example:

$this->_PrepareAuthentication() || return;

_ProcessLine ( $cmd ) inherited from Arc::Connection

Description: process an ARCv2 command. (protocol) Process a command by evaling $this->_R$cmd. Also checks if this command was expected now (looks into the $this->{_expectedcmds} array). Used by client and server.

Returns: true, if ARCv2 command has been in place, otherwise false

Example:

while (my $cmd = $this->_RecvCommand() && $this->_ProcessLine($cmd)) {}

_ReadWriteBinary ( *locfdin, *locfdout ) inherited from Arc::Connection

Description: function for reading and writing on the command connection. This function is always used by the Arc::Connection::Server to handle command data. When calling the ProcessCommand from Arc::Connection::Client this function is also used. Data is read from the local socket resp. pipe and is written encrypted to the network socket. The other side reads the data from network socket, decrypts it and writes it to its local socket. This function behaves differently on client and server sides, when the local or network socket is closed.

Returns: always true

Example:

$this->ReadWriteBinary(*STDIN,*STDOUT);

_RecvCommand ( ) inherited from Arc::Connection

Description: receives an ARCv2 Command. (protocol) This function gets a line from _RecvLine and extracts the ARCv2 command and the optional command parameter _cmdparameter.

Returns: ARCv2 command and true if everything works fine, otherwise false

Example:

while (my $cmd = $this->_RecvCommand()) { ... }

_RecvLine ( ) inherited from Arc::Connection

Description: receive a line (command). (protocol) This function receives data from the ARCv2 connection and fills the internal __linequeue and __partial. It returns a line from the internal buffer if there is any. It also handles timeouts and "connection closed by foreign host"'s.

Returns: true (and the line) if everything worked fine, otherwise false (undef)

Example:

if (my $line = $this->_RecvLine()) { ... }

_Sasl ( $saslstr ) inherited from Arc::Connection

Description: send the ARCv2 SASL command. (protocol) This function encodes the output from sasl_*_start and sasl_*_step with Base-64 and sends it to the other side

Returns: true if successful, otherwise false

Example:

$this->_Sasl($sasl->client_start());

_SendCommand ( $cmd, $parameter ) inherited from Arc::Connection

Description: send a command. (protocol) Send a command to the ARCv2 socket.

Returns: true if successful, otherwise false

Example:

$this->_SendCommand("CMDPASV",$consock->sockhost.':'.$consock->sockport);

_SendLine ( ... (line) ) inherited from Arc::Connection

Description: send a line. (protocol) This function sends a command line to the ARCv2 socket.

Returns: true if writing has succeeded, otherwise false.

Example:

$this->_SendLine($cmd,"test");

_Debug ( ... (message) ) inherited from Arc

Description: Debug function. Logs messages with "DEBUG"

Returns: always false

Example:

$this->_Debug("hello","world"); # message will be "hello world"

_SetError ( ... (message) ) inherited from Arc

Description: SetError function. This function prepends the error message (@_) to an existing error message (if any) and logs the message with LOG_ERR facility. Use this function for setting an error from class level. Users should use IsError to get the message if a function failed.

Returns: always false

Example:

return $this->_SetError("User is not allowed to do this."); # breaks when an error occured

PRIVATE METHODS

SEE ALSO

Arc, Arc::Command, Arc::Connection, Arc::Connection::Server, Arc::Connection::Client, arcx, arcxd, Authen::SASL, Authen::SASL::Cyrus Net::Server::PreFork

AUTHOR

Patrick Boettcher <patrick.boettcher@desy.de>

COPYRIGHT AND LICENSE

Copyright (c) 2003-5 Patrick Boettcher <patrick.boettcher@desy.de> and others. All rights reserved. Zeuthen, Germany, (old) Europe

This program is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.

Special thanks go to:
DESY Zeuthen, in particular:

- Wolfgang Friebel for bleeding edge testing and heavy bug reporting (and the idea of reimplementing ARC).

- Waltraut Niepraschk and Andreas Haupt for their help and support during the development.

cpanm Arc

perl -MCPAN -e shell
install Arc