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rfc:rfc2593

Network Working Group J. Schoenwaelder Request for Comments: 2593 TU Braunschweig Category: Experimental J. Quittek

                                                       NEC Europe Ltd.
                                                              May 1999
           Script MIB Extensibility Protocol Version 1.0

Status of this Memo

 This memo defines an Experimental Protocol for the Internet
 community.  It does not specify an Internet standard of any kind.
 Discussion and suggestions for improvement are requested.
 Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (1999).  All Rights Reserved.

Abstract

 The IETF Script MIB defines an interface for the delegation of
 management functions based on the Internet management framework. A
 management script is a set of instructions that are executed by a
 language specific runtime system. The Script MIB extensibility
 protocol (SMX) defined in this memo separates language specific
 runtime systems from language independent Script MIB implementations.

Table of Contents

 1. Introduction ................................................    2
 2. Process Model and Communication Model .......................    3
 3. Security Profiles ...........................................    3
 4. Start of Runtime Systems and Connection Establishment .......    4
 5. SMX Messages ................................................    5
 5.1 Common Definitions .........................................    5
 5.2 Commands ...................................................    7
 5.3 Replies ....................................................    8
 6. Elements of Procedure .......................................    9
 6.1 SMX Message Processing on the Runtime Systems ..............    9
 6.1.1 Processing the `hello' Command ...........................   10
 6.1.2 Processing the `start' Command ...........................   10
 6.1.3 Processing the `suspend' Command .........................   11
 6.1.4 Processing the `resume' Command ..........................   12
 6.1.5 Processing the `abort' Command ...........................   12
 6.1.6 Processing the `status' Command ..........................   12
 6.1.7 Generation of Asynchronous Notifications .................   13

Schoenwaelder & Quittek Experimental [Page 1] RFC 2593 SMX Protocol 1.0 May 1999

 6.2 SMX Message Processing on the SNMP Agent ...................   13
 6.2.1 Creating a Runtime System ................................   13
 6.2.2 Generating the `hello' Command ...........................   13
 6.2.3 Generating the `start' Command ...........................   14
 6.2.4 Generating the `suspend' Command .........................   15
 6.2.5 Generating the `resume' Command ..........................   16
 6.2.6 Generating the `abort' Command ...........................   16
 6.2.7 Generating the `status' Command ..........................   17
 6.2.8 Processing Asynchronous Notifications ....................   18
 7. An Example SMX Message Flow .................................   19
 8. Security Considerations .....................................   19
 9. Acknowledgments .............................................   20
 10. References .................................................   20
 11. Authors' Addresses .........................................   21
 12. Full Copyright Statement ...................................   22

1. Introduction

 The Script MIB [1] defines a standard interface for the delegation of
 management functions based on the Internet management framework. In
 particular, it provides the following capabilities:
 1.   Transfer of management scripts to a distributed manager.
 2.   Initiating, suspending, resuming and terminating management
      scripts.
 3.   Transfer of arguments for management scripts.
 4.   Monitoring and control of running management scripts.
 5.   Transfer of results produced by management scripts.
 A management script is a set of instructions executed by a language
 specific runtime system. The Script MIB does not prescribe a specific
 language. Instead, it allows to control scripts written in different
 languages that are executing concurrently.
 The Script MIB Extensibility protocol (SMX) defined in this memo can
 be used to separate language specific runtime systems from the
 runtime system independent Script MIB implementations. The
 lightweight SMX protocol can be used to support different runtime
 systems without any changes to the language neutral part of a Script
 MIB implementation.
 Examples of languages and runtime systems considered during the
 design of the SMX protocol are the Java virtual machine [2] and the
 Tool Command Language (Tcl) [3]. Other languages with comparable

Schoenwaelder & Quittek Experimental [Page 2] RFC 2593 SMX Protocol 1.0 May 1999

 features should be easy to integrate as well.

2. Process Model and Communication Model

 Figure 1 shows the process and communication model underlying the SMX
 protocol. The language and runtime system independent SNMP agent
 implementing the Script MIB communicates with one ore more runtime
 systems via the SMX protocol. A runtime system may be able to execute
 one or multiple scripts simultaneously (multi-threading). The SMX
 protocol supports multi-threading, but it does not require multi-
 threaded runtime systems.
 The SMX protocol uses a local storage device (usually implemented on
 top of the local file system) to transfer scripts from the SNMP agent
 to the runtime systems. The SNMP agent has read and write access to
 the script storage device while the runtime systems only need read
 access. The SMX protocol passes the location of a script in the local
 storage device to the runtime engines. It is then the responsibility
 of the runtime engines to load the script from the specified
 location.
                                                  runtime 1
                 +--------------+       SMX      +---------+
                 |              |<-------------->| O  O  O |<-+
         SNMP    |  Script MIB  |                +---------+  |
     <---------->|              |                             |
                 |  SNMP Agent  |                 runtime 2   |
                 |              |       SMX      +---------+  |
                 |              |<-------------->| O       |  |
                 +--------------+                +---------+  |
                         ^                            ^       |
                         |       +---------+          |       |
                         |       | script  |----------+       |
                         +------>| storage |------------------+
                                 +---------+
         Figure 1: SMX process and communication model

3. Security Profiles

 Security profiles control what a running script is allowed to do. It
 is useful to distinguish two different classes of security profiles:
  1. The operating system security profile specifies the set of

operating system services that can be used by the operating

      system level process which executes a script. Under UNIX, this
      maps to the effective user and group identity for the running

Schoenwaelder & Quittek Experimental [Page 3] RFC 2593 SMX Protocol 1.0 May 1999

      process. In addition, many UNIX versions allow to set other
      resource limits, such as the number of open files or the maximum
      stack sizes. Another mechanism in UNIX is the chroot() system
      call which changes the file system root for a process. The
      chroot() mechanism can be used to prevent runtime systems from
      accessing any system files. It is suggested to make use of all
      applicable operating system security mechanism in order to
      protect the operating system from malicious scripts or runtime
      systems.
  1. Secure runtime systems provide fine grained control over the set

of services that can be used by a running script at a particular

      point during script execution. A runtime security profile
      specifying fine grained access control is runtime system
      dependent. For a Java virtual machine, the runtime security
      profile is interpreted by the SecurityManager and ClassLoader
      classes[4]. For Tcl, the runtime security profile maps to the
      interpreter's security profile [5].
 The SMX protocol allows to execute scripts under different operating
 system profiles and runtime system profiles. Multiple operating
 system security profiles are realized by using multiple runtime
 systems which execute in operating system processes with different
 security profiles.  Multiple runtime security profiles are supported
 by passing a security profile name to a runtime system during script
 invocation.
 The Script MIB does not define how operating system or runtime system
 security profiles are identified. This memo suggests that the
 smLaunchOwner is mapped to an operating system security profile and a
 runtime system security profile when a script is started.

4. Start of Runtime Systems and Connection Establishment

 The SNMP agent starts runtime systems based on the static properties
 of the runtime system (multi-threaded or single-threaded) and the
 operating system security profiles. Starting a new runtime system
 requires to create a process environment which matches the operating
 system security profile.
 The SNMP agent initially passes information to the runtime system by
 means of environment variables. The information is needed to
 establish a trusted communication channel between the SNMP agent and
 a runtime system.
 The SNMP agent first creates a listening TCP socket which accepts
 connections from runtime systems. It is the responsibility of the
 runtime system to establish a connection to this TCP socket once it

Schoenwaelder & Quittek Experimental [Page 4] RFC 2593 SMX Protocol 1.0 May 1999

 has been started. The port number of the listening TCP socket is
 passed from the SNMP agent to the runtime system in the environment
 variable SMX_PORT.
 The SNMP agent must ensure that only authorized runtime systems
 establish a connection to the listening TCP socket. The following
 rules are used for this purpose:
  1. The TCP connection must originate from the local host.
  1. The SNMP agent queries the runtime system for a security cookie

and closes the TCP connection if no valid response is received

      within a given time interval. The security cookie is a random
      number generated by the SNMP agent and passed to the runtime
      system as part of its environment. The cookie is found in the
      environment variable SMX_COOKIE.
 The security assumption here is that access to the process
 environment is protected by the operating system.
 Alternate transports (e.g. UNIX domain sockets) are possible but not
 defined at this point in time. The reason to choose TCP as the
 transport protocol for SMX was that TCP is supported by all potential
 runtime systems, while other transports are not universally
 available.

5. SMX Messages

 The message formats described below are defined using the Augmented
 BNF (ABNF) defined in RFC 2234 [6]. The definitions for `ALPHA',
 `DIGIT', `HEXDIG', `WSP', `CRLF', `CR', `LF', `HTAB', `VCHAR' and
 `DQUOTE' are imported from appendix A of RFC 2234 and not repeated
 here.

5.1. Common Definitions

 The following ABNF definitions are used in subsequent sections to
 define the SMX protocol messages.
   Zero          = %x30          ; the ASCII character '0'
   AlNum         = DIGIT / ALPHA / %x2D-2F
                                 ; digits, alphas plus '-', '.', '/'
   QuotedString  = DQUOTE *(VCHAR / WSP) DQUOTE
   HexString     = 1*(HEXDIG HEXDIG)

Schoenwaelder & Quittek Experimental [Page 5] RFC 2593 SMX Protocol 1.0 May 1999

   Id            = 1*DIGIT       ; identifier for an SMX transaction
   Script        = QuotedString  ; script file name
   RunId         = 1*DIGIT       ; globally unique identifier for a
                                 ; running script (note, smRunIndex
                                 ; is only unique for a smLaunchOwner,
                                 ; smLaunchName pair)
   Profile       = 1*AlNum       ; security profile name
   RunState      =  "1"          ; smRunState `initializing'
   RunState      =/ "2"          ; smRunState `executing'
   RunState      =/ "3"          ; smRunState `suspending'
   RunState      =/ "4"          ; smRunState `suspended'
   RunState      =/ "5"          ; smRunState `resuming'
   RunState      =/ "6"          ; smRunState `aborting'
   RunState      =/ "7"          ; smRunState `terminated'
   ExitCode      =  "1"          ; smRunExitCode `noError'
   ExitCode      =/ "2"          ; smRunExitCode `halted'
   ExitCode      =/ "3"          ; smRunExitCode `lifeTimeExceeded'
   ExitCode      =/ "4"          ; smRunExitCode `noResourcesLeft'
   ExitCode      =/ "5"          ; smRunExitCode `languageError'
   ExitCode      =/ "6"          ; smRunExitCode `runtimeError'
   ExitCode      =/ "7"          ; smRunExitCode `invalidArgument'
   ExitCode      =/ "8"          ; smRunExitCode `securityViolation'
   ExitCode      =/ "9"          ; smRunExitCode `genericError'
   Cookie        = HexString     ; authentication cookie
   Version       = "SMX/1.0"     ; current version of the SMX protocol
   Argument      = HexString / QuotedString      ; see smRunArgument
   Result        = HexString / QuotedString      ; see smRunResult
   ErrorMsg      = HexString / QuotedString      ; see smRunError
 The definition of QuotedString requires further explanation. A quoted
 string may contain special character sequences, all starting with the
 backslash character (%x5C). The interpretation of these sequences is
 as follows:

Schoenwaelder & Quittek Experimental [Page 6] RFC 2593 SMX Protocol 1.0 May 1999

         `\\'   backslash character       (`%x5C')
         `\t'   tab character             (`HTAB')
         `\n'   newline character         (`LF')
         `\r'   carriage-return character (`CR')
         `\"'   quote character           (`DQUOTE')
 In all other cases not listed above, the backslash is dropped and the
 following character is treated as an ordinary character.  `Argument'
 and `Result' is either a QuotedString or a HexString.  The Script MIB
 defines script arguments and results as arbitrary octet strings. The
 SMX protocol supports a binary and a human readable representation
 since it is likely that printable argument and result strings will be
 used frequently. However, an implementation must be able to handle
 both formats in order to be compliant with the Script MIB.
 The `Cookie' is a HexString which does not carry any semantics other
 than being a random sequence of bytes. It is therefore not necessary
 to have a human readable representation.

5.2. Commands

 The following ABNF definitions define the set of SMX commands which
 can be sent from the SNMP agent to a runtime system.
   Command =  "hello"   WSP Id CRLF
   Command =/ "start"   WSP Id WSP RunId WSP Script WSP Profile
                        WSP Argument CRLF
   Command =/ "suspend" WSP Id WSP RunId CRLF
   Command =/ "resume"  WSP Id WSP RunId CRLF
   Command =/ "abort"   WSP Id WSP RunId CRLF
   Command =/ "status"  WSP Id WSP RunId CRLF
 The `hello' command is always the first command sent over a SMX
 connection. It is used to identify and authenticate the runtime
 system. The `start' command starts the execution of a script. The
 `suspend', `resume' and `abort' commands can be used to change the
 status of a running script. The `status' command is used to retrieve
 status information for a running script.
 There is no compile command. It is the responsibility of the SNMP
 agent to perform any compilation steps as needed before using the SMX
 `start' command. There is no SMX command to shutdown a runtime
 system. Closing the connection must be interpreted as a request to

Schoenwaelder & Quittek Experimental [Page 7] RFC 2593 SMX Protocol 1.0 May 1999

 terminate all running scripts in that runtime system and to shutdown
 the runtime system.

5.3. Replies

 Every reply message starts with a three digit reply code and ends
 with `CRLF'. The three digits in a reply code have a special meaning.
 The first digit identifies the class of a reply message. The
 following classes exist:
   1yz   transient positive response
   2yz   permanent positive response
   3yz   transient negative response
   4yz   permanent negative response
   5yz   asynchronous notification
 The classes 1yz and 3yz are currently not used by SMX version 1.0.
 They are defined only for future SMX extensions.
 The second digit encodes the specific category. The following
 categories exist:
   x0z   syntax errors that don't fit any other category
   x1z   replies for commands targeted at the whole runtime system
   x2z   replies for commands targeted at scripts
   x3z   replies for commands targeted at running instances of scripts
 The third digit gives a finer gradation of meaning in each category
 specified by the second digit. Below is the ABNF definition of all
 reply messages and codes:
   Reply =  "211" WSP Id WSP Version WSP Cookie CRLF
                                 ; identification of the
                                 ; runtime system
   Reply =/ "231" WSP Id WSP RunState CRLF
                                 ; status of a running script
   Reply =/ "232" WSP Id CRLF    ; abort of a running script
   Reply =/ "401" WSP Id CRLF    ; syntax error in command
   Reply =/ "402" WSP Id CRLF    ; unknown command
   Reply =/ "421" WSP Id CRLF    ; unknown or illegal Script
   Reply =/ "431" WSP Id CRLF    ; unknown or illegal RunId

Schoenwaelder & Quittek Experimental [Page 8] RFC 2593 SMX Protocol 1.0 May 1999

   Reply =/ "432" WSP Id CRLF    ; unknown or illegal Profile
   Reply =/ "433" WSP Id CRLF    ; illegal Argument
   Reply =/ "434" WSP Id CRLF    ; unable to change the status of
                                 ; a running script
   Reply =/ "511" WSP Zero WSP QuotedString CRLF
                                 ; an arbitrary message send from
                                 ; the runtime system
   Reply =/ "531" WSP Zero WSP RunId WSP RunState CRLF
                                 ; asynchronous running script
                                 ; status change
   Reply =/ "532" WSP Zero WSP RunId WSP RunState WSP Result CRLF
                                 ; intermediate script result
   Reply =/ "533" WSP Zero WSP RunId WSP RunState WSP Result CRLF
                                 ; intermediate script result that
                                 ; trigger an event report
   Reply =/ "534" WSP Zero WSP RunId WSP Result CRLF
                                 ; normal script termination
   Reply =/ "535" WSP Zero WSP RunId WSP ExitCode WSP ErrorMsg CRLF
                                 ; abnormal script termination.

6. Elements of Procedure

 This section describes in detail the processing steps performed by
 the SNMP agent and the runtime system with regard to the SMX
 protocol.

6.1. SMX Message Processing on the Runtime Systems

 This section describes the processing of SMX command messages by a
 runtime engine and the conditions under which asynchronous
 notifications are generated.
 When the runtime system receives a message, it first tries to
 recognize a command consisting of the command string and the
 transaction identifier. If the runtime system is not able to extract
 both the command string and the transaction identifier, then the
 message is discarded. An asynchronous `511' reply may be generated in
 this case. Otherwise, the command string is checked to be valid, i.e.
 to be one of the strings `hello', `start', `suspend', `resume',
 `abort', or `status'.  If the string is invalid, a `402' reply is

Schoenwaelder & Quittek Experimental [Page 9] RFC 2593 SMX Protocol 1.0 May 1999

 sent and processing of the message stops.  If a valid command has
 been detected, further processing of the message depends on the
 command as described below.
 The command specific processing describes several possible syntax
 errors for which specific reply messages are generated. If the
 runtime engine detects any syntax error which is not explicitely
 mentioned or which cannot be identified uniquely, a generic `401'
 reply is sent indicating that the command cannot be executed.

6.1.1. Processing the `hello' Command

 When the runtime system receives a `hello' command, it processes it
 as follows:
 1.   The runtime system obtains the security cookie from its process
      environment.
 2.   The runtime system sends a `211' reply containing the security
      cookie.

6.1.2. Processing the `start' Command

 When the runtime system receives a `start' command, it processes it
 as follows:
 1.   The syntax of the arguments of the `start' command is checked.
      The following four checks must be made:
      (a)   The syntax of the `RunId' parameter is checked and a `431'
            reply is sent if any syntax error is detected.
      (b)   The syntax of the `Script' parameter is checked and a
            `421' reply is sent if any syntax error is detected.
      (c)   The syntax of the `Profile' parameter is checked and a
            `432' reply is sent if any syntax error is detected.
      (d)   If syntax of the `Argument' parameter is checked and a
            `433' reply is sent if any syntax error is detected.
 2.   The runtime system checks whether the new `RunId' is already in
      use. If yes, a `431' reply is sent and processing stops.
 3.   The runtime system checks whether the `Script' parameter is the
      name of a file on the local storage device, that can be read. A
      `421' reply is sent and processing stops if the file does not
      exist or is not readable.

Schoenwaelder & Quittek Experimental [Page 10] RFC 2593 SMX Protocol 1.0 May 1999

 4.   The runtime system checks whether the security profile is known
      and sends a `432' reply and stops processing if not.
 5.   The runtime engine starts the script given by the script name.
      When the script has been started, a `231' reply is sent
      including the current run state.
 Processing of the `start' command stops, when the script reaches the
 state `running'. For each asynchronous state change of the running
 script, a `531' reply is sent. Processing of the `start' command is
 also stopped if an error occurs before the state `running' is
 reached. In this case, the run is aborted and a `535' reply is
 generated.
 If an `abort' command or a `suspend' command for the running script
 is received before processing of the `start' command is complete,
 then the processing of the `start' command may be stopped before the
 state `running' is reached. In this case, the resulting status of the
 running script is given by the respective reply to the `abort' or
 `suspend' command, and no reply with the transaction identifier of
 the `start' command is generated.

6.1.3. Processing the `suspend' Command

 When the runtime system receives a `suspend' command, it processes it
 as follows:
 1.   If there is a syntax error in the running script identifier or
      if there is no running script matching the identifier, a `431'
      reply is sent and processing of the command is stopped.
 2.   If the running script is already in the state `suspended', a
      '231' reply is sent and processing of the command is stopped.
 3.   If the running script is in the state `running', it is suspended
      and a `231' reply is sent after suspending. If suspending fails,
      a `434' reply is sent and processing of the command is stopped.
 4.   If the running script has not yet reached the state `running'
      (the `start' command still being processed), it may reach the
      state `suspended' without having been in the state `running'.
      After reaching the state `suspended', a `231' reply is sent.
 5.   If the running script is in any other state, a `434' reply is
      sent.

Schoenwaelder & Quittek Experimental [Page 11] RFC 2593 SMX Protocol 1.0 May 1999

6.1.4. Processing the `resume' Command

 When the runtime system receives a `resume' command, it processes it
 as follows:
 1.   If there is a syntax error in the running script identifier or
      if there is no running script matching the identifier, a `431'
      reply is sent and processing of the command is stopped.
 2.   If the running script is already in the state `running', a `231'
      reply is sent and processing of the command is stopped.
 3.   If the running script is in the state `suspended', it is resumed
      and a `231' reply is sent after resuming. If resuming fails, a
      `434' reply is sent and processing of the command is stopped.
 4.   If the `start' command is still being processed for the script,
      a `231' reply is sent when the state `running' has been reached.
 5.   If the running script is in any other state, a `434' reply is
      sent.

6.1.5. Processing the `abort' Command

 When the runtime system receives an `abort' command, it processes it
 as follows:
 1.   If there is a syntax error in the running script identifier or
      if there is no running script matching the identifier, a `431'
      reply is sent and processing of the command is stopped.
 2.   If the running script is already aborted, a `232' reply is sent
      and processing of the command is stopped.
 3.   The running script is aborted and a `232' reply is sent after
      aborting. If aborting fails, a `434' reply is sent and
      processing is stopped.

6.1.6. Processing the `status' Command

 When the runtime system receives a `status' command, it processes it
 as follows:
 1.   If there is a syntax error in the running script identifier or
      if there is no running script matching the identifier, a `431'
      reply is sent and processing of the command is stopped.
 2.   The status of the script is obtained and a `231' reply is sent.

Schoenwaelder & Quittek Experimental [Page 12] RFC 2593 SMX Protocol 1.0 May 1999

6.1.7. Generation of Asynchronous Notifications

 The runtime system generates or may generate the following
 notifications:
 1.   If a change of the status of a running script is observed by the
      runtime system, a `531' reply is sent.
 2.   A `534' reply is sent if a running script terminates normally.
 3.   A `535' reply is sent if a running script terminates abnormally.
 4.   If a script generates an intermediate result, a `532' reply is
      sent.
 5.   If a script requests the generation of a `smScriptResult'
      notification, a `533' reply is sent.
 6.   Besides the notifications mentioned above, the runtime system
      may generate arbitrary `511' replies, which are logged or
      displayed by the SNMP agent.

6.2. SMX Message Processing on the SNMP Agent

 This section describes the conditions under which an SNMP agent
 implementing the Script MIB generates SMX commands. It also describes
 how the SNMP agent processes replies to SMX commands.

6.2.1. Creating a Runtime System

 New runtime systems are started by the SNMP agent while processing
 set requests for a `smLaunchStart' variable. The SNMP agent first
 searches for an already running runtime systems which matches the
 security profiles associated with the `smLaunchStart' variable. If no
 suitable runtime system is available, a new runtime system is started
 by preparing the environment for the new runtime system and starting
 the executable for the runtime system in a new process which conforms
 to the operating system security profile. The SNMP agent prepares to
 accept a connection from the new runtime system. The `smRunState' of
 all scripts that should be executed in this new runtime system is set
 to `initializing'.

6.2.2. Generating the `hello' Command

 The `hello' command is generated once a connection request from a
 runtime system has been accepted. The SNMP agent sends the `hello'
 command as defined in section 5.2. The SNMP agent then expects a
 reply from the runtime system within a reasonable timeout interval.

Schoenwaelder & Quittek Experimental [Page 13] RFC 2593 SMX Protocol 1.0 May 1999

 1.   If the timeout expires before the SNMP agent received a reply,
      then the connection is closed and all data associated with it is
      deleted.  Any scripts that should be running in this runtime
      system are aborted, the `smRunExitCode' is set to `genericError'
      and `smRunError' is modified to describe the error situation.
 2.   If the received message can not be analyzed because it does not
      have the required format, then the connection is closed and all
      data associated with it is deleted. Any scripts that should be
      running in this runtime system are aborted, the `smRunExitCode'
      is set to `genericError' and `smRunError' is modified to
      describe the error situation.
 3.   If the received message is a `211' reply, then the `Id' is
      checked whether it matches the `Id' used in the `hello' command.
      If the `Id' matches, then the `Version' is checked. If the
      `Version' matches a supported SMX protocol version, then the
      `Cookie' is checked whether it matches the cookie passed to the
      runtime system. If any of these tests fails, then the connection
      is closed and all data associated with this runtime system is
      deleted. Any scripts that should be running in this runtime
      system are aborted, the `smRunExitCode' is set to `genericError'
      and `smRunError' is modified to describe the error situation.
 4.   Received messages are discarded if none of the previous rules
      applies.

6.2.3. Generating the `start' Command

 The `start' command is generated while processing set-requests for a
 `smLaunchStart' variable. The `start' command assumes that the SNMP
 agent already determined a runtime system suitable to execute the
 script associated with the `smLaunchStart' variable.  The SNMP agent
 sends the `start' command as defined in section 5.2 to the selected
 runtime system. The SNMP agent then expects a reply from the runtime
 system within a reasonable timeout interval.
 1.   If the timeout expires before the SNMP agent received a reply,
      then the SNMP agent sends an `abort' command to abort the
      running script and sets the `smRunState' of the running script
      to `terminated', the `smRunExitCode' to `genericError' and
      `smRunError' is modified to describe the timeout situation.
 2.   If the received message can not be analyzed because it does not
      have the required format, then the message is ignored. The SNMP
      agent continues to wait for a valid reply message until the
      timeout expires.

Schoenwaelder & Quittek Experimental [Page 14] RFC 2593 SMX Protocol 1.0 May 1999

 3.   If the received message is a `4yz' reply and the `Id' matches
      the `Id' of the `start' command, then the SNMP agent assumes
      that the script can not be started. The `smRunState' of the
      running script is set to `terminated', the `smRunExitCode' to
      `genericError' and the `smRunError' is modified to contain a
      message describing the error situation.
 4.   If the received message is a `231' reply and the `Id' matches
      the `Id' of the `start' command, then the `smRunState' variable
      of the running script is updated.
 5.   Received messages are discarded if none of the previous rules
      applies.

6.2.4. Generating the `suspend' Command

 The `suspend' command is generated while processing set-requests for
 the `smLaunchControl' and `smRunControl' variables which change the
 value to `suspend'. The SNMP agent sets the `smRunState' variable to
 `suspending' and sends the `suspend' command as defined in section
 5.2. The SNMP agent then expects a reply from the runtime system
 within a reasonable timeout interval.
 1.   If the timeout expires before the SNMP agent received a reply,
      then the SNMP agent sends an `abort' command to abort the
      running script and sets the `smRunState' of the running script
      to `terminated', the `smRunExitCode' to `genericError' and
      `smRunError' is modified to describe the timeout situation.
 2.   If the received message can not be analyzed because it does not
      have the required format, then the message is ignored. The SNMP
      agent continues to wait for a valid reply message until the
      timeout expires.
 3.   If the received message is a `401', `402' or a `431' reply and
      the `Id' matches the `Id' of the `suspend' command, then the
      runtime systems is assumed to not provide the suspend/resume
      capability and processing of the `suspend' command stops.
 4.   If the received message is a `231' reply and the `Id' matches
      the `Id' of the `suspend' command, then the `smRunState'
      variable of the running script is updated.
 5.   Received messages are discarded if none of the previous rules
      applies.

Schoenwaelder & Quittek Experimental [Page 15] RFC 2593 SMX Protocol 1.0 May 1999

6.2.5. Generating the `resume' Command

 The `resume' command is generated while processing set-requests for
 the `smLaunchControl' and `smRunControl' variables which change the
 value to `resume'. The SNMP agent sets the `smRunState' variable to
 `resuming' and sends the `resume' command as defined in section 5.2.
 The SNMP agent then expects a reply from the runtime system within a
 reasonable timeout interval.
 1.   If the timeout expires before the SNMP agent received a reply,
      then the SNMP agent sends an `abort' command to abort the
      running script and sets the `smRunState' of the running script
      to `terminated', the `smRunExitCode' to `genericError' and
      `smRunError' is modified to describe the timeout situation.
 2.   If the received message can not be analyzed because it does not
      have the required format, then the message is ignored. The SNMP
      agent continues to wait for a valid reply message until the
      timeout expires.
 3.   If the received message is a `401', `402' or a `431' reply and
      the `Id' matches the `Id' of the `resume' command, then the
      runtime systems is assumed to not provide the suspend/resume
      capability and processing of the `resume' command stops.
 4.   If the received message is a `231' reply and the `Id' matches
      the `Id' of the `resume' command, then the `smRunState' variable
      of the running script is updated.
 5.   Received messages are discarded if none of the previous rules
      applies.

6.2.6. Generating the `abort' Command

 The `abort' command is generated while processing set-requests for
 the `smLaunchControl' and `smRunControl' variables which change the
 value to `abort'. In addition, the `abort' command is also generated
 if the `smRunLifeTime' variable reaches the value 0. The SNMP agent
 sends the `abort' command as defined in section 5.2. The SNMP agent
 then expects a reply from the runtime system within a reasonable
 timeout interval.
 1.   If the timeout expires before the SNMP agent received a reply,
      then the SNMP agent sets the `smRunState' of the running script
      to `terminated', the `smRunExitCode' to `genericError' and
      `smRunError' is modified to describe the timeout situation.

Schoenwaelder & Quittek Experimental [Page 16] RFC 2593 SMX Protocol 1.0 May 1999

 2.   If the received message can not be analyzed because it does not
      have the required format, then the message is ignored. The SNMP
      agent continues to wait for a valid reply message until the
      timeout expires.
 3.   If the received message is a `4yz' reply and the `Id' matches
      the `Id' of the `abort' command, then the SNMP agent assumes
      that the script can not be aborted. The `smRunState' of the
      running script is set to `terminated', the `smRunExitCode' to
      `genericError' and the `smRunResult' is modified to describe the
      error situation.
 4.   If the received message is a `232' reply and the `Id' matches
      the `Id' of the `abort' command, then the `smRunExitCode'
      variable of the terminated script is changed to either `halted'
      (when processing a set-request for the `smLaunchControl' and
      `smRunControl' variables) or `lifeTimeExceeded' (if the `abort'
      command was generated because the `smRunLifeTime' variable
      reached the value 0). The `smRunState' variable is changed to
      the value `terminated'.
 5.   Received messages are discarded if none of the previous rules
      applies.

6.2.7. Generating the `status' Command

 The `status' command is generated either periodically or on demand by
 the SNMP agent in order to retrieve status information from running
 scripts. The SNMP agent sends the `status' command as defined in 5.2.
 The SNMP agent then expects a reply from the runtime system within a
 reasonable timeout interval.
 1.   If the timeout expires before the SNMP agent received a reply,
      then the SNMP agent sends an `abort' command to abort the
      running script and sets the `smRunState' of the running script
      to `terminated', the `smRunExitCode' to `genericError' and
      `smRunError' is modified to describe the timeout situation.
 2.   If the received message can not be analyzed because it does not
      have the required format, then the message is ignored. The SNMP
      agent continues to wait for a valid reply message until the
      timeout expires.
 3.   If the received message is a `4yz' reply and the `Id' matches
      the `Id' of the `status' command, then the SNMP agent assumes
      that the script status can not be read, which is a fatal error
      condition. The SNMP agent sends an `abort' command to abort the
      running script. The `smRunState' of the running script is set to

Schoenwaelder & Quittek Experimental [Page 17] RFC 2593 SMX Protocol 1.0 May 1999

      `terminated', the `smRunExitCode' to `genericError' and the
      `smRunError' is modified to describe the error situation.
 4.   If the received message is a `231' reply and the `Id' matches
      the `Id' of the `status' command, then the `smRunState' variable
      of the running script is updated.
 5.   Received messages are discarded if none of the previous rules
      applies.

6.2.8. Processing Asynchronous Notifications

 The runtime system can send asynchronous status change notifications.
 These `5yz' replies are processed as described below.
 1.   If the received message is a `511' reply, then the message is
      displayed or logged appropriately and processing stops.
 2.   If the received message is a `531' reply, then the SNMP agent
      checks whether a running script with the given `RunId' exists in
      the runtime system. Processing of the notification stops if
      there is no running script with the `RunId'. Otherwise, the
      `smRunState' is updated.
 3.   If the received message is a `532' reply, then the SNMP agent
      checks whether a running script with the given `RunId' exists in
      the runtime system. Processing of the notification stops if
      there is no running script with the `RunId'. Otherwise,
      `smRunState' and `smRunResult' are updated.
 4.   If the received message is a `533' reply, then the SNMP agent
      checks whether a running script with the given `RunId' exists in
      the runtime system. Processing of the notification stops if
      there is no running script with the `RunId'. Otherwise,
      `smRunState' and `smRunResult' are updated and the
      `smScriptResult' notification is generated.
 5.   If the received message is a `534' reply, then the SNMP agent
      checks whether a running script with the given `RunId' exists in
      the runtime system. Processing stops if there is no running
      script with the `RunId'. Otherwise, `smExitCode' is set to
      `noError', `smRunState' is set to `terminated' and `smRunResult'
      is updated.
 6.   If the received message is a `535' reply, then the SNMP agent
      checks whether a running script with the given `RunId' exists in
      the runtime system. Processing stops if there is no running
      script with the `RunId'. Otherwise, `smRunState' is set to

Schoenwaelder & Quittek Experimental [Page 18] RFC 2593 SMX Protocol 1.0 May 1999

      `terminated' and `smExitCode' and `smRunError' are updated.

7. An Example SMX Message Flow

 Below is an example SMX message exchange. Messages send from the SNMP
 agent are marked with `>' while replies send from the runtime system
 are marked with `<'. Line terminators (`CRLF') are not shown in order
 to make the example more readable.
   > hello 1
   < 211 1 SMX/1.0 0AF0BAED6F877FBC
   > start 2 42 "/var/snmp/scripts/foo.jar" untrusted ""
   > start 5 44 "/var/snmp/scripts/bar.jar" trusted "www.ietf.org"
   < 231 2 2
   > start 12 48 "/var/snmp/scripts/foo.jar" funny ""
   < 231 5 2
   < 532 0 44 2 "waiting for response"
   > status 18 42
   > status 19 44
   < 432 12
   < 231 19 2
   < 231 18 2
   > hello 578
   < 211 578 SMX/1.0 0AF0BAED6F877FBC
   > suspend 581 42
   < 231 581 4
   < 534 0 44 "test completed"
   > abort 611 42
   < 232 611

8. Security Considerations

 The SMX protocol runs on top of a local TCP connection. Protocol
 messages never leave the local system. It is therefore not possible
 to attack the message exchanges if the underlying operating system
 protects local TCP connections from other users on the same machine.
 The only critical situation is the connection establishment phase.
 The rules defined in section 4 ensure that only local connections are
 accepted and that a runtime system has to identify itself with a
 security cookie generated by the SNMP agent and passed to the runtime
 system process as part of its environment. This rule ensures that
 scripts will only be executed on authorized runtime systems. This
 scheme relies on the protection of process environments by the
 operating system. Well maintained UNIX operating systems have this
 property.

Schoenwaelder & Quittek Experimental [Page 19] RFC 2593 SMX Protocol 1.0 May 1999

 The SMX protocol allows to execute script under different operating
 system and runtime system security profiles. The memo suggests to map
 the smLaunchOwner value to an operating system and a runtime system
 security profile. The operating system security profile is enforced
 by the operating system by setting up a proper process environment.
 The runtime security profile is enforced by a secure runtime system
 (e.g. the Java virtual machine or a safe Tcl interpreter) [7].

9. Acknowledgments

 The protocol described in this memo is the result of a joint project
 between the Technical University of Braunschweig and C&C Research
 Laboratories of NEC Europe Ltd. in Berlin. We would like to thank the
 following project members for their contributions to the initial
 design and the implementation of the protocol described in this memo:
         M. Bolz         (TU Braunschweig)
         C. Kappler      (NEC Europe Ltd.)
         A. Kind         (NEC Europe Ltd.)
         S. Mertens      (TU Braunschweig)
         J. Nicklisch    (NEC Europe Ltd.)

10. References

 [1]  Levi, D. and J. Schoenwaelder, "Definitions of Managed Objects
      for the Delegation of Management Scripts", RFC 2592, May 1999.
 [2]  Lindholm, T., and F. Yellin, "The Java Virtual Machine
      Specification", Addison Wesley, 1997.
 [3]  J.K. Ousterhout, "Tcl and the Tk Toolkit", Addison Wesley, 1994.
 [4]  Fritzinger, J.S., and M. Mueller, "Java Security", White Paper,
      Sun Microsystems, Inc., 1996.
 [5]  Levy, J.Y., Demailly, L., Ousterhout, J.K., and B. Welch, "The
      Safe-Tcl Security Model", Proc. USENIX Annual Technical
      Conference, June 1998.
 [6]  Crocker, D., and P. Overell, "Augmented BNF for Syntax
      Specifications: ABNF", RFC 2234, Internet Mail Consortium, Demon
      Internet Ltd., November 1997.
 [7]  Schoenwaelder, J., and J. Quittek, "Secure Management by
      Delegation within the Internet Management", Proc. IFIP/IEEE
      International Symposium on Integrated Network Management '99,
      May 1999.

Schoenwaelder & Quittek Experimental [Page 20] RFC 2593 SMX Protocol 1.0 May 1999

11. Authors' Addresses

 Juergen Schoenwaelder
 TU Braunschweig
 Bueltenweg 74/75
 38106 Braunschweig
 Germany
 Phone: +49 531 391-3283
 EMail: schoenw@ibr.cs.tu-bs.de
 Juergen Quittek
 NEC Europe Ltd.
 C&C Research Laboratories
 Hardenbergplatz 2
 10623 Berlin
 Germany
 Phone: +49 30 254230-19
 EMail: quittek@ccrle.nec.de

Schoenwaelder & Quittek Experimental [Page 21] RFC 2593 SMX Protocol 1.0 May 1999

12. Full Copyright Statement

 Copyright (C) The Internet Society (1999). All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the  purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Schoenwaelder & Quittek Experimental [Page 22]

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