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rfc:rfc3179

Network Working Group J. Schoenwaelder Request for Comments: 3179 TU Braunschweig Obsoletes: 2593 J. Quittek Category: Experimental NEC Europe Ltd.

                                                          October 2001
           Script MIB Extensibility Protocol Version 1.1

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 (2001).  All Rights Reserved.

Abstract

 The Script MIB extensibility protocol (SMX) defined in this memo
 separates language specific runtime systems from language independent
 Script MIB implementations.  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.

Table of Contents

 1 Introduction .................................................    2
 2 Process Model and Communication Model ........................    3
 3 Security Profiles ............................................    4
 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 ....................................................    7
 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 3179 SMX Protocol 1.1 October 2001

 6.2 SMX Message Processing on the SNMP Agent ...................   13
 6.2.1 Creating a Runtime System ................................   14
 6.2.2 Generating the `hello' Command ...........................   14
 6.2.3 Generating the `start' Command ...........................   15
 6.2.4 Generating the `suspend' Command .........................   16
 6.2.5 Generating the `resume' Command ..........................   16
 6.2.6 Generating the `abort' Command ...........................   17
 6.2.7 Generating the `status' Command ..........................   18
 6.2.8 Processing Asynchronous Notifications ....................   19
 7 Example SMX Message Flow .....................................   20
 8 Transport Mappings ...........................................   20
 8.1 SMX over Bi-directional Pipes ..............................   21
 8.2 SMX over TCP ...............................................   21
 9 Security Considerations ......................................   21
 10 Changes from RFC 2593 .......................................   22
 11 Acknowledgments .............................................   23
 12 References ..................................................   23
 13 Authors' Addresses ..........................................   24
 14 Full Copyright Statement ....................................   25

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.

Schoenwaelder & Quittek Experimental [Page 2] RFC 3179 SMX Protocol 1.1 October 2001

 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
 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

Schoenwaelder & Quittek Experimental [Page 3] RFC 3179 SMX Protocol 1.1 October 2001

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 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.

Schoenwaelder & Quittek Experimental [Page 4] RFC 3179 SMX Protocol 1.1 October 2001

 In order to prevent SMX communication from untrusted peers the SNMP
 agent has to choose a secure SMX transport.  This memo defines two
 transports in Section 8: (a) a bi-directional pipe using standard
 input/output streams on the runtime engine side, and (b) a TCP
 connection where the SNMP agent acts as a listening server that
 accepts only connections from local runtime engines that authenticate
 themselves with a secret shared between the agent and the runtime
 engine.

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'
 ProfileChars  = DIGIT / ALPHA / %x2D-2F / %x3A / %x5F
                               ; digits, alphas, and the characters
                               ; '-', '.', '/', ':', '_'
 QuotedString  = DQUOTE *(VCHAR / WSP) DQUOTE
 HexString     = 1*(HEXDIG HEXDIG)
 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*ProfileChars ; security profile name
 RunState      =  "1"          ; smRunState `initializing'
 RunState      =/ "2"          ; smRunState `executing'
 RunState      =/ "3"          ; smRunState `suspending'
 RunState      =/ "4"          ; smRunState `suspended'
 RunState      =/ "5"          ; smRunState `resuming'

Schoenwaelder & Quittek Experimental [Page 5] RFC 3179 SMX Protocol 1.1 October 2001

 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'
 Authenticator = HexString     ; authentication cookie
 Version       = "SMX/1.1"     ; 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:
          `\\'   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 `Authenticator' 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.

Schoenwaelder & Quittek Experimental [Page 6] RFC 3179 SMX Protocol 1.1 October 2001

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
 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 1.1.
 They are defined only for future SMX extensions.

Schoenwaelder & Quittek Experimental [Page 7] RFC 3179 SMX Protocol 1.1 October 2001

 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 *1(WSP Authenticator) 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
    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

Schoenwaelder & Quittek Experimental [Page 8] RFC 3179 SMX Protocol 1.1 October 2001

    Reply =/ "533" WSP Zero WSP RunId WSP RunState WSP Result CRLF
                                  ; intermediate script result that
                                  ; triggers an event report
    Reply =/ "534" WSP Zero WSP RunId WSP Result CRLF
                                  ; normal script termination,
                                  ; deprecated
    Reply =/ "535" WSP Zero WSP RunId WSP ExitCode WSP ErrorMsg CRLF
                                  ; abnormal script termination,
                                  ; deprecated
    Reply =/ "536" WSP Zero WSP RunId WSP RunState WSP ErrorMsg CRLF
                                  ; script error
    Reply =/ "537" WSP Zero WSP RunId WSP RunState WSP ErrorMsg CRLF
                                  ; script error that
                                  ; triggers an event report
    Reply =/ "538" WSP Zero WSP RunId WSP ExitCode CRLF
                                  ; 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
 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.

Schoenwaelder & Quittek Experimental [Page 9] RFC 3179 SMX Protocol 1.1 October 2001

 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 explicitly
 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 sends a `211' reply.  If the runtime system has
    access to a shared secret, then the reply must contain the
    optional `Authenticator', which is a function of the shared
    secret.

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.
 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.

Schoenwaelder & Quittek Experimental [Page 10] RFC 3179 SMX Protocol 1.1 October 2001

    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 `538' reply is
 generated.  An optional `536' reply can be send before the `538'
 reply to report an error message.
 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 3179 SMX Protocol 1.1 October 2001

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 3179 SMX Protocol 1.1 October 2001

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.
    This reply is deprecated.  You can emulate this reply with a
    combination of a `532' reply and a `538' reply.
 3. A `535' reply is sent if a running script terminates abnormally.
    This reply is deprecated.  You can emulate this reply with a
    combination of a `536' reply and a `538' reply.
 4. A `532' reply is sent if a script generates an intermediate
    result.
 5. A `533' reply is sent if a script generates an intermediate result
    which causes the generation of a `smScriptResult' notification.
 6. A `536' reply is sent if a running script produces an error.  If
    the error is fatal, the script execution will be terminated and a
    538 reply will follow.  Otherwise, if the error is non-fatal, the
    script continues execution.
 7. A `537' reply is sent if a running script produces an error which
    should cause the generation of a `smScriptException' notification.
    If the error is fatal, the script execution will be terminated and
    a 538 reply will follow.  Otherwise, if the error is non-fatal,
    the script continues execution.
 8. A `538' reply is sent if a running script terminates.  The
    ExitCode is used to distinguish between normal termination
    (`noError') or abnormal termination.
 9. 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.

Schoenwaelder & Quittek Experimental [Page 13] RFC 3179 SMX Protocol 1.1 October 2001

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 either
 (a) starting the executable for the runtime system in a new process
     which conforms to the operating system security profile, and
     establishing a bi-directional pipe to the runtime systems
     standard input/output streams to be used for SMX transport, or
 (b) 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 the new
 runtime system is set to `initializing'.

6.2.2. Generating the `hello' Command

 The `hello' command is generated once an SMX connection is
 established.  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.
 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, if present, the
    `Authenticator' is checked.  If any of the tests fails or if the

Schoenwaelder & Quittek Experimental [Page 14] RFC 3179 SMX Protocol 1.1 October 2001

    SNMP agent requires an authenticator and it did not receive a
    matching `Authenticator' with the `211' reply, 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 `RunState' 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 `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.

Schoenwaelder & Quittek Experimental [Page 15] RFC 3179 SMX Protocol 1.1 October 2001

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.

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.

Schoenwaelder & Quittek Experimental [Page 16] RFC 3179 SMX Protocol 1.1 October 2001

 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.
 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'

Schoenwaelder & Quittek Experimental [Page 17] RFC 3179 SMX Protocol 1.1 October 2001

    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
    `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.

Schoenwaelder & Quittek Experimental [Page 18] RFC 3179 SMX Protocol 1.1 October 2001

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
    `terminated' and `smExitCode' and `smRunError' are updated.
 7. If the received message is a `536' 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 `smRunError' are updated.

Schoenwaelder & Quittek Experimental [Page 19] RFC 3179 SMX Protocol 1.1 October 2001

 8. If the received message is a `537' 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 `smRunError' are updated and the `smScriptException'
    notification is generated.
 9. If the received message is a `538' 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' is
    set to `terminated' and the `smExitCode' is updated.

7. Example SMX Message Flow

 Below is an example SMX message exchange.  Messages sent from the
 SNMP agent are marked with `>' while replies sent 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/1.1 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/1.1 0AF0BAED6F877FBC
    > suspend 581 42
    < 231 581 4
    < 532 0 44 7 "test completed"
    < 538 0 44 1
    > abort 611 42
    < 232 611

8. Transport Mappings

 In order to prevent SMX communication from untrusted peers the SNMP
 agent has to choose a secure SMX transport.  This memo defines two
 transports in Section 8: (a) a bi-directional pipe using standard
 input/output streams on the runtime engine side, and (b) a TCP

Schoenwaelder & Quittek Experimental [Page 20] RFC 3179 SMX Protocol 1.1 October 2001

 connection where the SNMP agent acts as a listening server that
 accepts only connections from local runtime engines that authenticate
 themselves with a secret shared between the agent and the runtime
 engine.
 For simplicity and security reasons the transport over bi-directional
 pipes is the preferred transport.
 Further transports (e.g., UNIX domain sockets) are possible but not
 defined at this point in time.  The reason for choosing pipes and TCP
 connections as the transport for SMX was that these IPC mechanisms
 are supported by most potential runtime systems, while other
 transports are not universally available.

8.1. SMX over Bi-directional Pipes

 The SNMP agent first creates a bi-directional pipe.  Then the agent
 creates the runtime system process with its standard input and
 standard output streams connected to the pipe.  Further
 authentication mechanisms are not required.

8.2. SMX over TCP

 The SNMP agent first creates a listening TCP socket which accepts
 connections from runtime systems.  Then the agent creates the runtime
 system process.  It is then the responsibility of the runtime system
 to establish a connection to the agent's TCP socket once it has been
 started.  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 must check the `Authenticator' in the `211' reply

if authentication is required and it must close the TCP connection

    if no valid response is received within a given time interval.

9. Security Considerations

 The SMX protocol as specified in this memo runs over a bi-directional
 pipe or over a local TCP connection between the agent and the runtime
 system.  Protocol messages never leave the local system.  It is
 therefore not possible to attack the message exchanges if the
 underlying operating system protects bi-directional pipes and local
 TCP connections from other users on the same machine.

Schoenwaelder & Quittek Experimental [Page 21] RFC 3179 SMX Protocol 1.1 October 2001

 The transport over a bi-directional pipe specifies that the pipe is
 created and connected to the standard input/output stream of the
 runtime engine by the agent before the runtime engine is started.  It
 is therefore not possible that an unauthorized process can exchange
 SMX messages over the bi-directional pipe.
 In case of the TCP transport, the only critical situation is the
 connection establishment phase.  The rules defined in section 8
 ensure that only local connections are accepted and that a runtime
 system has to authenticate itself with an authenticator if the agent
 requires authentication.  It is strongly suggested that agents
 require authentication, especially on multiuser systems.
 The SMX 1.0 specification in RFC 2593 suggested a scheme where the
 authenticator was passed to the runtime engines as part of the
 process environment.  This scheme relies on the protection of process
 environments by the operating system against unauthorized access.
 Some operating systems allow users to read the process environment of
 arbitrary processes.  Hence the scheme proposed in RFC 2593 is
 considered unsecure on these operating systems.  This memo does not
 dictate the mechanism by which the runtime obtains the shares secret.
 It is the responsibility of implementors or administrators to select
 a mechanism which is secure on the target platforms.
 The SMX protocol assumes a local script storage area which is used to
 pass script code from the SNMP agent to the runtime systems.  The SMX
 protocol passes file names from the agent to the runtime engines.  It
 is necessary that the script files in the local script storage area
 are properly protected so that only the SNMP agent has write access.
 Failure to properly protect write access to the local script storage
 area can allow attackers to execute arbitrary code in runtime systems
 that might have special privileges.
 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].

10. Changes from RFC 2593

 The following non-editorial changes have been made:
 1. Added the `536' and `537' replies which may be generated
    asynchronously by runtime engines to report error conditions.

Schoenwaelder & Quittek Experimental [Page 22] RFC 3179 SMX Protocol 1.1 October 2001

 2. Added the `538' reply which can be used to signal the (normal or
    abnormal) termination of a running script.  This new reply
    replaces the `534' and `535' replies, which are now deprecated.
 3. Relaxed the rules for ProfileChars to also include the characters
    ':'  and '_', which are frequently used in namespaces and
    identifiers.
 4. Changed the SMX protocol version number from 1.0 to 1.1.
 5. Added a second (and preferred) transport over a bi-directional
    pipe due to security risks when a shared secret is passed through
    an operating system's environment variable.
 6. Made the `Authenticator' in the `211' reply optional.

11. 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 Heidelberg.  The authors like to
 thank Matthias Bolz, Cornelia Kappler, Andreas Kind, Sven Mertens,
 Jan Nicklisch, and Frank Strauss for their contributions to the
 design and the implementation of the protocol described in this memo.
 The authors also like to thank David Wallis for pointing out a
 security risk in SMX 1.0 with passing a cookie via an operating
 system environment variable.

12. References

 [1]  Levi, D. and J. Schoenwaelder, "Definitions of Managed Objects
      for the Delegation of Management Scripts", RFC 3165, September
      2001.
 [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.

Schoenwaelder & Quittek Experimental [Page 23] RFC 3179 SMX Protocol 1.1 October 2001

 [6]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
      Specifications: ABNF", RFC 2234, November 1997.
 [7]  Schoenwaelder, J., and J. Quittek, "Secure Internet Management
      by Delegation", Computer Networks 35(1), January 2001.

13. 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
 Adenauerplatz 6
 69115 Heidelberg
 Germany
 Phone: +49 6221 90511-15
 EMail: quittek@ccrle.nec.de

Schoenwaelder & Quittek Experimental [Page 24] RFC 3179 SMX Protocol 1.1 October 2001

14. Full Copyright Statement

 Copyright (C) The Internet Society (2001).  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 25]

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