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

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

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:

- 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.

- 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

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:

- The TCP connection must originate from the local host.

- 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 RFC2234 [6]. The definitions for `ALPHA',
`DIGIT', `HEXDIG', `WSP', `CRLF', `CR', `LF', `HTAB', `VCHAR' and
`DQUOTE' are imported from appendix A of RFC2234 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)

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:

`' 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

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

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

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.

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.

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.

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.

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.

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.

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.

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

`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

`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.

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", RFC2592, 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", RFC2234, 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.

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

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