Windows PowerShell command on Get-command SafeBase

Manual Pages for UNIX Operating System command usage for man SafeBase

Tcl Built-In Commands Safe Tcl(1T)

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NAME

Safe Base - A mechanism for creating and manipulating safe

interpreters.

SYNOPSIS

::safe::interpCreate ?slave? ?options...? ::safe::interpInit slave ?options...? ::safe::interpConfigure slave ?options...? ::safe::interpDelete slave ::safe::interpAddToAccessPath slave directory ::safe::interpFindInAccessPath slave directory ::safe::setLogCmd ?cmd arg...? OPTIONS

?-accessPath pathList? ?-statics boolean? ?-noStatics?

?-nested boolean? ?-nestedLoadOk? ?-deleteHook script?

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DESCRIPTION

Safe Tcl is a mechanism for executing untrusted Tcl scripts safely and for providing mediated access by such scripts to potentially dangerous functionality. The Safe Base ensures that untrusted Tcl scripts cannot harm the hosting application. The Safe Base prevents integrity and privacy attacks. Untrusted Tcl scripts are prevented

from corrupting the state of the hosting application or com-

puter. Untrusted scripts are also prevented from disclosing information stored on the hosting computer or in the hosting application to any party. The Safe Base allows a master interpreter to create safe, restricted interpreters that contain a set of predefined

aliases for the source, load, file, encoding, and exit com-

mands and are able to use the auto-loading and package

mechanisms. No knowledge of the file system structure is leaked to the

safe interpreter, because it has access only to a virtual-

ized path containing tokens. When the safe interpreter requests to source a file, it uses the token in the virtual

path as part of the file name to source; the master inter-

preter transparently translates the token into a real Tcl Last change: 8.0 1

Tcl Built-In Commands Safe Tcl(1T)

directory name and executes the requested operation (see the section SECURITY below for details). Different levels of security can be selected by using the optional flags of the commands described below. All commands provided in the master interpreter by the Safe Base reside in the safe namespace: COMMANDS

The following commands are provided in the master inter-

preter: ::safe::interpCreate ?slave? ?options...? Creates a safe interpreter, installs the aliases described in the section ALIASES and initializes the

auto-loading and package mechanism as specified by the

supplied options. See the OPTIONS section below for a description of the optional arguments. If the slave argument is omitted, a name will be generated. ::safe::interpCreate always returns the interpreter name. ::safe::interpInit slave ?options...? This command is similar to interpCreate except it that does not create the safe interpreter. slave must have been created by some other means, like interp create

-safe.

::safe::interpConfigure slave ?options...? If no options are given, returns the settings for all options for the named safe interpreter as a list of options and their current values for that slave. If a single additional argument is provided, it will return a list of 2 elements name and value where name is the full name of that option and value the current value

for that option and the slave. If more than two addi-

tional arguments are provided, it will reconfigure the safe interpreter and change each and only the provided options. See the section on OPTIONS below for options description. Example of use:

# Create a new interp with the same configuration as "$i0" :

set i1 [eval safe::interpCreate [safe::interpConfigure $i0]]

# Get the current deleteHook

set dh [safe::interpConfigure $i0 -del]

# Change (only) the statics loading ok attribute of an interp

# and its deleteHook (leaving the rest unchanged) :

safe::interpConfigure $i0 -delete {foo bar} -statics 0 ;

::safe::interpDelete slave Deletes the safe interpreter and cleans up the corresponding master interpreter data structures. If a Tcl Last change: 8.0 2

Tcl Built-In Commands Safe Tcl(1T)

deleteHook script was specified for this interpreter it is evaluated before the interpreter is deleted, with the name of the interpreter as an additional argument. ::safe::interpFindInAccessPath slave directory This command finds and returns the token for the real directory directory in the safe interpreter's current virtual access path. It generates an error if the directory is not found. Example of use:

$slave eval [list set tk_library [::safe::interpFindInAccessPath $name $tk_library]]

::safe::interpAddToAccessPath slave directory

This command adds directory to the virtual path main-

tained for the safe interpreter in the master, and

returns the token that can be used in the safe inter-

preter to obtain access to files in that directory. If the directory is already in the virtual path, it only returns the token without adding the directory to the virtual path again. Example of use:

$slave eval [list set tk_library [::safe::interpAddToAccessPath $name $tk_library]]

::safe::setLogCmd ?cmd arg...? This command installs a script that will be called when

interesting life cycle events occur for a safe inter-

preter. When called with no arguments, it returns the

currently installed script. When called with one argu-

ment, an empty string, the currently installed script is removed and logging is turned off. The script will be invoked with one additional argument, a string describing the event of interest. The main purpose is to help in debugging safe interpreters. Using this facility you can get complete error messages while the safe interpreter gets only generic error messages. This prevents a safe interpreter from seeing messages

about failures and other events that might contain sen-

sitive information such as real directory names. Example of use: ::safe::setLogCmd puts stderr Below is the output of a sample session in which a safe interpreter attempted to source a file not found in its virtual access path. Note that the safe interpreter only received an error message saying that the file was not found: NOTICE for slave interp10 : Created NOTICE for slave interp10 : Setting accessPath=(/foo/bar) staticsok=1 nestedok=0 deletehook=()

NOTICE for slave interp10 : auto_path in interp10 has been set to {$p(:0:)}

ERROR for slave interp10 : /foo/bar/init.tcl: no such file or directory

OPTIONS The following options are common to ::safe::interpCreate, ::safe::interpInit, and ::safe::interpConfigure. Any option Tcl Last change: 8.0 3

Tcl Built-In Commands Safe Tcl(1T)

name can be abbreviated to its minimal non-ambiguous name.

Option names are not case sensitive.

-accessPath directoryList

This option sets the list of directories from which the safe interpreter can source and load files. If this option is not specified, or if it is given as the empty

list, the safe interpreter will use the same direc-

tories as its master for auto-loading. See the section

SECURITY below for more detail about virtual paths, tokens and access control.

-statics boolean

This option specifies if the safe interpreter will be allowed to load statically linked packages (like load {} Tk). The default value is true : safe interpreters are allowed to load statically linked packages.

-noStatics

This option is a convenience shortcut for -statics

false and thus specifies that the safe interpreter will not be allowed to load statically linked packages.

-nested boolean

This option specifies if the safe interpreter will be

allowed to load packages into its own sub-interpreters.

The default value is false : safe interpreters are not

allowed to load packages into their own sub-

interpreters.

-nestedLoadOk

This option is a convenience shortcut for -nested true

and thus specifies the safe interpreter will be allowed

to load packages into its own sub-interpreters.

-deleteHook script

When this option is given a non-empty script, it will

be evaluated in the master with the name of the safe

interpreter as an additional argument just before actu-

ally deleting the safe interpreter. Giving an empty value removes any currently installed deletion hook script for that safe interpreter. The default value ({}) is not to have any deletion call back. ALIASES The following aliases are provided in a safe interpreter: source fileName The requested file, a Tcl source file, is sourced into the safe interpreter if it is found. The source alias can only source files from directories in the virtual path for the safe interpreter. The source alias Tcl Last change: 8.0 4

Tcl Built-In Commands Safe Tcl(1T)

requires the safe interpreter to use one of the token names in its virtual path to denote the directory in which the file to be sourced can be found. See the section on SECURITY for more discussion of restrictions on valid filenames. load fileName

The requested file, a shared object file, is dynami-

cally loaded into the safe interpreter if it is found. The filename must contain a token name mentioned in the virtual path for the safe interpreter for it to be found successfully. Additionally, the shared object file must contain a safe entry point; see the manual page for the load command for more details. file ?subCmd args...? The file alias provides access to a safe subset of the

subcommands of the file command; it allows only dir-

name, join, extension, root, tail, pathname and split subcommands. For more details on what these subcommands do see the manual page for the file command. encoding ?subCmd args...? The encoding alias provides access to a safe subset of the subcommands of the encoding command; it disallows setting of the system encoding, but allows all other subcommands including system to check the current encoding. exit The calling interpreter is deleted and its computation

is stopped, but the Tcl process in which this inter-

preter exists is not terminated. SECURITY

The Safe Base does not attempt to completely prevent annoy-

ance and denial of service attacks. These forms of attack prevent the application or user from temporarily using the computer to perform useful work, for example by consuming all available CPU time or all available screen real estate. These attacks, while aggravating, are deemed to be of lesser importance in general than integrity and privacy attacks that the Safe Base is to prevent. The commands available in a safe interpreter, in addition to the safe set as defined in interp manual page, are mediated aliases for source, load, exit, and safe subsets of file and

encoding. The safe interpreter can also auto-load code and

it can request that packages be loaded. Because some of these commands access the local file system, there is a potential for information leakage about its Tcl Last change: 8.0 5

Tcl Built-In Commands Safe Tcl(1T)

directory structure. To prevent this, commands that take file names as arguments in a safe interpreter use tokens instead of the real directory names. These tokens are translated to the real directory name while a request to, e.g., source a file is mediated by the master interpreter.

This virtual path system is maintained in the master inter-

preter for each safe interpreter created by ::safe::interpCreate or initialized by ::safe::interpInit and the path maps tokens accessible in the safe interpreter

into real path names on the local file system thus prevent-

ing safe interpreters from gaining knowledge about the

structure of the file system of the host on which the inter-

preter is executing. The only valid file names arguments for the source and load aliases provided to the slave are path in the form of [file join token filename] (i.e. when using the native file path formats: token/filename on Unix, token\filename on Windows, and token:filename on the Mac), where token is representing one of the directories of the accessPath list and filename is one file in that directory (no sub directories access are allowed). When a token is used in a safe interpreter in a request to source or load a file, the token is checked and translated to a real path name and the file to be sourced or loaded is located on the file system. The safe interpreter never gains knowledge of the actual path name under which the file is stored on the file system.

To further prevent potential information leakage from sensi-

tive files that are accidentally included in the set of files that can be sourced by a safe interpreter, the source

alias restricts access to files meeting the following con-

straints: the file name must fourteen characters or shorter, must not contain more than one dot ("."), must end up with the extension .tcl or be called tclIndex. Each element of the initial access path list will be

assigned a token that will be set in the slave auto_path and

the first element of that list will be set as the

tcl_library for that slave.

If the access path argument is not given or is the empty list, the default behavior is to let the slave access the same packages as the master has access to (Or to be more precise: only packages written in Tcl (which by definition can't be dangerous as they run in the slave interpreter) and

C extensions that provides a Safe_Init entry point). For

that purpose, the master's auto_path will be used to con-

struct the slave access path. In order that the slave suc-

cessfully loads the Tcl library files (which includes the

auto-loading mechanism itself) the tcl_library will be added

or moved to the first position if necessary, in the slave Tcl Last change: 8.0 6

Tcl Built-In Commands Safe Tcl(1T)

access path, so the slave tcl_library will be the same as

the master's (its real path will still be invisible to the

slave though). In order that auto-loading works the same for

the slave and the master in this by default case, the

first-level sub directories of each directory in the master

auto_path will also be added (if not already included) to

the slave access path. You can always specify a more res-

trictive path for which sub directories will never be searched by explicitly specifying your directory list with

the -accessPath flag instead of relying on this default

mechanism. When the accessPath is changed after the first creation or

initialization (i.e. through interpConfigure -accessPath

list), an auto_reset is automatically evaluated in the safe

interpreter to synchronize its auto_index with the new token

list.

ATTRIBUTES

See attributes(5) for descriptions of the following attri-

butes:

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| ATTRIBUTE TYPE | ATTRIBUTE VALUE|

|____________________|__________________|_

| Availability | runtime/tcl-8 |

|____________________|__________________|_

| Interface Stability| Uncommitted |

|____________________|_________________|

NOTES Source for Tcl is available on http://opensolaris.org. Tcl Last change: 8.0 7

Manual Pages for UNIX Operating System command usage for man SafeBase

NAME

SYNOPSIS

DESCRIPTION

ERROR for slave interp10 : /foo/bar/init.tcl: no such file or directory

SEE ALSO

ATTRIBUTES

| ATTRIBUTE TYPE | ATTRIBUTE VALUE|