Package org.apache.commons.jexl3.introspection

Interface JexlPermissions

All Known Implementing Classes:

JexlPermissions.ClassPermissions, JexlPermissions.Delegate

public interface JexlPermissions

This interface describes permissions used by JEXL introspection that constrain which packages/classes/constructors/fields/methods are made visible to JEXL scripts.

By specifying or implementing permissions, it is possible to constrain precisely which objects can be manipulated by JEXL, allowing users to enter their own expressions or scripts whilst maintaining tight control over what can be executed. JEXL introspection mechanism will check whether it is permitted to access a constructor, method or field before exposition to the JexlUberspect. The restrictions are applied in all cases, for any JexlUberspect.ResolverStrategy.

This complements using a dedicated ClassLoader and/or SecurityManager - being deprecated - and possibly JexlSandbox with a simpler mechanism. The NoJexl annotation processing is actually performed using the result of calling parse(String...) with no arguments; implementations shall delegate calls to its methods for NoJexl to be processed.

A simple textual configuration can be used to create user-defined permissions using parse(String...).

To instantiate a JEXL engine using permissions, one should use a JexlBuilder and call JexlBuilder.permissions(JexlPermissions). Another approach would be to instantiate a JexlUberspect with those permissions and call JexlBuilder.uberspect(JexlUberspect).

To help migration from earlier versions, it is possible to revert to the JEXL 3.2 default lenient behavior by calling JexlBuilder.setDefaultPermissions(JexlPermissions) with UNRESTRICTED as parameter before creating a JEXL engine instance.

For the same reason, using JEXL through scripting, it is possible to revert the underlying JEXL behavior to JEXL 3.2 default by calling JexlScriptEngine.setPermissions(JexlPermissions) with UNRESTRICTED as parameter.

Since:

3.3

Nested Class Summary

Nested Classes

Modifier and Type	Interface	Description
static final class	JexlPermissions.ClassPermissions	A permission delegation that augments the RESTRICTED permission with an explicit set of classes.
static class	JexlPermissions.Delegate	A base for permission delegation allowing functional refinement.

Field Summary

Fields

Modifier and Type	Field	Description
static final JexlPermissions	RESTRICTED	A restricted singleton.
static final JexlPermissions	UNRESTRICTED	The unrestricted permissions.

Method Summary

Modifier and Type	Method	Description
boolean	allow(Class<?> clazz)	Checks whether a class allows JEXL introspection.
boolean	allow(Package pack)	Checks whether a package allows JEXL introspection.
boolean	allow(Constructor<?> ctor)	Checks whether a constructor allows JEXL introspection.
boolean	allow(Field field)	Checks whether a field explicitly disallows JEXL introspection.
boolean	allow(Method method)	Checks whether a method allows JEXL introspection.
JexlPermissions	compose(String... src)	Compose these permissions with a new set.
static JexlPermissions	parse(String... src)	Parses a set of permissions.
default boolean	validate(Class<?> clazz)	Checks that a class is valid for permission check.
default boolean	validate(Package pack)	Checks that a package is valid for permission check.
default boolean	validate(Constructor<?> constructor)	Checks that a constructor is valid for permission check.
default boolean	validate(Field field)	Checks that a field is valid for permission check.
default boolean	validate(Method method)	Checks that a method is valid for permission check.

Field Details

UNRESTRICTED

static final JexlPermissions UNRESTRICTED

The unrestricted permissions.

This enables any public class, method, constructor or field to be visible to JEXL and used in scripts.

Since:

3.3

RESTRICTED

static final JexlPermissions RESTRICTED

A restricted singleton.

The RESTRICTED set is built using the following allowed packages and denied packages/classes.

Of particular importance are the restrictions on the System, Runtime, ProcessBuilder, Class and those on java.net, java.net, java.io and java.lang.reflect that should provide a decent level of isolation between the scripts and its host.

As a simple guide, any line that ends with ".*" is allowing a package, any other is denying a package, class or method.

• java.nio.*
• java.io.*
• java.lang.*
• java.math.*
• java.text.*
• java.util.*
• org.w3c.dom.*
• org.apache.commons.jexl3.*
• org.apache.commons.jexl3 { JexlBuilder {} }
• org.apache.commons.jexl3.internal { Engine {} }
• java.lang { Runtime {} System {} ProcessBuilder {} Class {} }
• java.lang.annotation {}
• java.lang.instrument {}
• java.lang.invoke {}
• java.lang.management {}
• java.lang.ref {}
• java.lang.reflect {}
• java.net {}
• java.io { File { } }
• java.nio { Path { } Paths { } Files { } }
• java.rmi {}

Method Details

parse

static JexlPermissions parse(String... src)

Parses a set of permissions.

In JEXL 3.3, the syntax recognizes 2 types of permissions:

• Allowing access to a wildcard restricted set of packages.
• Denying access to packages, classes (and inner classes), methods and fields

Wildcards specifications determine the set of allowed packages. When empty, all packages can be used. When using JEXL to expose functional elements, their packages should be exposed through wildcards. These allow composing the volume of what is allowed by addition.

Restrictions behave exactly like the NoJexl annotation; they can restrict access to package, class, inner-class, methods and fields. These allow refining the volume of what is allowed by extrusion.

An example of a tight environment that would not allow scripts to wander could be:

  # allow a very restricted set of base classes
  java.math.*
  java.text.*
  java.util.*
  # deny classes that could pose a security risk
  java.lang { Runtime {} System {} ProcessBuilder {} Class {} }
  org.apache.commons.jexl3 { JexlBuilder {} }
  

• Syntax for wildcards is the name of the package suffixed by .*.
• Syntax for restrictions is a list of package restrictions.
• A package restriction is a package name followed by a block (as in curly-bracket block {}) that contains a list of class restrictions.
• A class restriction is a class name prefixed by an optional - or + sign followed by a block of member restrictions.
• A member restriction can be a class restriction - to restrict nested classes -, a field which is the Java field name suffixed with ;, a method composed of its Java name suffixed with ();. Constructor restrictions are specified like methods using the class name as method name.
• By default or when prefixed with a -, a class restriction is explicitly denying the members declared in its block (or the whole class)
• When prefixed with a +, a class restriction is explicitly allowing the members declared in its block (or the whole class)

All overrides and overloads of a constructors or method are allowed or restricted at the same time, the restriction being based on their names, not their whole signature. This differs from the @NoJexl annotation.

  # some wildcards
  java.lang.*; # java.lang is pretty much a must have
  my.allowed.package0.*
  another.allowed.package1.*
  # nojexl like restrictions
  my.package.internal {} # the whole package is hidden
  my.package {
   +class4 { theMethod(); } # only theMethod can be called in class4
   class0 {
     class1 {} # the whole class1 is hidden
     class2 {
         class2(); # class2 constructors can not be invoked
         class3 {
             aMethod(); # aMethod can not be called
             aField; # aField can not be accessed
         }
     } # end of class2
     class0(); # class0 constructors can not be invoked
     method(); # method can not be called
     field; # field can not be accessed
   } # end class0
 } # end package my.package
 

Parameters:

src - the permissions source, the default (NoJexl aware) permissions if null

Returns:

the permissions instance

Since:

3.3

allow

boolean allow(Class<?> clazz)

Checks whether a class allows JEXL introspection.

If the class disallows JEXL introspection, none of its constructors, methods or fields as well as derived classes are visible to JEXL and can not be used in scripts or expressions. If one of its super-classes is not allowed, tbe class is not allowed either.

For interfaces, only methods and fields are disallowed in derived interfaces or implementing classes.

Parameters:

clazz - the class to check

Returns:

true if JEXL is allowed to introspect, false otherwise

Since:

3.3

allow

boolean allow(Constructor<?> ctor)

Checks whether a constructor allows JEXL introspection.

If a constructor is not allowed, the new operator can not be used to instantiate its declared class in scripts or expressions.

Parameters:

ctor - the constructor to check

Returns:

true if JEXL is allowed to introspect, false otherwise

Since:

3.3

allow

boolean allow(Field field)

Checks whether a field explicitly disallows JEXL introspection.

If a field is not allowed, it can not resolved and accessed in scripts or expressions.

Parameters:

field - the field to check

Returns:

true if JEXL is allowed to introspect, false otherwise

Since:

3.3

allow

boolean allow(Method method)

Checks whether a method allows JEXL introspection.

If a method is not allowed, it can not resolved and called in scripts or expressions.

Since methods can be overridden and overloaded, this also checks that no superclass or interface explicitly disallows this methods.

Parameters:

method - the method to check

Returns:

true if JEXL is allowed to introspect, false otherwise

Since:

3.3

allow

boolean allow(Package pack)

Checks whether a package allows JEXL introspection.

If the package disallows JEXL introspection, none of its classes or interfaces are visible to JEXL and can not be used in scripts or expression.

Parameters:

pack - the package

Returns:

true if JEXL is allowed to introspect, false otherwise

Since:

3.3

compose

JexlPermissions compose(String... src)

Compose these permissions with a new set.

This is a convenience method meant to easily give access to the packages JEXL is used to integrate with. For instance, using RESTRICTED.compose("com.my.app.*") would extend the restricted set of permissions by allowing the com.my.app package.

Parameters:

src - the new constraints

Returns:

the new permissions

validate

default boolean validate(Class<?> clazz)

Checks that a class is valid for permission check.

Parameters:

clazz - the class

Returns:

true if the class is not null, false otherwise

validate

default boolean validate(Constructor<?> constructor)

Checks that a constructor is valid for permission check.

Parameters:

constructor - the constructor

Returns:

true if constructor is not null and public, false otherwise

validate

default boolean validate(Field field)

Checks that a field is valid for permission check.

Parameters:

field - the constructor

Returns:

true if field is not null and public, false otherwise

validate

default boolean validate(Method method)

Checks that a method is valid for permission check.

Parameters:

method - the method

Returns:

true if method is not null and public, false otherwise

validate

default boolean validate(Package pack)

Checks that a package is valid for permission check.

Parameters:

pack - the package

Returns:

true if the class is not null, false otherwise