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	/*
	* Copyright (c) 2008, 2018, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package sun.invoke.util;

	import java.lang.reflect.Modifier;
	import static java.lang.reflect.Modifier.*;
	import java.util.Objects;
	import jdk.internal.reflect.Reflection;

	/**
	* This class centralizes information about the JVM's linkage access control.
	* @author jrose
	*/
	public class VerifyAccess {

	private VerifyAccess() { } // cannot instantiate

	private static final int UNCONDITIONAL_ALLOWED = java.lang.invoke.MethodHandles.Lookup.UNCONDITIONAL;
	private static final int MODULE_ALLOWED = java.lang.invoke.MethodHandles.Lookup.MODULE;
	private static final int PACKAGE_ONLY = 0;
	private static final int PACKAGE_ALLOWED = java.lang.invoke.MethodHandles.Lookup.PACKAGE;
	private static final int PROTECTED_OR_PACKAGE_ALLOWED = (PACKAGE_ALLOWED\|PROTECTED);
	private static final int ALL_ACCESS_MODES = (PUBLIC\|PRIVATE\|PROTECTED\|PACKAGE_ONLY);

	/**
	* Evaluate the JVM linkage rules for access to the given method
	* on behalf of a caller class which proposes to perform the access.
	* Return true if the caller class has privileges to invoke a method
	* or access a field with the given properties.
	* This requires an accessibility check of the referencing class,
	* plus an accessibility check of the member within the class,
	* which depends on the member's modifier flags.
	* <p>
	* The relevant properties include the defining class ({@code defc})
	* of the member, and its modifier flags ({@code mods}).
	* Also relevant is the class used to make the initial symbolic reference
	* to the member ({@code refc}). If this latter class is not distinguished,
	* the defining class should be passed for both arguments ({@code defc == refc}).
	* <h3>JVM Specification, 5.4.4 "Access Control"</h3>
	* A field or method R is accessible to a class or interface D if
	* and only if any of the following is true:
	* <ul>
	* <li>R is public.</li>
	* <li>R is protected and is declared in a class C, and D is either
	* a subclass of C or C itself. Furthermore, if R is not static,
	* then the symbolic reference to R must contain a symbolic
	* reference to a class T, such that T is either a subclass of D,
	* a superclass of D, or D itself.
	* <p>During verification, it was also required that, even if T is
	* a superclass of D, the target reference of a protected instance
	* field access or method invocation must be an instance of D or a
	* subclass of D (4.10.1.8).</p></li>
	* <li>R is either protected or has default access (that is, neither
	* public nor protected nor private), and is declared by a class
	* in the same run-time package as D.</li>
	* <li>R is private and is declared in D by a class or interface
	* belonging to the same nest as D.</li>
	* </ul>
	* If a referenced field or method is not accessible, access checking
	* throws an IllegalAccessError. If an exception is thrown while
	* attempting to determine the nest host of a class or interface,
	* access checking fails for the same reason.
	*
	* @param refc the class used in the symbolic reference to the proposed member
	* @param defc the class in which the proposed member is actually defined
	* @param mods modifier flags for the proposed member
	* @param lookupClass the class for which the access check is being made
	* @return true iff the accessing class can access such a member
	*/
	public static boolean isMemberAccessible(Class<?> refc, // symbolic ref class
	Class<?> defc, // actual def class
	int mods, // actual member mods
	Class<?> lookupClass,
	int allowedModes) {
	if (allowedModes == 0) return false;
	assert((allowedModes & PUBLIC) != 0 &&
	(allowedModes & ~(ALL_ACCESS_MODES\|PACKAGE_ALLOWED\|MODULE_ALLOWED\|UNCONDITIONAL_ALLOWED)) == 0);
	// The symbolic reference class (refc) must always be fully verified.
	if (!isClassAccessible(refc, lookupClass, allowedModes)) {
	return false;
	}
	// Usually refc and defc are the same, but verify defc also in case they differ.
	if (defc == lookupClass &&
	(allowedModes & PRIVATE) != 0)
	return true; // easy check; all self-access is OK with a private lookup

	switch (mods & ALL_ACCESS_MODES) {
	case PUBLIC:
	return true; // already checked above
	case PROTECTED:
	assert !defc.isInterface(); // protected members aren't allowed in interfaces
	if ((allowedModes & PROTECTED_OR_PACKAGE_ALLOWED) != 0 &&
	isSamePackage(defc, lookupClass))
	return true;
	if ((allowedModes & PROTECTED) == 0)
	return false;
	// Protected members are accessible by subclasses, which does not include interfaces.
	// Interfaces are types, not classes. They should not have access to
	// protected members in j.l.Object, even though it is their superclass.
	if ((mods & STATIC) != 0 &&
	!isRelatedClass(refc, lookupClass))
	return false;
	if ((allowedModes & PROTECTED) != 0 &&
	isSubClass(lookupClass, defc))
	return true;
	return false;
	case PACKAGE_ONLY: // That is, zero. Unmarked member is package-only access.
	assert !defc.isInterface(); // package-private members aren't allowed in interfaces
	return ((allowedModes & PACKAGE_ALLOWED) != 0 &&
	isSamePackage(defc, lookupClass));
	case PRIVATE:
	// Rules for privates follows access rules for nestmates.
	boolean canAccess = ((allowedModes & PRIVATE) != 0 &&
	Reflection.areNestMates(defc, lookupClass));
	// for private methods the selected method equals the
	// resolved method - so refc == defc
	assert (canAccess && refc == defc) \|\| !canAccess;
	return canAccess;
	default:
	throw new IllegalArgumentException("bad modifiers: "+Modifier.toString(mods));
	}
	}

	static boolean isRelatedClass(Class<?> refc, Class<?> lookupClass) {
	return (refc == lookupClass \|\|
	isSubClass(refc, lookupClass) \|\|
	isSubClass(lookupClass, refc));
	}

	static boolean isSubClass(Class<?> lookupClass, Class<?> defc) {
	return defc.isAssignableFrom(lookupClass) &&
	!lookupClass.isInterface(); // interfaces are types, not classes.
	}

	static int getClassModifiers(Class<?> c) {
	// This would return the mask stored by javac for the source-level modifiers.
	// return c.getModifiers();
	// But what we need for JVM access checks are the actual bits from the class header.
	// ...But arrays and primitives are synthesized with their own odd flags:
	if (c.isArray() \|\| c.isPrimitive())
	return c.getModifiers();
	return Reflection.getClassAccessFlags(c);
	}

	/**
	* Evaluate the JVM linkage rules for access to the given class on behalf of caller.
	* <h3>JVM Specification, 5.4.4 "Access Control"</h3>
	* A class or interface C is accessible to a class or interface D
	* if and only if any of the following conditions are true:<ul>
	* <li>C is public and in the same module as D.
	* <li>D is in a module that reads the module containing C, C is public and in a
	* package that is exported to the module that contains D.
	* <li>C and D are members of the same runtime package.
	* </ul>
	* @param refc the symbolic reference class to which access is being checked (C)
	* @param lookupClass the class performing the lookup (D)
	*/
	public static boolean isClassAccessible(Class<?> refc, Class<?> lookupClass,
	int allowedModes) {
	if (allowedModes == 0) return false;
	assert((allowedModes & PUBLIC) != 0 &&
	(allowedModes & ~(ALL_ACCESS_MODES\|PACKAGE_ALLOWED\|MODULE_ALLOWED\|UNCONDITIONAL_ALLOWED)) == 0);
	int mods = getClassModifiers(refc);
	if (isPublic(mods)) {

	Module lookupModule = lookupClass.getModule();
	Module refModule = refc.getModule();

	// early VM startup case, java.base not defined
	if (lookupModule == null) {
	assert refModule == null;
	return true;
	}

	// trivially allow
	if ((allowedModes & MODULE_ALLOWED) != 0 &&
	(lookupModule == refModule))
	return true;

	// check readability when UNCONDITIONAL not allowed
	if (((allowedModes & UNCONDITIONAL_ALLOWED) != 0)
	\|\| lookupModule.canRead(refModule)) {

	// check that refc is in an exported package
	if ((allowedModes & MODULE_ALLOWED) != 0) {
	if (refModule.isExported(refc.getPackageName(), lookupModule))
	return true;
	} else {
	// exported unconditionally
	if (refModule.isExported(refc.getPackageName()))
	return true;
	}

	// not exported but allow access during VM initialization
	// because java.base does not have its exports setup
	if (!jdk.internal.misc.VM.isModuleSystemInited())
	return true;
	}

	// public class not accessible to lookupClass
	return false;
	}
	if ((allowedModes & PACKAGE_ALLOWED) != 0 &&
	isSamePackage(lookupClass, refc))
	return true;
	return false;
	}

	/**
	* Decide if the given method type, attributed to a member or symbolic
	* reference of a given reference class, is really visible to that class.
	* @param type the supposed type of a member or symbolic reference of refc
	* @param refc the class attempting to make the reference
	*/
	public static boolean isTypeVisible(Class<?> type, Class<?> refc) {
	if (type == refc) {
	return true; // easy check
	}
	while (type.isArray()) type = type.getComponentType();
	if (type.isPrimitive() \|\| type == Object.class) {
	return true;
	}
	ClassLoader typeLoader = type.getClassLoader();
	ClassLoader refcLoader = refc.getClassLoader();
	if (typeLoader == refcLoader) {
	return true;
	}
	if (refcLoader == null && typeLoader != null) {
	return false;
	}
	if (typeLoader == null && type.getName().startsWith("java.")) {
	// Note: The API for actually loading classes, ClassLoader.defineClass,
	// guarantees that classes with names beginning "java." cannot be aliased,
	// because class loaders cannot load them directly.
	return true;
	}

	// Do it the hard way: Look up the type name from the refc loader.
	//
	// Force the refc loader to report and commit to a particular binding for this type name (type.getName()).
	//
	// In principle, this query might force the loader to load some unrelated class,
	// which would cause this query to fail (and the original caller to give up).
	// This would be wasted effort, but it is expected to be very rare, occurring
	// only when an attacker is attempting to create a type alias.
	// In the normal case, one class loader will simply delegate to the other,
	// and the same type will be visible through both, with no extra loading.
	//
	// It is important to go through Class.forName instead of ClassLoader.loadClass
	// because Class.forName goes through the JVM system dictionary, which records
	// the class lookup once for all. This means that even if a not-well-behaved class loader
	// would "change its mind" about the meaning of the name, the Class.forName request
	// will use the result cached in the JVM system dictionary. Note that the JVM system dictionary
	// will record the first successful result. Unsuccessful results are not stored.
	//
	// We use doPrivileged in order to allow an unprivileged caller to ask an arbitrary
	// class loader about the binding of the proposed name (type.getName()).
	// The looked up type ("res") is compared for equality against the proposed
	// type ("type") and then is discarded. Thus, the worst that can happen to
	// the "child" class loader is that it is bothered to load and report a class
	// that differs from "type"; this happens once due to JVM system dictionary
	// memoization. And the caller never gets to look at the alternate type binding
	// ("res"), whether it exists or not.
	final String name = type.getName();
	Class<?> res = java.security.AccessController.doPrivileged(
	new java.security.PrivilegedAction<>() {
	public Class<?> run() {
	try {
	return Class.forName(name, false, refcLoader);
	} catch (ClassNotFoundException \| LinkageError e) {
	return null; // Assume the class is not found
	}
	}
	});
	return (type == res);
	}

	/**
	* Decide if the given method type, attributed to a member or symbolic
	* reference of a given reference class, is really visible to that class.
	* @param type the supposed type of a member or symbolic reference of refc
	* @param refc the class attempting to make the reference
	*/
	public static boolean isTypeVisible(java.lang.invoke.MethodType type, Class<?> refc) {
	if (!isTypeVisible(type.returnType(), refc)) {
	return false;
	}
	for (int n = 0, max = type.parameterCount(); n < max; n++) {
	if (!isTypeVisible(type.parameterType(n), refc)) {
	return false;
	}
	}
	return true;
	}

	/**
	* Tests if two classes are in the same module.
	* @param class1 a class
	* @param class2 another class
	* @return whether they are in the same module
	*/
	public static boolean isSameModule(Class<?> class1, Class<?> class2) {
	return class1.getModule() == class2.getModule();
	}

	/**
	* Test if two classes have the same class loader and package qualifier.
	* @param class1 a class
	* @param class2 another class
	* @return whether they are in the same package
	*/
	public static boolean isSamePackage(Class<?> class1, Class<?> class2) {
	if (class1 == class2)
	return true;
	if (class1.getClassLoader() != class2.getClassLoader())
	return false;
	return Objects.equals(class1.getPackageName(), class2.getPackageName());
	}

	/**
	* Test if two classes are defined as part of the same package member (top-level class).
	* If this is true, they can share private access with each other.
	* @param class1 a class
	* @param class2 another class
	* @return whether they are identical or nested together
	*/
	public static boolean isSamePackageMember(Class<?> class1, Class<?> class2) {
	if (class1 == class2)
	return true;
	if (!isSamePackage(class1, class2))
	return false;
	if (getOutermostEnclosingClass(class1) != getOutermostEnclosingClass(class2))
	return false;
	return true;
	}

	private static Class<?> getOutermostEnclosingClass(Class<?> c) {
	Class<?> pkgmem = c;
	for (Class<?> enc = c; (enc = enc.getEnclosingClass()) != null; )
	pkgmem = enc;
	return pkgmem;
	}

	private static boolean loadersAreRelated(ClassLoader loader1, ClassLoader loader2,
	boolean loader1MustBeParent) {
	if (loader1 == loader2 \|\| loader1 == null
	\|\| (loader2 == null && !loader1MustBeParent)) {
	return true;
	}
	for (ClassLoader scan2 = loader2;
	scan2 != null; scan2 = scan2.getParent()) {
	if (scan2 == loader1) return true;
	}
	if (loader1MustBeParent) return false;
	// see if loader2 is a parent of loader1:
	for (ClassLoader scan1 = loader1;
	scan1 != null; scan1 = scan1.getParent()) {
	if (scan1 == loader2) return true;
	}
	return false;
	}

	/**
	* Is the class loader of parentClass identical to, or an ancestor of,
	* the class loader of childClass?
	* @param parentClass a class
	* @param childClass another class, which may be a descendent of the first class
	* @return whether parentClass precedes or equals childClass in class loader order
	*/
	public static boolean classLoaderIsAncestor(Class<?> parentClass, Class<?> childClass) {
	return loadersAreRelated(parentClass.getClassLoader(), childClass.getClassLoader(), true);
	}
	}

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