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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * 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

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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);

    private static final boolean ALLOW_NESTMATE_ACCESS = false;

    /**

     * 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 conditions is true:<ul>

     * <li>R is public.

     * <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.

     * <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 runtime package as D.

     * <li>R is private and is declared in D.

     * </ul>

     * This discussion of access control omits a related restriction

     * on the target of a protected field access or method invocation

     * (the target must be of class D or a subtype of D). That

     * requirement is checked as part of the verification process

     * (5.4.1); it is not part of link-time access control.

     * @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

        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:

            // Loosened rules for privates follows access rules for inner classes.

            return (ALLOW_NESTMATE_ACCESS &&

                    (allowedModes & PRIVATE) != 0 &&

                    isSamePackageMember(defc, lookupClass));

        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) {

        assert(!class1.isArray() && !class2.isArray());

        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);

    }

}