1 /*
2 * Copyright (c) 2008, 2018, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package sun.invoke.util;
27
28 import java.lang.reflect.Modifier;
29 import static java.lang.reflect.Modifier.*;
30 import java.util.Objects;
31 import jdk.internal.reflect.Reflection;
32
33 /**
34 * This class centralizes information about the JVM's linkage access control.
35 * @author jrose
36 */
37 public class VerifyAccess {
38
39 private VerifyAccess() { } // cannot instantiate
40
41 private static final int UNCONDITIONAL_ALLOWED = java.lang.invoke.MethodHandles.Lookup.UNCONDITIONAL;
42 private static final int MODULE_ALLOWED = java.lang.invoke.MethodHandles.Lookup.MODULE;
43 private static final int PACKAGE_ONLY = 0;
44 private static final int PACKAGE_ALLOWED = java.lang.invoke.MethodHandles.Lookup.PACKAGE;
45 private static final int PROTECTED_OR_PACKAGE_ALLOWED = (PACKAGE_ALLOWED|PROTECTED);
46 private static final int ALL_ACCESS_MODES = (PUBLIC|PRIVATE|PROTECTED|PACKAGE_ONLY);
47
48 /**
49 * Evaluate the JVM linkage rules for access to the given method
50 * on behalf of a caller class which proposes to perform the access.
51 * Return true if the caller class has privileges to invoke a method
52 * or access a field with the given properties.
53 * This requires an accessibility check of the referencing class,
54 * plus an accessibility check of the member within the class,
55 * which depends on the member's modifier flags.
56 * <p>
57 * The relevant properties include the defining class ({@code defc})
58 * of the member, and its modifier flags ({@code mods}).
59 * Also relevant is the class used to make the initial symbolic reference
60 * to the member ({@code refc}). If this latter class is not distinguished,
61 * the defining class should be passed for both arguments ({@code defc == refc}).
62 * <h3>JVM Specification, 5.4.4 "Access Control"</h3>
63 * A field or method R is accessible to a class or interface D if
64 * and only if any of the following is true:
65 * <ul>
66 * <li>R is public.</li>
67 * <li>R is protected and is declared in a class C, and D is either
68 * a subclass of C or C itself. Furthermore, if R is not static,
69 * then the symbolic reference to R must contain a symbolic
70 * reference to a class T, such that T is either a subclass of D,
71 * a superclass of D, or D itself.
72 * <p>During verification, it was also required that, even if T is
73 * a superclass of D, the target reference of a protected instance
74 * field access or method invocation must be an instance of D or a
75 * subclass of D (4.10.1.8).</p></li>
76 * <li>R is either protected or has default access (that is, neither
77 * public nor protected nor private), and is declared by a class
78 * in the same run-time package as D.</li>
79 * <li>R is private and is declared in D by a class or interface
80 * belonging to the same nest as D.</li>
81 * </ul>
82 * If a referenced field or method is not accessible, access checking
83 * throws an IllegalAccessError. If an exception is thrown while
84 * attempting to determine the nest host of a class or interface,
85 * access checking fails for the same reason.
86 *
87 * @param refc the class used in the symbolic reference to the proposed member
88 * @param defc the class in which the proposed member is actually defined
89 * @param mods modifier flags for the proposed member
90 * @param lookupClass the class for which the access check is being made
91 * @return true iff the accessing class can access such a member
92 */
93 public static boolean isMemberAccessible(Class<?> refc, // symbolic ref class
94 Class<?> defc, // actual def class
95 int mods, // actual member mods
96 Class<?> lookupClass,
97 int allowedModes) {
98 if (allowedModes == 0) return false;
99 assert((allowedModes & PUBLIC) != 0 &&
100 (allowedModes & ~(ALL_ACCESS_MODES|PACKAGE_ALLOWED|MODULE_ALLOWED|UNCONDITIONAL_ALLOWED)) == 0);
101 // The symbolic reference class (refc) must always be fully verified.
102 if (!isClassAccessible(refc, lookupClass, allowedModes)) {
103 return false;
104 }
105 // Usually refc and defc are the same, but verify defc also in case they differ.
106 if (defc == lookupClass)
107 return true; // easy check; all self-access is OK
108
109 switch (mods & ALL_ACCESS_MODES) {
110 case PUBLIC:
111 return true; // already checked above
112 case PROTECTED:
113 assert !defc.isInterface(); // protected members aren't allowed in interfaces
114 if ((allowedModes & PROTECTED_OR_PACKAGE_ALLOWED) != 0 &&
115 isSamePackage(defc, lookupClass))
116 return true;
117 if ((allowedModes & PROTECTED) == 0)
118 return false;
119 // Protected members are accessible by subclasses, which does not include interfaces.
120 // Interfaces are types, not classes. They should not have access to
121 // protected members in j.l.Object, even though it is their superclass.
122 if ((mods & STATIC) != 0 &&
123 !isRelatedClass(refc, lookupClass))
124 return false;
125 if ((allowedModes & PROTECTED) != 0 &&
126 isSubClass(lookupClass, defc))
127 return true;
128 return false;
129 case PACKAGE_ONLY: // That is, zero. Unmarked member is package-only access.
130 assert !defc.isInterface(); // package-private members aren't allowed in interfaces
131 return ((allowedModes & PACKAGE_ALLOWED) != 0 &&
132 isSamePackage(defc, lookupClass));
133 case PRIVATE:
134 // Rules for privates follows access rules for nestmates.
135 return ((allowedModes & PRIVATE) != 0 &&
136 Reflection.areNestMates(defc, lookupClass));
137 default:
138 throw new IllegalArgumentException("bad modifiers: "+Modifier.toString(mods));
139 }
140 }
141
142 static boolean isRelatedClass(Class<?> refc, Class<?> lookupClass) {
143 return (refc == lookupClass ||
144 isSubClass(refc, lookupClass) ||
145 isSubClass(lookupClass, refc));
146 }
147
148 static boolean isSubClass(Class<?> lookupClass, Class<?> defc) {
149 return defc.isAssignableFrom(lookupClass) &&
150 !lookupClass.isInterface(); // interfaces are types, not classes.
151 }
152
153 static int getClassModifiers(Class<?> c) {
154 // This would return the mask stored by javac for the source-level modifiers.
155 // return c.getModifiers();
156 // But what we need for JVM access checks are the actual bits from the class header.
157 // ...But arrays and primitives are synthesized with their own odd flags:
158 if (c.isArray() || c.isPrimitive())
159 return c.getModifiers();
160 return Reflection.getClassAccessFlags(c);
161 }
162
163 /**
164 * Evaluate the JVM linkage rules for access to the given class on behalf of caller.
165 * <h3>JVM Specification, 5.4.4 "Access Control"</h3>
166 * A class or interface C is accessible to a class or interface D
167 * if and only if any of the following conditions are true:<ul>
168 * <li>C is public and in the same module as D.
169 * <li>D is in a module that reads the module containing C, C is public and in a
170 * package that is exported to the module that contains D.
171 * <li>C and D are members of the same runtime package.
172 * </ul>
173 * @param refc the symbolic reference class to which access is being checked (C)
174 * @param lookupClass the class performing the lookup (D)
175 */
176 public static boolean isClassAccessible(Class<?> refc, Class<?> lookupClass,
177 int allowedModes) {
178 if (allowedModes == 0) return false;
179 assert((allowedModes & PUBLIC) != 0 &&
180 (allowedModes & ~(ALL_ACCESS_MODES|PACKAGE_ALLOWED|MODULE_ALLOWED|UNCONDITIONAL_ALLOWED)) == 0);
181 int mods = getClassModifiers(refc);
182 if (isPublic(mods)) {
183
184 Module lookupModule = lookupClass.getModule();
185 Module refModule = refc.getModule();
186
187 // early VM startup case, java.base not defined
188 if (lookupModule == null) {
189 assert refModule == null;
190 return true;
191 }
192
193 // trivially allow
194 if ((allowedModes & MODULE_ALLOWED) != 0 &&
195 (lookupModule == refModule))
196 return true;
197
198 // check readability when UNCONDITIONAL not allowed
199 if (((allowedModes & UNCONDITIONAL_ALLOWED) != 0)
200 || lookupModule.canRead(refModule)) {
201
202 // check that refc is in an exported package
203 if ((allowedModes & MODULE_ALLOWED) != 0) {
204 if (refModule.isExported(refc.getPackageName(), lookupModule))
205 return true;
206 } else {
207 // exported unconditionally
208 if (refModule.isExported(refc.getPackageName()))
209 return true;
210 }
211
212 // not exported but allow access during VM initialization
213 // because java.base does not have its exports setup
214 if (!jdk.internal.misc.VM.isModuleSystemInited())
215 return true;
216 }
217
218 // public class not accessible to lookupClass
219 return false;
220 }
221 if ((allowedModes & PACKAGE_ALLOWED) != 0 &&
222 isSamePackage(lookupClass, refc))
223 return true;
224 return false;
225 }
226
227 /**
228 * Decide if the given method type, attributed to a member or symbolic
229 * reference of a given reference class, is really visible to that class.
230 * @param type the supposed type of a member or symbolic reference of refc
231 * @param refc the class attempting to make the reference
232 */
233 public static boolean isTypeVisible(Class<?> type, Class<?> refc) {
234 if (type == refc) {
235 return true; // easy check
236 }
237 while (type.isArray()) type = type.getComponentType();
238 if (type.isPrimitive() || type == Object.class) {
239 return true;
240 }
241 ClassLoader typeLoader = type.getClassLoader();
242 ClassLoader refcLoader = refc.getClassLoader();
243 if (typeLoader == refcLoader) {
244 return true;
245 }
246 if (refcLoader == null && typeLoader != null) {
247 return false;
248 }
249 if (typeLoader == null && type.getName().startsWith("java.")) {
250 // Note: The API for actually loading classes, ClassLoader.defineClass,
251 // guarantees that classes with names beginning "java." cannot be aliased,
252 // because class loaders cannot load them directly.
253 return true;
254 }
255
256 // Do it the hard way: Look up the type name from the refc loader.
257 //
258 // Force the refc loader to report and commit to a particular binding for this type name (type.getName()).
259 //
260 // In principle, this query might force the loader to load some unrelated class,
261 // which would cause this query to fail (and the original caller to give up).
262 // This would be wasted effort, but it is expected to be very rare, occurring
263 // only when an attacker is attempting to create a type alias.
264 // In the normal case, one class loader will simply delegate to the other,
265 // and the same type will be visible through both, with no extra loading.
266 //
267 // It is important to go through Class.forName instead of ClassLoader.loadClass
268 // because Class.forName goes through the JVM system dictionary, which records
269 // the class lookup once for all. This means that even if a not-well-behaved class loader
270 // would "change its mind" about the meaning of the name, the Class.forName request
271 // will use the result cached in the JVM system dictionary. Note that the JVM system dictionary
272 // will record the first successful result. Unsuccessful results are not stored.
273 //
274 // We use doPrivileged in order to allow an unprivileged caller to ask an arbitrary
275 // class loader about the binding of the proposed name (type.getName()).
276 // The looked up type ("res") is compared for equality against the proposed
277 // type ("type") and then is discarded. Thus, the worst that can happen to
278 // the "child" class loader is that it is bothered to load and report a class
279 // that differs from "type"; this happens once due to JVM system dictionary
280 // memoization. And the caller never gets to look at the alternate type binding
281 // ("res"), whether it exists or not.
282 final String name = type.getName();
283 Class<?> res = java.security.AccessController.doPrivileged(
284 new java.security.PrivilegedAction<>() {
285 public Class<?> run() {
286 try {
287 return Class.forName(name, false, refcLoader);
288 } catch (ClassNotFoundException | LinkageError e) {
289 return null; // Assume the class is not found
290 }
291 }
292 });
293 return (type == res);
294 }
295
296 /**
297 * Decide if the given method type, attributed to a member or symbolic
298 * reference of a given reference class, is really visible to that class.
299 * @param type the supposed type of a member or symbolic reference of refc
300 * @param refc the class attempting to make the reference
301 */
302 public static boolean isTypeVisible(java.lang.invoke.MethodType type, Class<?> refc) {
303 if (!isTypeVisible(type.returnType(), refc)) {
304 return false;
305 }
306 for (int n = 0, max = type.parameterCount(); n < max; n++) {
307 if (!isTypeVisible(type.parameterType(n), refc)) {
308 return false;
309 }
310 }
311 return true;
312 }
313
314 /**
315 * Tests if two classes are in the same module.
316 * @param class1 a class
317 * @param class2 another class
318 * @return whether they are in the same module
319 */
320 public static boolean isSameModule(Class<?> class1, Class<?> class2) {
321 return class1.getModule() == class2.getModule();
322 }
323
324 /**
325 * Test if two classes have the same class loader and package qualifier.
326 * @param class1 a class
327 * @param class2 another class
328 * @return whether they are in the same package
329 */
330 public static boolean isSamePackage(Class<?> class1, Class<?> class2) {
331 assert(!class1.isArray() && !class2.isArray());
332 if (class1 == class2)
333 return true;
334 if (class1.getClassLoader() != class2.getClassLoader())
335 return false;
336 return Objects.equals(class1.getPackageName(), class2.getPackageName());
337 }
338
339 private static boolean loadersAreRelated(ClassLoader loader1, ClassLoader loader2,
340 boolean loader1MustBeParent) {
341 if (loader1 == loader2 || loader1 == null
342 || (loader2 == null && !loader1MustBeParent)) {
343 return true;
344 }
345 for (ClassLoader scan2 = loader2;
346 scan2 != null; scan2 = scan2.getParent()) {
347 if (scan2 == loader1) return true;
348 }
349 if (loader1MustBeParent) return false;
350 // see if loader2 is a parent of loader1:
351 for (ClassLoader scan1 = loader1;
352 scan1 != null; scan1 = scan1.getParent()) {
353 if (scan1 == loader2) return true;
354 }
355 return false;
356 }
357
358 /**
359 * Is the class loader of parentClass identical to, or an ancestor of,
360 * the class loader of childClass?
361 * @param parentClass a class
362 * @param childClass another class, which may be a descendent of the first class
363 * @return whether parentClass precedes or equals childClass in class loader order
364 */
365 public static boolean classLoaderIsAncestor(Class<?> parentClass, Class<?> childClass) {
366 return loadersAreRelated(parentClass.getClassLoader(), childClass.getClassLoader(), true);
367 }
368 }