1 /*
2 * Copyright (c) 2008, 2017, 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 private static final boolean ALLOW_NESTMATE_ACCESS = false;
48
49 /**
50 * Evaluate the JVM linkage rules for access to the given method
51 * on behalf of a caller class which proposes to perform the access.
52 * Return true if the caller class has privileges to invoke a method
53 * or access a field with the given properties.
54 * This requires an accessibility check of the referencing class,
55 * plus an accessibility check of the member within the class,
56 * which depends on the member's modifier flags.
57 * <p>
58 * The relevant properties include the defining class ({@code defc})
59 * of the member, and its modifier flags ({@code mods}).
60 * Also relevant is the class used to make the initial symbolic reference
61 * to the member ({@code refc}). If this latter class is not distinguished,
62 * the defining class should be passed for both arguments ({@code defc == refc}).
63 * <h3>JVM Specification, 5.4.4 "Access Control"</h3>
64 * A field or method R is accessible to a class or interface D if
65 * and only if any of the following conditions is true:<ul>
66 * <li>R is public.
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
69 * static, then the symbolic reference to R must contain a
70 * symbolic reference to a class T, such that T is either a
71 * subclass of D, a superclass of D or D itself.
72 * <li>R is either protected or has default access (that is,
73 * neither public nor protected nor private), and is declared
74 * by a class in the same runtime package as D.
75 * <li>R is private and is declared in D.
76 * </ul>
77 * This discussion of access control omits a related restriction
78 * on the target of a protected field access or method invocation
79 * (the target must be of class D or a subtype of D). That
80 * requirement is checked as part of the verification process
81 * (5.4.1); it is not part of link-time access control.
82 * @param refc the class used in the symbolic reference to the proposed member
83 * @param defc the class in which the proposed member is actually defined
84 * @param mods modifier flags for the proposed member
85 * @param lookupClass the class for which the access check is being made
86 * @return true iff the accessing class can access such a member
87 */
88 public static boolean isMemberAccessible(Class<?> refc, // symbolic ref class
89 Class<?> defc, // actual def class
90 int mods, // actual member mods
91 Class<?> lookupClass,
92 int allowedModes) {
93 if (allowedModes == 0) return false;
94 assert((allowedModes & PUBLIC) != 0 &&
95 (allowedModes & ~(ALL_ACCESS_MODES|PACKAGE_ALLOWED|MODULE_ALLOWED|UNCONDITIONAL_ALLOWED)) == 0);
96 // The symbolic reference class (refc) must always be fully verified.
97 if (!isClassAccessible(refc, lookupClass, allowedModes)) {
98 return false;
99 }
100 // Usually refc and defc are the same, but verify defc also in case they differ.
101 if (defc == lookupClass &&
102 (allowedModes & PRIVATE) != 0)
103 return true; // easy check; all self-access is OK
104 switch (mods & ALL_ACCESS_MODES) {
105 case PUBLIC:
106 return true; // already checked above
107 case PROTECTED:
108 assert !defc.isInterface(); // protected members aren't allowed in interfaces
109 if ((allowedModes & PROTECTED_OR_PACKAGE_ALLOWED) != 0 &&
110 isSamePackage(defc, lookupClass))
111 return true;
112 if ((allowedModes & PROTECTED) == 0)
113 return false;
114 // Protected members are accessible by subclasses, which does not include interfaces.
115 // Interfaces are types, not classes. They should not have access to
116 // protected members in j.l.Object, even though it is their superclass.
117 if ((mods & STATIC) != 0 &&
118 !isRelatedClass(refc, lookupClass))
119 return false;
120 if ((allowedModes & PROTECTED) != 0 &&
121 isSubClass(lookupClass, defc))
122 return true;
123 return false;
124 case PACKAGE_ONLY: // That is, zero. Unmarked member is package-only access.
125 assert !defc.isInterface(); // package-private members aren't allowed in interfaces
126 return ((allowedModes & PACKAGE_ALLOWED) != 0 &&
127 isSamePackage(defc, lookupClass));
128 case PRIVATE:
129 // Loosened rules for privates follows access rules for inner classes.
130 return (ALLOW_NESTMATE_ACCESS &&
131 (allowedModes & PRIVATE) != 0 &&
132 isSamePackageMember(defc, lookupClass));
133 default:
134 throw new IllegalArgumentException("bad modifiers: "+Modifier.toString(mods));
135 }
136 }
137
138 static boolean isRelatedClass(Class<?> refc, Class<?> lookupClass) {
139 return (refc == lookupClass ||
140 isSubClass(refc, lookupClass) ||
141 isSubClass(lookupClass, refc));
142 }
143
144 static boolean isSubClass(Class<?> lookupClass, Class<?> defc) {
145 return defc.isAssignableFrom(lookupClass) &&
146 !lookupClass.isInterface(); // interfaces are types, not classes.
147 }
148
149 static int getClassModifiers(Class<?> c) {
150 // This would return the mask stored by javac for the source-level modifiers.
151 // return c.getModifiers();
152 // But what we need for JVM access checks are the actual bits from the class header.
153 // ...But arrays and primitives are synthesized with their own odd flags:
154 if (c.isArray() || c.isPrimitive())
155 return c.getModifiers();
156 return Reflection.getClassAccessFlags(c);
157 }
158
159 /**
160 * Evaluate the JVM linkage rules for access to the given class on behalf of caller.
161 * <h3>JVM Specification, 5.4.4 "Access Control"</h3>
162 * A class or interface C is accessible to a class or interface D
163 * if and only if any of the following conditions are true:<ul>
164 * <li>C is public and in the same module as D.
165 * <li>D is in a module that reads the module containing C, C is public and in a
166 * package that is exported to the module that contains D.
167 * <li>C and D are members of the same runtime package.
168 * </ul>
169 * @param refc the symbolic reference class to which access is being checked (C)
170 * @param lookupClass the class performing the lookup (D)
171 */
172 public static boolean isClassAccessible(Class<?> refc, Class<?> lookupClass,
173 int allowedModes) {
174 if (allowedModes == 0) return false;
175 assert((allowedModes & PUBLIC) != 0 &&
176 (allowedModes & ~(ALL_ACCESS_MODES|PACKAGE_ALLOWED|MODULE_ALLOWED|UNCONDITIONAL_ALLOWED)) == 0);
177 int mods = getClassModifiers(refc);
178 if (isPublic(mods)) {
179
180 Module lookupModule = lookupClass.getModule();
181 Module refModule = refc.getModule();
182
183 // early VM startup case, java.base not defined
184 if (lookupModule == null) {
185 assert refModule == null;
186 return true;
187 }
188
189 // trivially allow
190 if ((allowedModes & MODULE_ALLOWED) != 0 &&
191 (lookupModule == refModule))
192 return true;
193
194 // check readability when UNCONDITIONAL not allowed
195 if (((allowedModes & UNCONDITIONAL_ALLOWED) != 0)
196 || lookupModule.canRead(refModule)) {
197
198 // check that refc is in an exported package
199 if ((allowedModes & MODULE_ALLOWED) != 0) {
200 if (refModule.isExported(refc.getPackageName(), lookupModule))
201 return true;
202 } else {
203 // exported unconditionally
204 if (refModule.isExported(refc.getPackageName()))
205 return true;
206 }
207
208 // not exported but allow access during VM initialization
209 // because java.base does not have its exports setup
210 if (!jdk.internal.misc.VM.isModuleSystemInited())
211 return true;
212 }
213
214 // public class not accessible to lookupClass
215 return false;
216 }
217 if ((allowedModes & PACKAGE_ALLOWED) != 0 &&
218 isSamePackage(lookupClass, refc))
219 return true;
220 return false;
221 }
222
223 /**
224 * Decide if the given method type, attributed to a member or symbolic
225 * reference of a given reference class, is really visible to that class.
226 * @param type the supposed type of a member or symbolic reference of refc
227 * @param refc the class attempting to make the reference
228 */
229 public static boolean isTypeVisible(Class<?> type, Class<?> refc) {
230 if (type == refc) {
231 return true; // easy check
232 }
233 while (type.isArray()) type = type.getComponentType();
234 if (type.isPrimitive() || type == Object.class) {
235 return true;
236 }
237 ClassLoader typeLoader = type.getClassLoader();
238 ClassLoader refcLoader = refc.getClassLoader();
239 if (typeLoader == refcLoader) {
240 return true;
241 }
242 if (refcLoader == null && typeLoader != null) {
243 return false;
244 }
245 if (typeLoader == null && type.getName().startsWith("java.")) {
246 // Note: The API for actually loading classes, ClassLoader.defineClass,
247 // guarantees that classes with names beginning "java." cannot be aliased,
248 // because class loaders cannot load them directly.
249 return true;
250 }
251
252 // Do it the hard way: Look up the type name from the refc loader.
253 //
254 // Force the refc loader to report and commit to a particular binding for this type name (type.getName()).
255 //
256 // In principle, this query might force the loader to load some unrelated class,
257 // which would cause this query to fail (and the original caller to give up).
258 // This would be wasted effort, but it is expected to be very rare, occurring
259 // only when an attacker is attempting to create a type alias.
260 // In the normal case, one class loader will simply delegate to the other,
261 // and the same type will be visible through both, with no extra loading.
262 //
263 // It is important to go through Class.forName instead of ClassLoader.loadClass
264 // because Class.forName goes through the JVM system dictionary, which records
265 // the class lookup once for all. This means that even if a not-well-behaved class loader
266 // would "change its mind" about the meaning of the name, the Class.forName request
267 // will use the result cached in the JVM system dictionary. Note that the JVM system dictionary
268 // will record the first successful result. Unsuccessful results are not stored.
269 //
270 // We use doPrivileged in order to allow an unprivileged caller to ask an arbitrary
271 // class loader about the binding of the proposed name (type.getName()).
272 // The looked up type ("res") is compared for equality against the proposed
273 // type ("type") and then is discarded. Thus, the worst that can happen to
274 // the "child" class loader is that it is bothered to load and report a class
275 // that differs from "type"; this happens once due to JVM system dictionary
276 // memoization. And the caller never gets to look at the alternate type binding
277 // ("res"), whether it exists or not.
278 final String name = type.getName();
279 Class<?> res = java.security.AccessController.doPrivileged(
280 new java.security.PrivilegedAction<>() {
281 public Class<?> run() {
282 try {
283 return Class.forName(name, false, refcLoader);
284 } catch (ClassNotFoundException | LinkageError e) {
285 return null; // Assume the class is not found
286 }
287 }
288 });
289 return (type == res);
290 }
291
292 /**
293 * Decide if the given method type, attributed to a member or symbolic
294 * reference of a given reference class, is really visible to that class.
295 * @param type the supposed type of a member or symbolic reference of refc
296 * @param refc the class attempting to make the reference
297 */
298 public static boolean isTypeVisible(java.lang.invoke.MethodType type, Class<?> refc) {
299 if (!isTypeVisible(type.returnType(), refc)) {
300 return false;
301 }
302 for (int n = 0, max = type.parameterCount(); n < max; n++) {
303 if (!isTypeVisible(type.parameterType(n), refc)) {
304 return false;
305 }
306 }
307 return true;
308 }
309
310 /**
311 * Tests if two classes are in the same module.
312 * @param class1 a class
313 * @param class2 another class
314 * @return whether they are in the same module
315 */
316 public static boolean isSameModule(Class<?> class1, Class<?> class2) {
317 return class1.getModule() == class2.getModule();
318 }
319
320 /**
321 * Test if two classes have the same class loader and package qualifier.
322 * @param class1 a class
323 * @param class2 another class
324 * @return whether they are in the same package
325 */
326 public static boolean isSamePackage(Class<?> class1, Class<?> class2) {
327 assert(!class1.isArray() && !class2.isArray());
328 if (class1 == class2)
329 return true;
330 if (class1.getClassLoader() != class2.getClassLoader())
331 return false;
332 return Objects.equals(class1.getPackageName(), class2.getPackageName());
333 }
334
335 /**
336 * Test if two classes are defined as part of the same package member (top-level class).
337 * If this is true, they can share private access with each other.
338 * @param class1 a class
339 * @param class2 another class
340 * @return whether they are identical or nested together
341 */
342 public static boolean isSamePackageMember(Class<?> class1, Class<?> class2) {
343 if (class1 == class2)
344 return true;
345 if (!isSamePackage(class1, class2))
346 return false;
347 if (getOutermostEnclosingClass(class1) != getOutermostEnclosingClass(class2))
348 return false;
349 return true;
350 }
351
352 private static Class<?> getOutermostEnclosingClass(Class<?> c) {
353 Class<?> pkgmem = c;
354 for (Class<?> enc = c; (enc = enc.getEnclosingClass()) != null; )
355 pkgmem = enc;
356 return pkgmem;
357 }
358
359 private static boolean loadersAreRelated(ClassLoader loader1, ClassLoader loader2,
360 boolean loader1MustBeParent) {
361 if (loader1 == loader2 || loader1 == null
362 || (loader2 == null && !loader1MustBeParent)) {
363 return true;
364 }
365 for (ClassLoader scan2 = loader2;
366 scan2 != null; scan2 = scan2.getParent()) {
367 if (scan2 == loader1) return true;
368 }
369 if (loader1MustBeParent) return false;
370 // see if loader2 is a parent of loader1:
371 for (ClassLoader scan1 = loader1;
372 scan1 != null; scan1 = scan1.getParent()) {
373 if (scan1 == loader2) return true;
374 }
375 return false;
376 }
377
378 /**
379 * Is the class loader of parentClass identical to, or an ancestor of,
380 * the class loader of childClass?
381 * @param parentClass a class
382 * @param childClass another class, which may be a descendent of the first class
383 * @return whether parentClass precedes or equals childClass in class loader order
384 */
385 public static boolean classLoaderIsAncestor(Class<?> parentClass, Class<?> childClass) {
386 return loadersAreRelated(parentClass.getClassLoader(), childClass.getClassLoader(), true);
387 }
388 }