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 (allowedModes & PRIVATE) != 0)
108 return true; // easy check; all self-access is OK with a private lookup
109
110 switch (mods & ALL_ACCESS_MODES) {
111 case PUBLIC:
112 return true; // already checked above
113 case PROTECTED:
114 assert !defc.isInterface(); // protected members aren't allowed in interfaces
115 if ((allowedModes & PROTECTED_OR_PACKAGE_ALLOWED) != 0 &&
116 isSamePackage(defc, lookupClass))
117 return true;
118 if ((allowedModes & PROTECTED) == 0)
119 return false;
120 // Protected members are accessible by subclasses, which does not include interfaces.
121 // Interfaces are types, not classes. They should not have access to
122 // protected members in j.l.Object, even though it is their superclass.
123 if ((mods & STATIC) != 0 &&
124 !isRelatedClass(refc, lookupClass))
125 return false;
126 if ((allowedModes & PROTECTED) != 0 &&
127 isSubClass(lookupClass, defc))
128 return true;
129 return false;
130 case PACKAGE_ONLY: // That is, zero. Unmarked member is package-only access.
131 assert !defc.isInterface(); // package-private members aren't allowed in interfaces
132 return ((allowedModes & PACKAGE_ALLOWED) != 0 &&
133 isSamePackage(defc, lookupClass));
134 case PRIVATE:
135 // Rules for privates follows access rules for nestmates.
136 boolean canAccess = ((allowedModes & PRIVATE) != 0 &&
137 Reflection.areNestMates(defc, lookupClass));
138 // for private methods the selected method equals the
139 // resolved method - so refc == defc
140 assert (canAccess && refc == defc) || !canAccess;
141 return canAccess;
142 default:
143 throw new IllegalArgumentException("bad modifiers: "+Modifier.toString(mods));
144 }
145 }
146
147 static boolean isRelatedClass(Class<?> refc, Class<?> lookupClass) {
148 return (refc == lookupClass ||
149 isSubClass(refc, lookupClass) ||
150 isSubClass(lookupClass, refc));
151 }
152
153 static boolean isSubClass(Class<?> lookupClass, Class<?> defc) {
154 return defc.isAssignableFrom(lookupClass) &&
155 !lookupClass.isInterface(); // interfaces are types, not classes.
156 }
157
158 static int getClassModifiers(Class<?> c) {
159 // This would return the mask stored by javac for the source-level modifiers.
160 // return c.getModifiers();
161 // But what we need for JVM access checks are the actual bits from the class header.
162 // ...But arrays and primitives are synthesized with their own odd flags:
163 if (c.isArray() || c.isPrimitive())
164 return c.getModifiers();
165 return Reflection.getClassAccessFlags(c);
166 }
167
168 /**
169 * Evaluate the JVM linkage rules for access to the given class on behalf of caller.
170 * <h3>JVM Specification, 5.4.4 "Access Control"</h3>
171 * A class or interface C is accessible to a class or interface D
172 * if and only if any of the following conditions are true:<ul>
173 * <li>C is public and in the same module as D.
174 * <li>D is in a module that reads the module containing C, C is public and in a
175 * package that is exported to the module that contains D.
176 * <li>C and D are members of the same runtime package.
177 * </ul>
178 * @param refc the symbolic reference class to which access is being checked (C)
179 * @param lookupClass the class performing the lookup (D)
180 */
181 public static boolean isClassAccessible(Class<?> refc, Class<?> lookupClass,
182 int allowedModes) {
183 if (allowedModes == 0) return false;
184 assert((allowedModes & PUBLIC) != 0 &&
185 (allowedModes & ~(ALL_ACCESS_MODES|PACKAGE_ALLOWED|MODULE_ALLOWED|UNCONDITIONAL_ALLOWED)) == 0);
186 int mods = getClassModifiers(refc);
187 if (isPublic(mods)) {
188
189 Module lookupModule = lookupClass.getModule();
190 Module refModule = refc.getModule();
191
192 // early VM startup case, java.base not defined
193 if (lookupModule == null) {
194 assert refModule == null;
195 return true;
196 }
197
198 // trivially allow
199 if ((allowedModes & MODULE_ALLOWED) != 0 &&
200 (lookupModule == refModule))
201 return true;
202
203 // check readability when UNCONDITIONAL not allowed
204 if (((allowedModes & UNCONDITIONAL_ALLOWED) != 0)
205 || lookupModule.canRead(refModule)) {
206
207 // check that refc is in an exported package
208 if ((allowedModes & MODULE_ALLOWED) != 0) {
209 if (refModule.isExported(refc.getPackageName(), lookupModule))
210 return true;
211 } else {
212 // exported unconditionally
213 if (refModule.isExported(refc.getPackageName()))
214 return true;
215 }
216
217 // not exported but allow access during VM initialization
218 // because java.base does not have its exports setup
219 if (!jdk.internal.misc.VM.isModuleSystemInited())
220 return true;
221 }
222
223 // public class not accessible to lookupClass
224 return false;
225 }
226 if ((allowedModes & PACKAGE_ALLOWED) != 0 &&
227 isSamePackage(lookupClass, refc))
228 return true;
229 return false;
230 }
231
232 /**
233 * Decide if the given method type, attributed to a member or symbolic
234 * reference of a given reference class, is really visible to that class.
235 * @param type the supposed type of a member or symbolic reference of refc
236 * @param refc the class attempting to make the reference
237 */
238 public static boolean isTypeVisible(Class<?> type, Class<?> refc) {
239 if (type == refc) {
240 return true; // easy check
241 }
242 while (type.isArray()) type = type.getComponentType();
243 if (type.isPrimitive() || type == Object.class) {
244 return true;
245 }
246 ClassLoader typeLoader = type.getClassLoader();
247 ClassLoader refcLoader = refc.getClassLoader();
248 if (typeLoader == refcLoader) {
249 return true;
250 }
251 if (refcLoader == null && typeLoader != null) {
252 return false;
253 }
254 if (typeLoader == null && type.getName().startsWith("java.")) {
255 // Note: The API for actually loading classes, ClassLoader.defineClass,
256 // guarantees that classes with names beginning "java." cannot be aliased,
257 // because class loaders cannot load them directly.
258 return true;
259 }
260
261 // Do it the hard way: Look up the type name from the refc loader.
262 //
263 // Force the refc loader to report and commit to a particular binding for this type name (type.getName()).
264 //
265 // In principle, this query might force the loader to load some unrelated class,
266 // which would cause this query to fail (and the original caller to give up).
267 // This would be wasted effort, but it is expected to be very rare, occurring
268 // only when an attacker is attempting to create a type alias.
269 // In the normal case, one class loader will simply delegate to the other,
270 // and the same type will be visible through both, with no extra loading.
271 //
272 // It is important to go through Class.forName instead of ClassLoader.loadClass
273 // because Class.forName goes through the JVM system dictionary, which records
274 // the class lookup once for all. This means that even if a not-well-behaved class loader
275 // would "change its mind" about the meaning of the name, the Class.forName request
276 // will use the result cached in the JVM system dictionary. Note that the JVM system dictionary
277 // will record the first successful result. Unsuccessful results are not stored.
278 //
279 // We use doPrivileged in order to allow an unprivileged caller to ask an arbitrary
280 // class loader about the binding of the proposed name (type.getName()).
281 // The looked up type ("res") is compared for equality against the proposed
282 // type ("type") and then is discarded. Thus, the worst that can happen to
283 // the "child" class loader is that it is bothered to load and report a class
284 // that differs from "type"; this happens once due to JVM system dictionary
285 // memoization. And the caller never gets to look at the alternate type binding
286 // ("res"), whether it exists or not.
287 final String name = type.getName();
288 Class<?> res = java.security.AccessController.doPrivileged(
289 new java.security.PrivilegedAction<>() {
290 public Class<?> run() {
291 try {
292 return Class.forName(name, false, refcLoader);
293 } catch (ClassNotFoundException | LinkageError e) {
294 return null; // Assume the class is not found
295 }
296 }
297 });
298 return (type == res);
299 }
300
301 /**
302 * Decide if the given method type, attributed to a member or symbolic
303 * reference of a given reference class, is really visible to that class.
304 * @param type the supposed type of a member or symbolic reference of refc
305 * @param refc the class attempting to make the reference
306 */
307 public static boolean isTypeVisible(java.lang.invoke.MethodType type, Class<?> refc) {
308 if (!isTypeVisible(type.returnType(), refc)) {
309 return false;
310 }
311 for (int n = 0, max = type.parameterCount(); n < max; n++) {
312 if (!isTypeVisible(type.parameterType(n), refc)) {
313 return false;
314 }
315 }
316 return true;
317 }
318
319 /**
320 * Tests if two classes are in the same module.
321 * @param class1 a class
322 * @param class2 another class
323 * @return whether they are in the same module
324 */
325 public static boolean isSameModule(Class<?> class1, Class<?> class2) {
326 return class1.getModule() == class2.getModule();
327 }
328
329 /**
330 * Test if two classes have the same class loader and package qualifier.
331 * @param class1 a class
332 * @param class2 another class
333 * @return whether they are in the same package
334 */
335 public static boolean isSamePackage(Class<?> class1, Class<?> class2) {
336 assert(!class1.isArray() && !class2.isArray());
337 if (class1 == class2)
338 return true;
339 if (class1.getClassLoader() != class2.getClassLoader())
340 return false;
341 return Objects.equals(class1.getPackageName(), class2.getPackageName());
342 }
343
344 /**
345 * Test if two classes are defined as part of the same package member (top-level class).
346 * If this is true, they can share private access with each other.
347 * @param class1 a class
348 * @param class2 another class
349 * @return whether they are identical or nested together
350 */
351 public static boolean isSamePackageMember(Class<?> class1, Class<?> class2) {
352 if (class1 == class2)
353 return true;
354 if (!isSamePackage(class1, class2))
355 return false;
356 if (getOutermostEnclosingClass(class1) != getOutermostEnclosingClass(class2))
357 return false;
358 return true;
359 }
360
361 private static Class<?> getOutermostEnclosingClass(Class<?> c) {
362 Class<?> pkgmem = c;
363 for (Class<?> enc = c; (enc = enc.getEnclosingClass()) != null; )
364 pkgmem = enc;
365 return pkgmem;
366 }
367
368 private static boolean loadersAreRelated(ClassLoader loader1, ClassLoader loader2,
369 boolean loader1MustBeParent) {
370 if (loader1 == loader2 || loader1 == null
371 || (loader2 == null && !loader1MustBeParent)) {
372 return true;
373 }
374 for (ClassLoader scan2 = loader2;
375 scan2 != null; scan2 = scan2.getParent()) {
376 if (scan2 == loader1) return true;
377 }
378 if (loader1MustBeParent) return false;
379 // see if loader2 is a parent of loader1:
380 for (ClassLoader scan1 = loader1;
381 scan1 != null; scan1 = scan1.getParent()) {
382 if (scan1 == loader2) return true;
383 }
384 return false;
385 }
386
387 /**
388 * Is the class loader of parentClass identical to, or an ancestor of,
389 * the class loader of childClass?
390 * @param parentClass a class
391 * @param childClass another class, which may be a descendent of the first class
392 * @return whether parentClass precedes or equals childClass in class loader order
393 */
394 public static boolean classLoaderIsAncestor(Class<?> parentClass, Class<?> childClass) {
395 return loadersAreRelated(parentClass.getClassLoader(), childClass.getClassLoader(), true);
396 }
397 }