1 /* 2 * Copyright (c) 2008, 2021, 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 jdk.internal.reflect.Reflection; 31 32 /** 33 * This class centralizes information about the JVM's linkage access control. 34 * @author jrose 35 */ 36 public class VerifyAccess { 37 38 private VerifyAccess() { } // cannot instantiate 39 40 private static final int UNCONDITIONAL_ALLOWED = java.lang.invoke.MethodHandles.Lookup.UNCONDITIONAL; 41 private static final int ORIGINAL_ALLOWED = java.lang.invoke.MethodHandles.Lookup.ORIGINAL; 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 * @param prevLookupClass the class for which the access check is being made 92 * @param allowedModes allowed modes 93 * @return true iff the accessing class can access such a member 94 */ 95 public static boolean isMemberAccessible(Class<?> refc, // symbolic ref class 96 Class<?> defc, // actual def class 97 int mods, // actual member mods 98 Class<?> lookupClass, 99 Class<?> prevLookupClass, 100 int allowedModes) { 101 if (allowedModes == 0) return false; 102 assert((allowedModes & ~(ALL_ACCESS_MODES|PACKAGE_ALLOWED|MODULE_ALLOWED|UNCONDITIONAL_ALLOWED|ORIGINAL_ALLOWED)) == 0); 103 // The symbolic reference class (refc) must always be fully verified. 104 if (!isClassAccessible(refc, lookupClass, prevLookupClass, allowedModes)) { 105 return false; 106 } 107 // Usually refc and defc are the same, but verify defc also in case they differ. 108 if (defc == lookupClass && 109 (allowedModes & PRIVATE) != 0) 110 return true; // easy check; all self-access is OK with a private lookup 111 112 switch (mods & ALL_ACCESS_MODES) { 113 case PUBLIC: 114 assert (allowedModes & PUBLIC) != 0 || (allowedModes & UNCONDITIONAL_ALLOWED) != 0; 115 return true; // already checked above 116 case PROTECTED: 117 assert !defc.isInterface(); // protected members aren't allowed in interfaces 118 if ((allowedModes & PROTECTED_OR_PACKAGE_ALLOWED) != 0 && 119 isSamePackage(defc, lookupClass)) 120 return true; 121 if ((allowedModes & PROTECTED) == 0) 122 return false; 123 // Protected members are accessible by subclasses, which does not include interfaces. 124 // Interfaces are types, not classes. They should not have access to 125 // protected members in j.l.Object, even though it is their superclass. 126 if ((mods & STATIC) != 0 && 127 !isRelatedClass(refc, lookupClass)) 128 return false; 129 if ((allowedModes & PROTECTED) != 0 && 130 isSubClass(lookupClass, defc)) 131 return true; 132 return false; 133 case PACKAGE_ONLY: // That is, zero. Unmarked member is package-only access. 134 assert !defc.isInterface(); // package-private members aren't allowed in interfaces 135 return ((allowedModes & PACKAGE_ALLOWED) != 0 && 136 isSamePackage(defc, lookupClass)); 137 case PRIVATE: 138 // Rules for privates follows access rules for nestmates. 139 boolean canAccess = ((allowedModes & PRIVATE) != 0 && 140 Reflection.areNestMates(defc, lookupClass)); 141 // for private methods the selected method equals the 142 // resolved method - so refc == defc 143 assert (canAccess && refc == defc) || !canAccess; 144 return canAccess; 145 default: 146 throw new IllegalArgumentException("bad modifiers: "+Modifier.toString(mods)); 147 } 148 } 149 150 static boolean isRelatedClass(Class<?> refc, Class<?> lookupClass) { 151 return (refc == lookupClass || 152 isSubClass(refc, lookupClass) || 153 isSubClass(lookupClass, refc)); 154 } 155 156 static boolean isSubClass(Class<?> lookupClass, Class<?> defc) { 157 return defc.isAssignableFrom(lookupClass) && 158 !lookupClass.isInterface(); // interfaces are types, not classes. 159 } 160 161 static int getClassModifiers(Class<?> c) { 162 // This would return the mask stored by javac for the source-level modifiers. 163 // return c.getModifiers(); 164 // But what we need for JVM access checks are the actual bits from the class header. 165 // ...But arrays and primitives are synthesized with their own odd flags: 166 if (c.isArray() || c.isPrimitive()) 167 return c.getModifiers(); 168 return Reflection.getClassAccessFlags(c); 169 } 170 171 /** 172 * Evaluate the JVM linkage rules for access to the given class on behalf of caller. 173 * <h3>JVM Specification, 5.4.4 "Access Control"</h3> 174 * A class or interface C is accessible to a class or interface D 175 * if and only if any of the following conditions are true:<ul> 176 * <li>C is public and in the same module as D. 177 * <li>D is in a module that reads the module containing C, C is public and in a 178 * package that is exported to the module that contains D. 179 * <li>C and D are members of the same runtime package. 180 * </ul> 181 * 182 * @param refc the symbolic reference class to which access is being checked (C) 183 * @param lookupClass the class performing the lookup (D) 184 * @param prevLookupClass the class from which the lookup was teleported or null 185 * @param allowedModes allowed modes 186 */ 187 public static boolean isClassAccessible(Class<?> refc, 188 Class<?> lookupClass, 189 Class<?> prevLookupClass, 190 int allowedModes) { 191 if (allowedModes == 0) return false; 192 assert((allowedModes & ~(ALL_ACCESS_MODES|PACKAGE_ALLOWED|MODULE_ALLOWED|UNCONDITIONAL_ALLOWED|ORIGINAL_ALLOWED)) == 0); 193 194 if ((allowedModes & PACKAGE_ALLOWED) != 0 && 195 isSamePackage(lookupClass, refc)) 196 return true; 197 198 int mods = getClassModifiers(refc); 199 if (isPublic(mods)) { 200 201 Module lookupModule = lookupClass.getModule(); 202 Module refModule = refc.getModule(); 203 204 // early VM startup case, java.base not defined 205 if (lookupModule == null) { 206 assert refModule == null; 207 return true; 208 } 209 210 // allow access to public types in all unconditionally exported packages 211 if ((allowedModes & UNCONDITIONAL_ALLOWED) != 0) { 212 return refModule.isExported(refc.getPackageName()); 213 } 214 215 if (lookupModule == refModule && prevLookupClass == null) { 216 // allow access to all public types in lookupModule 217 if ((allowedModes & MODULE_ALLOWED) != 0) 218 return true; 219 220 assert (allowedModes & PUBLIC) != 0; 221 return refModule.isExported(refc.getPackageName()); 222 } 223 224 // cross-module access 225 // 1. refc is in different module from lookupModule, or 226 // 2. refc is in lookupModule and a different module from prevLookupModule 227 Module prevLookupModule = prevLookupClass != null ? prevLookupClass.getModule() 228 : null; 229 assert refModule != lookupModule || refModule != prevLookupModule; 230 if (isModuleAccessible(refc, lookupModule, prevLookupModule)) 231 return true; 232 233 // not exported but allow access during VM initialization 234 // because java.base does not have its exports setup 235 if (!jdk.internal.misc.VM.isModuleSystemInited()) 236 return true; 237 238 // public class not accessible to lookupClass 239 return false; 240 } 241 242 return false; 243 } 244 245 /* 246 * Tests if a class or interface REFC is accessible to m1 and m2 where m2 247 * may be null. 248 * 249 * A class or interface REFC in m is accessible to m1 and m2 if and only if 250 * both m1 and m2 read m and m exports the package of REFC at least to 251 * both m1 and m2. 252 */ 253 public static boolean isModuleAccessible(Class<?> refc, Module m1, Module m2) { 254 Module refModule = refc.getModule(); 255 assert refModule != m1 || refModule != m2; 256 int mods = getClassModifiers(refc); 257 if (isPublic(mods)) { 258 if (m1.canRead(refModule) && (m2 == null || m2.canRead(refModule))) { 259 String pn = refc.getPackageName(); 260 261 // refc is exported package to at least both m1 and m2 262 if (refModule.isExported(pn, m1) && (m2 == null || refModule.isExported(pn, m2))) 263 return true; 264 } 265 } 266 return false; 267 } 268 269 /** 270 * Decide if the given method type, attributed to a member or symbolic 271 * reference of a given reference class, is really visible to that class. 272 * @param type the supposed type of a member or symbolic reference of refc 273 * @param refc the class attempting to make the reference 274 */ 275 public static boolean isTypeVisible(Class<?> type, Class<?> refc) { 276 if (type == refc) { 277 return true; // easy check 278 } 279 while (type.isArray()) type = type.getComponentType(); 280 if (type.isPrimitive() || type == Object.class) { 281 return true; 282 } 283 ClassLoader typeLoader = type.getClassLoader(); 284 ClassLoader refcLoader = refc.getClassLoader(); 285 if (typeLoader == refcLoader) { 286 return true; 287 } 288 if (refcLoader == null && typeLoader != null) { 289 return false; 290 } 291 if (typeLoader == null && type.getName().startsWith("java.")) { 292 // Note: The API for actually loading classes, ClassLoader.defineClass, 293 // guarantees that classes with names beginning "java." cannot be aliased, 294 // because class loaders cannot load them directly. 295 return true; 296 } 297 298 // Do it the hard way: Look up the type name from the refc loader. 299 // 300 // Force the refc loader to report and commit to a particular binding for this type name (type.getName()). 301 // 302 // In principle, this query might force the loader to load some unrelated class, 303 // which would cause this query to fail (and the original caller to give up). 304 // This would be wasted effort, but it is expected to be very rare, occurring 305 // only when an attacker is attempting to create a type alias. 306 // In the normal case, one class loader will simply delegate to the other, 307 // and the same type will be visible through both, with no extra loading. 308 // 309 // It is important to go through Class.forName instead of ClassLoader.loadClass 310 // because Class.forName goes through the JVM system dictionary, which records 311 // the class lookup once for all. This means that even if a not-well-behaved class loader 312 // would "change its mind" about the meaning of the name, the Class.forName request 313 // will use the result cached in the JVM system dictionary. Note that the JVM system dictionary 314 // will record the first successful result. Unsuccessful results are not stored. 315 // 316 // We use doPrivileged in order to allow an unprivileged caller to ask an arbitrary 317 // class loader about the binding of the proposed name (type.getName()). 318 // The looked up type ("res") is compared for equality against the proposed 319 // type ("type") and then is discarded. Thus, the worst that can happen to 320 // the "child" class loader is that it is bothered to load and report a class 321 // that differs from "type"; this happens once due to JVM system dictionary 322 // memoization. And the caller never gets to look at the alternate type binding 323 // ("res"), whether it exists or not. 324 final String name = type.getName(); 325 @SuppressWarnings("removal") 326 Class<?> res = java.security.AccessController.doPrivileged( 327 new java.security.PrivilegedAction<>() { 328 public Class<?> run() { 329 try { 330 return Class.forName(name, false, refcLoader); 331 } catch (ClassNotFoundException | LinkageError e) { 332 return null; // Assume the class is not found 333 } 334 } 335 }); 336 return (type == res); 337 } 338 339 /** 340 * Decide if the given method type, attributed to a member or symbolic 341 * reference of a given reference class, is really visible to that class. 342 * @param type the supposed type of a member or symbolic reference of refc 343 * @param refc the class attempting to make the reference 344 */ 345 public static boolean isTypeVisible(java.lang.invoke.MethodType type, Class<?> refc) { 346 if (!isTypeVisible(type.returnType(), refc)) { 347 return false; 348 } 349 for (int n = 0, max = type.parameterCount(); n < max; n++) { 350 if (!isTypeVisible(type.parameterType(n), refc)) { 351 return false; 352 } 353 } 354 return true; 355 } 356 357 /** 358 * Tests if two classes are in the same module. 359 * @param class1 a class 360 * @param class2 another class 361 * @return whether they are in the same module 362 */ 363 public static boolean isSameModule(Class<?> class1, Class<?> class2) { 364 return class1.getModule() == class2.getModule(); 365 } 366 367 /** 368 * Test if two classes have the same class loader and package qualifier. 369 * @param class1 a class 370 * @param class2 another class 371 * @return whether they are in the same package 372 */ 373 public static boolean isSamePackage(Class<?> class1, Class<?> class2) { 374 if (class1 == class2) 375 return true; 376 if (class1.getClassLoader() != class2.getClassLoader()) 377 return false; 378 return class1.getPackageName() == class2.getPackageName(); 379 } 380 381 /** 382 * Test if two classes are defined as part of the same package member (top-level class). 383 * If this is true, they can share private access with each other. 384 * @param class1 a class 385 * @param class2 another class 386 * @return whether they are identical or nested together 387 */ 388 public static boolean isSamePackageMember(Class<?> class1, Class<?> class2) { 389 if (class1 == class2) 390 return true; 391 if (!isSamePackage(class1, class2)) 392 return false; 393 if (getOutermostEnclosingClass(class1) != getOutermostEnclosingClass(class2)) 394 return false; 395 return true; 396 } 397 398 private static Class<?> getOutermostEnclosingClass(Class<?> c) { 399 Class<?> pkgmem = c; 400 for (Class<?> enc = c; (enc = enc.getEnclosingClass()) != null; ) 401 pkgmem = enc; 402 return pkgmem; 403 } 404 405 private static boolean loadersAreRelated(ClassLoader loader1, ClassLoader loader2, 406 boolean loader1MustBeParent) { 407 if (loader1 == loader2 || loader1 == null 408 || (loader2 == null && !loader1MustBeParent)) { 409 return true; 410 } 411 for (ClassLoader scan2 = loader2; 412 scan2 != null; scan2 = scan2.getParent()) { 413 if (scan2 == loader1) return true; 414 } 415 if (loader1MustBeParent) return false; 416 // see if loader2 is a parent of loader1: 417 for (ClassLoader scan1 = loader1; 418 scan1 != null; scan1 = scan1.getParent()) { 419 if (scan1 == loader2) return true; 420 } 421 return false; 422 } 423 424 /** 425 * Is the class loader of parentClass identical to, or an ancestor of, 426 * the class loader of childClass? 427 * @param parentClass a class 428 * @param childClass another class, which may be a descendent of the first class 429 * @return whether parentClass precedes or equals childClass in class loader order 430 */ 431 public static boolean classLoaderIsAncestor(Class<?> parentClass, Class<?> childClass) { 432 return loadersAreRelated(parentClass.getClassLoader(), childClass.getClassLoader(), true); 433 } 434 }