Java tutorial
/* * Copyright (c) 1997, 2015, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * 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 * or visit www.oracle.com if you need additional information or have any * questions. */ package java.security; import java.util.ArrayList; import java.util.List; import sun.security.util.Debug; import sun.security.util.FilePermCompat; import sun.security.util.SecurityConstants; /** * An AccessControlContext is used to make system resource access decisions * based on the context it encapsulates. * * <p>More specifically, it encapsulates a context and * has a single method, {@code checkPermission}, * that is equivalent to the {@code checkPermission} method * in the AccessController class, with one difference: The AccessControlContext * {@code checkPermission} method makes access decisions based on the * context it encapsulates, * rather than that of the current execution thread. * * <p>Thus, the purpose of AccessControlContext is for those situations where * a security check that should be made within a given context * actually needs to be done from within a * <i>different</i> context (for example, from within a worker thread). * * <p> An AccessControlContext is created by calling the * {@code AccessController.getContext} method. * The {@code getContext} method takes a "snapshot" * of the current calling context, and places * it in an AccessControlContext object, which it returns. A sample call is * the following: * * <pre> * AccessControlContext acc = AccessController.getContext() * </pre> * * <p> * Code within a different context can subsequently call the * {@code checkPermission} method on the * previously-saved AccessControlContext object. A sample call is the * following: * * <pre> * acc.checkPermission(permission) * </pre> * * @see AccessController * * @author Roland Schemers * @since 1.2 */ public final class AccessControlContext { private ProtectionDomain[] context; // isPrivileged and isAuthorized are referenced by the VM - do not remove // or change their names private boolean isPrivileged; private boolean isAuthorized = false; // Note: This field is directly used by the virtual machine // native codes. Don't touch it. private AccessControlContext privilegedContext; private DomainCombiner combiner = null; // limited privilege scope private Permission[] permissions; private AccessControlContext parent; private boolean isWrapped; // is constrained by limited privilege scope? private boolean isLimited; private ProtectionDomain[] limitedContext; private static boolean debugInit = false; private static Debug debug = null; static Debug getDebug() { if (debugInit) return debug; else { if (Policy.isSet()) { debug = Debug.getInstance("access"); debugInit = true; } return debug; } } /** * Create an AccessControlContext with the given array of ProtectionDomains. * Context must not be null. Duplicate domains will be removed from the * context. * * @param context the ProtectionDomains associated with this context. * The non-duplicate domains are copied from the array. Subsequent * changes to the array will not affect this AccessControlContext. * @throws NullPointerException if {@code context} is {@code null} */ public AccessControlContext(ProtectionDomain[] context) { if (context.length == 0) { this.context = null; } else if (context.length == 1) { if (context[0] != null) { this.context = context.clone(); } else { this.context = null; } } else { List<ProtectionDomain> v = new ArrayList<>(context.length); for (int i = 0; i < context.length; i++) { if ((context[i] != null) && (!v.contains(context[i]))) v.add(context[i]); } if (!v.isEmpty()) { this.context = new ProtectionDomain[v.size()]; this.context = v.toArray(this.context); } } } /** * Create a new {@code AccessControlContext} with the given * {@code AccessControlContext} and {@code DomainCombiner}. * This constructor associates the provided * {@code DomainCombiner} with the provided * {@code AccessControlContext}. * * @param acc the {@code AccessControlContext} associated * with the provided {@code DomainCombiner}. * * @param combiner the {@code DomainCombiner} to be associated * with the provided {@code AccessControlContext}. * * @exception NullPointerException if the provided * {@code context} is {@code null}. * * @exception SecurityException if a security manager is installed and the * caller does not have the "createAccessControlContext" * {@link SecurityPermission} * @since 1.3 */ public AccessControlContext(AccessControlContext acc, DomainCombiner combiner) { this(acc, combiner, false); } /** * package private to allow calls from ProtectionDomain without performing * the security check for {@linkplain SecurityConstants#CREATE_ACC_PERMISSION} * permission */ AccessControlContext(AccessControlContext acc, DomainCombiner combiner, boolean preauthorized) { if (!preauthorized) { SecurityManager sm = System.getSecurityManager(); if (sm != null) { sm.checkPermission(SecurityConstants.CREATE_ACC_PERMISSION); this.isAuthorized = true; } } else { this.isAuthorized = true; } this.context = acc.context; // we do not need to run the combine method on the // provided ACC. it was already "combined" when the // context was originally retrieved. // // at this point in time, we simply throw away the old // combiner and use the newly provided one. this.combiner = combiner; } /** * package private for AccessController * * This "argument wrapper" context will be passed as the actual context * parameter on an internal doPrivileged() call used in the implementation. */ AccessControlContext(ProtectionDomain caller, DomainCombiner combiner, AccessControlContext parent, AccessControlContext context, Permission[] perms) { /* * Combine the domains from the doPrivileged() context into our * wrapper context, if necessary. */ ProtectionDomain[] callerPDs = null; if (caller != null) { callerPDs = new ProtectionDomain[] { caller }; } if (context != null) { if (combiner != null) { this.context = combiner.combine(callerPDs, context.context); } else { this.context = combine(callerPDs, context.context); } } else { /* * Call combiner even if there is seemingly nothing to combine. */ if (combiner != null) { this.context = combiner.combine(callerPDs, null); } else { this.context = combine(callerPDs, null); } } this.combiner = combiner; Permission[] tmp = null; if (perms != null) { tmp = new Permission[perms.length]; for (int i = 0; i < perms.length; i++) { if (perms[i] == null) { throw new NullPointerException("permission can't be null"); } /* * An AllPermission argument is equivalent to calling * doPrivileged() without any limit permissions. */ if (perms[i].getClass() == AllPermission.class) { parent = null; } // Add altPath into permission for compatibility. tmp[i] = FilePermCompat.newPermPlusAltPath(perms[i]); } } /* * For a doPrivileged() with limited privilege scope, initialize * the relevant fields. * * The limitedContext field contains the union of all domains which * are enclosed by this limited privilege scope. In other words, * it contains all of the domains which could potentially be checked * if none of the limiting permissions implied a requested permission. */ if (parent != null) { this.limitedContext = combine(parent.context, parent.limitedContext); this.isLimited = true; this.isWrapped = true; this.permissions = tmp; this.parent = parent; this.privilegedContext = context; // used in checkPermission2() } this.isAuthorized = true; } /** * package private constructor for AccessController.getContext() */ AccessControlContext(ProtectionDomain[] context, boolean isPrivileged) { this.context = context; this.isPrivileged = isPrivileged; this.isAuthorized = true; } /** * Constructor for JavaSecurityAccess.doIntersectionPrivilege() */ AccessControlContext(ProtectionDomain[] context, AccessControlContext privilegedContext) { this.context = context; this.privilegedContext = privilegedContext; this.isPrivileged = true; } /** * Returns this context's context. */ ProtectionDomain[] getContext() { return context; } /** * Returns true if this context is privileged. */ boolean isPrivileged() { return isPrivileged; } /** * get the assigned combiner from the privileged or inherited context */ DomainCombiner getAssignedCombiner() { AccessControlContext acc; if (isPrivileged) { acc = privilegedContext; } else { acc = AccessController.getInheritedAccessControlContext(); } if (acc != null) { return acc.combiner; } return null; } /** * Get the {@code DomainCombiner} associated with this * {@code AccessControlContext}. * * @return the {@code DomainCombiner} associated with this * {@code AccessControlContext}, or {@code null} * if there is none. * * @exception SecurityException if a security manager is installed and * the caller does not have the "getDomainCombiner" * {@link SecurityPermission} * @since 1.3 */ public DomainCombiner getDomainCombiner() { SecurityManager sm = System.getSecurityManager(); if (sm != null) { sm.checkPermission(SecurityConstants.GET_COMBINER_PERMISSION); } return getCombiner(); } /** * package private for AccessController */ DomainCombiner getCombiner() { return combiner; } boolean isAuthorized() { return isAuthorized; } /** * Determines whether the access request indicated by the * specified permission should be allowed or denied, based on * the security policy currently in effect, and the context in * this object. The request is allowed only if every ProtectionDomain * in the context implies the permission. Otherwise the request is * denied. * * <p> * This method quietly returns if the access request * is permitted, or throws a suitable AccessControlException otherwise. * * @param perm the requested permission. * * @exception AccessControlException if the specified permission * is not permitted, based on the current security policy and the * context encapsulated by this object. * @exception NullPointerException if the permission to check for is null. */ public void checkPermission(Permission perm) throws AccessControlException { boolean dumpDebug = false; if (perm == null) { throw new NullPointerException("permission can't be null"); } if (getDebug() != null) { // If "codebase" is not specified, we dump the info by default. dumpDebug = !Debug.isOn("codebase="); if (!dumpDebug) { // If "codebase" is specified, only dump if the specified code // value is in the stack. for (int i = 0; context != null && i < context.length; i++) { if (context[i].getCodeSource() != null && context[i].getCodeSource().getLocation() != null && Debug.isOn("codebase=" + context[i].getCodeSource().getLocation().toString())) { dumpDebug = true; break; } } } dumpDebug &= !Debug.isOn("permission=") || Debug.isOn("permission=" + perm.getClass().getCanonicalName()); if (dumpDebug && Debug.isOn("stack")) { Thread.dumpStack(); } if (dumpDebug && Debug.isOn("domain")) { if (context == null) { debug.println("domain (context is null)"); } else { for (int i = 0; i < context.length; i++) { debug.println("domain " + i + " " + context[i]); } } } } /* * iterate through the ProtectionDomains in the context. * Stop at the first one that doesn't allow the * requested permission (throwing an exception). * */ /* if ctxt is null, all we had on the stack were system domains, or the first domain was a Privileged system domain. This is to make the common case for system code very fast */ if (context == null) { checkPermission2(perm); return; } for (int i = 0; i < context.length; i++) { if (context[i] != null && !context[i].impliesWithAltFilePerm(perm)) { if (dumpDebug) { debug.println("access denied " + perm); } if (Debug.isOn("failure") && debug != null) { // Want to make sure this is always displayed for failure, // but do not want to display again if already displayed // above. if (!dumpDebug) { debug.println("access denied " + perm); } Thread.dumpStack(); final ProtectionDomain pd = context[i]; final Debug db = debug; AccessController.doPrivileged(new PrivilegedAction<>() { public Void run() { db.println("domain that failed " + pd); return null; } }); } throw new AccessControlException("access denied " + perm, perm); } } // allow if all of them allowed access if (dumpDebug) { debug.println("access allowed " + perm); } checkPermission2(perm); } /* * Check the domains associated with the limited privilege scope. */ private void checkPermission2(Permission perm) { if (!isLimited) { return; } /* * Check the doPrivileged() context parameter, if present. */ if (privilegedContext != null) { privilegedContext.checkPermission2(perm); } /* * Ignore the limited permissions and parent fields of a wrapper * context since they were already carried down into the unwrapped * context. */ if (isWrapped) { return; } /* * Try to match any limited privilege scope. */ if (permissions != null) { Class<?> permClass = perm.getClass(); for (int i = 0; i < permissions.length; i++) { Permission limit = permissions[i]; if (limit.getClass().equals(permClass) && limit.implies(perm)) { return; } } } /* * Check the limited privilege scope up the call stack or the inherited * parent thread call stack of this ACC. */ if (parent != null) { /* * As an optimization, if the parent context is the inherited call * stack context from a parent thread then checking the protection * domains of the parent context is redundant since they have * already been merged into the child thread's context by * optimize(). When parent is set to an inherited context this * context was not directly created by a limited scope * doPrivileged() and it does not have its own limited permissions. */ if (permissions == null) { parent.checkPermission2(perm); } else { parent.checkPermission(perm); } } } /** * Take the stack-based context (this) and combine it with the * privileged or inherited context, if need be. Any limited * privilege scope is flagged regardless of whether the assigned * context comes from an immediately enclosing limited doPrivileged(). * The limited privilege scope can indirectly flow from the inherited * parent thread or an assigned context previously captured by getContext(). */ AccessControlContext optimize() { // the assigned (privileged or inherited) context AccessControlContext acc; DomainCombiner combiner = null; AccessControlContext parent = null; Permission[] permissions = null; if (isPrivileged) { acc = privilegedContext; if (acc != null) { /* * If the context is from a limited scope doPrivileged() then * copy the permissions and parent fields out of the wrapper * context that was created to hold them. */ if (acc.isWrapped) { permissions = acc.permissions; parent = acc.parent; } } } else { acc = AccessController.getInheritedAccessControlContext(); if (acc != null) { /* * If the inherited context is constrained by a limited scope * doPrivileged() then set it as our parent so we will process * the non-domain-related state. */ if (acc.isLimited) { parent = acc; } } } // this.context could be null if only system code is on the stack; // in that case, ignore the stack context boolean skipStack = (context == null); // acc.context could be null if only system code was involved; // in that case, ignore the assigned context boolean skipAssigned = (acc == null || acc.context == null); ProtectionDomain[] assigned = (skipAssigned) ? null : acc.context; ProtectionDomain[] pd; // if there is no enclosing limited privilege scope on the stack or // inherited from a parent thread boolean skipLimited = ((acc == null || !acc.isWrapped) && parent == null); if (acc != null && acc.combiner != null) { // let the assigned acc's combiner do its thing if (getDebug() != null) { debug.println("AccessControlContext invoking the Combiner"); } // No need to clone current and assigned.context // combine() will not update them combiner = acc.combiner; pd = combiner.combine(context, assigned); } else { if (skipStack) { if (skipAssigned) { calculateFields(acc, parent, permissions); return this; } else if (skipLimited) { return acc; } } else if (assigned != null) { if (skipLimited) { // optimization: if there is a single stack domain and // that domain is already in the assigned context; no // need to combine if (context.length == 1 && context[0] == assigned[0]) { return acc; } } } pd = combine(context, assigned); if (skipLimited && !skipAssigned && pd == assigned) { return acc; } else if (skipAssigned && pd == context) { calculateFields(acc, parent, permissions); return this; } } // Reuse existing ACC this.context = pd; this.combiner = combiner; this.isPrivileged = false; calculateFields(acc, parent, permissions); return this; } /* * Combine the current (stack) and assigned domains. */ private static ProtectionDomain[] combine(ProtectionDomain[] current, ProtectionDomain[] assigned) { // current could be null if only system code is on the stack; // in that case, ignore the stack context boolean skipStack = (current == null); // assigned could be null if only system code was involved; // in that case, ignore the assigned context boolean skipAssigned = (assigned == null); int slen = (skipStack) ? 0 : current.length; // optimization: if there is no assigned context and the stack length // is less then or equal to two; there is no reason to compress the // stack context, it already is if (skipAssigned && slen <= 2) { return current; } int n = (skipAssigned) ? 0 : assigned.length; // now we combine both of them, and create a new context ProtectionDomain[] pd = new ProtectionDomain[slen + n]; // first copy in the assigned context domains, no need to compress if (!skipAssigned) { System.arraycopy(assigned, 0, pd, 0, n); } // now add the stack context domains, discarding nulls and duplicates outer: for (int i = 0; i < slen; i++) { ProtectionDomain sd = current[i]; if (sd != null) { for (int j = 0; j < n; j++) { if (sd == pd[j]) { continue outer; } } pd[n++] = sd; } } // if length isn't equal, we need to shorten the array if (n != pd.length) { // optimization: if we didn't really combine anything if (!skipAssigned && n == assigned.length) { return assigned; } else if (skipAssigned && n == slen) { return current; } ProtectionDomain[] tmp = new ProtectionDomain[n]; System.arraycopy(pd, 0, tmp, 0, n); pd = tmp; } return pd; } /* * Calculate the additional domains that could potentially be reached via * limited privilege scope. Mark the context as being subject to limited * privilege scope unless the reachable domains (if any) are already * contained in this domain context (in which case any limited * privilege scope checking would be redundant). */ private void calculateFields(AccessControlContext assigned, AccessControlContext parent, Permission[] permissions) { ProtectionDomain[] parentLimit = null; ProtectionDomain[] assignedLimit = null; ProtectionDomain[] newLimit; parentLimit = (parent != null) ? parent.limitedContext : null; assignedLimit = (assigned != null) ? assigned.limitedContext : null; newLimit = combine(parentLimit, assignedLimit); if (newLimit != null) { if (context == null || !containsAllPDs(newLimit, context)) { this.limitedContext = newLimit; this.permissions = permissions; this.parent = parent; this.isLimited = true; } } } /** * Checks two AccessControlContext objects for equality. * Checks that {@code obj} is * an AccessControlContext and has the same set of ProtectionDomains * as this context. * * @param obj the object we are testing for equality with this object. * @return true if {@code obj} is an AccessControlContext, and has the * same set of ProtectionDomains as this context, false otherwise. */ public boolean equals(Object obj) { if (obj == this) return true; if (!(obj instanceof AccessControlContext)) return false; AccessControlContext that = (AccessControlContext) obj; if (!equalContext(that)) return false; if (!equalLimitedContext(that)) return false; return true; } /* * Compare for equality based on state that is free of limited * privilege complications. */ private boolean equalContext(AccessControlContext that) { if (!equalPDs(this.context, that.context)) return false; if (this.combiner == null && that.combiner != null) return false; if (this.combiner != null && !this.combiner.equals(that.combiner)) return false; return true; } private boolean equalPDs(ProtectionDomain[] a, ProtectionDomain[] b) { if (a == null) { return (b == null); } if (b == null) return false; if (!(containsAllPDs(a, b) && containsAllPDs(b, a))) return false; return true; } /* * Compare for equality based on state that is captured during a * call to AccessController.getContext() when a limited privilege * scope is in effect. */ private boolean equalLimitedContext(AccessControlContext that) { if (that == null) return false; /* * If neither instance has limited privilege scope then we're done. */ if (!this.isLimited && !that.isLimited) return true; /* * If only one instance has limited privilege scope then we're done. */ if (!(this.isLimited && that.isLimited)) return false; /* * Wrapped instances should never escape outside the implementation * this class and AccessController so this will probably never happen * but it only makes any sense to compare if they both have the same * isWrapped state. */ if ((this.isWrapped && !that.isWrapped) || (!this.isWrapped && that.isWrapped)) { return false; } if (this.permissions == null && that.permissions != null) return false; if (this.permissions != null && that.permissions == null) return false; if (!(this.containsAllLimits(that) && that.containsAllLimits(this))) return false; /* * Skip through any wrapped contexts. */ AccessControlContext thisNextPC = getNextPC(this); AccessControlContext thatNextPC = getNextPC(that); /* * The protection domains and combiner of a privilegedContext are * not relevant because they have already been included in the context * of this instance by optimize() so we only care about any limited * privilege state they may have. */ if (thisNextPC == null && thatNextPC != null && thatNextPC.isLimited) return false; if (thisNextPC != null && !thisNextPC.equalLimitedContext(thatNextPC)) return false; if (this.parent == null && that.parent != null) return false; if (this.parent != null && !this.parent.equals(that.parent)) return false; return true; } /* * Follow the privilegedContext link making our best effort to skip * through any wrapper contexts. */ private static AccessControlContext getNextPC(AccessControlContext acc) { while (acc != null && acc.privilegedContext != null) { acc = acc.privilegedContext; if (!acc.isWrapped) return acc; } return null; } private static boolean containsAllPDs(ProtectionDomain[] thisContext, ProtectionDomain[] thatContext) { boolean match = false; // // ProtectionDomains within an ACC currently cannot be null // and this is enforced by the constructor and the various // optimize methods. However, historically this logic made attempts // to support the notion of a null PD and therefore this logic continues // to support that notion. ProtectionDomain thisPd; for (int i = 0; i < thisContext.length; i++) { match = false; if ((thisPd = thisContext[i]) == null) { for (int j = 0; (j < thatContext.length) && !match; j++) { match = (thatContext[j] == null); } } else { Class<?> thisPdClass = thisPd.getClass(); ProtectionDomain thatPd; for (int j = 0; (j < thatContext.length) && !match; j++) { thatPd = thatContext[j]; // Class check required to avoid PD exposure (4285406) match = (thatPd != null && thisPdClass == thatPd.getClass() && thisPd.equals(thatPd)); } } if (!match) return false; } return match; } private boolean containsAllLimits(AccessControlContext that) { boolean match = false; Permission thisPerm; if (this.permissions == null && that.permissions == null) return true; for (int i = 0; i < this.permissions.length; i++) { Permission limit = this.permissions[i]; Class<?> limitClass = limit.getClass(); match = false; for (int j = 0; (j < that.permissions.length) && !match; j++) { Permission perm = that.permissions[j]; match = (limitClass.equals(perm.getClass()) && limit.equals(perm)); } if (!match) return false; } return match; } /** * Returns the hash code value for this context. The hash code * is computed by exclusive or-ing the hash code of all the protection * domains in the context together. * * @return a hash code value for this context. */ public int hashCode() { int hashCode = 0; if (context == null) return hashCode; for (int i = 0; i < context.length; i++) { if (context[i] != null) hashCode ^= context[i].hashCode(); } return hashCode; } }