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 * Copyright (c) 1997, 2015, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

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;
 }
}