AccessControlContext.java :  » 6.0-JDK-Modules » j2me » java » security » Java Open Source

Java Open Source » 6.0 JDK Modules » j2me 
j2me » java » security » AccessControlContext.java
/*
 * @(#)AccessControlContext.java  1.40 06/10/10
 *
 * Copyright  1990-2006 Sun Microsystems, Inc. All Rights Reserved.  
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER  
 *   
 * This program 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.   
 *   
 * This program 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 at /legal/license.txt).   
 *   
 * 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 Sun Microsystems, Inc., 4150 Network Circle, Santa  
 * Clara, CA 95054 or visit www.sun.com if you need additional  
 * information or have any questions. 
 *
 */
 
package java.security;

import java.util.Vector;
import sun.security.util.Debug;
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</code>,
 * that is equivalent to the <code>checkPermission</code> method
 * in the AccessController class, with one difference: The AccessControlContext
 * <code>checkPermission</code> 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</code> method. 
 * The <code>getContext</code> 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</code> method on the
 * previously-saved AccessControlContext object. A sample call is the
 * following:
 * 
 * <pre>
 * 
 *   acc.checkPermission(permission)
 * 
 * </pre> 
 * 
 * @see AccessController
 *
 * @author Roland Schemers
 */

public final class AccessControlContext {

    private ProtectionDomain context[];
    private boolean isPrivileged;
    private AccessControlContext privilegedContext;
    private DomainCombiner combiner = null;

    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 set of ProtectionDomains.
     * Context must not be null. Duplicate domains will be removed from the
     * context.
     *
     * @param context the ProtectionDomains associated with this context.
     */

    public AccessControlContext(ProtectionDomain context[])
    {
  if (context.length == 0) {
      this.context = null;
  } else if (context.length == 1) {
      this.context = (ProtectionDomain[])context.clone();
  } else {
      Vector v = new Vector(context.length);
      for (int i =0; i< context.length; i++) {
    if ((context[i] != null) &&  (!v.contains(context[i])))
        v.addElement(context[i]);
      }
      this.context = new ProtectionDomain[v.size()];
      v.copyInto(this.context);
  }
    }

    /**
     * Create a new <code>AccessControlContext</code> with the given
     * <code>AccessControlContext</code> and <code>DomainCombiner</code>.
     * This constructor associates the provided
     * <code>DomainCombiner</code> with the provided
     * <code>AccessControlContext</code>.
     *
     * <p>
     *
     * @param acc the <code>AccessControlContext</code> associated
     *    with the provided <code>DomainCombiner</code>. <p>
     *
     * @param combiner the <code>DomainCombiner</code> to be associated
     *    with the provided <code>AccessControlContext</code>.
     *
     * @exception NullPointerException if the provided
     *    <code>context</code> is <code>null</code>. <p>
     *
     * @exception SecurityException if the caller does not have permission
     *    to invoke this constructor.
     */
    public AccessControlContext(AccessControlContext acc,
        DomainCombiner combiner) {

  SecurityManager sm = System.getSecurityManager();
  if (sm != null) {
      sm.checkPermission(SecurityConstants.CREATE_ACC_PERMISSION);
  }

  if (acc == null ){
      throw new NullPointerException
    ("null AccessControlContext was provided");
  }

  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;
    }

    private AccessControlContext(ProtectionDomain context[], 
        DomainCombiner combiner) {
  this.context = (ProtectionDomain[])context.clone();
  this.combiner = combiner;
    }

    /**
     * package private constructor for AccessController
     */

    AccessControlContext(ProtectionDomain context[], boolean isPrivileged,
        AccessControlContext privilegedContext)
    {
  this.context = context;
  this.isPrivileged = isPrivileged;
  this.privilegedContext = privilegedContext;
    }

    private AccessControlContext(ProtectionDomain context[],
         boolean isPrivileged)
    {
  this(context, isPrivileged, null);
    }

    /**
     * Returns true if this context is privileged.
     */
    boolean isPrivileged() 
    {
  return isPrivileged;

    }

    /**
     * Get the <code>DomainCombiner</code> associated with this
     * <code>AccessControlContext</code>.
     *
     * <p>
     *
     * @return the <code>DomainCombiner</code> associated with this
     *    <code>AccessControlContext</code>, or <code>null</code>
     *    if there is none.
     *
     * @exception SecurityException if the caller does not have permission
     *    to get the <code>DomainCombiner</code> associated with this
     *    <code>AccessControlContext</code>.
     */
    public DomainCombiner getDomainCombiner() {

  SecurityManager sm = System.getSecurityManager();
  if (sm != null) {
      sm.checkPermission(SecurityConstants.GET_COMBINER_PERMISSION);
  }
  return combiner;
    }

    /** 
     * 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.
     * <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 
    {
  if (perm == null) {
      throw new NullPointerException("permission can't be null");
  }
  if (getDebug() != null) {
      if (Debug.isOn("stack"))
      Thread.currentThread().dumpStack();
      if (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)
      return;

  for (int i=0; i< context.length; i++) {
      if (context[i] != null &&  !context[i].implies(perm)) {
    if (debug != null) {
        debug.println("access denied "+perm);
        if (Debug.isOn("failure")) {
      Thread.currentThread().dumpStack();
      final ProtectionDomain pd = context[i];
      final Debug db = debug;
      AccessController.doPrivileged (new PrivilegedAction() {
          public Object run() {
        db.println("domain that failed "+pd);
        return null;
          }
      });
        }
    }
    throw new AccessControlException("access denied "+perm, perm);
      }
  }

  // allow if all of them allowed access
  if (debug != null)
      debug.println("access allowed "+perm);

  return;  
    }

    /**
     * Take the stack-based context (this) and combine it with the
     * privileged or inherited context, if need be.
     */
    AccessControlContext optimize()
    {
  // the assigned (privileged or inherited) context
  AccessControlContext acc;
  if (isPrivileged) {
      acc = privilegedContext;
  } else {
      acc = AccessController.getInheritedAccessControlContext();
  }

  // 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);

  // optimization: if neither have contexts; return acc if possible
  // rather than this, because acc might have a combiner
  if (skipAssigned && skipStack) {
      return (acc != null) ? acc : this;
  }

  if (acc != null && acc.combiner != null) {
      // let the assigned acc's combiner do its thing
      return goCombiner(context, acc);
  }

  // optimization: if there is no stack context; there is no reason
  // to compress the assigned context, it already is compressed
  if (skipStack) {
      return acc;
  }

  int slen = context.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 this;
  }

  // optimization: if there is a single stack domain and that domain
  // is already in the assigned context; no need to combine
  if ((slen == 1) && (context[0] == acc.context[0])) {
      return acc;
  }

  int n = (skipAssigned) ? 0 : acc.context.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(acc.context, 0, pd, 0, n);
  }

  // now add the stack context domains, discarding nulls and duplicates
    outer:
  for (int i = 0; i < context.length; i++) {
      ProtectionDomain sd = context[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 == acc.context.length) {
    return acc;
      } else if (skipAssigned && n == slen) {
    return this;
      }
      ProtectionDomain tmp[] = new ProtectionDomain[n];
      System.arraycopy(pd, 0, tmp, 0, n);
      pd = tmp;
  }

  return new AccessControlContext(pd, false);
    }

    private AccessControlContext goCombiner(ProtectionDomain[] current,
          AccessControlContext assigned) {

  // the assigned ACC's combiner is not null --
  // let the combiner do its thing

  // We could add optimizations to 'current' here ...

  if (getDebug() != null) {
      debug.println("AccessControlContext invoking the Combiner");
  }

  ProtectionDomain[] combinedPds = assigned.combiner.combine
    (current == null ?
      null :
      (ProtectionDomain[])current.clone(),
    assigned.context == null ?
      null :
      (ProtectionDomain[])assigned.context.clone());

  // return the new ACC
  return new AccessControlContext(combinedPds, assigned.combiner);
    }

    /**
     * Checks two AccessControlContext objects for equality. 
     * Checks that <i>obj</i> is
     * an AccessControlContext and has the same set of ProtectionDomains
     * as this context.
     * <P>
     * @param obj the object we are testing for equality with this object.
     * @return true if <i>obj</i> 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 (context == null) {
      return (that.context == null);
  }

  if (that.context == null)
      return false;

  if (!(this.containsAllPDs(that) && that.containsAllPDs(this)))
      return false;

  if (this.combiner == null)
      return (that.combiner == null);

  if (that.combiner == null)
      return false;

  if (!this.combiner.equals(that.combiner))
      return false;

  return true;

    }

    private boolean containsAllPDs(AccessControlContext that) {
  boolean match = false;
  //
  // ProtectionDomains within an ACC currently cannot be null
  // and this is enforced by the contructor 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.
  for (int i = 0; i < context.length; i++) {
      match = false;
      if (context[i] == null) {
    for (int j = 0; (j < that.context.length) && !match; j++) {
        match = (that.context[j] == null);
    }
      } else {
    for (int j = 0; (j < that.context.length) && !match; j++) {
        if (that.context[j] != null) {
      match =
          ((context[i].getClass()==that.context[j].getClass()) &&
           (context[i].equals(that.context[j])));
        }
    }
      }
      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;
    }
}
java2s.com  | Contact Us | Privacy Policy
Copyright 2009 - 12 Demo Source and Support. All rights reserved.
All other trademarks are property of their respective owners.