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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   *  Unless required by applicable law or agreed to in writing, software
12   *  distributed under the License is distributed on an "AS IS" BASIS,
13   *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   *  See the License for the specific language governing permissions and
15   *  limitations under the License.
16   *
17   */
18  package org.apache.bcel.verifier.statics;
19  
20  
21  import org.apache.bcel.Repository;
22  import org.apache.bcel.classfile.ClassFormatException;
23  import org.apache.bcel.classfile.JavaClass;
24  import org.apache.bcel.verifier.PassVerifier;
25  import org.apache.bcel.verifier.VerificationResult;
26  import org.apache.bcel.verifier.Verifier;
27  import org.apache.bcel.verifier.exc.LoadingException;
28  import org.apache.bcel.verifier.exc.Utility;
29  
30  /**
31   * This PassVerifier verifies a class file according to pass 1 as
32   * described in The Java Virtual Machine Specification, 2nd edition.
33   * More detailed information is to be found at the do_verify() method's
34   * documentation.
35   *
36   * @see #do_verify()
37   */
38  public final class Pass1Verifier extends PassVerifier{
39      /**
40       * DON'T USE THIS EVEN PRIVATELY! USE getJavaClass() INSTEAD.
41       * @see #getJavaClass()
42       */
43      private JavaClass jc;
44  
45      /**
46       * The Verifier that created this.
47       */
48      private final Verifier myOwner;
49  
50      /**
51       * Used to load in and return the myOwner-matching JavaClass object when needed.
52       * Avoids loading in a class file when it's not really needed!
53       */
54      private JavaClass getJavaClass() {
55          if (jc == null) {
56              try {
57                  jc = Repository.lookupClass(myOwner.getClassName());
58              } catch (final ClassNotFoundException e) {
59                  // FIXME: currently, Pass1Verifier treats jc == null as a special
60                  // case, so we don't need to do anything here.  A better solution
61                  // would be to simply throw the ClassNotFoundException
62                  // out of this method.
63              }
64          }
65          return jc;
66      }
67  
68      /**
69       * Should only be instantiated by a Verifier.
70       *
71       * @see Verifier
72       */
73      public Pass1Verifier(final Verifier owner) {
74          myOwner = owner;
75      }
76  
77      /**
78       * Pass-one verification basically means loading in a class file.
79       * The Java Virtual Machine Specification is not too precise about
80       * what makes the difference between passes one and two.
81       * The answer is that only pass one is performed on a class file as
82       * long as its resolution is not requested; whereas pass two and
83       * pass three are performed during the resolution process.
84       * Only four constraints to be checked are explicitly stated by
85       * The Java Virtual Machine Specification, 2nd edition:
86       * <UL>
87       *  <LI>The first four bytes must contain the right magic number (0xCAFEBABE).
88       *  <LI>All recognized attributes must be of the proper length.
89       *  <LI>The class file must not be truncated or have extra bytes at the end.
90       *  <LI>The constant pool must not contain any superficially unrecognizable information.
91       * </UL>
92       * A more in-depth documentation of what pass one should do was written by
93       * <A HREF=mailto:pwfong@cs.sfu.ca>Philip W. L. Fong</A>:
94       * <UL>
95       *  <LI> the file should not be truncated.
96       *  <LI> the file should not have extra bytes at the end.
97       *  <LI> all variable-length structures should be well-formatted:
98       *  <UL>
99       *   <LI> there should only be constant_pool_count-1 many entries in the constant pool.
100      *   <LI> all constant pool entries should have size the same as indicated by their type tag.
101      *   <LI> there are exactly interfaces_count many entries in the interfaces array of the class file.
102      *   <LI> there are exactly fields_count many entries in the fields array of the class file.
103      *   <LI> there are exactly methods_count many entries in the methods array of the class file.
104      *   <LI> there are exactly attributes_count many entries in the attributes array of the class file,
105      *        fields, methods, and code attribute.
106      *   <LI> there should be exactly attribute_length many bytes in each attribute.
107      *        Inconsistency between attribute_length and the actually size of the attribute content should be uncovered.
108      *        For example, in an Exceptions attribute, the actual number of exceptions as required by the number_of_exceptions field
109      *        might yeild an attribute size that doesn't match the attribute_length. Such an anomaly should be detected.
110      *   <LI> all attributes should have proper length. In particular, under certain context (e.g. while parsing method_info),
111      *        recognizable attributes (e.g. "Code" attribute) should have correct format (e.g. attribute_length is 2).
112      *  </UL>
113      *  <LI> Also, certain constant values are checked for validity:
114      *  <UL>
115      *   <LI> The magic number should be 0xCAFEBABE.
116      *   <LI> The major and minor version numbers are valid.
117      *   <LI> All the constant pool type tags are recognizable.
118      *   <LI> All undocumented access flags are masked off before use. Strictly speaking, this is not really a check.
119      *   <LI> The field this_class should point to a string that represents a legal non-array class name,
120      *        and this name should be the same as the class file being loaded.
121      *   <LI> the field super_class should point to a string that represents a legal non-array class name.
122      *   <LI> Because some of the above checks require cross referencing the constant pool entries,
123      *        guards are set up to make sure that the referenced entries are of the right type and the indices
124      *        are within the legal range (0 &lt; index &lt; constant_pool_count).
125      *  </UL>
126      *  <LI> Extra checks done in pass 1:
127      *  <UL>
128      *   <LI> the constant values of static fields should have the same type as the fields.
129      *   <LI> the number of words in a parameter list does not exceed 255 and locals_max.
130      *   <LI> the name and signature of fields and methods are verified to be of legal format.
131      *  </UL>
132      * </UL>
133      * (From the Paper <A HREF="http://www.cs.sfu.ca/people/GradStudents/pwfong/personal/JVM/pass1/">
134      * The Mysterious Pass One, first draft, September 2, 1997</A>.)
135      *
136      * <P>However, most of this is done by parsing a class file or generating a class file into BCEL's internal data structure.
137      * <B>Therefore, all that is really done here is look up the class file from BCEL's repository.</B>
138      * This is also motivated by the fact that some omitted things
139      * (like the check for extra bytes at the end of the class file) are handy when actually using BCEL to repair a class file
140      * (otherwise you would not be able to load it into BCEL).</P>
141      *
142      * @see org.apache.bcel.Repository
143      * @see org.apache.bcel.Const#JVM_CLASSFILE_MAGIC
144      */
145     @Override
146     public VerificationResult do_verify() {
147         JavaClass jc;
148         try{
149             jc = getJavaClass();    //loads in the class file if not already done.
150 
151             if (jc != null) {
152                 /* If we find more constraints to check, we should do this in an own method. */
153                 if (! myOwner.getClassName().equals(jc.getClassName())) {
154                     // This should maybe caught by BCEL: In case of renamed .class files we get wrong
155                     // JavaClass objects here.
156                     throw new LoadingException("Wrong name: the internal name of the .class file '"+jc.getClassName()+
157                         "' does not match the file's name '"+myOwner.getClassName()+"'.");
158                 }
159             }
160 
161         }
162         catch(final LoadingException e) {
163             return new VerificationResult(VerificationResult.VERIFIED_REJECTED, e.getMessage());
164         }
165         catch(final ClassFormatException e) {
166             return new VerificationResult(VerificationResult.VERIFIED_REJECTED, e.getMessage());
167         }
168         catch(final RuntimeException e) {
169             // BCEL does not catch every possible RuntimeException; e.g. if
170             // a constant pool index is referenced that does not exist.
171             return new VerificationResult(VerificationResult.VERIFIED_REJECTED, "Parsing via BCEL did not succeed. "+
172                 e.getClass().getName()+" occured:\n"+Utility.getStackTrace(e));
173         }
174 
175         if (jc != null) {
176             return VerificationResult.VR_OK;
177         }
178         //TODO: Maybe change Repository's behavior to throw a LoadingException instead of just returning "null"
179         //      if a class file cannot be found or in another way be looked up.
180         return new VerificationResult(VerificationResult.VERIFIED_REJECTED, "Repository.lookup() failed. FILE NOT FOUND?");
181     }
182 
183     /**
184      * Currently this returns an empty array of String.
185      * One could parse the error messages of BCEL
186      * (written to java.lang.System.err) when loading
187      * a class file such as detecting unknown attributes
188      * or trailing garbage at the end of a class file.
189      * However, Markus Dahm does not like the idea so this
190      * method is currently useless and therefore marked as
191      * <B>TODO</B>.
192      */
193     @Override
194     public String[] getMessages() {
195         // This method is only here to override the javadoc-comment.
196         return super.getMessages();
197     }
198 
199 }