8331655: ClassFile API ClassCastException with verbose output of certain class files

Reviewed-by: psandoz

Author: asotona

src/java.base/share/classes/jdk/internal/classfile/impl/ClassReaderImpl.java

@@ -391,21 +391,10 @@ private PoolEntry entryByIndex(int index, int lowerBoundTag, int upperBoundTag)
 
     @Override
     public AbstractPoolEntry.Utf8EntryImpl utf8EntryByIndex(int index) {
-        if (index <= 0 || index >= constantPoolCount) {
-            throw new ConstantPoolException("Bad CP UTF8 index: " + index);
-        }
-        PoolEntry info = cp[index];
-        if (info == null) {
-            int offset = cpOffset[index];
-            int tag = readU1(offset);
-            final int q = offset + 1;
-            if (tag != TAG_UTF8) throw new ConstantPoolException("Not a UTF8 - index: " + index);
-            AbstractPoolEntry.Utf8EntryImpl uinfo
-                    = new AbstractPoolEntry.Utf8EntryImpl(this, index, buffer, q + 2, readU2(q));
-            cp[index] = uinfo;
-            return uinfo;
+        if (entryByIndex(index, TAG_UTF8, TAG_UTF8) instanceof AbstractPoolEntry.Utf8EntryImpl utf8) {
+            return utf8;
         }
-        return (AbstractPoolEntry.Utf8EntryImpl) info;
+        throw new ConstantPoolException("Not a UTF8 - index: " + index);
     }
 
     @Override

test/jdk/jdk/classfile/LimitsTest.java

@@ -23,7 +23,7 @@
 
 /*
  * @test
- * @bug 8320360 8330684 8331320
+ * @bug 8320360 8330684 8331320 8331655
  * @summary Testing ClassFile limits.
  * @run junit LimitsTest
  */
@@ -36,6 +36,7 @@
 import java.lang.classfile.Opcode;
 import java.lang.classfile.attribute.CodeAttribute;
 import java.lang.classfile.constantpool.ConstantPoolException;
+import java.lang.classfile.constantpool.IntegerEntry;
 import jdk.internal.classfile.impl.DirectMethodBuilder;
 import jdk.internal.classfile.impl.LabelContext;
 import jdk.internal.classfile.impl.UnboundAttribute;
@@ -106,6 +107,14 @@ void testInvalidClassEntry() {
             0, 0, 0, 0, 0, 2, ClassFile.TAG_METHODREF, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}).thisClass());
     }
 
+    @Test
+    void testInvalidUtf8Entry() {
+        var cp = ClassFile.of().parse(new byte[]{(byte)0xCA, (byte)0xFE, (byte)0xBA, (byte)0xBE,
+            0, 0, 0, 0, 0, 3, ClassFile.TAG_INTEGER, 0, 0, 0, 0, ClassFile.TAG_NAMEANDTYPE, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}).constantPool();
+        assertTrue(cp.entryByIndex(1) instanceof IntegerEntry); //parse valid int entry first
+        assertThrows(ConstantPoolException.class, () -> cp.entryByIndex(2));
+    }
+
     @Test
     void testInvalidLookupSwitch() {
         assertThrows(IllegalArgumentException.class, () ->