GH-1261: Reject out-of-range dictionary indices in decode

Author: Arawoof06

vector/src/main/java/org/apache/arrow/vector/dictionary/DictionaryEncoder.java

@@ -165,7 +165,7 @@ static void retrieveIndexVector(
     for (int i = start; i < end; i++) {
       if (!indices.isNull(i)) {
         int indexAsInt = (int) indices.getValueAsLong(i);
-        if (indexAsInt > dictionaryCount) {
+        if (indexAsInt < 0 || indexAsInt >= dictionaryCount) {
           throw new IllegalArgumentException(
               "Provided dictionary does not contain value for index " + indexAsInt);
         }

vector/src/test/java/org/apache/arrow/vector/TestDictionaryVector.java

@@ -942,6 +942,33 @@ public void testNoMemoryLeak() {
     assertEquals(0, allocator.getAllocatedMemory(), "decode memory leak");
   }
 
+  @Test
+  public void testDecodeIndexOutOfBounds() {
+    // valid indices are 0..dictionaryCount-1; index == dictionaryCount and negative indices
+    // must be rejected before dereferencing the dictionary vector.
+    try (final IntVector indices = newVector(IntVector.class, "", Types.MinorType.INT, allocator);
+        final VarCharVector dictionaryVector = newVarCharVector("dict", allocator)) {
+      setVector(dictionaryVector, zero, one);
+      Dictionary dictionary =
+          new Dictionary(dictionaryVector, new DictionaryEncoding(1L, false, null));
+
+      setVector(indices, 2);
+      try (final ValueVector decoded = DictionaryEncoder.decode(indices, dictionary, allocator)) {
+        fail("There should be an exception when decoding an index equal to the dictionary size");
+      } catch (IllegalArgumentException e) {
+        assertEquals("Provided dictionary does not contain value for index 2", e.getMessage());
+      }
+
+      setVector(indices, -1);
+      try (final ValueVector decoded = DictionaryEncoder.decode(indices, dictionary, allocator)) {
+        fail("There should be an exception when decoding a negative index");
+      } catch (IllegalArgumentException e) {
+        assertEquals("Provided dictionary does not contain value for index -1", e.getMessage());
+      }
+    }
+    assertEquals(0, allocator.getAllocatedMemory(), "decode memory leak");
+  }
+
   @Test
   public void testListNoMemoryLeak() {
     // Create a new value vector
@@ -1053,7 +1080,7 @@ public void testStructNoMemoryLeak() {
       NullableStructWriter writer = indices.getWriter();
       writer.allocate();
       writer.start();
-      writer.integer("f0").writeInt(1);
+      writer.integer("f0").writeInt(0);
       writer.integer("f1").writeInt(3);
       writer.end();
       writer.setValueCount(1);