Fix offset 0 handling by LZ4 decompression

Author: Marcono1234

lucene/core/src/java/org/apache/lucene/util/compress/LZ4.java

@@ -111,7 +111,9 @@ public static int decompress(DataInput compressed, int decompressedLen, byte[] d
 
       // matchs
       final int matchDec = compressed.readShort() & 0xFFFF;
-      assert matchDec > 0;
+      if (matchDec == 0) {
+        throw new IOException("offset 0 is invalid");
+      }
 
       int matchLen = token & 0x0F;
       if (matchLen == 0x0F) {

lucene/core/src/test/org/apache/lucene/util/compress/LZ4TestCase.java

@@ -143,15 +143,18 @@ private void doTest(byte[] data, int offset, int length, LZ4.HashTable hashTable
 
     // Now restore and compare bytes
     byte[] restored = new byte[length + random().nextInt(10)];
-    LZ4.decompress(new ByteArrayDataInput(compressed), length, restored, 0);
+    int restoreOffsetEnd = LZ4.decompress(new ByteArrayDataInput(compressed), length, restored, 0);
+    assertEquals(length, restoreOffsetEnd);
     assertArrayEquals(
         ArrayUtil.copyOfSubArray(data, offset, offset + length),
         ArrayUtil.copyOfSubArray(restored, 0, length));
 
     // Now restore with an offset
     int restoreOffset = TestUtil.nextInt(random(), 1, 10);
     restored = new byte[restoreOffset + length + random().nextInt(10)];
-    LZ4.decompress(new ByteArrayDataInput(compressed), length, restored, restoreOffset);
+    restoreOffsetEnd =
+        LZ4.decompress(new ByteArrayDataInput(compressed), length, restored, restoreOffset);
+    assertEquals(length, restoreOffsetEnd - restoreOffset);
     assertArrayEquals(
         ArrayUtil.copyOfSubArray(data, offset, offset + length),
         ArrayUtil.copyOfSubArray(restored, restoreOffset, restoreOffset + length));
@@ -381,4 +384,34 @@ public void testUseDictionary() throws IOException {
     // own
     assertTrue(out.size() < len);
   }
+
+  public void testDecompressOffset0() {
+    byte[] input =
+        new byte[] {
+          // token
+          0xE,
+          // offset 0
+          0,
+          0,
+          // last literal
+          // token
+          7 << 4,
+          // literal
+          0,
+          0,
+          0,
+          0,
+          0,
+          0,
+          0
+        };
+
+    byte[] output = new byte[18];
+
+    var e =
+        assertThrows(
+            IOException.class,
+            () -> LZ4.decompress(new ByteArrayDataInput(input), output.length, output, 0));
+    assertEquals("offset 0 is invalid", e.getMessage());
+  }
 }