From 9e1fcb0eb47637082d15700a92e52f0b1c155bc7 Mon Sep 17 00:00:00 2001
From: Adrien Grand <jpountz@gmail.com>
Date: Tue, 16 May 2017 18:31:57 +0200
Subject: [PATCH] LUCENE-7831: CodecUtil should not seek to negative offsets.

---
 lucene/CHANGES.txt                                  |  5 ++++-
 .../java/org/apache/lucene/codecs/CodecUtil.java    |  6 ++++++
 .../org/apache/lucene/codecs/TestCodecUtil.java     | 13 +++++++++++++
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index bbdc7bdfa18..ce6ba678805 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -93,7 +93,10 @@ Other
   (Daniel Jelinski via Adrien Grand)
 
 ======================= Lucene 6.7.0 =======================
-(No Changes)
+
+Bug Fixes
+
+* LUCENE-7831: CodecUtil should not seek to negative offsets. (Adrien Grand)
 
 ======================= Lucene 6.6.0 =======================
 
diff --git a/lucene/core/src/java/org/apache/lucene/codecs/CodecUtil.java b/lucene/core/src/java/org/apache/lucene/codecs/CodecUtil.java
index a625b47a060..c49946b7ffb 100644
--- a/lucene/core/src/java/org/apache/lucene/codecs/CodecUtil.java
+++ b/lucene/core/src/java/org/apache/lucene/codecs/CodecUtil.java
@@ -331,6 +331,9 @@ public final class CodecUtil {
   /** Retrieves the full footer from the provided {@link IndexInput}.  This throws
    *  {@link CorruptIndexException} if this file does not have a valid footer. */
   public static byte[] readFooter(IndexInput in) throws IOException {
+    if (in.length() < footerLength()) {
+      throw new CorruptIndexException("misplaced codec footer (file truncated?): length=" + in.length() + " but footerLength==" + footerLength(), in);
+    }
     in.seek(in.length() - footerLength());
     validateFooter(in);
     in.seek(in.length() - footerLength());
@@ -516,6 +519,9 @@ public final class CodecUtil {
     clone.seek(0);
     ChecksumIndexInput in = new BufferedChecksumIndexInput(clone);
     assert in.getFilePointer() == 0;
+    if (in.length() < footerLength()) {
+      throw new CorruptIndexException("misplaced codec footer (file truncated?): length=" + in.length() + " but footerLength==" + footerLength(), input);
+    }
     in.seek(in.length() - footerLength());
     return checkFooter(in);
   }
diff --git a/lucene/core/src/test/org/apache/lucene/codecs/TestCodecUtil.java b/lucene/core/src/test/org/apache/lucene/codecs/TestCodecUtil.java
index d403f81b54f..0ff7f7c9cf8 100644
--- a/lucene/core/src/test/org/apache/lucene/codecs/TestCodecUtil.java
+++ b/lucene/core/src/test/org/apache/lucene/codecs/TestCodecUtil.java
@@ -303,4 +303,17 @@ public class TestCodecUtil extends LuceneTestCase {
     fakeChecksum.set((1L << 32) - 1); // ok
     CodecUtil.writeCRC(fakeOutput);
   }
+
+  public void testTruncatedFileThrowsCorruptIndexException() throws IOException {
+    RAMFile file = new RAMFile();
+    IndexOutput output = new RAMOutputStream(file, false);
+    output.close();
+    IndexInput input = new RAMInputStream("file", file);
+    CorruptIndexException e = expectThrows(CorruptIndexException.class,
+        () -> CodecUtil.checksumEntireFile(input));
+    assertEquals("misplaced codec footer (file truncated?): length=0 but footerLength==16 (resource=RAMInputStream(name=file))", e.getMessage());
+    e = expectThrows(CorruptIndexException.class,
+        () -> CodecUtil.retrieveChecksum(input));
+    assertEquals("misplaced codec footer (file truncated?): length=0 but footerLength==16 (resource=RAMInputStream(name=file))", e.getMessage());
+  }
 }