From 7a408431fe6b77bc7a317b86c7adfb1aeebd5def Mon Sep 17 00:00:00 2001
From: Jean Chalard <jchalard@google.com>
Date: Tue, 30 Aug 2011 21:46:33 +0900
Subject: [PATCH] Check the magic number of a decoded file
Checking the magic number of a file upon decoding is necessary,
because if the file is corrupt and we don't check it, we will
fall back to a simple copy of the corrupted file. Latin IME
would realize this and would not crash, but would not use the
corrupted dictionary. If this happened to be a main dictionary,
then the user would lose the ability to use the correct
built-in dictionary.
Not the same, but kinda similar to
Bug: 5223031
Change-Id: Ic2783dc9dd5f3dcf2865623d9452765fe3778db7
---
.../latin/BinaryDictionaryFileDumper.java | 42 ++++++++++++++++---
1 file changed, 36 insertions(+), 6 deletions(-)
diff --git a/java/src/com/android/inputmethod/latin/BinaryDictionaryFileDumper.java b/java/src/com/android/inputmethod/latin/BinaryDictionaryFileDumper.java
index e95172d1f8..38563be4a4 100644
--- a/java/src/com/android/inputmethod/latin/BinaryDictionaryFileDumper.java
+++ b/java/src/com/android/inputmethod/latin/BinaryDictionaryFileDumper.java
@@ -25,12 +25,15 @@ import android.net.Uri;
import android.text.TextUtils;
import android.util.Log;
+import java.io.BufferedInputStream;
+import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
+import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Locale;
@@ -46,7 +49,9 @@ public class BinaryDictionaryFileDumper {
/**
* The size of the temporary buffer to copy files.
*/
- static final int FILE_READ_BUFFER_SIZE = 1024;
+ private static final int FILE_READ_BUFFER_SIZE = 1024;
+ // TODO: make the following data common with the native code
+ private static final byte[] MAGIC_NUMBER = new byte[] { 0x78, (byte)0xB1 };
private static final String DICTIONARY_PROJECTION[] = { "id" };
@@ -135,6 +140,7 @@ public class BinaryDictionaryFileDumper {
for (int mode = MODE_MIN; mode <= MODE_MAX; ++mode) {
InputStream originalSourceStream = null;
InputStream inputStream = null;
+ File outputFile = null;
FileOutputStream outputStream = null;
AssetFileDescriptor afd = null;
try {
@@ -144,7 +150,8 @@ public class BinaryDictionaryFileDumper {
if (null == afd) return null;
originalSourceStream = afd.createInputStream();
// Open output.
- outputStream = new FileOutputStream(outputFileName);
+ outputFile = new File(outputFileName);
+ outputStream = new FileOutputStream(outputFile);
// Get the appropriate decryption method for this try
switch (mode) {
case COMPRESSED_CRYPTED_COMPRESSED:
@@ -171,7 +178,7 @@ public class BinaryDictionaryFileDumper {
inputStream = originalSourceStream;
break;
}
- copyFileTo(inputStream, outputStream);
+ checkMagicAndCopyFileTo(new BufferedInputStream(inputStream), outputStream);
if (0 >= resolver.delete(wordListUri, null, null)) {
Log.e(TAG, "Could not have the dictionary pack delete a word list");
}
@@ -181,6 +188,12 @@ public class BinaryDictionaryFileDumper {
if (DEBUG) {
Log.i(TAG, "Can't open word list in mode " + mode + " : " + e);
}
+ if (null != outputFile) {
+ // This may or may not fail. The file may not have been created if the
+ // exception was thrown before it could be. Hence, both failure and
+ // success are expected outcomes, so we don't check the return value.
+ outputFile.delete();
+ }
// Try the next method.
} finally {
// Ignore exceptions while closing files.
@@ -234,12 +247,29 @@ public class BinaryDictionaryFileDumper {
}
/**
- * Copies the data in an input stream to a target file.
+ * Copies the data in an input stream to a target file if the magic number matches.
+ *
+ * If the magic number does not match the expected value, this method throws an
+ * IOException. Other usual conditions for IOException or FileNotFoundException
+ * also apply.
+ *
* @param input the stream to be copied.
* @param outputFile an outputstream to copy the data to.
*/
- private static void copyFileTo(final InputStream input, final FileOutputStream output)
- throws FileNotFoundException, IOException {
+ private static void checkMagicAndCopyFileTo(final BufferedInputStream input,
+ final FileOutputStream output) throws FileNotFoundException, IOException {
+ // Check the magic number
+ final byte[] magicNumberBuffer = new byte[MAGIC_NUMBER.length];
+ final int readMagicNumberSize = input.read(magicNumberBuffer, 0, MAGIC_NUMBER.length);
+ if (readMagicNumberSize < MAGIC_NUMBER.length) {
+ throw new IOException("Less bytes to read than the magic number length");
+ }
+ if (!Arrays.equals(MAGIC_NUMBER, magicNumberBuffer)) {
+ throw new IOException("Wrong magic number for downloaded file");
+ }
+ output.write(MAGIC_NUMBER);
+
+ // Actually copy the file
final byte[] buffer = new byte[FILE_READ_BUFFER_SIZE];
for (int readBytes = input.read(buffer); readBytes >= 0; readBytes = input.read(buffer))
output.write(buffer, 0, readBytes);
--
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