Manually calculate attachment offsets

The CipherInputStream skip() method is pretty non-functional

Fixes #7438

src/org/thoughtcrime/securesms/crypto/ModernDecryptingPartInputStream.java

@@ -3,9 +3,10 @@ package org.thoughtcrime.securesms.crypto;
 
 import android.support.annotation.NonNull;
 
+import org.thoughtcrime.securesms.util.Conversions;
+
 import java.io.File;
 import java.io.FileInputStream;
-import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
 import java.security.InvalidAlgorithmParameterException;
@@ -21,13 +22,13 @@ import javax.crypto.spec.SecretKeySpec;
 
 public class ModernDecryptingPartInputStream {
 
-  public static InputStream createFor(@NonNull AttachmentSecret attachmentSecret, @NonNull byte[] random, @NonNull File file)
+  public static InputStream createFor(@NonNull AttachmentSecret attachmentSecret, @NonNull byte[] random, @NonNull File file, long offset)
       throws IOException
   {
-    return createFor(attachmentSecret, random, new FileInputStream(file));
+    return createFor(attachmentSecret, random, new FileInputStream(file), offset);
   }
 
-  public static InputStream createFor(@NonNull AttachmentSecret attachmentSecret, @NonNull File file)
+  public static InputStream createFor(@NonNull AttachmentSecret attachmentSecret, @NonNull File file, long offset)
       throws IOException
   {
     FileInputStream inputStream = new FileInputStream(file);
@@ -35,25 +36,37 @@ public class ModernDecryptingPartInputStream {
 
     readFully(inputStream, random);
 
-    return createFor(attachmentSecret, random, inputStream);
+    return createFor(attachmentSecret, random, inputStream, offset);
   }
 
-  private static InputStream createFor(@NonNull AttachmentSecret attachmentSecret, @NonNull byte[] random, @NonNull InputStream inputStream) {
+  private static InputStream createFor(@NonNull AttachmentSecret attachmentSecret, @NonNull byte[] random, @NonNull InputStream inputStream, long offset) throws IOException {
     try {
-      Mac mac = Mac.getInstance("HmacSHA256");
+      Mac mac  = Mac.getInstance("HmacSHA256");
       mac.init(new SecretKeySpec(attachmentSecret.getModernKey(), "HmacSHA256"));
 
-      byte[] iv  = new byte[16];
+      byte[] iv        = new byte[16];
-      byte[] key = mac.doFinal(random);
+      int    remainder = (int) (offset % 16);
+      Conversions.longTo4ByteArray(iv, 12, offset / 16);
 
+      byte[] key    = mac.doFinal(random);
       Cipher cipher = Cipher.getInstance("AES/CTR/NoPadding");
       cipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(key, "AES"), new IvParameterSpec(iv));
 
-      return new CipherInputStream(inputStream, cipher);
+      long skipped = inputStream.skip(offset - remainder);
+
+      if (skipped != offset - remainder) {
+        throw new IOException("Skip failed: " + skipped + " vs " + (offset - remainder));
+      }
+
+      CipherInputStream cipherInputStream = new CipherInputStream(inputStream, cipher);
+      byte[]            remainderBuffer   = new byte[remainder];
+
+      readFully(cipherInputStream, remainderBuffer);
+
+      return cipherInputStream;
     } catch (NoSuchAlgorithmException | InvalidKeyException | InvalidAlgorithmParameterException | NoSuchPaddingException e) {
       throw new AssertionError(e);
     }
-
   }
 
   private static void readFully(InputStream in, byte[] buffer) throws IOException {

src/org/thoughtcrime/securesms/database/AttachmentDatabase.java

@@ -124,10 +124,10 @@ public class AttachmentDatabase extends Database {
     this.attachmentSecret = attachmentSecret;
   }
 
-  public @NonNull InputStream getAttachmentStream(AttachmentId attachmentId)
+  public @NonNull InputStream getAttachmentStream(AttachmentId attachmentId, long offset)
       throws IOException
   {
-    InputStream dataStream = getDataStream(attachmentId, DATA);
+    InputStream dataStream = getDataStream(attachmentId, DATA, offset);
 
     if (dataStream == null) throw new IOException("No stream for: " + attachmentId);
     else                    return dataStream;
@@ -137,7 +137,7 @@ public class AttachmentDatabase extends Database {
       throws IOException
   {
     Log.w(TAG, "getThumbnailStream(" + attachmentId + ")");
-    InputStream dataStream = getDataStream(attachmentId, THUMBNAIL);
+    InputStream dataStream = getDataStream(attachmentId, THUMBNAIL, 0);
 
     if (dataStream != null) {
       return dataStream;
@@ -380,7 +380,7 @@ public class AttachmentDatabase extends Database {
 
   @SuppressWarnings("WeakerAccess")
   @VisibleForTesting
-  protected @Nullable InputStream getDataStream(AttachmentId attachmentId, String dataType)
+  protected @Nullable InputStream getDataStream(AttachmentId attachmentId, String dataType, long offset)
   {
     DataInfo dataInfo = getAttachmentDataFileInfo(attachmentId, dataType);
 
@@ -390,9 +390,17 @@ public class AttachmentDatabase extends Database {
 
     try {
       if (dataInfo.random != null && dataInfo.random.length == 32) {
-        return ModernDecryptingPartInputStream.createFor(attachmentSecret, dataInfo.random, dataInfo.file);
+        return ModernDecryptingPartInputStream.createFor(attachmentSecret, dataInfo.random, dataInfo.file, offset);
       } else {
-        return ClassicDecryptingPartInputStream.createFor(attachmentSecret, dataInfo.file);
+        InputStream stream  = ClassicDecryptingPartInputStream.createFor(attachmentSecret, dataInfo.file);
+        long        skipped = stream.skip(offset);
+
+        if (skipped != offset) {
+          Log.w(TAG, "Skip failed: " + skipped + " vs " + offset);
+          return null;
+        }
+
+        return stream;
       }
     } catch (IOException e) {
       Log.w(TAG, e);
@@ -590,7 +598,7 @@ public class AttachmentDatabase extends Database {
     @Override
     public @Nullable InputStream call() throws Exception {
       Log.w(TAG, "Executing thumbnail job...");
-      final InputStream stream = getDataStream(attachmentId, THUMBNAIL);
+      final InputStream stream = getDataStream(attachmentId, THUMBNAIL, 0);
 
       if (stream != null) {
         return stream;
@@ -616,7 +624,7 @@ public class AttachmentDatabase extends Database {
 
       updateAttachmentThumbnail(attachmentId, data.toDataStream(), data.getAspectRatio());
 
-      return getDataStream(attachmentId, THUMBNAIL);
+      return getDataStream(attachmentId, THUMBNAIL, 0);
     }
 
     @SuppressLint("NewApi")

src/org/thoughtcrime/securesms/mms/PartAuthority.java

@@ -47,7 +47,7 @@ public class PartAuthority {
     int match = uriMatcher.match(uri);
     try {
       switch (match) {
-      case PART_ROW:       return DatabaseFactory.getAttachmentDatabase(context).getAttachmentStream(new PartUriParser(uri).getPartId());
+      case PART_ROW:       return DatabaseFactory.getAttachmentDatabase(context).getAttachmentStream(new PartUriParser(uri).getPartId(), 0);
       case THUMB_ROW:      return DatabaseFactory.getAttachmentDatabase(context).getThumbnailStream(new PartUriParser(uri).getPartId());
       case PERSISTENT_ROW: return PersistentBlobProvider.getInstance(context).getStream(context, ContentUris.parseId(uri));
       case SINGLE_USE_ROW: return SingleUseBlobProvider.getInstance().getStream(ContentUris.parseId(uri));

src/org/thoughtcrime/securesms/providers/PartProvider.java

@@ -158,10 +158,10 @@ public class PartProvider extends ContentProvider {
   }
 
   private ParcelFileDescriptor getParcelStreamForAttachment(AttachmentId attachmentId) throws IOException {
-    long       plaintextLength = Util.getStreamLength(DatabaseFactory.getAttachmentDatabase(getContext()).getAttachmentStream(attachmentId));
+    long       plaintextLength = Util.getStreamLength(DatabaseFactory.getAttachmentDatabase(getContext()).getAttachmentStream(attachmentId, 0));
     MemoryFile memoryFile      = new MemoryFile(attachmentId.toString(), Util.toIntExact(plaintextLength));
 
-    InputStream  in  = DatabaseFactory.getAttachmentDatabase(getContext()).getAttachmentStream(attachmentId);
+    InputStream  in  = DatabaseFactory.getAttachmentDatabase(getContext()).getAttachmentStream(attachmentId, 0);
     OutputStream out = memoryFile.getOutputStream();
 
     Util.copy(in, out);

src/org/thoughtcrime/securesms/providers/PersistentBlobProvider.java

@@ -160,7 +160,7 @@ public class PersistentBlobProvider {
 
     FileData fileData = getFile(context, id);
 
-    if (fileData.modern) return ModernDecryptingPartInputStream.createFor(attachmentSecret, fileData.file);
+    if (fileData.modern) return ModernDecryptingPartInputStream.createFor(attachmentSecret, fileData.file, 0);
     else                 return ClassicDecryptingPartInputStream.createFor(attachmentSecret, fileData.file);
   }
 

src/org/thoughtcrime/securesms/video/EncryptedMediaDataSource.java

@@ -58,13 +58,9 @@ public class EncryptedMediaDataSource extends MediaDataSource {
   private int readAtModern(long position, byte[] bytes, int offset, int length) throws IOException {
     assert(random != null);
 
-    InputStream inputStream = ModernDecryptingPartInputStream.createFor(attachmentSecret, random, mediaFile);
+    InputStream inputStream = ModernDecryptingPartInputStream.createFor(attachmentSecret, random, mediaFile, position);
+    int         returnValue = inputStream.read(bytes, offset, length);
 
-    if (inputStream.skip(position) != position) {
-      throw new IOException("Skip failed: " + position);
-    }
-
-    int returnValue = inputStream.read(bytes, offset, length);
     inputStream.close();
 
     return returnValue;

src/org/thoughtcrime/securesms/video/exo/PartDataSource.java

@@ -11,7 +11,6 @@ import com.google.android.exoplayer2.upstream.DataSpec;
 import com.google.android.exoplayer2.upstream.TransferListener;
 
 import org.thoughtcrime.securesms.attachments.Attachment;
-import org.thoughtcrime.securesms.crypto.MasterSecret;
 import org.thoughtcrime.securesms.database.AttachmentDatabase;
 import org.thoughtcrime.securesms.database.DatabaseFactory;
 import org.thoughtcrime.securesms.mms.PartUriParser;
@@ -28,8 +27,7 @@ public class PartDataSource implements DataSource {
   private Uri         uri;
   private InputStream inputSteam;
 
-  public PartDataSource(@NonNull Context context, @Nullable TransferListener<? super PartDataSource> listener)
+  PartDataSource(@NonNull Context context, @Nullable TransferListener<? super PartDataSource> listener) {
-  {
     this.context  = context.getApplicationContext();
     this.listener = listener;
   }
@@ -44,13 +42,7 @@ public class PartDataSource implements DataSource {
 
     if (attachment == null) throw new IOException("Attachment not found");
 
-    this.inputSteam = attachmentDatabase.getAttachmentStream(partUri.getPartId());
+    this.inputSteam = attachmentDatabase.getAttachmentStream(partUri.getPartId(), dataSpec.position);
-
-    if (inputSteam == null) throw new IOException("InputStream not foudn");
-
-    long skipped = this.inputSteam.skip(dataSpec.position);
-
-    if (skipped != dataSpec.position) throw new IOException("Skip failed!");
 
     if (listener != null) {
       listener.onTransferStart(this, dataSpec);