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Redact ISOBMFF boxes with 'free'

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Test: atest MediaStore_Video_MediaTest android.os.RedactingFileDescriptorTest
Bug: 135499138
Change-Id: Idaa8ad30300d5427f91bb2543be3152881018cf6
This commit is contained in:
Andrew Lewis
2019-07-10 13:14:24 +01:00
parent 6f672a3835
commit 4ec5fda3d6
2 changed files with 97 additions and 9 deletions
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26
core/java/android/os/RedactingFileDescriptor.java
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@@ -35,7 +35,7 @@ import java.util.Arrays;
/**
* Variant of {@link FileDescriptor} that allows its creator to specify regions
* that should be redacted (appearing as zeros to the reader).
* that should be redacted.
*
* @hide
*/
@@ -44,13 +44,16 @@ public class RedactingFileDescriptor {
private static final boolean DEBUG = true;
private volatile long[] mRedactRanges;
private volatile long[] mFreeOffsets;
private FileDescriptor mInner = null;
private ParcelFileDescriptor mOuter = null;
private RedactingFileDescriptor(Context context, File file, int mode, long[] redactRanges)
private RedactingFileDescriptor(
Context context, File file, int mode, long[] redactRanges, long[] freeOffsets)
throws IOException {
mRedactRanges = checkRangesArgument(redactRanges);
mFreeOffsets = freeOffsets;
try {
try {
@@ -88,13 +91,17 @@ public class RedactingFileDescriptor {
*
* @param file The underlying file to open.
* @param mode The {@link ParcelFileDescriptor} mode to open with.
* @param redactRanges List of file offsets that should be redacted, stored
* @param redactRanges List of file ranges that should be redacted, stored
* as {@code [start1, end1, start2, end2, ...]}. Start values are
* inclusive and end values are exclusive.
* @param freePositions List of file offsets at which the four byte value 'free' should be
* written instead of zeros within parts of the file covered by {@code redactRanges}.
* Non-redacted bytes will not be modified even if covered by a 'free'. This is
* useful for overwriting boxes in ISOBMFF files with padding data.
*/
public static ParcelFileDescriptor open(Context context, File file, int mode,
long[] redactRanges) throws IOException {
return new RedactingFileDescriptor(context, file, mode, redactRanges).mOuter;
long[] redactRanges, long[] freePositions) throws IOException {
return new RedactingFileDescriptor(context, file, mode, redactRanges, freePositions).mOuter;
}
/**
@@ -169,6 +176,15 @@ public class RedactingFileDescriptor {
for (long j = start; j < end; j++) {
data[(int) (j - offset)] = 0;
}
// Overwrite data at 'free' offsets within the redaction ranges.
for (long freeOffset : mFreeOffsets) {
final long freeEnd = freeOffset + 4;
final long redactFreeStart = Math.max(freeOffset, start);
final long redactFreeEnd = Math.min(freeEnd, end);
for (long j = redactFreeStart; j < redactFreeEnd; j++) {
data[(int) (j - offset)] = (byte) "free".charAt((int) (j - freeOffset));
}
}
}
return n;
}