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/*
* Copyright (C) 2017 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.os;
import android.content.Context;
import android.os.storage.StorageManager;
import android.system.ErrnoException;
import android.system.Os;
import android.system.OsConstants;
import android.util.Slog;
import libcore.io.IoUtils;
import java.io.File;
import java.io.FileDescriptor;
import java.io.IOException;
import java.io.InterruptedIOException;
/**
* Variant of {@link FileDescriptor} that allows its creator to revoke all
* access to the underlying resource.
* <p>
* This is useful when the code that originally opened a file needs to strongly
* assert that any clients are completely hands-off for security purposes.
*
* @hide
*/
public class RevocableFileDescriptor {
private static final String TAG = "RevocableFileDescriptor";
private static final boolean DEBUG = true;
private FileDescriptor mInner;
private ParcelFileDescriptor mOuter;
private volatile boolean mRevoked;
/** {@hide} */
public RevocableFileDescriptor() {
}
/**
* Create an instance that references the given {@link File}.
*/
public RevocableFileDescriptor(Context context, File file) throws IOException {
try {
init(context, Os.open(file.getAbsolutePath(),
OsConstants.O_CREAT | OsConstants.O_RDWR, 0700));
} catch (ErrnoException e) {
throw e.rethrowAsIOException();
}
}
/**
* Create an instance that references the given {@link FileDescriptor}.
*/
public RevocableFileDescriptor(Context context, FileDescriptor fd) throws IOException {
init(context, fd);
}
/** {@hide} */
public void init(Context context, FileDescriptor fd) throws IOException {
mInner = fd;
mOuter = context.getSystemService(StorageManager.class)
.openProxyFileDescriptor(ParcelFileDescriptor.MODE_READ_WRITE, mCallback);
}
/**
* Return a {@link ParcelFileDescriptor} which can safely be passed to an
* untrusted process. After {@link #revoke()} is called, all operations will
* fail with {@link OsConstants#EPERM}.
*/
public ParcelFileDescriptor getRevocableFileDescriptor() {
return mOuter;
}
/**
* Revoke all future access to the {@link ParcelFileDescriptor} returned by
* {@link #getRevocableFileDescriptor()}. From this point forward, all
* operations will fail with {@link OsConstants#EPERM}.
*/
public void revoke() {
mRevoked = true;
IoUtils.closeQuietly(mInner);
}
public boolean isRevoked() {
return mRevoked;
}
private final ProxyFileDescriptorCallback mCallback = new ProxyFileDescriptorCallback() {
private void checkRevoked() throws ErrnoException {
if (mRevoked) {
throw new ErrnoException(TAG, OsConstants.EPERM);
}
}
@Override
public long onGetSize() throws ErrnoException {
checkRevoked();
return Os.fstat(mInner).st_size;
}
@Override
public int onRead(long offset, int size, byte[] data) throws ErrnoException {
checkRevoked();
int n = 0;
while (n < size) {
try {
n += Os.pread(mInner, data, n, size - n, offset + n);
break;
} catch (InterruptedIOException e) {
n += e.bytesTransferred;
}
}
return n;
}
@Override
public int onWrite(long offset, int size, byte[] data) throws ErrnoException {
checkRevoked();
int n = 0;
while (n < size) {
try {
n += Os.pwrite(mInner, data, n, size - n, offset + n);
break;
} catch (InterruptedIOException e) {
n += e.bytesTransferred;
}
}
return n;
}
@Override
public void onFsync() throws ErrnoException {
if (DEBUG) Slog.v(TAG, "onFsync()");
checkRevoked();
Os.fsync(mInner);
}
@Override
public void onRelease() {
if (DEBUG) Slog.v(TAG, "onRelease()");
mRevoked = true;
IoUtils.closeQuietly(mInner);
}
};
}
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