/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.hadoop.io;
import java.io.File;
import java.io.FileDescriptor;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileStatus;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.fs.permission.FsPermission;
import org.apache.hadoop.io.nativeio.Errno;
import org.apache.hadoop.io.nativeio.NativeIO;
import org.apache.hadoop.io.nativeio.NativeIOException;
import org.apache.hadoop.io.nativeio.NativeIO.Stat;
import org.apache.hadoop.security.UserGroupInformation;
/**
* This class provides secure APIs for opening and creating files on the local
* disk. The main issue this class tries to handle is that of symlink traversal.
* <br/>
* An example of such an attack is:
* <ol>
* <li> Malicious user removes his task's syslog file, and puts a link to the
* jobToken file of a target user.</li>
* <li> Malicious user tries to open the syslog file via the servlet on the
* tasktracker.</li>
* <li> The tasktracker is unaware of the symlink, and simply streams the contents
* of the jobToken file. The malicious user can now access potentially sensitive
* map outputs, etc. of the target user's job.</li>
* </ol>
* A similar attack is possible involving the
* {@link org.apache.hadoop.mapred.TaskLogsTruncater}, but here it is to do
* with unsecure write to a file.
* <br/>
*/
public class SecureIOUtils {
/**
* Ensure that we are set up to run with the appropriate native support code.
* If security is disabled, and the support code is unavailable, this class
* still tries its best to be secure, but is vulnerable to some race condition
* attacks.
*
* If security is enabled but the support code is unavailable, throws a
* RuntimeException since we don't want to run insecurely.
*/
static {
boolean shouldBeSecure = UserGroupInformation.isSecurityEnabled();
boolean canBeSecure = NativeIO.isAvailable();
if (!canBeSecure && shouldBeSecure) {
throw new RuntimeException(
"Secure IO is not possible without native code extensions.");
}
// Pre-cache an instance of the raw FileSystem since we sometimes
// do secure IO in a shutdown hook, where this call could fail.
try {
rawFilesystem = FileSystem.getLocal(new Configuration()).getRaw();
} catch (IOException ie) {
throw new RuntimeException(
"Couldn't obtain an instance of RawLocalFileSystem.");
}
// SecureIO just skips security checks in the case that security is
// disabled
skipSecurity = !canBeSecure;
}
private final static boolean skipSecurity;
private final static FileSystem rawFilesystem;
/**
* Open the given File for read access, verifying the expected user/group
* constraints.
* @param f the file that we are trying to open
* @param expectedOwner the expected user owner for the file
* @param expectedGroup the expected group owner for the file
* @throws IOException if an IO Error occurred, or the user/group does not
* match
*/
public static FileInputStream openForRead(File f, String expectedOwner,
String expectedGroup) throws IOException {
if (skipSecurity) {
// Subject to race conditions but this is the best we can do
FileStatus status =
rawFilesystem.getFileStatus(new Path(f.getAbsolutePath()));
checkStat(f, status.getOwner(), status.getGroup(),
expectedOwner, expectedGroup);
return new FileInputStream(f);
}
FileInputStream fis = new FileInputStream(f);
boolean success = false;
try {
Stat stat = NativeIO.fstat(fis.getFD());
checkStat(f, stat.getOwner(), stat.getGroup(), expectedOwner,
expectedGroup);
success = true;
return fis;
} finally {
if (!success) {
fis.close();
}
}
}
private static FileOutputStream insecureCreateForWrite(File f,
int permissions) throws IOException {
// If we can't do real security, do a racy exists check followed by an
// open and chmod
if (f.exists()) {
throw new AlreadyExistsException("File " + f + " already exists");
}
FileOutputStream fos = new FileOutputStream(f);
boolean success = false;
try {
rawFilesystem.setPermission(new Path(f.getAbsolutePath()),
new FsPermission((short)permissions));
success = true;
return fos;
} finally {
if (!success) {
fos.close();
}
}
}
/**
* Open the specified File for write access, ensuring that it does not exist.
* @param f the file that we want to create
* @param permissions we want to have on the file (if security is enabled)
*
* @throws AlreadyExistsException if the file already exists
* @throws IOException if any other error occurred
*/
public static FileOutputStream createForWrite(File f, int permissions)
throws IOException {
if (skipSecurity) {
return insecureCreateForWrite(f, permissions);
} else {
// Use the native wrapper around open(2)
try {
FileDescriptor fd = NativeIO.open(f.getAbsolutePath(),
NativeIO.O_WRONLY | NativeIO.O_CREAT | NativeIO.O_EXCL,
permissions);
return new FileOutputStream(fd);
} catch (NativeIOException nioe) {
if (nioe.getErrno() == Errno.EEXIST) {
throw new AlreadyExistsException(nioe);
}
throw nioe;
}
}
}
private static void checkStat(File f, String owner, String group,
String expectedOwner,
String expectedGroup) throws IOException {
if (expectedOwner != null &&
!expectedOwner.equals(owner)) {
throw new IOException(
"Owner '" + owner + "' for path " + f + " did not match " +
"expected owner '" + expectedOwner + "'");
}
if (expectedGroup != null &&
!expectedGroup.equals(group)) {
throw new IOException(
"Group '" + group + "' for path " + f + " did not match " +
"expected group '" + expectedGroup + "'");
}
}
/**
* Signals that an attempt to create a file at a given pathname has failed
* because another file already existed at that path.
*/
public static class AlreadyExistsException extends IOException {
public AlreadyExistsException(String msg) {
super(msg);
}
public AlreadyExistsException(Throwable cause) {
super(cause);
}
}
}