AllowSymLinkAliasChecker.java

//
//  ========================================================================
//  Copyright (c) 1995-2017 Mort Bay Consulting Pty. Ltd.
//  ------------------------------------------------------------------------
//  All rights reserved. This program and the accompanying materials
//  are made available under the terms of the Eclipse Public License v1.0
//  and Apache License v2.0 which accompanies this distribution.
//
//      The Eclipse Public License is available at
//      http://www.eclipse.org/legal/epl-v10.html
//
//      The Apache License v2.0 is available at
//      http://www.opensource.org/licenses/apache2.0.php
//
//  You may elect to redistribute this code under either of these licenses.
//  ========================================================================
//

package org.eclipse.jetty.server.handler;

import java.nio.file.Files;
import java.nio.file.Path;

import org.eclipse.jetty.server.handler.ContextHandler.AliasCheck;
import org.eclipse.jetty.util.log.Log;
import org.eclipse.jetty.util.log.Logger;
import org.eclipse.jetty.util.resource.PathResource;
import org.eclipse.jetty.util.resource.Resource;


/* ------------------------------------------------------------ */

/**
 * Symbolic Link AliasChecker.
 * <p>An instance of this class can be registered with {@link ContextHandler#addAliasCheck(AliasCheck)}
 * to check resources that are aliased to other locations.   The checker uses the
 * Java {@link Files#readSymbolicLink(Path)} and {@link Path#toRealPath(java.nio.file.LinkOption...)}
 * APIs to check if a file is aliased with symbolic links.</p>
 */
public class AllowSymLinkAliasChecker implements AliasCheck
{
    private static final Logger LOG = Log.getLogger(AllowSymLinkAliasChecker.class);
    
    @Override
    public boolean check(String uri, Resource resource)
    {
        // Only support PathResource alias checking
        if (!(resource instanceof PathResource))
            return false;
        
        PathResource pathResource = (PathResource) resource;

        try
        {
            Path path = pathResource.getPath();
            Path alias = pathResource.getAliasPath();

            if (path.equals(alias))
                return false; // Unknown why this is an alias

            if (hasSymbolicLink(path) && Files.isSameFile(path, alias))
            {
                if (LOG.isDebugEnabled())
                    LOG.debug("Allow symlink {} --> {}", resource, pathResource.getAliasPath());
                return true;
            }
        }
        catch (Exception e)
        {
            LOG.ignore(e);
        }
        
        return false;
    }

    private boolean hasSymbolicLink(Path path)
    {
        // Is file itself a symlink?
        if (Files.isSymbolicLink(path))
        {
            return true;
        }

        // Lets try each path segment
        Path base = path.getRoot();
        for (Path segment : path)
        {
            base = base.resolve(segment);
            if (Files.isSymbolicLink(base))
            {
                return true;
            }
        }

        return false;
    }

}