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https://issues.apache.org/jira/browse/VFS-437?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13467966#comment-13467966
]
Dennis Zhu commented on VFS-437:
--------------------------------
Here it is:
VFS-437
1. Configure the remote FTP server's local_root to be a certain directory by
modifying vsftpd.conf, for example "local_root=/Vol1". This will cause all
users who log in to this FTP server to see "/Vol1" as the root "/" folder.
2. Navigate to this local_root folder, and create a symbolic link with the same
name that links to this folder. For example, we create a symlink also called
"Vol1" that links to "/Vol1", so that "Vol1 -> /Vol1".
3. Use VFS to access this FTP server using a URL such as
"ftp://test:[email protected]/Vol1";. For example, using the following
test code:
@Test
public void test()
throws FileSystemException {
FileSystemOptions opts = new FileSystemOptions();
FtpFileSystemConfigBuilder.getInstance().setUserDirIsRoot( opts, true );
final FileObject file = VFS.getManager().resolveFile(
"ftp://test:[email protected]/Vol1";, opts );
System.out.println( file );
for ( FileObject child : file.getChildren() ) {
System.out.println( child );
if ( child.getType() == FileType.FOLDER )
for ( FileObject child2 : child.getChildren() ) {
System.out.println( child2 );
}
}
}
This will reproduce the StackOverFlow Exception because our URL tries to
resolve the directory "/Vol1", thinking that our root directory is the "/"
directory. However, what actually happens is that our URL actually will try to
resolve "/Vol1/Vol1" on the FTP file system. This is due to the fact that we
have setUserDirIsRoot( opts, true ). Now, since resolving "/Vol1" will bring us
back to the "Vol1" symbolic link itself and not the actual directory, we'll be
infinitely trying to perform doGetType() in FtpFileObject on the symbolic link.
In summary, the StackOverFlow is guaranteed to happen when the user is in
relative path mode (setUserDirIsRoot to true) and using a symbolic link to
access a file or directory, with the same name as the symbolic link, on the
file system that he doesn't have access to. This is an edge case that is only
likly to happen when the user sets up these kind of symbolic links that he's
not supposed to use in an FTP server. However, this case WILL crash
applications when it comes up.
> [FTP] Program crashes when StackOverFlow Exception happens from pulling a
> softlinked directory that link to the directory that has the same name one
> level above
> -----------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: VFS-437
> URL: https://issues.apache.org/jira/browse/VFS-437
> Project: Commons VFS
> Issue Type: Bug
> Affects Versions: 2.0
> Environment: java version "1.7.0_02"
> Java(TM) SE Runtime Environment (build 1.7.0_02-b13)
> Java HotSpot(TM) 64-Bit Server VM (build 22.0-b10, mixed mode)
> Linux version 2.6.18-238.el5 ([email protected]) (gcc version
> 4.1.2 20080704 (Red Hat 4.1.2-48)) #1 SMP Thu Jan 13 15:51:15 EST 2011
> Reporter: Jason
> Priority: Blocker
> Fix For: 2.1
>
>
> With the setting below, StackOverFlow exceptions occur and server crashes
> set the builder.setUserDirlsRoot (opt, true)
> Attept to pull with:
> ftp://root:password@ip:/Vol1
> Vol directory has the following info
> lrwxrwxrwx 1 root root 5 Oct 5 2007 Vol1 -> /Vol1
> When it tries to look for the parent of the Vol1, it goes back to the same
> Vol1, which causes a infinite loop that eventually creates stackoverflow
> exception.
> The problem is inside the doGetType() method in FtpFileObject
> @Override
> protected FileType doGetType()
> throws Exception
> {
> // VFS-210
> synchronized (getFileSystem())
> {
> if (this.fileInfo == null)
> {
> getInfo(false);
> }
> if (this.fileInfo == UNKNOWN)
> {
> return FileType.IMAGINARY;
> }
> else if (this.fileInfo.isDirectory())
> {
> return FileType.FOLDER;
> }
> else if (this.fileInfo.isFile())
> {
> return FileType.FILE;
> }
> else if (this.fileInfo.isSymbolicLink())
> {
> return getLinkDestination().getType();
> }
> }
> throw new FileSystemException("vfs.provider.ftp/get-type.error",
> getName());
> }
> It will keep hitting the "else if (this.fileinfo.isSymbolicLink())" condition
> and the fileinfo displayed is always the Vol1 under root directory.
> Exception is shown below
> java.lang.StackOverflowError
> at org.apache.commons.net.ftp.FTPFile.isDirectory(FTPFile.java:116)
> at
> org.apache.commons.vfs2.provider.ftp.FtpFileObject.doGetType(FtpFileObject.java:334)
> at
> org.apache.commons.vfs2.provider.AbstractFileObject.getType(AbstractFileObject.java:496)
> at
> org.apache.commons.vfs2.provider.ftp.FtpFileObject.doGetType(FtpFileObject.java:344)
> at
> org.apache.commons.vfs2.provider.AbstractFileObject.getType(AbstractFileObject.java:496)
> at
> org.apache.commons.vfs2.provider.ftp.FtpFileObject.doGetType(FtpFileObject.java:344)
> at
> org.apache.commons.vfs2.provider.AbstractFileObject.getType(AbstractFileObject.java:496)
> at
> org.apache.commons.vfs2.provider.ftp.FtpFileObject.doGetType(FtpFileObject.java:344)
> at
> org.apache.commons.vfs2.provider.AbstractFileObject.getType(AbstractFileObject.java:496)
> at
> org.apache.commons.vfs2.provider.ftp.FtpFileObject.doGetType(FtpFileObject.java:344)
> at
> org.apache.commons.vfs2.provider.AbstractFileObject.getType(AbstractFileObject.java:496)
> at
> org.apache.commons.vfs2.provider.ftp.FtpFileObject.doGetType(FtpFileObject.java:344)
> at
> org.apache.commons.vfs2.provider.AbstractFileObject.getType(AbstractFileObject.java:496)
> at
> org.apache.commons.vfs2.provider.ftp.FtpFileObject.doGetType(FtpFileObject.java:344)
> at
> org.apache.commons.vfs2.provider.AbstractFileObject.getType(AbstractFileObject.java:496)
> at
> org.apache.commons.vfs2.provider.ftp.FtpFileObject.doGetType(FtpFileObject.java:344)
> at
> org.apache.commons.vfs2.provider.AbstractFileObject.getType(AbstractFileObject.java:496)
> at
> org.apache.commons.vfs2.provider.ftp.FtpFileObject.doGetType(FtpFileObject.java:344)
> at
> org.apache.commons.vfs2.provider.AbstractFileObject.getType(AbstractFileObject.java:496)
> at
> org.apache.commons.vfs2.provider.ftp.FtpFileObject.doGetType(FtpFileObject.java:344)
> at
> org.apache.commons.vfs2.provider.AbstractFileObject.getType(AbstractFileObject.java:496)
> at
> org.apache.commons.vfs2.provider.ftp.FtpFileObject.doGetType(FtpFileObject.java:344)
> at
> org.apache.commons.vfs2.provider.AbstractFileObject.getType(AbstractFileObject.java:496)
> at
> org.apache.commons.vfs2.provider.ftp.FtpFileObject.doGetType(FtpFileObject.java:344)
> at
> org.apache.commons.vfs2.provider.AbstractFileObject.getType(AbstractFileObject.java:496)
> at
> org.apache.commons.vfs2.provider.ftp.FtpFileObject.doGetType(FtpFileObject.java:344)
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