Java应用程序是否有获得root权限的方法？ [英] Is there a way for a Java app to gain root permissions?

问题描述

当运行 Files.walk（Paths.get（/ var /））。count（）作为非特权用户时，执行可能会抛出异常是 / var / 中的文件夹，需要遍历root权限。

我 不 寻找以root身份执行bash命令的方法（例如 sudo find / var ），使用 Process 等。

我只想确保 Files.walk（Paths.get（/ var /） ）.count（）不会抛出 AccessDeniedException ：

 线程中的异常restartedMainjava.lang.reflect.InvocationTargetException 
 at sun.reflect.NativeMethodAccessorImpl.invoke0 
 at sun.reflect.NativeMethodAccessorImpl.invoke 
 at sun.reflect .DelegatingMethodAccessorImpl.invoke 
 at java.lang.reflect.Method.invoke 
 at org.springframework.boot.devtools.restart.RestartLauncher.run 
引起：java.io.UncheckedIOException：java .nio.fi le.AccessDeniedException：/ var / cache / httpd 
 at java.nio.file.FileTreeIterator.fetchNextIfNeeded 
 at java.nio.file.FileTreeIterator.hasNext 
 at java.util.Iterator.forEachRemaining 
 at java.util.Spliterators $ IteratorSpliterator.forEachRemaining 
 at java.util.stream.AbstractPipeline.copyInto 
 at java.util.stream.AbstractPipeline.wrapAndCopyInto 
 at java.util .stream.ReduceOps $ ReduceOp.evaluateSequential 
 java.util.stream.AbstractPipeline.evaluate 
 at java.util.stream.LongPipeline.reduce 
 at java.util.stream.LongPipeline.sum 
 at java.util.stream.ReferencePipeline.count 
 at com.example.DemoApplication.main 
 ... 5 more 
引起：java.nio.file.AccessDeniedException： / var / cache / httpd 
 at sun.nio.fs.UnixException.translateToIOException 
 at sun.nio.fs.UnixException.rethrowAsIOException 
 at sun.nio.fs.UnixException.rethrowAsIOException 
 at sun.nio.fs.Unix FileSystemProvider.newDirectoryStream 
 at java.nio.file.Files.newDirectoryStream 
 at java.nio.file.FileTreeWalker.visit 
 at java.nio.file.FileTreeWalker.next 
 at java.nio.file.FileTreeIterator.fetchNextIfNeeded 
  

这只是一个例子。使用 filter（...）可以解决异常问题。但是这个例子也可以扩展到其他用例。

所以简而言之这是否可能，对于CLI，JavaFX等应用程序获得root权限后已经通过 java -jar app.jar ？

解决方案<等方法从命令行执行/ div>

如果你想要的实际上是跳过你无法访问的路径，你有两种方法：

Streams

在这个问题的答案中解释了如何获取您可以访问的子树的所有文件的流。

但是这个例子也可以扩展到其他用例。

FileVisitor

使用 FileVisitor 添加了大量代码，但在行走目录时可以更灵活树木。要解决同样的问题，你可以用以下代码替换 Files.walk（）：

  Files.walkFileTree（Path start，FileVisitor<？super path> visitor）; 
  

扩展SimpleFileVisitor（计算文件）并覆盖某些方法。

您可以：

1. 覆盖 visitFileFailed 方法，处理案例由于某些原因你无法访问文件; （Lukasz_Plawny的建议）


2. （可选）覆盖 preVisitDirectory 方法，在访问目录之前检查权限：如果无法访问它，您可以简单地跳过它的子树（请记住，您可以访问目录，但不能访问其所有文件）;

例如1

  @Override 
 public FileVisitResult visitFileFailed（Path file，IOException exc）{
 //你可以记录异常'exc'
返回FileVisitResult.SKIP_SUBTREE; 
} 
  

例如。 2

  @Override 
 public FileVisitResult preVisitDirectory（Path dir，BasicFileAttributes attrs）{
 
 if（！Files.isReadable（dir））
返回FileVisitResult.SKIP_SUBTREE; 
 
返回FileVisitResult.CONTINUE; 
 
} 
  

FileVisitor docs

< a href =https://docs.oracle.com/javase/tutorial/essential/io/walk.html =nofollow noreferrer> FileVisitor教程

希望它有所帮助。

When running Files.walk(Paths.get("/var/")).count() as an unprivileged user, the execution might throw an exception as there are folders inside /var/ that need root permission to be traversed.

I am not looking for a way to execute a bash command as root (e.g. sudo find /var), using Process, etc.

I just want to make sure Files.walk(Paths.get("/var/")).count() does not throw an AccessDeniedException:

Exception in thread "restartedMain" java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0
    at sun.reflect.NativeMethodAccessorImpl.invoke
    at sun.reflect.DelegatingMethodAccessorImpl.invoke
    at java.lang.reflect.Method.invoke
    at org.springframework.boot.devtools.restart.RestartLauncher.run
Caused by: java.io.UncheckedIOException: java.nio.file.AccessDeniedException: /var/cache/httpd
    at java.nio.file.FileTreeIterator.fetchNextIfNeeded
    at java.nio.file.FileTreeIterator.hasNext
    at java.util.Iterator.forEachRemaining
    at java.util.Spliterators$IteratorSpliterator.forEachRemaining
    at java.util.stream.AbstractPipeline.copyInto
    at java.util.stream.AbstractPipeline.wrapAndCopyInto
    at java.util.stream.ReduceOps$ReduceOp.evaluateSequential
    at java.util.stream.AbstractPipeline.evaluate
    at java.util.stream.LongPipeline.reduce
    at java.util.stream.LongPipeline.sum
    at java.util.stream.ReferencePipeline.count
    at com.example.DemoApplication.main
    ... 5 more
Caused by: java.nio.file.AccessDeniedException: /var/cache/httpd
    at sun.nio.fs.UnixException.translateToIOException
    at sun.nio.fs.UnixException.rethrowAsIOException
    at sun.nio.fs.UnixException.rethrowAsIOException
    at sun.nio.fs.UnixFileSystemProvider.newDirectoryStream
    at java.nio.file.Files.newDirectoryStream
    at java.nio.file.FileTreeWalker.visit
    at java.nio.file.FileTreeWalker.next
    at java.nio.file.FileTreeIterator.fetchNextIfNeeded

This is just an example. Using filter(...) it is possible to work around the exception. But this example can be expanded to other use cases too.

So in short Is this possible at all, for CLI, JavaFX, etc. apps to gain root permission after they have been executed from command line via a method such as java -jar app.jar?

解决方案

If what you want is actually skipping the paths where you have no access, you have two approaches:

Streams

In the answer to this question it is explained how to obtain the stream of all files of a subtree you can access.

But this example can be expanded to other use cases too.

FileVisitor

Using a FileVisitor adds a lot of code, but grants you much more flexibility when walking directory trees. To solve the same problem you can replace Files.walk() with:

Files.walkFileTree(Path start, FileVisitor<? super Path> visitor);

extending SimpleFileVisitor (to count the files) and overriding some methods.

You can:

1. Override the visitFileFailed method, to handle the case you cannot access a file for some reasons; (Lukasz_Plawny's advice)
2. (optional) Override the preVisitDirectory method, checking for permissions before accessing the directory: if you can't access it, you can simply skip its subtree (keep in mind that you may be able to access a directory, but not all its files);

e.g. 1

@Override
public FileVisitResult visitFileFailed(Path file, IOException exc) {
    // you can log the exception 'exc'
    return FileVisitResult.SKIP_SUBTREE;
}

e.g. 2

@Override
public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) {

    if(!Files.isReadable(dir))
        return FileVisitResult.SKIP_SUBTREE;

    return FileVisitResult.CONTINUE;

}

FileVisitor docs

FileVisitor tutorial

Hope it helps.

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