Comment 0 for bug 1172961

This is the same issue already reported for the now defunct sun-java6 package in bug 552612 , and it also affects both OpenJDK 7 and 6. The description below is thus very similar:

The problem is that the binfmt entry for Jar files created by OpenJDK also matches regular Zip files and Office 2007 files. This means that if you get these files from a FAT filesystem (typically a USB stick), or an NTFS "data partition" (common scenario when dual-booting) then they become 'almost' executable. Here's how to reproduce the problem:

   $ echo foo >foo.txt
   $ zip foo.zip foo.txt
   $ chmod +x foo.zip

Now on a system without java installed if you try to run or exec that file you would get:

   $ ./foo.zip; echo $?
   bash: ./foo.zip: cannot execute binary file
   126
   $ exec ./foo.zip
   bash: /tmp/foo.zip: cannot execute binary file
   bash: /tmp/foo.zip: Success

But on a system where sun-java6-bin has been installed you get:

   $ ./foo.zip; echo $?
   invalid file (bad magic number): Exec format error
   1
   $ exec ./foo.zip
   <xterm is gone because exec succeeded>

The reason is that Jar files look like Zip files so the content matching pattern used by /proc/sys/fs/binfmt_misc/jar matches both. The issue is the same with the new Office 2007 files such as docx and pptx files.

Options:
1) Make the binfmt magic distinguish between Jar files and Zip files.
    This may not be possible.

2) Match based on the extension instead as documented in the kernel Documentation/java.txt file.
    This means only files with the .jar extension will be runnable which may be too limiting if the goal is to make it possible to have /usr/bin binaries actually be Java applications. However, are these really Jar files or would they be Class files? Or would wrapping them with a Class file be ok?

3) Remove the Jar binfmt altogether.
    Do the advantages of wrapper-less execution of no-extension Jar files justify changing the exec() behavior of zip and Office 2007 files? Are such files actually common?

There is also an underlying philosophical question: what should a file manager do when the user double-clicks on an executable file?
 1) fork()+exec() it and if exec() fails, then look for an association as a fallback
 2) or look for an association first and only try fork()+exec() as a fallback (or even have no fallback at all)

Nautilus seems to implement option 2 so it's not impacted by this issue.