Review Request: JDK-8173096 jmod files are not world-readable

[Peter Levart]

Hi Mandy,

On 01/20/2017 05:55 PM, Mandy Chung wrote:
> Webrev:
>     http://cr.openjdk.java.net/~mchung/jdk9/webrevs/8173096/webrev.00/index.html
>
> A recent change in jmod tool [1] creates the JMOD file with no group
> and other readable permission as that’s the default permission when
> creating a temporary file with Files::createTempFile.  This fixes
> the permission issue by creating the JMOD file in a temporary directory.
>
> Mandy
> [1] https://bugs.openjdk.java.net/browse/JDK-8173096

I guess the JmodTask is creating a temp file because it wants the file 
to not be observed by other processes while it is being written to, 
right? At the end when the tempTarget is fully written, it is renamed to 
its intended name with:

Files.move(tempTarget, target);


...but that operation will not be atomic since you didn't pass 
ATOMIC_MOVE to the CopyOption... options. Even if you did, the atomic 
move will succeed only when both tempTarget and target point to the same 
filesystem. Since you are creating tempTarget in default temporary files 
location (/tmp on UNIXes) this might not be the case (depending on where 
the real target is located).

So why don't you simply append a .tmp suffix to the intended target file 
name when opening the JmodOutputStream. This would ensure the file 
location will be on the same filesystem as the final target name as it 
will be created in the same directory. Module path scanning should skip 
files with .tmp extension then.

Regards, Peter