RFR: 8236489: Java heap file on daxfs should be more secure

[Yasumasa Suenaga]

Hi all,

I filed this to JBS. Could you review?

   JBS: https://bugs.openjdk.java.net/browse/JDK-8236489
   webrev: http://cr.openjdk.java.net/~ysuenaga/JDK-8236489/webrev.00/

It has passed all tests on submit repo. (mach5-one-ysuenaga-JDK-8236489-20191226-0145-7795073)


Thanks,

Yasumasa


On 2019/12/19 14:58, Yasumasa Suenaga wrote:
> Hi all,
> 
> HotSpot allocates Java heap on daxfs if we pass -XX:AllocateHeapAt.
> It performs open(2) and unlink(2) on daxfs, and it is used via mmap'ed address.
> 
> mmap(2) would be called with MAP_SHARED, and it is not atomically between open(2) and unlink(2). If malicious user open Java heap file before unlink(2), it might be exposed.
> 
> So I think we can use open(2) with O_TMPFILE instead of mkstemp(3) as below.
> 
>    http://cr.openjdk.java.net/~ysuenaga/dax/
> 
> O_TMPFILE would create inode on filesystem, and it cannot be accessed from out-of-process.
> However it cannot be provided in older Linux kernel. So I keep current code as fall back.
> 
>    http://man7.org/linux/man-pages/man2/open.2.html
> 
> What do you think about it? or someone is working for it?
> If it is ok, I will file it to JBS and will send review request.
> 
> 
> Thanks,
> 
> Yasumasa
> 
> 
> P.S.
>    I tried to use MAP_PRIVATE for it, but it was slower than MAP_SHARED.