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

[Yasumasa Suenaga]

PING: Could you review it?

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


Yasumasa


On 2019/12/26 11:50, Yasumasa Suenaga wrote:
> 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.