Re: Practical questions about locking and re-encrypting

[Tyler Hicks <tyhicks@canonical.com>]

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On 2014-09-23 11:39:55, Kenneth Waegeman wrote:
> 
> ----- Message from Tyler Hicks <tyhicks@canonical.com> ---------
>    Date: Mon, 22 Sep 2014 10:58:25 -0500
>    From: Tyler Hicks <tyhicks@canonical.com>
> Subject: Re: Practical questions about locking and re-encrypting
>      To: Kenneth Waegeman <Kenneth.Waegeman@UGent.be>
>      Cc: ecryptfs@vger.kernel.org
> 
> 
> >On 2014-09-22 17:32:57, Kenneth Waegeman wrote:
> >>Hi all,
> >
> >Hi Kenneth
> >
> >>
> >>
> >>We want to use ecryptfs on GPFS. How does ecryptfs handles locking if an
> >>encrypted directory is mounted on different boxes ? Is data corruption
> >>possible while writing?
> >
> >eCryptfs is not well suited for being stacked on top of a distributed
> >file system such as GPFS.
> >
> >That would result in each node having its own eCryptfs mount. Each
> >eCryptfs mount has its own page cache. eCryptfs doesn't do any sort of
> >coordination between remote mounts and there's no way for the lower
> >filesystem to make eCryptfs aware that file contents, which may be in
> >the eCryptfs page cache, have been modified by a remote node.
> >
> >That means that if a file is read into the eCryptfs page cache on node A
> >and then that file is updated on node B, node A will never know an
> >update has been made and will never invalidate the old, cached file
> >contents from its page cache.
> 
> When is the pagecache flushed?

The typical times (periodic background writeout, sync, unmount, etc.)
and when a file is closed.

> is sync honoured? or does that happen only on unmount?

Sync is honored.

> Does this also apply for directories?

Yes

> What happens if 2 hosts modifying different files in same directory?

If one host has pieces of a file cached and then another host modifies
those pieces, then the first host will have outdated cached contents. It
doesn't matter if the files are in the same directory or in different
directories.

Tyler

> 
> Thank you for the explanation!
> 
> Kenneth
> 
> >
> >>
> >>Another question: Is there an easy way to re-encrypt a directory with
> >>another key? (when having compromised key or so).
> >
> >Unfortunately, no. You'd need to set up a new eCryptfs mount, with a new
> >key, and copy the files between the two eCryptfs mounts.
> >
> >Tyler
> >
> >>
> >>
> >>Thank you!!
> >>
> >>Kenneth
> >>
> >>
> >>--
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> >>the body of a message to majordomo@vger.kernel.org
> >>More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 
> 
> ----- End message from Tyler Hicks <tyhicks@canonical.com> -----
> 
> -- 
> 
> Met vriendelijke groeten,
> Kenneth Waegeman
> 

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