linux-ext4 - Re: Atomic non-durable file write API

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Message-ID: <AANLkTinJVJM0Gb2osYQeTUetuVTkJYyXfQR0fkmwS_Pg@mail.gmail.com>
Date:	Tue, 28 Dec 2010 17:15:57 -0500
From:	Greg Freemyer <greg.freemyer@...il.com>
To:	Olaf van der Spek <olafvdspek@...il.com>
Cc:	Neil Brown <neilb@...e.de>,
	Christian Stroetmann <stroetmann@...olinux.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-ext4@...r.kernel.org, "Ted Ts'o" <tytso@....edu>,
	Nick Piggin <npiggin@...il.com>
Subject: Re: Atomic non-durable file write API

On Tue, Dec 28, 2010 at 5:06 PM, Olaf van der Spek <olafvdspek@...il.com> wrote:
> On Tue, Dec 28, 2010 at 11:00 PM, Greg Freemyer <greg.freemyer@...il.com> wrote:
>> create temp file
>> write out new data
>> delete old file
>> rename temp file to primary name
>> ===
>>
>> If so there is still a little window of vulnerability where the whole
>> file can be lost.  (Or at least only the temp file is present).
>
> Delete isn't used, rename will overwrite the old file. So it's safe.
> Meta-data is probably lost, file owner is certainly lost.
>
> Olaf

So ACLs are lost?

That seems like a potentially bigger issue than loosing the owner/group info.

And I assume if the owner changes, then the new owner has privileges
to modify ACLs he didn't have previously.

So if I want to instigate a simple denial of service in a multi-user
environment, I edit a few key docs that I have privileges to edit.  By
doing so I take ownership.  As owner I  change the permissions and
ACLs so that no one but me can access them.

Seems like a security hole to me.

Greg
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