Natty SRU: eCryptfs: Clear ECRYPTFS_NEW_FILE flag during truncate

[Tim Gardner]

On 10/11/2011 01:53 PM, Tim Gardner wrote:
> On 10/10/2011 04:26 PM, Tyler Hicks wrote:
>> On 2011-10-10 07:16:59, Leann Ogasawara wrote:
>>> On Mon, 2011-10-10 at 14:46 +0100, Tim Gardner wrote:
>>>> On 10/10/2011 02:42 PM, Leann Ogasawara wrote:
>>>>> On Sun, 2011-10-09 at 05:12 -0600, Tim Gardner wrote:
>>>>>> From 27ed7cb2b00512e81016419715c1d9b6794b06ae Mon Sep 17 00:00:00
>>>>>> 2001
>>>>>> From: Tyler Hicks<tyhicks at canonical.com>
>>>>>> Date: Fri, 7 Oct 2011 15:54:26 -0500
>>>>>> Subject: [PATCH] eCryptfs: Clear ECRYPTFS_NEW_FILE flag during
>>>>>> truncate
>>>>>>
>>>>>> BugLink: http://bugs.launchpad.net/bugs/745836
>>>>>>
>>>>>> The ECRYPTFS_NEW_FILE crypt_stat flag is set upon creation of a new
>>>>>> eCryptfs file. When the flag is set, eCryptfs reads directly from the
>>>>>> lower filesystem when bringing a page up to date. This means that no
>>>>>> offset translation (for the eCryptfs file metadata in the lower file)
>>>>>> and no decryption is performed. The flag is cleared just before the
>>>>>> first write is completed (at the beginning of
>>>>>> ecryptfs_write_begin()).
>>>>>>
>>>>>> It was discovered that if a new file was created and then extended
>>>>>> with
>>>>>> truncate, the ECRYPTFS_NEW_FILE flag was not cleared. If pages
>>>>>> corresponding to this file are ever reclaimed, any subsequent reads
>>>>>> would result in userspace seeing eCryptfs file metadata and encrypted
>>>>>> file contents instead of the expected decrypted file contents.
>>>>>>
>>>>>> Data corruption is possible if the file is written to before the
>>>>>> eCryptfs directory is unmounted. The data written will be copied into
>>>>>> pages which have been read directly from the lower file rather than
>>>>>> zeroed pages, as would be expected after extending the file with
>>>>>> truncate.
>>>>>>
>>>>>> This flag, and the functionality that used it, was removed in
>>>>>> upstream
>>>>>> kernels in 2.6.39 with the following commits:
>>>>>>
>>>>>> bd4f0fe8bb7c73c738e1e11bc90d6e2cf9c6e20e
>>>>>> fed8859b3ab94274c986cbdf7d27130e0545f02c
>>>>>
>>>>> Is there a reason we're not just cherry-picking the upstream patches?
>>>>> And so I would assume this patch should be marked as SAUCE?
>>>>>
>>>>> Thanks,
>>>>> Leann
>>>>>
>>>>
>>>> Yeah, 'UBUNTU: SAUCE:' for sure. Tyler said in the LP report that
>>>> backporting those 2 commits was getting too involved and complicated.
>>>> Given the simplicity of his ultimate solution I thought the backport
>>>> seemed better.
>>>
>>> Hrm, those two patches appear to cherry-pick cleanly for me, although I
>>> could be missing other external factors. Reading the bug report it
>>> sounds like Tyler originally thought this was fixed with upstream commit
>>> 3b06b3ebf44170c90c893c6c80916db6e922b9f2 and it was that commit which
>>> was problematic to backport (see comment #85).
>>
>> Yep, I was wrong about 3b06b3eb being the fix. Bad assumption on my
>> part.
>>
>>> It's in the following
>>> comment #86 that he identifies the actual fix being commits bd4f0fe8 and
>>> fed8859b.
>>>
>>> Regardless, the SAUCE patch looks fine to me. It's straightforward and
>>> tested. I was just more curious as to why we don't just cherry-pick the
>>> upstream patches. I've CC'd Tyler to get his reasoning.
>>
>> While bd4f0fe8 and fed8859b will cherry-pick cleanly and get rid of the
>> buggy code, they weren't intended to be bug fixes when I wrote them.
>> They were just intended to remove some functionality in order to make
>> the file creation process a bit faster. To me, it just didn't feel like
>> something that should be backported consider how simple the real fix
>> was.
>>
>> Tyler
>
> Tyler - these 2 patches are simple enough that I'd prefer the clean
> cherry-picks (which we try to use as a matter of policy). I'll retest
> and send out the results...
>
> rtg

The attached patches are clean cherry-picks and produce the same result 
without regression.

rtg
-- 
Tim Gardner tim.gardner at canonical.com
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