ACK: Natty SRU: eCryptfs: Clear ECRYPTFS_NEW_FILE flag during truncate

[Stefan Bader]

On 11.10.2011 15:38, Tim Gardner wrote:
> 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
> 

Matches the upstream changes and was tested...

Acked-by: Stefan Bader <smb at canonical.com>