Natty SRU: eCryptfs: Clear ECRYPTFS_NEW_FILE flag during truncate

[Tim Gardner]

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
-- 
Tim Gardner tim.gardner at canonical.com