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On 12/03/2013 06:13 PM, Ben Nemec wrote:
> On 2013-12-03 17:09, Sean Dague wrote:
>> On 12/03/2013 05:50 PM, Mark McLoughlin wrote:
>>> On Tue, 2013-12-03 at 16:23 -0600, Ben Nemec wrote:
>>>> On 2013-12-03 15:56, Sean Dague wrote:
>>>>> This cinder patch - https://review.openstack.org/#/c/48935/
>>>>>
>>>>> Is blocked on failing upgrade because the updated oslo lockutils won't
>>>>> function until there is a specific configuration variable added to the
>>>>> cinder.conf.
>>>>>
>>>>> That work around is proposed here -
>>>>> https://review.openstack.org/#/c/52070/3
>>>>>
>>>>> However I think this is exactly the kind of forward breaks that we
>>>>> want
>>>>> to prevent with grenade, as cinder failing to function after a rolling
>>>>> upgrade because a config item wasn't added is exactly the kind of pain
>>>>> we are trying to prevent happening to ops.
>>>>>
>>>>> So the question is, how is this done correctly so that a default
>>>>> can be
>>>>> set in the cinder code for this value, and it not require a config
>>>>> change to work?
>>>
>>> You're absolutely correct, in principle - if the default value for
>>> lock_path worked for users before, we should absolutely continue to
>>> support it.
>>>
>>>> I don't know that I have a good answer on how to handle this, but for
>>>> context this change is the result of a nasty bug in lockutils that
>>>> meant
>>>> external locks were doing nothing if lock_path wasn't set.  Basically
>>>> it's something we should never have allowed in the first place.
>>>>
>>>> As far as setting this in code, it's important that all of the
>>>> processes
>>>> for a service are using the same value to avoid the same bad situation
>>>> we were in before.  For tests, we have a lockutils wrapper
>>>> (https://github.com/openstack/oslo-incubator/blob/master/openstack/common/lockutils.py#L282)
>>>> that sets an environment variable to address this, but that only
>>>> works if all of the processes are going to be spawned from within
>>>> the same wrapper, and I'm not sure how secure that is for production
>>>> deployments since it puts all of the lock files in a temporary
>>>> directory.
>>>
>>> Right, I don't think the previous default really "worked" - if you used
>>> the default, then external locking was broken.
>>>
>>> I suspect most distros do set a default - I see RDO has this in its
>>> default nova.conf:
>>>
>>>   lock_path = /var/lib/nova/tmp
>>>
>>> So, yes - this is all terrible.
>>>
>>> IMHO, rather than raise an exception we should log a big fat warning
>>> about relying on the default and perhaps just treat the lock as an
>>> in-process lock in that case ... since that's essentially what it was
>>> before, right?
>>
>> So a default of lock_path = /tmp will work (FHS says that path has to be
>> there), even if not optimal. Could we make it a default value like that
>> instead of the current default which is null (and hence the problem).
> 
> IIRC, my initial fix was something similar to that, but it got shot down
> because putting the lock files in a known world writeable location was a
> security issue.
> 
> Although maybe if we put them in a subdirectory of /tmp and ensured that
> the permissions were such that only the user running the service could
> use that directory, it might be acceptable?  We could still log a
> warning if we wanted.
> 
> This seems like it would have implications for people running services
> on Windows too, but we can probably find a way to make that work if we
> decide on a solution.

How is that a security issue? Are the lock files being written with some
sensitive data in them and have g or o permissions on? The sticky bit
(+t) on /tmp will prevent other users from deleting the file.

(from the chmod man page):

RESTRICTED DELETION FLAG OR STICKY BIT
       The restricted deletion flag or sticky bit is a single bit, whose
interpretation depends on the file type.  For directories, it prevents
unprivi‐
       leged  users  from  removing or renaming a file in the directory
unless they own the file or the directory; this is called the restricted
deletion
       flag for the directory, and is commonly found on world-writable
directories like /tmp.  For regular files on some older systems, the bit
saves the
       program's text image on the swap device so it will load more
quickly when run; this is called the sticky bit.


	-Sean

-- 
Sean Dague
http://dague.net

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