[SSSD] Unexpected behavior with 'simple_allow_users ='

Dmitri Pal dpal at redhat.com
Tue Nov 6 15:26:57 UTC 2012


On 11/06/2012 09:24 AM, Simo Sorce wrote:
> On Tue, 2012-11-06 at 15:10 +0100, Ondrej Kos wrote:
>> On 11/06/2012 02:52 PM, Simo Sorce wrote:
>>> On Tue, 2012-11-06 at 14:46 +0100, Ondrej Kos wrote:
>>>> On 11/02/2012 05:32 PM, Simo Sorce wrote:
>>>>> On Fri, 2012-11-02 at 10:10 -0400, Dmitri Pal wrote:
>>>>>> On 11/02/2012 09:50 AM, Stef Walter wrote:
>>>>>>> On 11/02/2012 01:57 PM, Dmitri Pal wrote:
>>>>>>>> First let us define a general rule about how we treat the cases:
>>>>>>>> X =
>>>>>>>> Is it treated as X being undefined or X having an empty value.
>>>>>>>> It should be a general documented rule for the application.
>>>>>>>>
>>>>>>>> Current behavior is to ignore and I think it is the right one.
>>>>>>>> May be it should be clearly stated in the man for sssd.conf if not yet
>>>>>>>> stated.
>>>>>>> Understood.
>>>>>>>
>>>>>>> But to me it seems that this policy does not make sense in this
>>>>>>> situation. It's completely counter intuitive that the following, instead
>>>>>>> of allowing no users, allows any user.
>>>>>>>
>>>>>>> simple_allow_users =
>>>>>>>
>>>>>>> Sure, you can say that anyone deploying sssd, should read over every
>>>>>>> line of the documentation and be well informed.
>>>>>> One does not preclude the other. The point about man pages is just to
>>>>>> make a statement explicit not implied. I do not expect everyone to read
>>>>>> it but it is better to be explicit.
>>>>>>>    But there's also
>>>>>>> something to be said for readability and principle-of-least-surprise.
>>>>>> Sure. Whatever we decide should be consistent and logical.
>>>>>> I seems that so far we had the rule that empty values are ignored.
>>>>>> Is it consistent and logical to change it for one attribute?
>>>>>> I doubt but your argument is valid too.
>>>>>> May be the way out is to have a different attribute
>>>>>> simple_default_allow_rule = [all] | [none]
>>>>>> By default it will be "all" meaning that if the simple_allow_users is
>>>>>> not specified or empty then all users are allowed - current behavior
>>>>>> If it is set to none then if the filter is not specified no one is allowed.
>>>>>>
>>>>>> Would that be more logical?
>>>>> I was thinking along these lines too.
>>>>>
>>>>> If we have a default of ALL, then 'none' is not necessary at all as long
>>>>> as a 'simple_allow_users = ' line in the conf causes the attribute to be
>>>>> completely removed from confdb
>>>>> at that point the code, not finding the special default of 'ALL' would
>>>>> cause everyone to be denied as Stef expects.
>>>>> The bonus is that an admin can explicitly allow all by setting ALL,
>>>>> which is also clearer than having to delete the configure attribute or
>>>>> disable the access check plugin.
>>>>>
>>>>> I do not like the $ suggestion as in Windows machine names have the $
>>>>> sign in it so $none$ and none$ would be valid yet easily confused.
>>>>>
>>>>> 'ALL' is used in many tools so it is unlikely someone will have an upper
>>>>> case user or group name named that way, and if so .. well I guess they
>>>>> will have to cope.
>>>>>
>>>>> There is one other character that nobosy uses in usernames and that is
>>>>> ':' because historically that's the spearator in /etc/passwd so it
>>>>> simply can't be used in the user name.
>>>>>
>>>>> So maybe ':ALL' is also a possibility, or maybe we consider ':ALL' the
>>>>> 'escaping' version to be able to reference and actual entity called
>>>>> 'ALL' (I would prefer the escaping rule).
>>>>>
>>>>> Simo.
>>>>>
>>>>>
>>>> So should i prepare patch introducing this behaviour?
>>>>
>>>> - add configuration option
>>>>     simple_default_allow_rule = [true|false] / [all|-?-]
>>>>
>>>> - if <false>
>>>>     simple_allow_* list would be expected to contain some users/groups,
>>>> empty list results in no-one being allowed.
>>>>
>>>> - if <true|all>
>>>>     all users are allowed by default, limitations are derived from
>>>> simple_deny_* lists.
>>>>
>>>>
>>>> is this correct?
>>> Nope
>>>
>>>>   or should we use something like:
>>> This is what we were proposing.
>>>
>>>> simple_allow_users = <ALL_keyword> | <user list>
>>>>
>>>> and not add the new option at all? in that case, what would be the
>>>> keyword and how should we handle the situation, when the configuration
>>>> file would contain the following:
>>>>
>>>> simple_allow_users = <ALL_keyword>, user1, user2, ...
>>> users here would simply be redunant as the ALL keyword alreay matches
>>> everyone.
>>>
>> the question here is, should we treat this as an configuration error, or 
>> allow it?
> allow it, it could be a temporary change where the admin wants to keep
> the original list around.
>
>>>> also this method would require *simple_allow_users* rule to be present,
>>>> or would be handled as empty.
>>> when empty it will mean that nobody is allowed. (the default internally
>>> if not present at all is 'ALL'
>> that is the problem. we can't distinguish if list is empty or not 
>> present at all without modifying confdb
> That's why I say we have a default of ALL that we set in the confdb
> before reading the config file, ie if the confdb returns NULL it means
> that the file had 'simple_allow_users = ' and 'ALL' was explicitly
> removed.
>
> Simo.
>
I do not like it. I think the option when you control the default via a
different config item like described in the first variant is better than
hard coding it.
The default should be ALL but there should be a way to change it IMO.

-- 
Thank you,
Dmitri Pal

Sr. Engineering Manager for IdM portfolio
Red Hat Inc.


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