[SSSD] Unexpected behavior with 'simple_allow_users ='

Simo Sorce simo at redhat.com
Tue Nov 6 14:24:23 UTC 2012


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.

-- 
Simo Sorce * Red Hat, Inc * New York




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