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From SCHEDENIG Marian <Marian.Schede...@qualysoft.com>
Subject RE: How does Jackrabbit resolve ACL permissions?
Date Wed, 13 Feb 2013 14:51:49 GMT
Hi Angela,

thanks for the quick reply. I had a bug in my test code and could indeed get it working now
with multiple grant/denies on the same node, as long as I make sure to put the grants before
the denies.

I still can't reproduce your suggested example though (Miroslav's fix taken into account).
By default I do indeed provide ALL permissions to "everyone" on root, as otherwise (i.e. if
I remove that ACE at the beginning of my test case), non-admins cannot access the repository
content at all. In fact (I'm doing all my access through WebDAV), I get a 401 (authentication
required) from the repository if I don't explicitly grant permissions on the root folder.
And that goes for a subfolder with granted ALL as well: No root permissions, no permissions
anywhere.

Not sure if perhaps I'm doing something wrong there. But solution 2 (deny rights to everyone
and grant them to a certain group per relevant folder) should be good enough for us.

Cheers,
Marian.

-----Original Message-----
From: Angela Schreiber [mailto:anchela@adobe.com] 
Sent: Mittwoch, 13. Februar 2013 13:30
To: users@jackrabbit.apache.org
Subject: Re: How does Jackrabbit resolve ACL permissions?

hi marian

imo there shouldn't be any major obstacles in setting up the ACL to reflect the permissions
as you describe below.
in quickly tried it out on the crx-explorer using the following
setup:

groups
---------------------------------------------------------------
- groupA
- groupB

users
---------------------------------------------------------------
- userA: member of groupA (and everyone)
- userB: member of groupB (and everyone)
- userC: member of groupA and groupB (and everyone)

acl setup
---------------------------------------------------------------
+ root
   + a
     + rep:policy
       + allow
         - jcr:primaryType = rep:GrantACE
         - rep:principalName = groupA
         - rep:privileges = [jcr:read]
   + b
     + rep:policy
       + allow
         - jcr:primaryType = rep:DenyACE
         - rep:principalName = groupB
         - rep:privileges = [jcr:read]

result
---------------------------------------------------------------

- userA can read /a but not /b
- userB can read /b but not /a
- userC can read /a and /b

additional adding an DENY ace for everyone on the root is redundant and doesn't not have an
effect on the result.


general notes
---------------------------------------------------------------

- ACEs are inherited through the node hierarchy. ACEs defined on
   a particular node take precedence over inherited onces.
   defining addition restrictions may be used to limit the effect to
   certain parts of the subtree defined by the access controlled node

- as long as ACEs are defined from group principals the evaluation
   is strictly hierarchical. on a single ACL the order of ACEs matters.

- if you define ACEs for non-group principal they will take predecence
   in any case: over the group principals and over the inheritance rule
   defined above.

regarding your comments below:
---------------------------------------------------------------

1) that works for me... see above. in don't think you analysis
    matches the way the permissions are evaluated.
2) that would work as well but the ACE for everyone is redundant.
    it would not work if you would allow group A first and deny everyone
    group after that... as the ACE for A would become redundant.

hope that helps
angela


On 2/13/13 11:34 AM, SCHEDENIG Marian wrote:
> Hi,
>
> we're using the standard ACLProvider for permission handling. We're 
> now running into problems when trying to set up slightly more complex 
> ACLs than we've used so far:
>
> Say we have three groups, "everyone" (which is Jackrabbit's
> EveryonePrincipal) and "A" and "B". We want to allow only users in the 
> A group to be able to access the folder /a_folder and only members of 
> B to access /b_folder. A user may be a member of A, B, A and B or of 
> neither group. If user X is a member of A and not a member of B, X 
> should still have access to /a_folder.
>
> We've tried two approaches:
>
> 1. Deny full permissions to "everyone" on the root folder and then 
> grant full permissions to A on /a_folder and to B on /b_folder. This 
> fails, apparently because permissions are resolved in a "top down" 
> manner, and as soon as it has been established that a user doesn't 
> have access to a parent folder, its subfolders are no longer 
> evaluated. That's fine, if we can find a different way to do it.
>
> 2. Deny full permissions to "everyone" on /a_folder and grant full 
> permissions to A on the same folder (and the same with "everyone" and 
> B on /b_folder). This also fails, although apparently it works for 
> user X if we deny "everyone" and grant X (specifically the user) on the folder.
>
> I'm now wondering: How exactly does Jackrabbit resolve permissions? 
> Case
> 1 seems to be clear, but what are the exact rules for overlapping 
> grants and denies on the same resource? And what is the correct way to 
> solve our requirement?
>
> Thanks,
>
> Marian.
>
> --
>
> *DI Marian Schedenig*
>
> Senior Developer
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