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SubjectRe: [RFC v7 10/41] richacl: Permission check algorithm
From
2015-09-11 23:16 GMT+02:00 J. Bruce Fields <bfields@fieldses.org>:
> On Sat, Sep 05, 2015 at 12:27:05PM +0200, Andreas Gruenbacher wrote:
>> + /*
>> + * Apply the group file mask to entries other than owner@ and
>> + * everyone@ or user entries matching the owner. This ensures
>> + * that we grant the same permissions as the acl computed by
>> + * richacl_apply_masks().
>> + *
>> + * Without this restriction, the following richacl would grant
>> + * rw access to processes which are both the owner and in the
>> + * owning group, but not to other users in the owning group,
>> + * which could not be represented without masks:
>> + *
>> + * owner:rw::mask
>> + * group@:rw::allow
>> + */
>> + if ((acl->a_flags & RICHACL_MASKED) && richace_is_allow(ace))
>> + ace_mask &= acl->a_group_mask;
>
> I'm having trouble understanding this. I think the problem is that I
> don't really understand the notation in your example. Is a_group_mask
> zero in that example? I think it must be, in which case, OK I think I
> get it.

Yes. I'm not sure if the example becomes easier to understand when the
empty group mask and perhaps also the other mask is included.

> (Though I still have to think about it a little more to convince myself
> that richacl_apply_masks() always gets the same result.)

I have tried to break the algorithm into digestible pieces. Do you see
another way to make things easier to understand?

Thanks,
Andreas


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