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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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