Re: [PATCH v4] secilc/docs: document expandtypeattribute

[James Carter <jwcart2@gmail.com>]

On Tue, Aug 4, 2020 at 11:48 AM Dominick Grift
<dominick.grift@defensec.nl> wrote:
>
> James Carter <jwcart2@gmail.com> writes:
>
> > On Tue, Aug 4, 2020 at 3:18 AM Dominick Grift
> > <dominick.grift@defensec.nl> wrote:
> >>
> >> James Carter <jwcart2@gmail.com> writes:
> >>
> >> > On Sun, Aug 2, 2020 at 8:39 AM Dominick Grift
> >> > <dominick.grift@defensec.nl> wrote:
> >> >>
> >> >> This was added for Androids Treble in 2017.
> >> >>
> >> >> Signed-off-by: Dominick Grift <dominick.grift@defensec.nl>
> >> >> ---
> >> >> v2: overriden is overridden
> >> >> v3: add link to README.md
> >> >> v4: rephrase and add another example
> >> >>
> >> >>  secilc/docs/README.md              |  1 +
> >> >>  secilc/docs/cil_type_statements.md | 44 ++++++++++++++++++++++++++++++
> >> >>  2 files changed, 45 insertions(+)
> >> >>
> >> >> diff --git a/secilc/docs/README.md b/secilc/docs/README.md
> >> >> index 3f1838e6..efab2a71 100644
> >> >> --- a/secilc/docs/README.md
> >> >> +++ b/secilc/docs/README.md
> >> >> @@ -126,6 +126,7 @@ CIL (Common Intermediate Language)
> >> >>    * [typealiasactual](cil_type_statements.md#typealiasactual)
> >> >>    * [typeattribute](cil_type_statements.md#typeattribute)
> >> >>    * [typeattributeset](cil_type_statements.md#typeattributeset)
> >> >> +  * [expandtypeattribute](cil_type_statements.md#expandtypeattribute)
> >> >>    * [typebounds](cil_type_statements.md#typebounds)
> >> >>    * [typechange](cil_type_statements.md#typechange)
> >> >>    * [typemember](cil_type_statements.md#typemember)
> >> >> diff --git a/secilc/docs/cil_type_statements.md b/secilc/docs/cil_type_statements.md
> >> >> index f9dd3a76..41f0f01a 100644
> >> >> --- a/secilc/docs/cil_type_statements.md
> >> >> +++ b/secilc/docs/cil_type_statements.md
> >> >> @@ -213,6 +213,50 @@ This example is equivalent to `{ domain -kernel.process -ueventd.process -init.p
> >> >>          )
> >> >>      )
> >> >>
> >> >> +expandtypeattribute
> >> >> +-------------------
> >> >> +
> >> >> +Overrides the compiler defaults for the expansion of one or more previously declared [`typeattribute`](cil_type_statements.md#typeattribute) identifiers.
> >> >> +
> >> >> +Note that this statement can be overridden at compile-time with `secilc -X SIZE` and that this functionality is not intended to override `secilc -X SIZE` for individual type attributes!
> >> >> +
> >>
> >> <snip>
> >> > When the value
> >> > is false, the type attribute will not be removed from the policy, even
> >> > if the default expand rules or "-X" option cause the rules involving
> >> > the type attribute to be expanded.
> >>
> >> Yes but I cannot produce that. In my earlier test the type attribute
> >> was expanded regardless of the -X option.
> >>
> >> In my test I instructed secilc to expand all attributes with more than 3
> >> members (-X 4), then I added a expandtypeattribute statement telling
> >> secilc to not expand pets and colors.
> >>
> >> The result was that it expanded pets and colors anyway.
> >>
> >
> > I see the source of your confusion now. "-X 4" means that all
> > attributes with LESS than 4 types associated with it will be expanded.
>
> I think its important to clarify this in the documentation. ie:
> expandattribute false will not work if you use -X (-X will override the
> false statement)
>
> I think that is unintuitive, I would actually want to be able to for
> example expand all attributes with less then 4 members except a few
> specific ones.
>

It is poorly named at this point. I think it was a victim of multiple
changes over time. A better name now would be removeattribute. That
would be more accurate, because what is really being controlled is
whether the attribute is kept as defined in the policy or not.

I am not sure what advantage there would be to expanding and removing
all except a few selected attributes with less than 4 members, except
for the case when you needed those selected attributes to remain
defined in the policy.  Not much space is going to be saved by not
expanding them. Ok, I guess the advantage would be that the name of
the rule would make more sense. I will grant that.

At any rate, the name stinks, but the functionality is exactly what is
needed. I can trade a large policy for quicker access checks by using
the "-X SIZE" option and I can retain the definitions of the
attributes that need to be defined using expandattribute false.

This whole discussion is why keeping the selinux-notebook in sync with
language changes will be very valuable practice.

Thanks,
Jim

> >
> > Jim
> >
> >> >
> >> > Thanks,
> >> > Jim
> >> >
> >> >> +**Statement definition:**
> >> >> +
> >> >> +    (expandtypeattribute typeattribute_id true|false)
> >> >> +
> >> >> +**Where:**
> >> >> +
> >> >> +<table>
> >> >> +<colgroup>
> >> >> +<col width="25%" />
> >> >> +<col width="75%" />
> >> >> +</colgroup>
> >> >> +<tbody>
> >> >> +<tr class="odd">
> >> >> +<td align="left"><p><code>expandtypeattribute</code></p></td>
> >> >> +<td align="left"><p>The <code>expandtypeattribute</code> keyword.</p></td>
> >> >> +</tr>
> >> >> +<tr class="even">
> >> >> +<td align="left"><p><code>typeattribute_id</code></p></td>
> >> >> +<td align="left"><p>One or more previously declared
> >> >> <code>typeattribute</code> identifiers. Multiple entries consist of
> >> >> a space separated list enclosed in parentheses '()'.</p></td>
> >> >> +</tr>
> >> >> +<tr class="odd">
> >> >> +<td align="left"><p><code>true | false</code></p></td>
> >> >> +<td align="left"><p>Either true or false.</p></td>
> >> >> +</tr>
> >> >> +</tbody>
> >> >> +</table>
> >> >> +
> >> >> +**Examples:**
> >> >> +
> >> >> +This example uses the expandtypeattribute statement to forcibly expand a previously declared `domain` type attribute.
> >> >> +
> >> >> +    (expandtypeattribute domain true)
> >> >> +
> >> >> +This example uses the expandtypeattribute statement to not expand
> >> >> previously declared `file_type` and `port_type` type attributes
> >> >> regardless of compiler defaults.
> >> >> +
> >> >> +    (expandtypeattribute (file_type port_type) false)
> >> >> +
> >> >>  typebounds
> >> >>  ----------
> >> >>
> >> >> --
> >> >> 2.28.0
> >> >>
> >>
> >> --
> >> gpg --locate-keys dominick.grift@defensec.nl
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> >> Dominick Grift
>
> --
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> Dominick Grift