Re: [PATCH v3] secilc/docs: document expandtypeattribute

[Dominick Grift <dominick.grift@defensec.nl>]

James Carter <jwcart2@gmail.com> writes:

> On Fri, Jul 31, 2020 at 3:26 AM Dominick Grift
> <dominick.grift@defensec.nl> wrote:
>>
>> James Carter <jwcart2@gmail.com> writes:
>>
>> > On Thu, Jul 30, 2020 at 9:14 AM Dominick Grift
>> > <dominick.grift@defensec.nl> wrote:
>> >>
>> >> This was added for Androids Treble in 2017.
>> >>
>> >> I was unsure whether this belongs in type_statements or in conditional_statements.
>> >>
>> >
>> > I think that it fits best with the type statements as you have it.
>> >
>> >> Signed-off-by: Dominick Grift <dominick.grift@defensec.nl>
>> >> ---
>> >> v2: overriden is overridden
>> >> v3: add link to README.md
>> >>
>> >>  secilc/docs/README.md              |  1 +
>> >>  secilc/docs/cil_type_statements.md | 38 ++++++++++++++++++++++++++++++
>> >>  2 files changed, 39 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..f819b3c6 100644
>> >> --- a/secilc/docs/cil_type_statements.md
>> >> +++ b/secilc/docs/cil_type_statements.md
>> >> @@ -213,6 +213,44 @@ This example is equivalent to `{ domain -kernel.process -ueventd.process -init.p
>> >>          )
>> >>      )
>> >>
>> >> +expandtypeattribute
>> >> +-------------------
>> >> +
>> >> +Allows expansion compiler defaults for one or more previously declared [`typeattribute`](cil_type_statements.md#typeattribute) identifiers to be overridden.
>> >
>> > The wording confused me at first.
>> > I think "Overrides the compiler defaults for the expansion of one ...
>> > identifiers." would be clearer.
>> >
>> >> +
>> >> +**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.</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>
>> >> +
>> >> +**Example:**
>> >> +
>> >> +This example will use the expandtypeattribute statement to forcibly expand a previously declared `domain` type attribute.
>> >> +
>> >> +    (expandtypeattribute domain true)
>> >> +
>> >
>> > It would be nice to have another example that shows a list of type
>> > attributes, so there is an example of that syntax as well.
>>
>> I was looking into an example but turns out that either i am
>> misunderstanding this functionality or that it does not work as advertised:
>>
>> Example:
>>
>> 1. compiler defaults to expand typeattributes with less
>> than four members
>> 2. override pets and dogs expansion in policy
>>
>> # cat > mytest.cil <<EOF
>> (sid mysid)
>> (sidorder (mysid))
>>
>> (class myclass (mypermission))
>> (classorder (unordered myclass))
>>
>> (type blue)
>> (type green)
>> (type red)
>> (typeattribute colors)
>> (typeattributeset colors (blue green red))
>>
>> (type dog)
>> (type cat)
>> (type goldfish)
>> (typeattribute pets)
>> (typeattributeset pets (dog cat goldfish))
>>
>> (dontaudit pets colors (myclass (mypermission)))
>>
>> (expandtypeattribute (colors pets) false)
>> EOF
>>
>> # secilc -v -X 4 mytest.cil
>> # sesearch policy.32 --dontaudit
>>
>
> The key is that expandtypeattribute works differently for the default
> behavior than when you ask for attributes to be expanded.
>
> The default rules for removing attributes are complex. In general,
> attributes automatically created when converting a binary module to
> CIL; attributes that are not used in allow and dontaudit rules; and
> attributes that have only one type assigned are all removed. This
> means that the attribute rule and the typeattributeset rules for the
> attribute are removed and all rules using the attribute are expanded.
> Using expandtypeattribute in this case will keep the attribute
> declaration, the typeattributeset rules, and any allow rules.
>
> When you use "-X SIZE" all allow rules with attributes that contain
> less than SIZE types will be expanded and the attribute removed. Using
> expandtypeattribute in this case will cause the attribute declaration
> and the typeattributeset rules to be retained, but the allow rules
> will still be expanded.
>
> I just verified that everything does work like that.
>
> It is a bit of a mess, but it is working as intended.
>
> I probably need to document how the default expansion works. ;)


So that makes the "false" scenario practically irrelevant? when would
one ever use "false" instead of "true"?

>
> Thanks,
> Jim
>
>
>> >
>> > Thanks for doing this.
>> > Jim
>> >
>> >>  typebounds
>> >>  ----------
>> >>
>> >> --
>> >> 2.28.0.rc1
>> >>
>>
>> --
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>> Dominick Grift

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Dominick Grift