# Re: \[PATCH\] capabilities: Ambient capability set V1

- From: Andy Lutomirski \<luto@amacapital.net\>
- Date: 2015-02-26 20:52:23 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2015/02/4438540
- Thread: https://ratatoskr.run/linux-api/2015/02/4426512/t.md

```text
On Thu, Feb 26, 2015 at 12:34 PM, Serge E. Hallyn [ref] wrote:
> On Thu, Feb 26, 2015 at 02:13:00PM -0600, Christoph Lameter wrote:
>> On Thu, 26 Feb 2015, Serge E. Hallyn wrote:
>>
>> > Andrew Morgan was against that.  What if we changed
>> >
>> > pE' = pP' & (fE | pA)
>> >
>> > to
>> >
>> >     if (pA)
>> >             pE' = pP' & fE
>> >     else
>> >             pE' = pP'
>> >
>>
>> Same problem as before. The ambient bits will not be set in pE'.
>
> And what if I weren't scatterbrained and we did
>
>         if (pA)
>                 pE' = pP'
>         else
>                 pE' = pP' & fE
>
> All pP' bits would be set in pE'.

That seems reasonable to me, except for my paranoia:

What if there's a program with CAP_DAC_OVERRIDE in fP and fE set to
the empty set (i.e. the magic effective bit cleared), and the program
relies on that.  A malicious user has CAP_NET_BIND and sets pA =
CAP_NET_BIND.  Boom!

If we changed that to if (pA') and zeroed pA if fP is non-empty then
this problem goes away.

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC
```