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

- From: Andy Lutomirski \<luto@amacapital.net\>
- Date: 2015-02-26 19:38:24 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2015/02/4438499
- Thread: https://ratatoskr.run/linux-api/2015/02/4426512/t.md

```text
On Thu, Feb 26, 2015 at 11:32 AM, Serge E. Hallyn [ref] wrote:
> On Thu, Feb 26, 2015 at 12:28:30PM -0600, Christoph Lameter wrote:
>> On Thu, 26 Feb 2015, Serge E. Hallyn wrote:
>>
>> > > Well doing that breaks su.
>> >
>> > Don't what exactly?  You're saying that doing
>> >
>> > pI' = pI
>> > pA' = pA  (pA is ambient)
>> > pP' = (X & fP) | (pI & (fI | pA))
>> > pE' = pP' & (fE | pA)
>> >
>> > stopped su from having CAP_SETGID while
>> >
>> > pI' = pI
>> > pA' = pA  (pA is ambient)
>> > pP' = (X & fP) | (pI & (fI | pA))
>> > pE' = pP' & fE
>> >
>> > worked?  I'll hope you're saying both "fail", in which case
>>
>> fE does not exist in cpu_vfs_cap_data. We only get fI and fP. Why in the
>> world does setcap allow setting fE?
>
> It sets a bit in the magic_etc.  So fE is either all on or all off.
>
>> V1 does not use fE. In my newer attempt, I seemed to have worked
>> with zeroed field that I assumed was filled in.
>>
>> I will just do
>>
>> pE' = pP'
>>
>> Ok?
>
> Andrew Morgan was against that.  What if we changed
>
> pE' = pP' & (fE | pA)
>
> to
>
>         if (pA)
>                 pE' = pP' & fE
>         else
>                 pE' = pP'
>

Is this backwards?

Also, on further bikeshedding consideration, I think I like the name
"persistent" much better than "ambient".  Alas, "persistent" starts
with a P.

--Andy
```