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

- From: Serge Hallyn \<hidden\>
- Date: 2015-02-24 16:44:41 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2015/02/4436667
- Thread: https://ratatoskr.run/linux-api/2015/02/4426512/t.md

```text
Quoting Christoph Lameter (cl@linux.com):
> On Tue, 24 Feb 2015, Serge E. Hallyn wrote:
> 
> > The other way to look at it then is that it's basically as though the
> > privileged task (which has CAP_SETFCAP) could've just added fI=full to
> > all binaries on the filesystem;  instead it's using the ambient set
> > so that the risk from fI=full is contained to its own process tree.
> 
> The way that our internal patch works is to leave these things alone and
> just check the ambient mask in the *capable*() functions. That way the
> behavior of the existing cap bits does not change but the ambient caps
> stay available. Apps have no surprises.

Unless I'm misunderstanding what you are saying, apps do have surprises.
They drop capabilities, execute a file, and the result has capabilities
which the app couldn't have expected.  At least if the bits have to be
in fI to become part of pP', the app has a clue.

To be clear, I'm suggesting that the rules at exec become:

pI' = pI
pA' = pA  (pA is ambient)
pP' = (X & fP) | (pI & (fI | pA))
pE' = pP' & fE
```