Re: [capabilities] Allow normal inheritance for a configurable set of capabilities

Casey Schaufler
2015-02-02T20:54:04Z

On 2/2/2015 12:37 PM, Andy Lutomirski wrote:
> On Mon, Feb 2, 2015 at 10:08 AM, Serge Hallyn <serge.hallyn@ubuntu.com> wrote:
>> Quoting Casey Schaufler (casey@schaufler-ca.com):
>>> I'm game to participate in such an effort. The POSIX scheme
>>> is workable, but given that it's 20 years old and hasn't
>>> developed real traction it's hard to call it successful.
>> Over the years we've several times discussed possible reasons for this
>> and how to help. I personally think it's two things: 1. lack of
>> toolchain and fs support. The fact that we cannot to this day enable
>> ping using capabilities by default because of cpio, tar and non-xattr
>> filesystems is disheartening. 2. It's hard for users and applications
>> to know what caps they need. yes the API is a bear to use, but we can
>> hide that behind fancier libraries. But using capabilities requires too
>> much in-depth knowledge of precisely what caps you might need for
>> whatever operations library may now do when you asked for something.
> None of this could address the problem here, though: if I hold a
> capability and I want to pass that capability to an exec'd helper, I
> shouldn't need the fs's help to do this.

One of the holes in the 1003.1e spec is what to do with a program file
that does not have a capability set attached to it. The two options are
drop all capabilities and leave the capabilities alone. The latter gives
you what you're asking for. The former is arguably safer.

>
> --Andy
>