DBUS_TYPE_LINUX_CRED ?

[Lennart Poettering]

On Fri, 13.12.13 15:58, Serge Hallyn (serge.hallyn at ubuntu.com) wrote:

> 
> Quoting Thiago Macieira (thiago at kde.org):
> > On sexta-feira, 13 de dezembro de 2013 15:53:26, Serge Hallyn wrote:
> > > Quoting Thiago Macieira (thiago at kde.org):
> > > > On sexta-feira, 13 de dezembro de 2013 14:19:14, Serge Hallyn wrote:
> > > > > > I am pretty sure it would be wrong to have something like this as data
> > > > > > type. This data should be appended implicitly, not explicitly.
> > > > 
> > > > So it should send them all, like Lennart said that kdbus is already doing.
> > > 
> > > Send all of what?
> > 
> > All of the credentials.
> > 
> > He said: "In kdbus you will also get a variety of creds attached to all 
> > messages implicitly (pid, gid, uid, pid_starttime, tid, comm, tid_comm, 
> > cmdline, cgroup, unit, slice, user unit, session, owner uid, eff caps, inh 
> > caps, perm caps, bounding caps, selinux context, audit session, audit login
> > uid)"
> > 
> > > > > It can't be done implicitly, though, since dbus doesn't know which
> > > > > ucred I want to send.  I'm not authenticating as that task, I just need
> > > > > an unambiguous namespace-independent identifier for it.
> > > > 
> > > > Use the unique connection ID.
> > > 
> > > an unambiguous namespace-independent identifier for a task not involved
> > > in the connection.
> > 
> 
> Sorry, I think I'm failing to make myself clear.
> 
> > The task is involved in the connection since it's sending data in the first 
> > place.
> 
> That task, c, is making a request involving another task, v.  It is v's
> pid which needs to be sent with an scm_cred so the kernel can translate
> it to the server's namespace.

So you want to attach fake SCM_CREDS to messages to send over the bus so
that the kernel will do the translation for you? That sounds a highly
specialist operation and is really nothing that D-Bus should take care
of.

Also, why even, you can easily implement that on top of D-Bus without
hacking it into pieces. For example, if the sender wants to send the
identity of some process to somebody else, make the sender
get itself a AF_UNIX/SOCK_DGRAM socket pair via socketpair(), and send
an empty datagram with the SCM_CREDENTIALS of your choice into the
writing side, then close that. And send the reading side over the bus as
file handler use the dbus "h" type. Then also close the reading
side. The receiver can then read the datagram out of it, with the creds
translated and then closes it.

Lennart

-- 
Lennart Poettering, Red Hat