On Wed, Oct 29, 2014 at 3:27 PM, Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > On Wed, Oct 29, 2014 at 03:15:51PM -0700, Andy Lutomirski wrote: >> (reply 1/2 -- I'm replying twice to keep the threading sane) >> >> On Wed, Oct 29, 2014 at 3:00 PM, Greg Kroah-Hartman >> <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: >> > kdbus is a kernel-level IPC implementation that aims for resemblance to >> > the the protocol layer with the existing userspace D-Bus daemon while >> > enabling some features that couldn't be implemented before in userspace. >> > >> >> > * Support for multiple domains, completely separated from each other, >> > allowing multiple virtualized instances to be used at the same time. >> >> Given that there is no such thing as a device namespace, how does this work? > > See the document for the details. They seem insufficient to me, so I tried to dig in to the code. My understanding is: The parent container has /dev mounted. It sends an IOCTL (which requires global capabilities). In response, kdbus creates a whole bunch of devices that get put (by udev or devtmpfs, I presume) in a subdirectory. Then the parent container mounts that subdirectory in the new container. This is IMO rather problematic. First, it enforces the existence of a kdbus domain hierarchy where none should be needed. Second, it's incompatible with nested user namespaces. The middle namespace can't issue the ioctl. Third, it requires a devtmpfs submount in the child container. This scares me, especially since there are no device namespaces. Also, the child container appears to be dependent on the host udev to arbitrate everything, which seems totally wrong to me. (Also, now we're exposed to attacks where the child container creates busses or endpoints or whatever with malicious names to try to trick the host into screwing up.) ISTM this should be solved either with device namespaces (which is well known to be a giant can of worms) or by abandoning the concept of kdbus using device nodes entirely. What if kdbus were kdbusfs? If you want to use it in a container, you mount a brand-new kdbusfs there. No weird domain hierarchy, no global privilege, no need to name containers, obvious migration semantics, no dependence on udev/devtmpfs at all, etc. Eric, any thoughts here? --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
