On Tue, Jan 21, 2020 at 01:59:07PM +0000, Stefan Hajnoczi wrote: > On Tue, Jan 21, 2020 at 10:07:06AM +0100, Stefano Garzarella wrote: > > On Mon, Jan 20, 2020 at 11:02 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > > On Mon, Jan 20, 2020 at 05:53:39PM +0100, Stefano Garzarella wrote: > > > > On Mon, Jan 20, 2020 at 5:04 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > > > > On Mon, Jan 20, 2020 at 02:58:01PM +0100, Stefano Garzarella wrote: > > > > > > On Mon, Jan 20, 2020 at 1:03 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > > > > > > On Mon, Jan 20, 2020 at 11:17:35AM +0100, Stefano Garzarella wrote: > > > > > > > > On Mon, Jan 20, 2020 at 10:06:10AM +0100, David Miller wrote: > > > > > > > > > From: Stefano Garzarella <sgarzare@xxxxxxxxxx> > > > > > > > > > Date: Thu, 16 Jan 2020 18:24:26 +0100 > > > > > > > > > > > > > > > > > > > This patch adds 'netns' module param to enable this new feature > > > > > > > > > > (disabled by default), because it changes vsock's behavior with > > > > > > > > > > network namespaces and could break existing applications. > > > > > > > > > > > > > > > > > > Sorry, no. > > > > > > > > > > > > > > > > > > I wonder if you can even design a legitimate, reasonable, use case > > > > > > > > > where these netns changes could break things. > > > > > > > > > > > > > > > > I forgot to mention the use case. > > > > > > > > I tried the RFC with Kata containers and we found that Kata shim-v1 > > > > > > > > doesn't work (Kata shim-v2 works as is) because there are the following > > > > > > > > processes involved: > > > > > > > > - kata-runtime (runs in the init_netns) opens /dev/vhost-vsock and > > > > > > > > passes it to qemu > > > > > > > > - kata-shim (runs in a container) wants to talk with the guest but the > > > > > > > > vsock device is assigned to the init_netns and kata-shim runs in a > > > > > > > > different netns, so the communication is not allowed > > > > > > > > But, as you said, this could be a wrong design, indeed they already > > > > > > > > found a fix, but I was not sure if others could have the same issue. > > > > > > > > > > > > > > > > In this case, do you think it is acceptable to make this change in > > > > > > > > the vsock's behavior with netns and ask the user to change the design? > > > > > > > > > > > > > > David's question is what would be a usecase that's broken > > > > > > > (as opposed to fixed) by enabling this by default. > > > > > > > > > > > > Yes, I got that. Thanks for clarifying. > > > > > > I just reported a broken example that can be fixed with a different > > > > > > design (due to the fact that before this series, vsock devices were > > > > > > accessible to all netns). > > > > > > > > > > > > > > > > > > > > If it does exist, you need a way for userspace to opt-in, > > > > > > > module parameter isn't that. > > > > > > > > > > > > Okay, but I honestly can't find a case that can't be solved. > > > > > > So I don't know whether to add an option (ioctl, sysfs ?) or wait for > > > > > > a real case to come up. > > > > > > > > > > > > I'll try to see better if there's any particular case where we need > > > > > > to disable netns in vsock. > > > > > > > > > > > > Thanks, > > > > > > Stefano > > > > > > > > > > Me neither. so what did you have in mind when you wrote: > > > > > "could break existing applications"? > > > > > > > > I had in mind: > > > > 1. the Kata case. It is fixable (the fix is not merged on kata), but > > > > older versions will not work with newer Linux. > > > > > > meaning they will keep not working, right? > > > > Right, I mean without this series they work, with this series they work > > only if the netns support is disabled or with a patch proposed but not > > merged in kata. > > > > > > > > > 2. a single process running on init_netns that wants to communicate with > > > > VMs handled by VMMs running in different netns, but this case can be > > > > solved opening the /dev/vhost-vsock in the same netns of the process > > > > that wants to communicate with the VMs (init_netns in this case), and > > > > passig it to the VMM. > > > > > > again right now they just don't work, right? > > > > Right, as above. > > > > What do you recommend I do? > > Existing userspace applications must continue to work. > > Guests are fine because G2H transports are always in the initial network > namespace. > > On the host side we have a real case where Kata Containers and other > vsock users break. Existing applications run in other network > namespaces and assume they can communicate over vsock (it's only > available in the initial network namespace by default). > > It seems we cannot isolate new network namespaces from the initial > network namespace by default because it will break existing > applications. That's a bummer. > > There is one solution that maintains compatibility: > > Introduce a per-namespace vsock isolation flag that can only transition > from false to true. Once it becomes true it cannot be reset to false > anymore (for security). > > When vsock isolation is false the initial network namespace is used for > <CID, port> addressing. > > When vsock isolation is true the current namespace is used for <CID, > port> addressing. > > I guess the vsock isolation flag would be set via a rtnetlink message, > but I haven't checked. > > The upshot is: existing software doesn't benefit from namespaces for > vsock isolation but it continues to work! New software makes 1 special > call after creating the namespace to opt in to vsock isolation. > > This approach is secure because whoever sets up namespaces can > transition the flag from false to true and know that it can never be > reset to false anymore. > > Does this make sense to everyone? > > Stefan Anything wrong with a separate device? whoever opens it decides whether netns will work ... -- MST
