Re: [kata-dev] vsock & network namespaces in Kata
Hi Stefano, On Wed, 2019-12-11 at 18:27 +0100, Stefano Garzarella wrote:
Hi Sebastien,
On Thu, Dec 5, 2019 at 9:07 AM Boeuf, Sebastien < sebastien.boeuf@intel.com> wrote:
On Wed, 2019-12-04 at 17:36 +0000, Montes, Julio wrote:
Stefano,
Do you think could be an easy change in the Kata runtime? I need to look better, but if you already know the answer you'll save me some time :)
ok, this means all kata components must be in the same network namespace.
fortunately, kata-shim and qemu run in the same network namespace, so the change should be easy, just move kata-proxy and kata-runtime into the same net namespace
Well in case of vsock, we don't need kata-proxy, the shim being directly connected to the VM through vsock. And the kata-shim runs in the same netns as the VMM, so we're good from this perspective.
In case of containerd-shimv2, we don't have kata-shim anymore, the shim being a simple thread part of the kata-runtime process, which means kata-runtime needs to enter the netns, and that's where it might be pretty complex. IIRC, Julio did some experiments to run the kata-runtime in a set of namespaces, but I don't think we merged it, did we?
Looking in the code seems that kata-runtime uses the "vhostfd" parameter of the vsock device, this means that the vhost device (/dev/vhost- vsock) is opened by the runtime and then the file descriptor is passed to QEMU. This is great for this case because the netns assigned to the device is the one of the process that opened the /dev/vhost-vsock.
I tried containerd-shimv2 with the vhost-vsock modified to support netns and seems to work well.
Instead with v1 it doesn't work, maybe because kata-runtime and kata-shim run in two different netns. (or maybe I did something wrong, but it works disabling vsock or using the vhost-vsock without netns)
Does that make sense?
Yes I think your experiment and the result makes sense. In case of v1, kata-shim runs in the same netns as QEMU, but kata- runtime runs in a separate one (the default netns). Later when kata- shim tries to access the fd, because it runs in a different netns than kata-runtime, the permission is denied. In case of v2, there's only one process, the containerd-shimv2, which again runs on the default netns, but later will be the one trying to connect to the vhost-vsock fd, which is why it will succeed. In this case there's no more additional process connecting through vsock, it is simply a different thread from containerd-shimv2. At first, I didn't get the fact that the netns authorized to access vsock had to be the one where the device was opened from. That's why my analysis was completely reversed :) Thanks, Sebastien
Thanks, Stefano
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Boeuf, Sebastien