Root Mount Propagation Option must Specify Private or Slave: "rshared" about gvisor HOT 7 CLOSED

Rootfs mount propagation option (as specified in OCI spec in spec.Linux.RootfsPropagation) should not be shared. As the error mentions, this option should specify private or slave (if specified at all). Shared propagation would break the sandbox's isolation, as documented here.

Related: opencontainers/runc#1755

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In other words, this is working as intended. Do you require the rootfs to have shared propagation? If not, please remove the RootfsPropagation option from the container spec and it should work.

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@ayushr2 I was testing if the docker plugin can be enabled with gVisor, I think docker allows RootfsPropagation ( especially with capabilities with SYS_ADMIM ) for plugins and they are incompatible with gVisor sandbox. Thanks for the info

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Could you tell which plugin you are trying to use?

I was testing if the docker plugin can be enabled with gVisor

Is there a "docker" Docker plugin that you are trying to use? Or are you testing if docker plugins in general work or not?

I tried using a sample plugin from Docker documentation. It seemed to work fine with gVisor:

$ docker plugin install tiborvass/sample-volume-plugin
latest: Pulling from tiborvass/sample-volume-plugin
Digest: sha256:00b42de88f3a3e0342e7b35fa62394b0a9ceb54d37f4c50be5d3167899994639
eb9c16fbdc53: Complete 
Installed plugin tiborvass/sample-volume-plugin
$ docker plugin ls
ID             NAME                                    DESCRIPTION                         ENABLED
089be7bfac20   tiborvass/sample-volume-plugin:latest   A sample volume plugin for Docker   true
$ docker volume create -d tiborvass/sample-volume-plugin samplevol
samplevol
$ docker run --runtime=runsc --rm -v samplevol:/tmp ubuntu echo hello
hello

from gvisor.

am trying to install a CSI-compatible plugin ollijanatuinen/swarm-csi-nfs:v4.1.0 or just vieux/sshfs.

Plugin "ollijanatuinen/swarm-csi-nfs:v4.1.0" is requesting the following privileges:
 - network: [host]
 - mount: [/etc/hostname]
 - capabilities: [CAP_SYS_ADMIN]
Do you grant the above permissions? [y/N] y
v4.1.0: Pulling from ollijanatuinen/swarm-csi-nfs
Digest: sha256:0ea452bf0c8e6b9280c79e23ea39274898d6eac86b93451cdc707d7674a304b9
0d607dafa59e: Complete 
Error response from daemon: failed to create task for container: failed to create shim task: OCI runtime create failed: reading spec: root mount propagation option must specify private or slave: "rshared": unknown

It works if I use runc but if its runsc it will be downloaded but not enabled
In my daemon.json I set default-runtime to runsc

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In my daemon.json I set default-runtime to runsc

I see, that is a very relevant detail. I can now reproduce this too. So when using runsc as your default runtime, installing any docker plugin fails with the above error. The plugin is downloaded alright, but to enable it, Docker spawns a container with spec.Linux.RootfsPropagation = rshared, which fails with gVisor.

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The sandbox's mount table is maintained in sentry memory. Mount operations in the container are not propagated to the host. So even if we allow this mount option (i.e. MS_SHARED|MS_REC), the mount operations from the container will not appear on the host, as the application might expect. (For example, volume plugins won't work as expected.) So it will lead to wrong behavior. Hence we disallow this option.

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