Prior to this commit, `readOnly` volumes were not recursively read-only and
could result in compromise of data;
e.g., even if `/mnt` was mounted as read-only, its submounts such as
`/mnt/usbstorage` were not read-only.
This commit utilizes runc's "rro" bind mount option to make read-only bind
mounts literally read-only. The "rro" bind mount options is implemented by
calling `mount_setattr(2)` with `MOUNT_ATTR_RDONLY` and `AT_RECURSIVE`.
The "rro" bind mount options requires kernel >= 5.12, with runc >= 1.1 or
a compatible runtime such as crun >= 1.4.
When the "rro" bind mount options is not available, containerd falls back
to the legacy non-recursive read-only mounts by default.
The behavior is configurable via `/etc/containerd/config.toml`:
```toml
version = 2
[plugins."io.containerd.grpc.v1.cri".containerd.runtimes.runc]
# treat_ro_mounts_as_rro ("Enabled"|"IfPossible"|"Disabled")
# treats read-only mounts as recursive read-only mounts.
# An empty string means "IfPossible".
# "Enabled" requires Linux kernel v5.12 or later.
# This configuration does not apply to non-volume mounts such as "/sys/fs/cgroup".
treat_ro_mounts_as_rro = ""
```
Replaces:
- kubernetes/enhancements issue 3857
- kubernetes/enhancements PR 3858
Note: this change does not affect non-CRI clients such as ctr, nerdctl, and Docker/Moby.
RRO mounts have been supported since nerdctl v0.14 (containerd/nerdctl PR 511)
and Docker v25 (moby/moby PR 45278).
Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>
When the kubelet sends the uid/gid mappings for a mount, just pass them
down to the OCI runtime.
OCI runtimes support this since runc 1.2 and crun 1.8.1.
And whenever we add mounts (container mounts or image spec volumes) and
userns are requested by the kubelet, we use those mappings in the mounts
so the mounts are idmapped correctly. If no userns is used, we don't
send any mappings which just keeps the current behavior.
Signed-off-by: Rodrigo Campos <rodrigoca@microsoft.com>
If kubelet passes the swap limit (default memory limit = swap limit ),
it is configured for container irrespective if the node supports swap.
Signed-off-by: Qasim Sarfraz <qasimsarfraz@microsoft.com>
We need support in containerd and the OCI runtime to use idmap mounts.
Let's just throw an error for now if the kubelet requests some mounts
with mappings.
Signed-off-by: Rodrigo Campos <rodrigoca@microsoft.com>
