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Linux bridge: Harden SCC by restricting SELinux context and allowed volume types #2331

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Linux bridge: Harden SCC by restricting SELinux context and allowed volume types #2331

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75ea8e9
linux-bridge, scc: Restrict SELinux context to MustRunAs with spc_t type
RamLavi Jun 3, 2025
dbea23a
linux-bridge, scc: Restrict volumes paths.
RamLavi Jun 3, 2025
26d5db9
linux-bridge, scc: Enable readOnlyRootFilesystem with writable /tmp e…
RamLavi Jun 5, 2025
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11 changes: 8 additions & 3 deletions data/linux-bridge/001-rbac.yaml
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Original file line number Diff line number Diff line change
Expand Up @@ -16,13 +16,18 @@ allowHostIPC: false
allowHostNetwork: false
allowHostPID: false
allowHostPorts: false
readOnlyRootFilesystem: false
readOnlyRootFilesystem: true
runAsUser:
type: RunAsAny
seLinuxContext:
type: RunAsAny
type: MustRunAs
seLinuxOptions:
type: spc_t
users:
- system:serviceaccount:{{ .Namespace }}:linux-bridge
volumes:
- "*"
- hostPath
- configMap
- secret
- emptyDir
{{ end }}
5 changes: 5 additions & 0 deletions data/linux-bridge/002-linux-bridge.yaml
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Expand Up @@ -69,11 +69,16 @@ spec:
memory: "15Mi"
securityContext:
privileged: true
readOnlyRootFilesystem: true
volumeMounts:
- name: cnibin
mountPath: /opt/cni/bin
- name: tmp
mountPath: /tmp
Comment on lines +76 to +77
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why do we need access to /tmp ? Seems we didn't need it before. Why add it now ?

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From the commit message:

Since some system utilities (e.g., bash, cp, sha256sum) may require a
writable /tmp directory, mount an emptyDir at /tmp to provide a writable
scratch space, following container security best practices [0].
Also update the associated SCC to enforce readOnlyRootFilesystem: true
at the policy level.

[0]
https://redhat-best-practices-for-k8s.github.io/guide/#k8s-best-practices-storage:-emptydir

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IOW, if the files are too big they sometimes write to tmp. To be safe - mount an empty tmp folder, so that it won't explode should some cp decides to use that folder..

terminationMessagePolicy: FallbackToLogsOnError
volumes:
- name: cnibin
hostPath:
path: {{ .CNIBinDir }}
- name: tmp
emptyDir: { }