fix(virtiofs): scope host-edge read-only to directory bind mounts#233
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fix(virtiofs): scope host-edge read-only to directory bind mounts#233ndeloof wants to merge 1 commit into
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A read-only file bind mount shares its *parent* directory via virtio-fs (virtio-fs operates on directories), and that parent typically holds unrelated writable files — the container's own runtime state and stdio fifos. Marking the whole share read-only at the host edge therefore denies writes to those siblings and stalls container start. Restrict host-edge read-only to directory bind mounts, where the share maps exactly to the read-only mount. A read-only file bind mount keeps its read-only guarantee through the guest `ro` mount option preserved in the OCI spec. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> Signed-off-by: Nicolas De Loof <nicolas.deloof@gmail.com>
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Superseding this with a downstream fix: downstram stops marking its own generated /etc files (resolv.conf, trust-store bundle) read-only, so a read-only file mount no longer makes its shared parent directory read-only at the host edge. That removes the need for this directory-only refinement on the nerdbox side for the immediate use case. Closing for now; can revisit if a general nerdbox-side guard is wanted later. |
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Problem
bindMountermarks a virtio-fs share read-only at the host edge whenever the OCI bind mount carries therooption. For a file bind mount this is incorrect: virtio-fs operates on directories, so a file mount is backed by sharing its parent directory. That parent typically contains unrelated writable files — the container's own runtime state and stdio fifos — so flagging the whole share read-only at the host edge denies writes to those siblings and stalls container start.Fix
Only directory bind mounts get host-edge read-only, where the shared device maps exactly to the read-only mount. A read-only file bind mount keeps its read-only guarantee through the guest
romount option that is still preserved in the OCI spec (defense in depth — unchanged behavior for files).Test plan
go build ./...robind mount: writes are rejected at the host edge and cannot be re-enabled from inside the guest.robind mount: container starts normally; sibling runtime files in the shared parent stay writable; the mounted file itself stays read-only via the guest mount.🤖 Generated with Claude Code