Fix known_hosts race condition with concurrent clush SSH connections

[berendt]

Add UserKnownHostsFile=/dev/null to clush ssh_options to prevent multiple parallel SSH connections (fanout: 64) from colliding on hard link updates to /root/.ssh/known_hosts.

AI-assisted: Claude Code

[sourcery-ai]

Hey - I've found 1 issue, and left some high level feedback:

• Using UserKnownHostsFile=/dev/null avoids the race but fully disables host key persistence; consider whether pointing to an isolated temporary known_hosts file (per run or per user) would give you the same concurrency safety with better security properties.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Using `UserKnownHostsFile=/dev/null` avoids the race but fully disables host key persistence; consider whether pointing to an isolated temporary known_hosts file (per run or per user) would give you the same concurrency safety with better security properties.

## Individual Comments

### Comment 1
<location path="files/clustershell/clush.conf" line_range="10" />
<code_context>
 node_count: yes
 verbosity: 1
-ssh_options: -o IdentityFile=/ansible/secrets/id_rsa.operator -o StrictHostKeyChecking=no -o LogLevel=ERROR
+ssh_options: -o IdentityFile=/ansible/secrets/id_rsa.operator -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -o LogLevel=ERROR
</code_context>
<issue_to_address>
**🚨 issue (security):** Using UserKnownHostsFile=/dev/null removes host key persistence and may hide MITM issues.

Combined with `StrictHostKeyChecking=no`, this effectively disables SSH host key verification. If this is only for ephemeral or non-production use, please scope it more narrowly (e.g., limited inventories or an explicit opt‑in flag) and ensure it cannot be reused in production or other sensitive contexts.
</issue_to_address>

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[sourcery-ai]

New security issues found

[sourcery-ai]

security (python.lang.security.audit.dangerous-subprocess-use-audit): Detected subprocess function 'call' without a static string. If this data can be controlled by a malicious actor, it may be an instance of command injection. Audit the use of this call to ensure it is not controllable by an external resource. You may consider using 'shlex.escape()'.

Source: opengrep