[Bug 1987842] Re: wireguard: netdev file can leak private key

[Mark Esler]

Please refer to this issue as CVE-2022-4968.

** CVE added: https://cve.mitre.org/cgi-bin/cvename.cgi?name=2022-4968

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Title:
  wireguard: netdev file can leak private key

Status in Netplan:
  Triaged

Bug description:
  When using netplan with wireguard, netplan will render the
  /run/systemd/network/10-netplan-${name}.netdev file with 0644
  permissions.

  
  That file contains the wireguard private key, which, if specified literally (instead of using a file), will leak that key to all local users of the system. This may not be desirable.

  For example, I have this yaml in /etc/netplan/home0.yaml:
  network:
    version: 2
    tunnels:
      home0:
        mode: wireguard
        key: <base64 private key contents>
        port: 51000
        addresses: [10.10.11.2/24]
        peers:
          - keys:
              public: <base64 public key contents>
            endpoint: 10.48.132.39:51000
            allowed-ips: [10.10.11.0/24,10.10.10.0/24]
        routes:
          - to: 10.10.10.0/24
            from: 10.10.11.2
            scope: link

  When that is rendered and applied with `netplan apply`, this error is logged in /var/log/syslog:
  Aug 26 14:23:30 laptop-coffee-shop systemd-networkd[537]: /run/systemd/network/10-netplan-home0.netdev has 0644 mode that is too permissive, please adjust the ownership and access mode.

  
  And indeed, that file contains the same literal private key, as expected:

  # cat /run/systemd/network/10-netplan-home0.netdev
  [NetDev]
  Name=home0
  Kind=wireguard

  [WireGuard]
  PrivateKey=<base64 private key contents>
  ListenPort=51000

  [WireGuardPeer]
  PublicKey=<base64 public key contents>
  AllowedIPs=10.10.11.0/24,10.10.10.0/24
  Endpoint=10.48.132.39:51000

  Its permissions should probably be 0640 root:systemd-networkd.

  This is not an issue if the private key is specified via a file, in
  which case systemd-networkd won't even issue that warning.

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