ssh: manage hostkeys and global known_hosts

bundles/ssh/files/ssh_config

@@ -0,0 +1,5 @@
+Host *
+    #UserKnownHostsFile ~/.ssh/known_hosts ~/.ssh/known_hosts.d/%k
+    SendEnv LANG LC_*
+    HashKnownHosts yes
+    GSSAPIAuthentication yes

bundles/ssh/files/sshd_config

@@ -10,7 +10,7 @@ MaxSessions 255
 PubkeyAuthentication yes
 PasswordAuthentication no
 ChallengeResponseAuthentication no
-AuthorizedKeysFile	.ssh/authorized_keys
+AuthorizedKeysFile .ssh/authorized_keys
 UsePAM yes
 
 AllowUsers ${' '.join(users)}

bundles/ssh/items.py

@@ -1,14 +1,61 @@
 if not node.metadata.get('FIXME_dont_touch_sshd', False):
     # on debian bullseye raspberry images, starting the systemd ssh
     # daemon seems to collide with an existing sysv daemon
-    files['/etc/ssh/sshd_config'] = {
-        'content_type': 'mako',
-        'context': {
-            'users': sorted(node.metadata.get('ssh/allow_users')),
+    directories = {
+        '/etc/ssh': {
+            'purge': True,
+            'mode': '0755',
+        }
+    }
+    
+    files = {
+        '/etc/ssh/moduli': {
+            'content_type': 'any',
+        },
+        '/etc/ssh/ssh_config': {
+            'triggers': [
+                'svc_systemd:ssh:restart'
+            ],
+        },
+        '/etc/ssh/ssh_config': {
+            'content_type': 'mako',
+            'context': {
+            },
+            'triggers': [
+                'svc_systemd:ssh:restart'
+            ],
+        },
+        '/etc/ssh/sshd_config': {
+            'content_type': 'mako',
+            'context': {
+                'users': sorted(node.metadata.get('ssh/allow_users')),
+            },
+            'triggers': [
+                'svc_systemd:ssh:restart'
+            ],
+        },
+        '/etc/ssh/ssh_host_ed25519_key': {
+            'content': node.metadata.get('ssh/host_key/private') + '\n',
+            'mode': '0600',
+            'triggers': [
+                'svc_systemd:ssh:restart'
+            ],
+        },
+        '/etc/ssh/ssh_host_ed25519_key.pub': {
+            'content': node.metadata.get('ssh/host_key/public') + '\n',
+            'mode': '0644',
+            'triggers': [
+                'svc_systemd:ssh:restart'
+            ],
+        },
+        '/etc/ssh/ssh_known_hosts': {
+            'content': '\n'.join(
+                repo.libs.ssh.known_hosts_entry_for(other_node)
+                    for other_node in sorted(repo.nodes)
+                    if other_node != node
+                    and other_node.has_bundle('ssh')
+            ) + '\n',
         },
-        'triggers': [
-            'svc_systemd:ssh:restart'
-        ],
     }
 
     svc_systemd['ssh'] = {

bundles/ssh/metadata.py

@@ -1,3 +1,6 @@
+from base64 import b64decode
+
+
 @metadata_reactor.provides(
     'ssh/allow_users',
 )
@@ -11,3 +14,21 @@ def users(metadata):
             ),
         },
     }
+
+
+@metadata_reactor.provides(
+    'ssh/host_key',
+)
+def host_key(metadata):
+    private, public = repo.libs.ssh.generate_ed25519_key_pair(
+        b64decode(str(repo.vault.random_bytes_as_base64_for(f"HostKey {metadata.get('id')}", length=32)))
+    )
+
+    return {
+        'ssh': {
+            'host_key': {
+                'private': private + '\n',
+                'public': public + f' root@{node.name}',
+            }
+        },
+    }

libs/ssh.py

@@ -1,6 +1,8 @@
 from base64 import b64decode, b64encode
-from hashlib import sha3_224
+from hashlib import sha3_224, sha1
 from functools import cache
+import hmac
+from ipaddress import ip_interface
 
 from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey
 from cryptography.hazmat.primitives.serialization import Encoding, PrivateFormat, PublicFormat, NoEncryption
@@ -46,3 +48,43 @@ def generate_ed25519_key_pair(secret):
     # RETURN
     
     return (deterministic_privatekey, public_key)
+
+
+#https://www.fragmentationneeded.net/2017/10/ssh-hashknownhosts-file-format.html
+# test this:
+# - `ssh-keyscan -H 10.0.0.5`
+# - take the salt from the ssh-ed25519 entry (first field after '|1|')
+# - `bw debug -c 'repo.libs.ssh.known_hosts_entry_for(repo.get_node(<node with hostname 10.0.0.5>), <salt from ssh-keygen>)'`
+@cache
+def known_hosts_entry_for(node, test_salt=None):
+    ips = set()
+
+    for network in node.metadata.get('network').values():
+        if network.get('ipv4', None):
+            ips.add(str(ip_interface(network['ipv4']).ip))
+        if network.get('ipv6', None):
+            ips.add(str(ip_interface(network['ipv6']).ip))
+
+    domains = {
+        domain
+            for domain, records in node.metadata.get('dns').items()
+            for type, values in records.items()
+            if type in {'A', 'AAAA'}
+            and set(values) & ips
+    }
+
+    lines = set()
+
+    for hostname in {node.hostname, *ips, *domains}:
+    
+        if test_salt:
+            salt = b64decode(test_salt)
+        else:
+            salt = sha1(node.metadata.get('id').encode()).digest()
+
+        hash = hmac.new(salt, hostname.encode(), sha1).digest()
+        pubkey = node.metadata.get('ssh/host_key/public')
+        
+        lines.add(f'|1|{b64encode(salt).decode()}|{b64encode(hash).decode()} {" ".join(pubkey.split()[:2])}')
+        
+    return '\n'.join(sorted(lines))