conntrack: arp: move handling to guest chains

In order to make sure we are only affecting VM traffic and no host
interfaces that are bridged, move the rules into a chain that gets
executed inside the guest chain, rather than setting the rules
globally.

Since ether type matches on the respective Ethernet header, it
doesn't work for packets with VLAN header. Matching via meta protocol
ensures that VLAN encapsulated ARP packets are matched as well.
Otherwise ARP traffic inside VLANs gets dropped, due to them having
conntrack state invalid.

Signed-off-by: Stefan Hanreich <s.hanreich@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

proxmox-firewall/resources/proxmox-firewall.nft

@@ -35,7 +35,9 @@ add chain bridge proxmox-firewall-guests allow-ra-out
 add chain bridge proxmox-firewall-guests block-ra-out
 add chain bridge proxmox-firewall-guests allow-icmp
 add chain bridge proxmox-firewall-guests do-reject
+add chain bridge proxmox-firewall-guests pre-vm-out
 add chain bridge proxmox-firewall-guests vm-out {type filter hook prerouting priority 0; policy accept;}
+add chain bridge proxmox-firewall-guests pre-vm-in
 add chain bridge proxmox-firewall-guests vm-in {type filter hook postrouting priority 0; policy accept;}
 
 flush chain inet proxmox-firewall do-reject
@@ -68,7 +70,9 @@ flush chain bridge proxmox-firewall-guests allow-ra-out
 flush chain bridge proxmox-firewall-guests block-ra-out
 flush chain bridge proxmox-firewall-guests allow-icmp
 flush chain bridge proxmox-firewall-guests do-reject
+flush chain bridge proxmox-firewall-guests pre-vm-out
 flush chain bridge proxmox-firewall-guests vm-out
+flush chain bridge proxmox-firewall-guests pre-vm-in
 flush chain bridge proxmox-firewall-guests vm-in
 
 table inet proxmox-firewall {
@@ -311,18 +315,24 @@ table bridge proxmox-firewall-guests {
         drop
     }
 
+    chain pre-vm-out {
+        meta protocol != arp ct state vmap { established : accept, related : accept, invalid : drop }
+    }
+
     chain vm-out {
         type filter hook prerouting priority 0; policy accept;
         jump allow-icmp
-        ether type != arp ct state vmap { established : accept, related : accept, invalid : drop }
         iifname vmap @vm-map-out
     }
 
+    chain pre-vm-in {
+        meta protocol != arp ct state vmap { established : accept, related : accept, invalid : drop }
+        meta protocol arp accept
+    }
+
     chain vm-in {
         type filter hook postrouting priority 0; policy accept;
         jump allow-icmp
-        ether type != arp ct state vmap { established : accept, related : accept, invalid : drop }
-        ether type arp accept
         oifname vmap @vm-map-in
     }
 }

proxmox-firewall/src/firewall.rs

@@ -758,7 +758,16 @@ impl Firewall {
 
         let chain = Self::guest_chain(direction, vmid);
 
-        commands.append(&mut vec![Add::chain(chain.clone()), Flush::chain(chain)]);
+        let pre_chain = match direction {
+            Direction::In => "pre-vm-in",
+            Direction::Out => "pre-vm-out",
+        };
+
+        commands.append(&mut vec![
+            Add::chain(chain.clone()),
+            Flush::chain(chain.clone()),
+            Add::rule(AddRule::from_statement(chain, Statement::jump(pre_chain))),
+        ]);
 
         Ok(())
     }

proxmox-firewall/tests/snapshots/integration_tests__firewall.snap

@@ -2543,6 +2543,22 @@ expression: "firewall.full_host_fw().expect(\"firewall can be generated\")"
         }
       }
     },
+    {
+      "add": {
+        "rule": {
+          "family": "bridge",
+          "table": "proxmox-firewall-guests",
+          "chain": "guest-100-in",
+          "expr": [
+            {
+              "jump": {
+                "target": "pre-vm-in"
+              }
+            }
+          ]
+        }
+      }
+    },
     {
       "add": {
         "chain": {
@@ -2561,6 +2577,22 @@ expression: "firewall.full_host_fw().expect(\"firewall can be generated\")"
         }
       }
     },
+    {
+      "add": {
+        "rule": {
+          "family": "bridge",
+          "table": "proxmox-firewall-guests",
+          "chain": "guest-100-out",
+          "expr": [
+            {
+              "jump": {
+                "target": "pre-vm-out"
+              }
+            }
+          ]
+        }
+      }
+    },
     {
       "add": {
         "set": {
@@ -3362,6 +3394,22 @@ expression: "firewall.full_host_fw().expect(\"firewall can be generated\")"
         }
       }
     },
+    {
+      "add": {
+        "rule": {
+          "family": "bridge",
+          "table": "proxmox-firewall-guests",
+          "chain": "guest-101-in",
+          "expr": [
+            {
+              "jump": {
+                "target": "pre-vm-in"
+              }
+            }
+          ]
+        }
+      }
+    },
     {
       "add": {
         "chain": {
@@ -3380,6 +3428,22 @@ expression: "firewall.full_host_fw().expect(\"firewall can be generated\")"
         }
       }
     },
+    {
+      "add": {
+        "rule": {
+          "family": "bridge",
+          "table": "proxmox-firewall-guests",
+          "chain": "guest-101-out",
+          "expr": [
+            {
+              "jump": {
+                "target": "pre-vm-out"
+              }
+            }
+          ]
+        }
+      }
+    },
     {
       "add": {
         "set": {