feat(nat): Add whole NAT

examples/infra.yaml

@@ -37,7 +37,7 @@ filter:
         vrrp: true
       verdict: accept
 
-    - src: adm
+    - src: [adm, 10.10.10.10]
       protocols:
         tcp:
           dport: 179
@@ -71,11 +71,14 @@ filter:
       dst: [10.0.0.1, internet]
       verdict: accept
 
-# TODO: Nat translation
-#
-# nat:
-#   - src: mgmt
-#     snat:
-#       addr: 45.66.108.14
-#       persistent: true
+nat:
+  - src: 100.64.0.0/26
+    dst: internet
+    snat:
+      addr: 45.66.108.0/28
+  - src: 100.64.0.0/26
+    dst: internet
+    snat:
+      addr: 45.66.108.1
+      port: 1000..5000
 ...

firewall.py

@@ -72,7 +72,7 @@ class PortRange(str):
         if start > end:
             raise ValueError("invalid port range: start must be less than end")
 
-        return range(start, end)
+        return range(start, end + 1)
 
 
 # Zones
@@ -175,6 +175,7 @@ class SNat(RestrictiveBaseModel):
 
 
 class Nat(RestrictiveBaseModel):
+    protocols: set[str] = {"icmp", "udp", "tcp"}
     src: AutoSet[IPv4Network | ZoneName]
     dst: AutoSet[IPv4Network | ZoneName]
     snat: SNat
@@ -421,25 +422,25 @@ def parse_filter_rule(rule: Rule, zones: Zones) -> Iterator[nft.Rule]:
     for attr, field in (("src", "saddr"), ("dst", "daddr")):
         if getattr(rule, attr, None) is not None:
             addrs, negated = zones_into_ip(getattr(rule, attr), zones)
-            addr_v4, addr_v6 = split_v4_v6(addrs)
+            addrs_v4, addrs_v6 = split_v4_v6(addrs)
 
-            if addr_v4:
+            if addrs_v4:
                 builder.add_v4(
                     nft.Match(
                         op=("!=" if negated else "=="),
                         left=nft.Payload(protocol="ip", field=field),
-                        right=addr_v4,
+                        right=addrs_v4,
                     )
                 )
             else:
                 builder.disable_v4()
 
-            if addr_v6:
+            if addrs_v6:
                 builder.add_v6(
                     nft.Match(
                         op=("!=" if negated else "=="),
                         left=nft.Payload(protocol="ip6", field=field),
-                        right=addr_v6,
+                        right=addrs_v6,
                     )
                 )
             else:
@@ -547,16 +548,68 @@ def parse_filter(filter: Filter, zones: Zones) -> nft.Table:
     return table
 
 
+def parse_nat(nat: list[Nat], zones: Zones) -> nft.Table:
+    chain = nft.Chain(
+        name="postrouting",
+        type="nat",
+        hook="postrouting",
+        policy="accept",
+        priority=100,
+    )
+
+    for entry in nat:
+        rule = nft.Rule()
+
+        for attr, field in (("src", "saddr"), ("dst", "daddr")):
+            addrs, negated = zones_into_ip(getattr(entry, attr), zones)
+            addrs_v4, _ = split_v4_v6(addrs)
+
+            if addrs_v4:
+                rule.stmts.append(
+                    nft.Match(
+                        op=("!=" if negated else "=="),
+                        left=nft.Payload(protocol="ip", field=field),
+                        right=addrs_v4,
+                    )
+                )
+
+        rule.stmts.append(
+            nft.Match(
+                op="==",
+                left=nft.Payload(protocol="ip", field="protocol"),
+                right=entry.protocols,
+            )
+        )
+
+        rule.stmts.append(
+            nft.Snat(
+                addr=entry.snat.addr,
+                port=entry.snat.port,
+                persistent=entry.snat.persistent,
+            )
+        )
+
+        chain.rules.append(rule)
+
+    # Resulting table
+    table = nft.Table(name="nat", family="ip")
+
+    table.chains.append(chain)
+
+    return table
+
+
 def parse_firewall(firewall: Firewall, zones: Zones) -> nft.Ruleset:
     # Tables
     blacklist = parse_blacklist(firewall.blacklist, zones)
     rpf = parse_reverse_path_filter(firewall.reverse_path_filter)
     filter = parse_filter(firewall.filter, zones)
+    nat = parse_nat(firewall.nat, zones)
 
     # Resulting ruleset
     ruleset = nft.Ruleset(flush=True)
 
-    ruleset.tables.extend([blacklist, rpf, filter])
+    ruleset.tables.extend([blacklist, rpf, filter, nat])
 
     return ruleset
 

nft.py

@@ -1,6 +1,6 @@
 from dataclasses import dataclass, field
 from itertools import chain
-from ipaddress import IPv4Network, IPv6Network
+from ipaddress import IPv4Address, IPv4Network, IPv6Network
 from typing import Any, Generic, TypeVar, get_args
 
 T = TypeVar("T")
@@ -115,6 +115,29 @@ class Match:
         return {"match": match}
 
 
+@dataclass
+class Snat:
+    addr: IPv4Network | IPv4Address
+    port: range | None
+    persistent: bool
+
+    def to_nft(self) -> JsonNftables:
+        snat: JsonNftables = {}
+
+        if isinstance(self.addr, IPv4Network):
+            snat["addr"] = {"range": [str(self.addr[0]), str(self.addr[-1])]}
+        else:
+            snat["addr"] = str(self.addr)
+
+        if self.port is not None:
+            snat["port"] = imm_to_nft(self.port)
+
+        if self.persistent:
+            snat["flags"] = "persistent"
+
+        return {"snat": snat}
+
+
 @dataclass
 class Verdict:
     verdict: str
@@ -125,7 +148,7 @@ class Verdict:
         return {self.verdict: self.target}
 
 
-Statement = Counter | Goto | Jump | Match | Verdict
+Statement = Counter | Goto | Jump | Match | Snat | Verdict
 
 
 # Ruleset
@@ -156,7 +179,7 @@ class Set:
 
 @dataclass
 class Rule:
-    stmts: list[Statement]
+    stmts: list[Statement] = field(default_factory=list)
 
     def to_nft(self, family: str, table: str, chain: str) -> JsonNftables:
         rule = {