feat(#14): network isolation rust side — PRIVATE_NETWORK + veth wiring in set_nspawn_flags

hive-c0re/src/lifecycle.rs

@@ -55,6 +55,17 @@ const WEB_PORT_RANGE: u16 = 900;
 const DEFAULT_MEMORY_MAX: &str = "2G";
 const DEFAULT_CPU_QUOTA: &str = "50%";
 
+/// FNV-1a hash of a string — shared by `agent_web_port` and
+/// `agent_network_ip` so the derivation rule is identical.
+fn fnv1a(s: &str) -> u32 {
+    let mut hash: u32 = 2_166_136_261;
+    for b in s.bytes() {
+        hash ^= u32::from(b);
+        hash = hash.wrapping_mul(16_777_619);
+    }
+    hash
+}
+
 /// Per-agent web UI port — `WEB_PORT_BASE + FNV-1a(name) %
 /// WEB_PORT_RANGE` for every agent including the manager. The port
 /// allocation rule reads the same for every name; collisions are
@@ -64,13 +75,56 @@ const DEFAULT_CPU_QUOTA: &str = "50%";
 /// no state-file dance.
 #[must_use]
 pub fn agent_web_port(name: &str) -> u16 {
-    let mut hash: u32 = 2_166_136_261;
-    for b in name.bytes() {
-        hash ^= u32::from(b);
-        hash = hash.wrapping_mul(16_777_619);
-    }
     // Modulo of a u32 by a u16's value is guaranteed < u16::MAX, so try_from never fails.
-    WEB_PORT_BASE + u16::try_from(hash % u32::from(WEB_PORT_RANGE)).unwrap_or(0)
+    WEB_PORT_BASE + u16::try_from(fnv1a(name) % u32::from(WEB_PORT_RANGE)).unwrap_or(0)
+}
+
+/// Deterministic IPv4 address for an agent inside an isolated subnet.
+///
+/// Parses `subnet_cidr` as `<network_ip>/<prefix_len>` (e.g.
+/// `"10.42.0.0/24"`), then computes:
+///
+/// ```text
+/// host_count = 2^(32 - prefix_len)
+/// usable     = host_count - 3  // skip .0 (network), .1 (gateway), .255 (broadcast)
+/// offset     = FNV-1a(name) % usable + 2   // .2 is the first agent slot
+/// agent_ip   = network_base_u32 + offset
+/// ```
+///
+/// Returns `None` when `subnet_cidr` can't be parsed (invalid format,
+/// prefix out of range, etc.) so callers can fall back gracefully.
+/// Collisions are possible (birthday paradox) and the operator resolves
+/// them by renaming an agent, same as for port collisions.
+#[must_use]
+pub fn agent_network_ip(name: &str, subnet_cidr: &str) -> Option<String> {
+    let (ip_str, prefix_str) = subnet_cidr.split_once('/')?;
+    let prefix_len: u32 = prefix_str.parse().ok()?;
+    if prefix_len > 30 {
+        // /31 and /32 have no room for agents; /30 has 1 usable slot.
+        return None;
+    }
+    // Parse dotted-decimal IPv4.
+    let octets: Vec<u8> = ip_str
+        .split('.')
+        .map(|o| o.parse::<u8>().ok())
+        .collect::<Option<Vec<_>>>()?;
+    if octets.len() != 4 {
+        return None;
+    }
+    let base_u32 = u32::from_be_bytes([octets[0], octets[1], octets[2], octets[3]]);
+    // Mask off host bits to get the true network address.
+    let mask = if prefix_len == 0 { 0u32 } else { !0u32 << (32 - prefix_len) };
+    let network_base = base_u32 & mask;
+    let host_count: u32 = 1u32.checked_shl(32 - prefix_len).unwrap_or(0);
+    // `.0` = network, `.1` = bridge gateway, last = broadcast → 3 reserved.
+    let usable = host_count.saturating_sub(3);
+    if usable == 0 {
+        return None;
+    }
+    let offset = fnv1a(name) % usable + 2; // +2: skip .0 and .1
+    let ip_u32 = network_base + offset;
+    let [a, b, c, d] = ip_u32.to_be_bytes();
+    Some(format!("{a}.{b}.{c}.{d}"))
 }
 
 #[must_use]
@@ -1120,8 +1174,34 @@ async fn set_nspawn_flags(
     }
     binds.push(BindMount { host_path: socket_dir.to_string_lossy().into_owned(), container_path: socket_dir.to_string_lossy().into_owned(), read_only: false });
 
+    // Network isolation: when HIVE_NETWORK_ISOLATION=1 is set (by the
+    // hive-network.nix module's `isolateContainers` option), flip the
+    // container to a private network namespace with a veth pair attached
+    // to the host bridge. Applies to all containers including the manager
+    // (all hive-c0re<->agent comms go through bind-mounted UDS, not TCP).
+    let isolation = {
+        let isolate = std::env::var("HIVE_NETWORK_ISOLATION").ok().as_deref() == Some("1");
+        let bridge = std::env::var("HIVE_NETWORK_BRIDGE").unwrap_or_default();
+        let subnet = std::env::var("HIVE_NETWORK_SUBNET").unwrap_or_default();
+        if isolate && !bridge.is_empty() && !subnet.is_empty() {
+            let Some(agent_ip) = agent_network_ip(agent_name, &subnet) else {
+                tracing::warn!(
+                    %agent_name, %subnet,
+                    "HIVE_NETWORK_SUBNET is set but could not derive a valid IP for agent \
+                     (bad CIDR? prefix too narrow?); skipping PRIVATE_NETWORK write to \
+                     avoid misconfigured isolation"
+                );
+                return crate::priv_client::write_nspawn_flags(container, &binds, None).await;
+            };
+            tracing::info!(%agent_name, %agent_ip, %bridge, "network isolation: PRIVATE_NETWORK=1");
+            Some(hive_sh4re::priv_proto::NetworkIsolation { agent_ip, bridge })
+        } else {
+            None
+        }
+    };
+
     // Delegate the actual conf-file rewrite to hive-priv (runs as root).
-    crate::priv_client::write_nspawn_flags(container, &binds).await
+    crate::priv_client::write_nspawn_flags(container, &binds, isolation).await
 }
 
 /// Execute a container operation via hive-priv and integrate with
@@ -1256,6 +1336,47 @@ mod tests {
         assert!(tracked.contains("flake.nix"), "flake.nix not committed");
     }
 
+    #[test]
+    fn agent_network_ip_is_in_subnet() {
+        // Default subnet 10.42.0.0/24 — agents get .2 to .254.
+        let ip = agent_network_ip("alice", "10.42.0.0/24").expect("should produce an IP");
+        let octets: Vec<u8> = ip.split('.').map(|o| o.parse().unwrap()).collect();
+        assert_eq!(&octets[..3], &[10, 42, 0], "wrong /24 prefix");
+        assert!(octets[3] >= 2 && octets[3] <= 254, "host byte {}", octets[3]);
+    }
+
+    #[test]
+    fn agent_network_ip_stable() {
+        // Same name + subnet must always produce the same IP.
+        let a = agent_network_ip("damocles", "10.42.0.0/24");
+        let b = agent_network_ip("damocles", "10.42.0.0/24");
+        assert_eq!(a, b);
+    }
+
+    #[test]
+    fn agent_network_ip_different_agents() {
+        // Different agent names very likely produce different IPs (not guaranteed,
+        // but for these two names the hashes don't collide).
+        let alice = agent_network_ip("alice", "10.42.0.0/24").unwrap();
+        let bob = agent_network_ip("bob", "10.42.0.0/24").unwrap();
+        assert_ne!(alice, bob, "alice and bob collide — rename one");
+    }
+
+    #[test]
+    fn agent_network_ip_different_subnet() {
+        let ip = agent_network_ip("alice", "192.168.5.0/24").expect("should produce an IP");
+        let octets: Vec<u8> = ip.split('.').map(|o| o.parse().unwrap()).collect();
+        assert_eq!(&octets[..3], &[192, 168, 5]);
+    }
+
+    #[test]
+    fn agent_network_ip_rejects_bad_input() {
+        assert!(agent_network_ip("alice", "notanip/24").is_none());
+        assert!(agent_network_ip("alice", "10.0.0.0/33").is_none()); // prefix > 32
+        assert!(agent_network_ip("alice", "10.0.0.0/31").is_none()); // too small
+        assert!(agent_network_ip("alice", "10.0.0.0").is_none());    // no prefix
+    }
+
     /// `setup_proposed` is idempotent: calling it on an existing repo is a
     /// no-op (the fresh guard skips all writes).
     #[tokio::test]

hive-c0re/src/priv_client.rs

@@ -7,7 +7,9 @@
 //! a persistent connection.
 
 use anyhow::{Context as _, Result, bail};
-use hive_sh4re::priv_proto::{BindMount, JournalOutput, PRIV_SOCK, PrivRequest, PrivResponse};
+use hive_sh4re::priv_proto::{
+    BindMount, JournalOutput, NetworkIsolation, PRIV_SOCK, PrivRequest, PrivResponse,
+};
 use tokio::io::{AsyncBufReadExt, AsyncWriteExt, BufReader};
 use tokio::net::UnixStream;
 
@@ -112,10 +114,15 @@ pub async fn read_container_journal(
     )
 }
 
-pub async fn write_nspawn_flags(container: &str, binds: &[BindMount]) -> Result<()> {
+pub async fn write_nspawn_flags(
+    container: &str,
+    binds: &[BindMount],
+    isolation: Option<NetworkIsolation>,
+) -> Result<()> {
     ok(call(&PrivRequest::WriteNspawnFlags {
         container: container.to_owned(),
         binds: binds.to_vec(),
+        isolation,
     })
     .await?)
 }

hive-priv/src/main.rs

@@ -21,8 +21,8 @@ use std::path::{Path, PathBuf};
 
 use anyhow::{Context as _, Result, bail};
 use hive_sh4re::priv_proto::{
-    AGENT_PREFIX, BindMount, JournalOutput, MANAGER_NAME, META_DIR, PRIV_SOCK, PrivRequest,
+    AGENT_PREFIX, BindMount, JournalOutput, MANAGER_NAME, META_DIR, NetworkIsolation, PRIV_SOCK,
-    PrivResponse, SIBLING_CONTAINERS,
+    PrivRequest, PrivResponse, SIBLING_CONTAINERS,
 };
 use tokio::io::{AsyncBufReadExt, AsyncWriteExt, BufReader};
 use tokio::net::{UnixListener, UnixStream};
@@ -207,13 +207,14 @@ async fn exec(req: PrivRequest) -> Result<(String, String)> {
         PrivRequest::WriteNspawnFlags {
             ref container,
             ref binds,
+            ref isolation,
         } => {
             validate_container_system_name(container)?;
             for bind in binds {
                 validate_bind_path(&bind.host_path)?;
                 validate_bind_path(&bind.container_path)?;
             }
-            write_nspawn_flags(container, binds)?;
+            write_nspawn_flags(container, binds, isolation.as_ref())?;
             Ok((String::new(), String::new()))
         }
 
@@ -477,9 +478,15 @@ fn validate_bind_path(path: &str) -> Result<()> {
 
 /// Update `/etc/nixos-containers/<container>.conf`: strips network-isolation
 /// vars (`PRIVATE_NETWORK`, `HOST_ADDRESS*`, `LOCAL_ADDRESS*`, `HOST_BRIDGE`,
-/// `EXTRA_NSPAWN_FLAGS`), forces `PRIVATE_NETWORK=0` and blank network vars,
+/// Update `/etc/nixos-containers/<container>.conf`: strip old network vars,
-/// then appends `EXTRA_NSPAWN_FLAGS="<flags>"`.
+/// write network isolation settings, then append `EXTRA_NSPAWN_FLAGS`.
-fn write_nspawn_flags(container: &str, binds: &[BindMount]) -> Result<()> {
+/// When `isolation` is `Some`, writes `PRIVATE_NETWORK=1` + veth wiring;
+/// when `None`, writes `PRIVATE_NETWORK=0`.
+fn write_nspawn_flags(
+    container: &str,
+    binds: &[BindMount],
+    isolation: Option<&NetworkIsolation>,
+) -> Result<()> {
     let path = format!("/etc/nixos-containers/{container}.conf");
     let original = std::fs::read_to_string(&path).with_context(|| format!("read {path}"))?;
     let lines: Vec<&str> = original
@@ -499,12 +506,21 @@ fn write_nspawn_flags(container: &str, binds: &[BindMount]) -> Result<()> {
     if !out.is_empty() {
         out.push('\n');
     }
-    out.push_str("PRIVATE_NETWORK=0\n");
+    if let Some(iso) = isolation {
-    out.push_str("HOST_ADDRESS=\n");
+        out.push_str("PRIVATE_NETWORK=1\n");
-    out.push_str("LOCAL_ADDRESS=\n");
+        out.push_str("HOST_ADDRESS=\n");
-    out.push_str("HOST_ADDRESS6=\n");
+        out.push_str(&format!("LOCAL_ADDRESS={}\n", iso.agent_ip));
-    out.push_str("LOCAL_ADDRESS6=\n");
+        out.push_str("HOST_ADDRESS6=\n");
-    out.push_str("HOST_BRIDGE=\n");
+        out.push_str("LOCAL_ADDRESS6=\n");
+        out.push_str(&format!("HOST_BRIDGE={}\n", iso.bridge));
+    } else {
+        out.push_str("PRIVATE_NETWORK=0\n");
+        out.push_str("HOST_ADDRESS=\n");
+        out.push_str("LOCAL_ADDRESS=\n");
+        out.push_str("HOST_ADDRESS6=\n");
+        out.push_str("LOCAL_ADDRESS6=\n");
+        out.push_str("HOST_BRIDGE=\n");
+    }
     let flags: Vec<String> = binds
         .iter()
         .map(|b| {

hive-sh4re/src/priv_proto.rs

@@ -55,6 +55,17 @@ pub struct BindMount {
     pub read_only: bool,
 }
 
+/// Network isolation parameters for `WriteNspawnFlags`. When `Some`,
+/// hive-priv writes `PRIVATE_NETWORK=1` + veth bridge wiring instead
+/// of the default `PRIVATE_NETWORK=0`.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct NetworkIsolation {
+    /// Static IP address to assign to this container on the bridge subnet.
+    pub agent_ip: String,
+    /// Host bridge interface name (e.g. `hive0`).
+    pub bridge: String,
+}
+
 /// A request to the privileged helper.
 ///
 /// Wire format: one JSON object per line over `/run/hive/priv.sock`.
@@ -128,12 +139,18 @@ pub enum PrivRequest {
     },
 
     // --- Config file writes ---
-    /// Update `/etc/nixos-containers/<container>.conf`: strip network-isolation
+    /// Update `/etc/nixos-containers/<container>.conf`: strip old network-isolation
-    /// vars, force `PRIVATE_NETWORK=0`, and set `EXTRA_NSPAWN_FLAGS` from the
+    /// vars, write `PRIVATE_NETWORK` + bridge settings, and set `EXTRA_NSPAWN_FLAGS`
-    /// provided bind-mount list. Written by `lifecycle::set_nspawn_flags`.
+    /// from the provided bind-mount list. Written by `lifecycle::set_nspawn_flags`.
+    /// When `isolation` is `Some`, writes `PRIVATE_NETWORK=1` + veth wiring;
+    /// when `None`, writes `PRIVATE_NETWORK=0`.
     WriteNspawnFlags {
         container: String,
         binds: Vec<BindMount>,
+        /// `None` = host netns (PRIVATE_NETWORK=0). `Some` = private netns with
+        /// veth on the specified bridge (PRIVATE_NETWORK=1).
+        #[serde(default)]
+        isolation: Option<NetworkIsolation>,
     },
 
     /// Write `/run/systemd/system/container@<container>.service.d/hyperhive-limits.conf`