Prevent multiple --allow flags (#35)

* Prevent multiple --allow flags

* --allow: better value name instead of just <ALLOW>

.cirrus.yml

@@ -4,17 +4,18 @@ env:
 task:
   name: Build
   macos_instance:
-    image: ghcr.io/cirruslabs/macos-monterey-xcode:14
+    image: ghcr.io/cirruslabs/macos-sonoma-xcode:latest
   install_rust_script:
     - curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
+    - rustup target add x86_64-apple-darwin
   build_script:
-    - cargo build
+    - cargo build --target aarch64-apple-darwin --target x86_64-apple-darwin
 
 task:
   name: Release
   only_if: $CIRRUS_TAG != ''
   macos_instance:
-    image: ghcr.io/cirruslabs/macos-monterey-xcode:14
+    image: ghcr.io/cirruslabs/macos-sonoma-xcode:latest
   env:
     GITHUB_TOKEN: ENCRYPTED[!98ace8259c6024da912c14d5a3c5c6aac186890a8d4819fad78f3e0c41a4e0cd3a2537dd6e91493952fb056fa434be7c!]
     GORELEASER_KEY: ENCRYPTED[!9b80b6ef684ceaf40edd4c7af93014ee156c8aba7e6e5795f41c482729887b5c31f36b651491d790f1f668670888d9fd!]
@@ -23,13 +24,14 @@ task:
     SENTRY_AUTH_TOKEN: ENCRYPTED[!c16a5cf7da5f856b4bc2f21fe8cb7aa2a6c981f851c094ed4d3025fd02ea59a58a86cee8b193a69a1fc20fa217e56ac3!]
   install_rust_script:
     - curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
+    - rustup target add x86_64-apple-darwin
   install_script:
     - brew install go goreleaser/tap/goreleaser-pro getsentry/tools/sentry-cli
   build_script:
-    - cargo build --profile release-with-debug
+    - cargo build --target aarch64-apple-darwin --target x86_64-apple-darwin --profile release-with-debug
   release_script: goreleaser
   upload_sentry_debug_files_script:
-    - cd target/release-with-debug/
+    - cd target/aarch64-apple-darwin/release-with-debug/
     # Generate and upload symbols
     - dsymutil softnet
     - sentry-cli debug-files upload -o $SENTRY_ORG -p $SENTRY_PROJECT softnet.dSYM/

.gitignore

@@ -1 +1,3 @@
+/.idea
+/dist
 /target

.goreleaser.yml

@@ -1,29 +1,27 @@
 project_name: softnet
 
 builds:
-  - builder: prebuilt
+  - id: softnet
+    builder: prebuilt
+    goamd64: [v1]
     goos:
       - darwin
     goarch:
       - arm64
+      - amd64
     prebuilt:
-      path: "target/release-with-debug/softnet"
+      path: 'target/{{- if eq .Arch "arm64" }}aarch64{{- else }}x86_64{{ end }}-apple-darwin/release-with-debug/softnet'
 
 archives:
-  - id: binary
-    format: binary
-    name_template: "{{ .ProjectName }}"
   - id: regular
-    name_template: "{{ .ProjectName }}"
+    name_template: "{{ .ProjectName }}-{{ .Arch }}"
 
 release:
   prerelease: auto
 
 brews:
   - name: softnet
-    ids:
-      - regular
-    tap:
+    repository:
       owner: cirruslabs
       name: homebrew-cli
     caveats: See the Github repository for more information

Cargo.toml

@@ -14,16 +14,19 @@ debug = true
 [dependencies]
 smoltcp = "0.8.1"
 libc = "0.2.126"
-polling = "2.2.0"
+polling = { git = "https://github.com/smol-rs/polling.git" }
 dhcproto = "0.7.0"
 vmnet = "0.1.1"
-clap = { version = "3.1.18", features = ["derive"] }
+clap = { version = "4.5.2", features = ["derive"] }
 mac_address = "1.1.3"
 privdrop = "0.5.2"
 anyhow = { version = "1.0.66", features = ["backtrace"] }
 ip_network = "0.4.1"
-users = "0.11.0"
+uzers = "0.11.3"
 system-configuration = "0.5.0"
 num_enum = "0.5.7"
 sentry = { version = "0.29.1", features = ["debug-images"] }
 sentry-anyhow = { version = "0.29.1", features = ["backtrace"] }
+nix = "0.26.2"
+prefix-trie = "0.3.0"
+ipnet = "2.9.0"

README.md

@@ -1,13 +1,14 @@
 # Softnet
 
 Softnet is a software networking for [Tart](https://github.com/cirruslabs/tart) which provides better network isolation and alleviates DHCP shortage on production systems.
+Please check out [this blog post](https://cirrus-ci.org/blog/2022/07/07/isolating-network-between-tarts-macos-virtual-machines/) for backstory.
 
 ## Working model
 
 Softnet solves two problems:
 
 1. VM network isolation
-  * [`VZNATNetworkDeviceAttachment`](https://developer.apple.com/documentation/virtualization/vznatnetworkdeviceattachment) (the default networking in Tart) enables [vmnet's bridge isolation](https://developer.apple.com/documentation/vmnet/vmnet_enable_isolation_key) by default and prevents cross-VM traffic, however it's still possible for any VM to spoof the host's ARP-table and capture other VMs traffic, for example
+  * [`VZNATNetworkDeviceAttachment`](https://developer.apple.com/documentation/virtualization/vznatnetworkdeviceattachment) (the default networking in Tart) enables [vmnet's bridge isolation](https://developer.apple.com/documentation/vmnet/vmnet_enable_isolation_key) by default and prevents cross-VM traffic, however it's still possible for any VM to spoof the host's ARP-table and capture other VMs traffic
 2. DHCP exhaustion
   * macOS built-in DHCP-server allocates a `/24` subnet with 86400 seconds lease time by default, which only allows for ~253 VMs a day (or 1 VM every ~6 minutes) to be spawned without causing a denial-of-service, which is pretty limiting for CI services like Cirrus CI
 
@@ -30,4 +31,4 @@ For proper functioning, Softnet binary requires two things:
 
 ## Running
 
-Softnet is started and managed automatically by Tart if `--with-softnet` flag is present when calling `tart run`.
+Softnet is started and managed automatically by Tart if `--net-softnet` flag is provided when calling `tart run`.

lib/host.rs

@@ -1,4 +1,5 @@
 use anyhow::{anyhow, Context, Result};
+use clap::ValueEnum;
 use std::net::Ipv4Addr;
 use std::os::unix::io::{AsRawFd, RawFd};
 use std::os::unix::net::UnixDatagram;
@@ -8,6 +9,18 @@ use vmnet::mode::Mode;
 use vmnet::parameters::{Parameter, ParameterKind};
 use vmnet::{Events, Options};
 
+#[derive(ValueEnum, Clone, Debug)]
+pub enum NetType {
+    /// Shared network
+    ///
+    /// Uses NAT-translation to give guests access to the global network
+    Nat,
+    /// Host network
+    ///
+    /// Guests will be able to talk only to the host without access to global network
+    Host,
+}
+
 pub struct Host {
     interface: vmnet::Interface,
     new_packets_rx: UnixDatagram,
@@ -18,10 +31,13 @@ pub struct Host {
 }
 
 impl Host {
-    pub fn new() -> Result<Host> {
-        // Initialize a vmnet.framework NAT interface with isolation enabled
+    pub fn new(vm_net_type: NetType) -> Result<Host> {
+        // Initialize a vmnet.framework NAT or Host interface with isolation enabled
         let mut interface = vmnet::Interface::new(
-            Mode::Shared(Default::default()),
+            match vm_net_type {
+                NetType::Nat => Mode::Shared(Default::default()),
+                NetType::Host => Mode::Host(Default::default()),
+            },
             Options {
                 enable_isolation: Some(true),
                 ..Default::default()
@@ -30,15 +46,23 @@ impl Host {
         .context("failed to initialize vmnet interface")?;
 
         // Retrieve first IP (gateway) used for this interface
-        let Some(Parameter::StartAddress(gateway_ip)) = interface.parameters().get(ParameterKind::StartAddress) else {
-            return Err(anyhow!("failed to retrieve vmnet's interface start address"));
+        let Some(Parameter::StartAddress(gateway_ip)) =
+            interface.parameters().get(ParameterKind::StartAddress)
+        else {
+            return Err(anyhow!(
+                "failed to retrieve vmnet's interface start address"
+            ));
         };
         let gateway_ip = Ipv4Addr::from_str(&gateway_ip)
             .context("failed to parse vmnet's interface start address")?;
 
         // Retrieve max packet size for this interface
-        let Some(Parameter::MaxPacketSize(max_packet_size)) = interface.parameters().get(ParameterKind::MaxPacketSize) else {
-            return Err(anyhow!("failed to retrieve vmnet's interface max packet size"));
+        let Some(Parameter::MaxPacketSize(max_packet_size)) =
+            interface.parameters().get(ParameterKind::MaxPacketSize)
+        else {
+            return Err(anyhow!(
+                "failed to retrieve vmnet's interface max packet size"
+            ));
         };
 
         // Set up a socketpair() to emulate polling of the vmnet interface

lib/mod.rs

@@ -1,5 +1,6 @@
 mod dhcp_snooper;
 mod host;
+pub use host::NetType;
 mod poller;
 pub mod proxy;
 mod vm;

lib/poller.rs

@@ -1,5 +1,7 @@
 use anyhow::Result;
 use num_enum::IntoPrimitive;
+use polling::os::kqueue::PollerKqueueExt;
+use polling::PollMode;
 use std::os::unix::io::RawFd;
 use std::time::Duration;
 
@@ -15,6 +17,7 @@ pub struct Poller {
 enum EventKey {
     VM,
     Host,
+    Interrupt,
 }
 
 impl Poller {
@@ -34,6 +37,15 @@ impl Poller {
         self.poller
             .add(self.host_fd as RawFd, self.host_interest())?;
 
+        let interrupt_signal = polling::os::kqueue::Signal(libc::SIGINT);
+        self.poller
+            .add_filter(
+                interrupt_signal,
+                EventKey::Interrupt.into(),
+                PollMode::Oneshot,
+            )
+            .unwrap();
+
         Ok(())
     }
 
@@ -45,10 +57,17 @@ impl Poller {
         self.poller
             .modify(self.host_fd as RawFd, self.host_interest())?;
 
+        let interrupt_signal = polling::os::kqueue::Signal(libc::SIGINT);
+        self.poller.modify_filter(
+            interrupt_signal,
+            EventKey::Interrupt.into(),
+            PollMode::Oneshot,
+        )?;
+
         Ok(())
     }
 
-    pub fn wait(&mut self) -> Result<(bool, bool)> {
+    pub fn wait(&mut self) -> Result<(bool, bool, bool)> {
         self.poller
             .wait(&mut self.events, Some(Duration::from_millis(100)))?;
 
@@ -60,8 +79,12 @@ impl Poller {
             .events
             .iter()
             .any(|ev| ev.key == Into::<usize>::into(EventKey::Host));
+        let interrupt = self
+            .events
+            .iter()
+            .any(|ev| ev.key == Into::<usize>::into(EventKey::Interrupt));
 
-        Ok((vm_readable, host_readable))
+        Ok((vm_readable, host_readable, interrupt))
     }
 
     fn vm_interest(&self) -> polling::Event {

lib/proxy/mod.rs

@@ -4,10 +4,13 @@ mod vm;
 
 use crate::dhcp_snooper::DhcpSnooper;
 use crate::host::Host;
+use crate::host::NetType;
 use crate::poller::Poller;
 use crate::vm::VM;
 use anyhow::Result;
+use ipnet::Ipv4Net;
 use mac_address::MacAddress;
+use prefix_trie::PrefixSet;
 use smoltcp::wire::EthernetFrame;
 use std::io::ErrorKind;
 use std::os::unix::io::{AsRawFd, RawFd};
@@ -18,13 +21,19 @@ pub struct Proxy {
     poller: Poller,
     vm_mac_address: smoltcp::wire::EthernetAddress,
     dhcp_snooper: DhcpSnooper,
+    allow: PrefixSet<Ipv4Net>,
     enobufs_encountered: bool,
 }
 
 impl Proxy {
-    pub fn new(vm_fd: RawFd, vm_mac_address: MacAddress) -> Result<Proxy> {
+    pub fn new(
+        vm_fd: RawFd,
+        vm_mac_address: MacAddress,
+        vm_net_type: NetType,
+        allow: PrefixSet<Ipv4Net>,
+    ) -> Result<Proxy> {
         let vm = VM::new(vm_fd)?;
-        let host = Host::new()?;
+        let host = Host::new(vm_net_type)?;
         let poller = Poller::new(vm.as_raw_fd(), host.as_raw_fd())?;
 
         Ok(Proxy {
@@ -33,6 +42,7 @@ impl Proxy {
             poller,
             vm_mac_address: smoltcp::wire::EthernetAddress(vm_mac_address.bytes()),
             dhcp_snooper: Default::default(),
+            allow,
             enobufs_encountered: false,
         })
     }
@@ -43,7 +53,7 @@ impl Proxy {
         self.poller.arm()?;
 
         loop {
-            let (vm_readable, host_readable) = self.poller.wait()?;
+            let (vm_readable, host_readable, interrupt) = self.poller.wait()?;
 
             if vm_readable {
                 self.read_from_vm(buf.as_mut_slice())?;
@@ -53,6 +63,11 @@ impl Proxy {
                 self.read_from_host(buf.as_mut_slice())?;
             }
 
+            // Graceful termination
+            if interrupt {
+                return Ok(());
+            }
+
             self.poller.rearm()?;
         }
     }

lib/proxy/vm.rs

@@ -2,6 +2,7 @@ use crate::proxy::udp_packet_helper::UdpPacketHelper;
 use crate::proxy::Proxy;
 use anyhow::Context;
 use anyhow::Result;
+use ipnet::Ipv4Net;
 use smoltcp::wire::{
     ArpPacket, EthernetFrame, EthernetProtocol, IpProtocol, Ipv4Packet, UdpPacket,
 };
@@ -58,15 +59,22 @@ impl Proxy {
     }
 
     fn allowed_from_vm_ipv4(&self, ipv4_pkt: Ipv4Packet<&[u8]>) -> Option<()> {
-        // Once we've learned the VM's IP from the DHCP snooping,
-        // allow all global traffic for that VM's IP
+        // Have we learned the VM's IP from the DHCP snooping?
         if let Some(lease) = &self.dhcp_snooper.lease() {
-            let dst_is_global =
-                ip_network::IpNetwork::from(Ipv4Addr::from(ipv4_pkt.dst_addr().0)).is_global();
+            // If so, allow all global traffic
+            let dst_addr = Ipv4Addr::from(ipv4_pkt.dst_addr().0);
+            let dst_is_global = ip_network::IpNetwork::from(dst_addr).is_global();
 
             if lease.valid_ip_source(ipv4_pkt.src_addr()) && dst_is_global {
                 return Some(());
             }
+
+            // Also allow all traffic to the user-specified CIDRs
+            let dst_net = Ipv4Net::from(dst_addr);
+
+            if self.allow.get_spm(&dst_net).is_some() {
+                return Some(());
+            }
         }
 
         // Allow communication with host

src/main.rs

@@ -1,9 +1,14 @@
 use anyhow::{anyhow, Context};
 use clap::Parser;
+use ipnet::Ipv4Net;
+use nix::sys::signal::{signal, SigHandler, Signal};
+use prefix_trie::PrefixSet;
 use privdrop::PrivDrop;
 use softnet::proxy::Proxy;
+use softnet::NetType;
 use std::borrow::Cow;
 use std::env;
+
 use std::os::raw::c_int;
 use std::os::unix::io::RawFd;
 use std::os::unix::process::CommandExt;
@@ -14,7 +19,7 @@ use system_configuration::core_foundation::number::CFNumber;
 use system_configuration::core_foundation::string::CFString;
 use system_configuration::preferences::SCPreferences;
 use system_configuration::sys::preferences::{SCPreferencesCommitChanges, SCPreferencesSetValue};
-use users::{get_current_groupname, get_current_username, get_effective_uid};
+use uzers::{get_current_groupname, get_current_username, get_effective_uid};
 
 #[derive(Parser, Debug)]
 struct Args {
@@ -27,6 +32,9 @@ struct Args {
     #[clap(long, help = "MAC address to enforce for the VM")]
     vm_mac_address: mac_address::MacAddress,
 
+    #[clap(long, value_enum, help = "type of network to use for the VM", default_value_t=NetType::Nat)]
+    vm_net_type: NetType,
+
     #[clap(
         long,
         help = "set bootpd(8) lease time to this value (in seconds) before starting the VM",
@@ -40,6 +48,15 @@ struct Args {
     #[clap(long, help = "group name to drop privileges to")]
     group: Option<String>,
 
+    #[clap(
+        long,
+        help = "comma-separated list of CIDRs to allow the traffic to (e.g. --allow=192.168.0.0/24)",
+        value_name = "comma-separated CIDRs",
+        use_value_delimiter = true,
+        action = clap::ArgAction::Set
+    )]
+    allow: Vec<Ipv4Net>,
+
     #[clap(long, hide = true)]
     sudo_escalation_probing: bool,
 
@@ -55,7 +72,7 @@ fn main() -> ExitCode {
 
     // Initialize Sentry
     let _sentry = sentry::init(sentry::ClientOptions {
-        release: option_env!("CIRRUS_TAG").map(|tag| { Cow::from(format!("softnet@{tag}")) }),
+        release: option_env!("CIRRUS_TAG").map(|tag| Cow::from(format!("softnet@{tag}"))),
         ..Default::default()
     });
 
@@ -84,6 +101,14 @@ fn main() -> ExitCode {
 }
 
 fn try_main() -> anyhow::Result<()> {
+    // The default signal(3)[1] action for SIGINT is to interrupt program,
+    // but we want to handle SIGINT ourselves, so we ignore it. The kqueue(2)'s[2]
+    // EVFILT_SIGNAL will receive it anyways, because it has lower precedence.
+    //
+    // [1]: https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man3/signal.3.html
+    // [2]: https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man2/kqueue.2.html
+    unsafe { signal(Signal::SIGINT, SigHandler::SigIgn) }?;
+
     let args: Args = Args::parse();
 
     // No need to run anything, just return
@@ -131,8 +156,13 @@ fn try_main() -> anyhow::Result<()> {
     set_bootpd_lease_time(args.bootpd_lease_time);
 
     // Initialize the proxy while still having the root privileges
-    let mut proxy = Proxy::new(args.vm_fd as RawFd, args.vm_mac_address)
-        .context("failed to initialize proxy")?;
+    let mut proxy = Proxy::new(
+        args.vm_fd as RawFd,
+        args.vm_mac_address,
+        args.vm_net_type,
+        PrefixSet::from_iter(args.allow),
+    )
+    .context("failed to initialize proxy")?;
 
     // Drop effective privileges to the user
     // and group which have had invoked us