Fix unaligned read by switching from unmaintained users crate (#26)

* Fix unaligned read by switching from unmaintained users crate

* Bump proc-macro2 to to fix "unknown feature `proc_macro_span_shrink`"

.cirrus.yml

@@ -23,12 +23,11 @@ task:
     SENTRY_AUTH_TOKEN: ENCRYPTED[!c16a5cf7da5f856b4bc2f21fe8cb7aa2a6c981f851c094ed4d3025fd02ea59a58a86cee8b193a69a1fc20fa217e56ac3!]
   install_rust_script:
     - curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
-  install_goreleaser_script:
+  install_script:
-    - brew install go goreleaser/tap/goreleaser-pro
+    - brew install go goreleaser/tap/goreleaser-pro getsentry/tools/sentry-cli
   build_script:
     - cargo build --profile release-with-debug
-  install_sentry_cli_script:
+  release_script: goreleaser
-    - brew install getsentry/tools/sentry-cli
   upload_sentry_debug_files_script:
     - cd target/release-with-debug/
     # Generate and upload symbols
@@ -37,4 +36,8 @@ task:
     # Bundle and upload sources
     - sentry-cli debug-files bundle-sources softnet.dSYM/
     - sentry-cli debug-files upload -o $SENTRY_ORG -p $SENTRY_PROJECT softnet.src.zip
-  release_script: goreleaser
+  create_sentry_release_script:
+    - export SENTRY_RELEASE="softnet@$CIRRUS_TAG"
+    - sentry-cli releases new $SENTRY_RELEASE
+    - sentry-cli releases set-commits $SENTRY_RELEASE --auto
+    - sentry-cli releases finalize $SENTRY_RELEASE

Cargo.toml

@@ -14,7 +14,7 @@ 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"] }
@@ -22,8 +22,9 @@ 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"

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/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(())
     }
 
@@ -45,17 +57,34 @@ 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)))?;
 
-        let vm_readable = self.events.iter().any(|ev| ev.key == EventKey::VM.into());
+        let vm_readable = self
-        let host_readable = self.events.iter().any(|ev| ev.key == EventKey::Host.into());
+            .events
+            .iter()
+            .any(|ev| ev.key == Into::<usize>::into(EventKey::VM));
+        let host_readable = self
+            .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/host.rs

@@ -16,10 +16,24 @@ impl Proxy {
             self.snoop(frame);
         }
 
-        self.vm
+        match self.vm.write(frame.as_ref()) {
-            .write(frame.as_ref())
+            Ok(_) => Ok(()),
-            .map(|_| ())
+            Err(err) => {
-            .context("failed to write to the VM")
+                if let Some(libc::ENOBUFS) = err.raw_os_error() {
+                    if !self.enobufs_encountered {
+                        sentry::capture_message(
+                            "No buffer space available in VM's socket",
+                            sentry::Level::Warning,
+                        );
+                        self.enobufs_encountered = true;
+                    }
+
+                    return Ok(());
+                }
+
+                Err(err).context("failed to write to the VM")
+            }
+        }
     }
 
     fn allowed_from_host(&mut self, frame: &EthernetFrame<&[u8]>) -> Option<()> {

lib/proxy/mod.rs

@@ -18,6 +18,7 @@ pub struct Proxy {
     poller: Poller,
     vm_mac_address: smoltcp::wire::EthernetAddress,
     dhcp_snooper: DhcpSnooper,
+    enobufs_encountered: bool,
 }
 
 impl Proxy {
@@ -32,6 +33,7 @@ impl Proxy {
             poller,
             vm_mac_address: smoltcp::wire::EthernetAddress(vm_mac_address.bytes()),
             dhcp_snooper: Default::default(),
+            enobufs_encountered: false,
         })
     }
 
@@ -41,7 +43,7 @@ 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())?;
@@ -51,6 +53,11 @@ impl Proxy {
                 self.read_from_host(buf.as_mut_slice())?;
             }
 
+            // Graceful termination
+            if interrupt {
+                return Ok(());
+            }
+
             self.poller.rearm()?;
         }
     }

rust-toolchain

@@ -0,0 +1 @@
+nightly

src/main.rs

@@ -1,7 +1,9 @@
 use anyhow::{anyhow, Context};
 use clap::Parser;
+use nix::sys::signal::{signal, SigHandler, Signal};
 use privdrop::PrivDrop;
 use softnet::proxy::Proxy;
+use std::borrow::Cow;
 use std::env;
 use std::os::raw::c_int;
 use std::os::unix::io::RawFd;
@@ -13,7 +15,7 @@ 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 {
@@ -54,13 +56,14 @@ fn main() -> ExitCode {
 
     // Initialize Sentry
     let _sentry = sentry::init(sentry::ClientOptions {
+        release: option_env!("CIRRUS_TAG").map(|tag| Cow::from(format!("softnet@{tag}"))),
         ..Default::default()
     });
 
     // Enrich future events with Cirrus CI-specific tags
     if let Ok(tags) = env::var("CIRRUS_SENTRY_TAGS") {
         sentry::configure_scope(|scope| {
-            for (key, value) in tags.split(",").map(|tag| tag.split_once("=")).flatten() {
+            for (key, value) in tags.split(',').filter_map(|tag| tag.split_once('=')) {
                 scope.set_tag(key, value);
             }
         });
@@ -82,6 +85,14 @@ 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