Pass Softnet policy control FD through Tart

Sources/tart/Commands/Run.swift

@@ -224,6 +224,13 @@ struct Run: AsyncParsableCommand {
   """, valueName: "comma-separated CIDRs"))
   var netSoftnetBlock: String?
 
+  @Option(help: ArgumentHelp("Connected Unix stream socket file descriptor to use for the Softnet control channel (e.g. --net-softnet-control-fd=3)", discussion: """
+  This option enables the Softnet control channel on an inherited Unix stream socket. It can be used to dynamically replace Softnet allow and block lists while the VM is running.
+
+  The file descriptor must be greater than 2. Implies --net-softnet.
+  """, valueName: "file descriptor"))
+  var netSoftnetControlFd: Int32?
+
   @Option(help: ArgumentHelp("Comma-separated list of TCP ports to expose (e.g. --net-softnet-expose 2222:22,8080:80)", discussion: """
   Options are comma-separated and are as follows:
 
@@ -313,7 +320,7 @@ struct Run: AsyncParsableCommand {
     }
 
     // Automatically enable --net-softnet when any of its related options are specified
-    if netSoftnetAllow != nil || netSoftnetBlock != nil || netSoftnetExpose != nil {
+    if netSoftnetAllow != nil || netSoftnetBlock != nil || netSoftnetExpose != nil || netSoftnetControlFd != nil {
       netSoftnet = true
     }
 
@@ -681,13 +688,13 @@ struct Run: AsyncParsableCommand {
     if netSoftnet {
       let config = try VMConfig.init(fromURL: vmDir.configURL)
 
-      return try Softnet(vmMACAddress: config.macAddress.string, extraArguments: softnetExtraArguments)
+      return try Softnet(vmMACAddress: config.macAddress.string, extraArguments: softnetExtraArguments, controlFD: netSoftnetControlFd)
     }
 
     if netHost {
       let config = try VMConfig.init(fromURL: vmDir.configURL)
 
-      return try Softnet(vmMACAddress: config.macAddress.string, extraArguments: ["--vm-net-type", "host"] + softnetExtraArguments)
+      return try Softnet(vmMACAddress: config.macAddress.string, extraArguments: ["--vm-net-type", "host"] + softnetExtraArguments, controlFD: netSoftnetControlFd)
     }
 
     if netBridged.count > 0 {

Sources/tart/Network/Softnet.swift

@@ -16,7 +16,18 @@ class Softnet: Network {
 
   let vmFD: Int32
 
-  init(vmMACAddress: String, extraArguments: [String] = []) throws {
+  init(vmMACAddress: String, extraArguments: [String] = [], controlFD: Int32? = nil) throws {
+    var controlFileHandle: FileHandle?
+
+    if let controlFD = controlFD {
+      guard controlFD > STDERR_FILENO else {
+        throw SoftnetError.InitializationFailed(why: "Softnet control file descriptor must be greater than 2")
+      }
+
+      controlFileHandle = FileHandle(fileDescriptor: controlFD, closeOnDealloc: true)
+      try Self.validateControlFD(controlFD)
+    }
+
     let fds = UnsafeMutablePointer<Int32>.allocate(capacity: MemoryLayout<Int>.stride * 2)
 
     let ret = socketpair(AF_UNIX, SOCK_DGRAM, 0, fds)
@@ -33,6 +44,44 @@ class Softnet: Network {
     process.executableURL = try Self.softnetExecutableURL()
     process.arguments = ["--vm-fd", String(STDIN_FILENO), "--vm-mac-address", vmMACAddress] + extraArguments
     process.standardInput = FileHandle(fileDescriptor: softnetFD, closeOnDealloc: false)
+
+    if let controlFileHandle = controlFileHandle {
+      process.arguments! += ["--control-fd", String(STDOUT_FILENO)]
+      process.standardOutput = controlFileHandle
+    }
+  }
+
+  static func validateControlFD(_ fd: Int32) throws {
+    guard fd > STDERR_FILENO else {
+      throw SoftnetError.InitializationFailed(why: "Softnet control file descriptor must be greater than 2")
+    }
+
+    var socketType: Int32 = 0
+    var socketTypeLength = socklen_t(MemoryLayout<Int32>.size)
+    guard getsockopt(fd, SOL_SOCKET, SO_TYPE, &socketType, &socketTypeLength) == 0 else {
+      let details = Errno(rawValue: CInt(errno))
+      throw SoftnetError.InitializationFailed(why: "Softnet control file descriptor is not a socket: \(details)")
+    }
+
+    guard socketType == SOCK_STREAM else {
+      throw SoftnetError.InitializationFailed(why: "Softnet control file descriptor must be a Unix stream socket")
+    }
+
+    var peerAddress = sockaddr_storage()
+    var peerAddressLength = socklen_t(MemoryLayout<sockaddr_storage>.size)
+    let result = withUnsafeMutablePointer(to: &peerAddress) { pointer in
+      pointer.withMemoryRebound(to: sockaddr.self, capacity: 1) {
+        getpeername(fd, $0, &peerAddressLength)
+      }
+    }
+    guard result == 0 else {
+      let details = Errno(rawValue: CInt(errno))
+      throw SoftnetError.InitializationFailed(why: "Softnet control file descriptor is not connected: \(details)")
+    }
+
+    guard peerAddress.ss_family == sa_family_t(AF_UNIX) else {
+      throw SoftnetError.InitializationFailed(why: "Softnet control file descriptor must be a Unix stream socket")
+    }
   }
 
   static func softnetExecutableURL() throws -> URL {
@@ -46,6 +95,8 @@ class Softnet: Network {
   }
 
   func run(_ sema: AsyncSemaphore) throws {
+    defer { try? (process.standardOutput as? FileHandle)?.close() }
+
     try process.run()
 
     monitorTask = Task {

Tests/TartTests/SoftnetControlFDTests.swift

@@ -0,0 +1,183 @@
+import XCTest
+@testable import tart
+
+import Semaphore
+
+final class SoftnetControlFDTests: XCTestCase {
+  func testConnectedUnixStreamSocketIsAccepted() throws {
+    var fds: [Int32] = [-1, -1]
+    XCTAssertEqual(socketpair(AF_UNIX, SOCK_STREAM, 0, &fds), 0)
+    defer {
+      close(fds[0])
+      close(fds[1])
+    }
+
+    XCTAssertNoThrow(try Softnet.validateControlFD(fds[0]))
+  }
+
+  func testUnixDatagramSocketIsRejected() throws {
+    var fds: [Int32] = [-1, -1]
+    XCTAssertEqual(socketpair(AF_UNIX, SOCK_DGRAM, 0, &fds), 0)
+    defer {
+      close(fds[0])
+      close(fds[1])
+    }
+
+    XCTAssertThrowsError(try Softnet.validateControlFD(fds[0]))
+  }
+
+  func testUnconnectedUnixStreamSocketIsRejected() throws {
+    let fd = socket(AF_UNIX, SOCK_STREAM, 0)
+    XCTAssertGreaterThan(fd, STDERR_FILENO)
+    defer { close(fd) }
+
+    XCTAssertThrowsError(try Softnet.validateControlFD(fd))
+  }
+
+  func testPipeIsRejected() throws {
+    var fds: [Int32] = [-1, -1]
+    XCTAssertEqual(pipe(&fds), 0)
+    defer {
+      close(fds[0])
+      close(fds[1])
+    }
+
+    XCTAssertThrowsError(try Softnet.validateControlFD(fds[0]))
+  }
+
+  func testStandardDescriptorsAreRejected() throws {
+    XCTAssertThrowsError(try Softnet.validateControlFD(STDIN_FILENO))
+    XCTAssertThrowsError(try Softnet.validateControlFD(STDOUT_FILENO))
+    XCTAssertThrowsError(try Softnet.validateControlFD(STDERR_FILENO))
+  }
+
+  func testStandardDescriptorsRemainOpenWhenInitializationFails() throws {
+    for fd in [STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO] {
+      let flags = fcntl(fd, F_GETFD)
+      XCTAssertNotEqual(flags, -1)
+
+      XCTAssertThrowsError(try Softnet(vmMACAddress: "02:00:00:00:00:01", controlFD: fd))
+      XCTAssertEqual(fcntl(fd, F_GETFD), flags)
+    }
+  }
+
+  func testControlChannelIsPassedToSoftnetAndVMFDRemainsDatagram() async throws {
+    let temporaryDirectory = URL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent(UUID().uuidString)
+    try FileManager.default.createDirectory(at: temporaryDirectory, withIntermediateDirectories: false)
+    defer { try? FileManager.default.removeItem(at: temporaryDirectory) }
+
+    let executable = temporaryDirectory.appendingPathComponent("softnet")
+    let script = """
+    #!/usr/bin/env python3
+    import socket
+    import sys
+
+    assert sys.argv[1:] == ["--vm-fd", "0", "--vm-mac-address", "02:00:00:00:00:01", "--control-fd", "1"]
+    vm = socket.socket(fileno=0)
+    control = socket.socket(fileno=1)
+    assert vm.family == socket.AF_UNIX and vm.type == socket.SOCK_DGRAM
+    assert control.family == socket.AF_UNIX and control.type == socket.SOCK_STREAM
+    assert control.recv(4096) == b"softnet.policy.set\\n"
+    control.sendall(b"ok\\n")
+    """
+    try script.write(to: executable, atomically: true, encoding: .utf8)
+    try FileManager.default.setAttributes([.posixPermissions: 0o755], ofItemAtPath: executable.path)
+
+    let previousPath = ProcessInfo.processInfo.environment["PATH"] ?? ""
+    setenv("PATH", "\(temporaryDirectory.path):\(previousPath)", 1)
+    defer { setenv("PATH", previousPath, 1) }
+
+    var fds: [Int32] = [-1, -1]
+    XCTAssertEqual(socketpair(AF_UNIX, SOCK_STREAM, 0, &fds), 0)
+    defer { close(fds[1]) }
+
+    var timeout = timeval(tv_sec: 5, tv_usec: 0)
+    XCTAssertEqual(setsockopt(fds[1], SOL_SOCKET, SO_RCVTIMEO, &timeout, socklen_t(MemoryLayout<timeval>.size)), 0)
+
+    let semaphore = AsyncSemaphore(value: 0)
+    let softnet = try Softnet(vmMACAddress: "02:00:00:00:00:01", controlFD: fds[0])
+    try softnet.run(semaphore)
+
+    XCTAssertEqual(fcntl(fds[0], F_GETFD), -1)
+    XCTAssertEqual(errno, EBADF)
+
+    let request = Array("softnet.policy.set\n".utf8)
+    XCTAssertEqual(request.withUnsafeBytes { send(fds[1], $0.baseAddress, $0.count, 0) }, request.count)
+
+    var response = [UInt8](repeating: 0, count: 128)
+    let received = recv(fds[1], &response, response.count, 0)
+    XCTAssertGreaterThan(received, 0)
+    XCTAssertEqual(String(decoding: response.prefix(Int(max(received, 0))), as: UTF8.self), "ok\n")
+
+    await semaphore.wait()
+  }
+
+  func testControlFDIsClosedWhenSoftnetInitializationFails() throws {
+    let previousPath = ProcessInfo.processInfo.environment["PATH"] ?? ""
+    setenv("PATH", "/this/path/does/not/exist", 1)
+    defer { setenv("PATH", previousPath, 1) }
+
+    var fds: [Int32] = [-1, -1]
+    XCTAssertEqual(socketpair(AF_UNIX, SOCK_STREAM, 0, &fds), 0)
+    defer { close(fds[1]) }
+
+    XCTAssertThrowsError(try Softnet(vmMACAddress: "02:00:00:00:00:01", controlFD: fds[0]))
+    XCTAssertEqual(fcntl(fds[0], F_GETFD), -1)
+    XCTAssertEqual(errno, EBADF)
+  }
+
+  func testControlFDIsClosedWhenSoftnetValidationFails() throws {
+    var fds: [Int32] = [-1, -1]
+    XCTAssertEqual(socketpair(AF_UNIX, SOCK_DGRAM, 0, &fds), 0)
+    defer { close(fds[1]) }
+
+    XCTAssertThrowsError(try Softnet(vmMACAddress: "02:00:00:00:00:01", controlFD: fds[0]))
+    XCTAssertEqual(fcntl(fds[0], F_GETFD), -1)
+    XCTAssertEqual(errno, EBADF)
+  }
+
+  func testControlFDImpliesSoftnet() throws {
+    let temporaryHome = try createTemporaryTartHome()
+    defer { try? FileManager.default.removeItem(at: temporaryHome) }
+    let previousHome = ProcessInfo.processInfo.environment["TART_HOME"]
+    setenv("TART_HOME", temporaryHome.path, 1)
+    defer { restoreEnvironment("TART_HOME", value: previousHome) }
+
+    let command = try Run.parse(["vm", "--net-softnet-control-fd", "3"])
+
+    XCTAssertTrue(command.netSoftnet)
+    XCTAssertEqual(command.netSoftnetControlFd, 3)
+  }
+
+  func testControlFDIsRejectedWithHostNetworking() throws {
+    let temporaryHome = try createTemporaryTartHome()
+    defer { try? FileManager.default.removeItem(at: temporaryHome) }
+    let previousHome = ProcessInfo.processInfo.environment["TART_HOME"]
+    setenv("TART_HOME", temporaryHome.path, 1)
+    defer { restoreEnvironment("TART_HOME", value: previousHome) }
+
+    XCTAssertThrowsError(
+      try Run.parse(["vm", "--net-host", "--net-softnet-control-fd", "3"])
+    )
+  }
+
+  private func createTemporaryTartHome() throws -> URL {
+    let temporaryHome = URL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent(UUID().uuidString)
+    let vm = temporaryHome.appendingPathComponent("vms/vm")
+    try FileManager.default.createDirectory(at: vm, withIntermediateDirectories: true)
+
+    for name in ["config.json", "disk.img", "nvram.bin"] {
+      XCTAssertTrue(FileManager.default.createFile(atPath: vm.appendingPathComponent(name).path, contents: nil))
+    }
+
+    return temporaryHome
+  }
+
+  private func restoreEnvironment(_ name: String, value: String?) {
+    if let value = value {
+      setenv(name, value, 1)
+    } else {
+      unsetenv(name)
+    }
+  }
+}