Initial implementation of mac forwarding using a privileged docker sock claim helper

Signed-off-by: Jason T. Greene <jason.greene@redhat.com>

4 files changed, 538 insertions, 0 deletions

diff --git a/cmd/podman-mac-helper/install.go b/cmd/podman-mac-helper/install.go
new file mode 100644
index 000000000..7f623ecb6
--- /dev/null
+++ b/cmd/podman-mac-helper/install.go
@@ -0,0 +1,244 @@
+//go:build darwin
+// +build darwin
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"strings"
+	"syscall"
+	"text/template"
+
+	"github.com/pkg/errors"
+	"github.com/spf13/cobra"
+)
+
+const (
+	rwx_rx_rx = 0755
+	rw_r_r    = 0644
+)
+
+const launchConfig = `<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>Label</key>
+	<string>com.github.containers.podman.helper-{{.User}}</string>
+	<key>ProgramArguments</key>
+	<array>
+		<string>{{.Program}}</string>
+		<string>service</string>
+		<string>{{.Target}}</string>
+	</array>
+	<key>inetdCompatibility</key>
+	<dict>
+		<key>Wait</key>
+		<false/>
+	</dict>
+	<key>UserName</key>
+	<string>root</string>
+	<key>Sockets</key>
+	<dict>
+		<key>Listeners</key>
+		<dict>
+			<key>SockFamily</key>
+			<string>Unix</string>
+			<key>SockPathName</key>
+			<string>/private/var/run/podman-helper-{{.User}}.socket</string>
+			<key>SockPathOwner</key>
+			<integer>{{.UID}}</integer>
+			<key>SockPathMode</key>
+			<!-- SockPathMode takes base 10 (384 = 0600) -->
+			<integer>384</integer>
+			<key>SockType</key>
+			<string>stream</string>
+		</dict>
+	</dict>
+</dict>
+</plist>
+`
+
+type launchParams struct {
+	Program string
+	User    string
+	UID     string
+	Target  string
+}
+
+var installCmd = &cobra.Command{
+	Use:    "install",
+	Short:  "installs the podman helper agent",
+	Long:   "installs the podman helper agent, which manages the /var/run/docker.sock link",
+	PreRun: silentUsage,
+	RunE:   install,
+}
+
+func init() {
+	addPrefixFlag(installCmd)
+	rootCmd.AddCommand(installCmd)
+}
+
+func install(cmd *cobra.Command, args []string) error {
+	userName, uid, homeDir, err := getUser()
+	if err != nil {
+		return err
+	}
+
+	labelName := fmt.Sprintf("com.github.containers.podman.helper-%s.plist", userName)
+	fileName := filepath.Join("/Library", "LaunchDaemons", labelName)
+
+	if _, err := os.Stat(fileName); err == nil || !os.IsNotExist(err) {
+		return errors.New("helper is already installed, uninstall first")
+	}
+
+	prog, err := installExecutable(userName)
+	if err != nil {
+		return err
+	}
+
+	target := filepath.Join(homeDir, ".local", "share", "containers", "podman", "machine", "podman.sock")
+	var buf bytes.Buffer
+	t := template.Must(template.New("launchdConfig").Parse(launchConfig))
+	err = t.Execute(&buf, launchParams{prog, userName, uid, target})
+	if err != nil {
+		return err
+	}
+
+	file, err := os.OpenFile(fileName, os.O_WRONLY|os.O_CREATE|os.O_EXCL, rw_r_r)
+	if err != nil {
+		return errors.Wrap(err, "error creating helper plist file")
+	}
+	defer file.Close()
+	_, err = buf.WriteTo(file)
+	if err != nil {
+		return err
+	}
+
+	if err = runDetectErr("launchctl", "load", fileName); err != nil {
+		return errors.Wrap(err, "launchctl failed loading service")
+	}
+
+	return nil
+}
+
+func restrictRecursive(targetDir string, until string) error {
+	for targetDir != until && len(targetDir) > 1 {
+		info, err := os.Lstat(targetDir)
+		if err != nil {
+			return err
+		}
+		if info.Mode()&fs.ModeSymlink != 0 {
+			return errors.Errorf("symlinks not allowed in helper paths (remove them and rerun): %s", targetDir)
+		}
+		if err = os.Chown(targetDir, 0, 0); err != nil {
+			return errors.Wrap(err, "could not update ownership of helper path")
+		}
+		if err = os.Chmod(targetDir, rwx_rx_rx|fs.ModeSticky); err != nil {
+			return errors.Wrap(err, "could not update permissions of helper path")
+		}
+		targetDir = filepath.Dir(targetDir)
+	}
+
+	return nil
+}
+
+func verifyRootDeep(path string) error {
+	path = filepath.Clean(path)
+	current := "/"
+	segs := strings.Split(path, "/")
+	depth := 0
+	for i := 1; i < len(segs); i++ {
+		seg := segs[i]
+		current = filepath.Join(current, seg)
+		info, err := os.Lstat(current)
+		if err != nil {
+			return err
+		}
+
+		stat := info.Sys().(*syscall.Stat_t)
+		if stat.Uid != 0 {
+			return errors.Errorf("installation target path must be solely owned by root: %s is not", current)
+		}
+
+		if info.Mode()&fs.ModeSymlink != 0 {
+			target, err := os.Readlink(current)
+			if err != nil {
+				return err
+			}
+
+			targetParts := strings.Split(target, "/")
+			segs = append(targetParts, segs[i+1:]...)
+
+			if depth++; depth > 1000 {
+				return errors.New("reached max recursion depth, link structure is cyclical or too complex")
+			}
+
+			if !filepath.IsAbs(target) {
+				current = filepath.Dir(current)
+				i = -1 // Start at 0
+			} else {
+				current = "/"
+				i = 0 // Skip empty first segment
+			}
+		}
+	}
+
+	return nil
+}
+
+func installExecutable(user string) (string, error) {
+	// Since the installed executable runs as root, as a precaution verify root ownership of
+	// the entire installation path, and utilize sticky + read only perms for the helper path
+	// suffix. The goal is to help users harden against privilege escalation from loose
+	// filesystem permissions.
+	//
+	// Since userpsace package management tools, such as brew, delegate management of system
+	// paths to standard unix users, the daemon executable is copied into a separate more
+	// restricted area of the filesystem.
+	if err := verifyRootDeep(installPrefix); err != nil {
+		return "", err
+	}
+
+	targetDir := filepath.Join(installPrefix, "podman", "helper", user)
+	if err := os.MkdirAll(targetDir, rwx_rx_rx); err != nil {
+		return "", errors.Wrap(err, "could not create helper directory structure")
+	}
+
+	// Correct any incorrect perms on previously existing directories and verify no symlinks
+	if err := restrictRecursive(targetDir, installPrefix); err != nil {
+		return "", err
+	}
+
+	exec, err := os.Executable()
+	if err != nil {
+		return "", err
+	}
+	install := filepath.Join(targetDir, filepath.Base(exec))
+
+	return install, copyFile(install, exec, rwx_rx_rx)
+}
+
+func copyFile(dest string, source string, perms fs.FileMode) error {
+	in, err := os.Open(source)
+	if err != nil {
+		return err
+	}
+
+	defer in.Close()
+	out, err := os.OpenFile(dest, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, perms)
+	if err != nil {
+		return err
+	}
+
+	defer out.Close()
+	if _, err := io.Copy(out, in); err != nil {
+		return err
+	}
+
+	return nil
+}
diff --git a/cmd/podman-mac-helper/main.go b/cmd/podman-mac-helper/main.go
new file mode 100644
index 000000000..8d995519f
--- /dev/null
+++ b/cmd/podman-mac-helper/main.go
@@ -0,0 +1,149 @@
+//go:build darwin
+// +build darwin
+
+package main
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"regexp"
+	"strconv"
+	"strings"
+
+	"github.com/pkg/errors"
+	"github.com/spf13/cobra"
+)
+
+const (
+	defaultPrefix = "/usr/local"
+	dockerSock    = "/var/run/docker.sock"
+)
+
+var installPrefix string
+
+var rootCmd = &cobra.Command{
+	Use:               "podman-mac-helper",
+	Short:             "A system helper to manage docker.sock",
+	Long:              `podman-mac-helper is a system helper service and tool for managing docker.sock `,
+	CompletionOptions: cobra.CompletionOptions{DisableDefaultCmd: true},
+	SilenceErrors:     true,
+}
+
+// Note, this code is security sensitive since it runs under privilege.
+// Limit actions to what is strictly necessary, and take appropriate
+// safeguards
+//
+// After installation the service call is ran under launchd in a nowait
+// inetd style fashion, so stdin, stdout, and stderr are all pointing to
+// an accepted connection
+//
+// This service is installed once per user and will redirect
+// /var/run/docker to the fixed user-assigned unix socket location.
+//
+// Control communication is restricted to each user specific service via
+// unix file permissions
+
+func main() {
+	if os.Geteuid() != 0 {
+		fmt.Printf("This command must be ran as root via sudo or osascript\n")
+		os.Exit(1)
+	}
+
+	if err := rootCmd.Execute(); err != nil {
+		fmt.Fprintf(os.Stderr, "Error: %s\n", err.Error())
+	}
+}
+
+func getUserInfo(name string) (string, string, string, error) {
+	// We exec id instead of using user.Lookup to remain compat
+	// with CGO disabled.
+	cmd := exec.Command("/usr/bin/id", "-P", name)
+	output, err := cmd.StdoutPipe()
+	if err != nil {
+		return "", "", "", err
+	}
+
+	if err := cmd.Start(); err != nil {
+		return "", "", "", err
+	}
+
+	entry := readCapped(output)
+	elements := strings.Split(entry, ":")
+	if len(elements) < 9 || elements[0] != name {
+		return "", "", "", errors.New("Could not lookup user")
+	}
+
+	return elements[0], elements[2], elements[8], nil
+}
+
+func getUser() (string, string, string, error) {
+	name, found := os.LookupEnv("SUDO_USER")
+	if !found {
+		name, found = os.LookupEnv("USER")
+		if !found {
+			return "", "", "", errors.New("could not determine user")
+		}
+	}
+
+	_, uid, home, err := getUserInfo(name)
+	if err != nil {
+		return "", "", "", fmt.Errorf("could not lookup user: %s", name)
+	}
+	id, err := strconv.Atoi(uid)
+	if err != nil {
+		return "", "", "", fmt.Errorf("invalid uid for user: %s", name)
+	}
+	if id == 0 {
+		return "", "", "", fmt.Errorf("unexpected root user")
+	}
+
+	return name, uid, home, nil
+}
+
+// Used for commands that don't return a proper exit code
+func runDetectErr(name string, args ...string) error {
+	cmd := exec.Command(name, args...)
+	errReader, err := cmd.StderrPipe()
+	if err != nil {
+		return err
+	}
+
+	err = cmd.Start()
+	if err == nil {
+		errString := readCapped(errReader)
+		if len(errString) > 0 {
+			re := regexp.MustCompile(`\r?\n`)
+			err = errors.New(re.ReplaceAllString(errString, ": "))
+		}
+	}
+
+	if werr := cmd.Wait(); werr != nil {
+		err = werr
+	}
+
+	return err
+}
+
+func readCapped(reader io.Reader) string {
+	// Cap output
+	buffer := make([]byte, 2048)
+	n, _ := io.ReadFull(reader, buffer)
+	_, _ = io.Copy(ioutil.Discard, reader)
+	if n > 0 {
+		return string(buffer[:n])
+	}
+
+	return ""
+}
+
+func addPrefixFlag(cmd *cobra.Command) {
+	cmd.Flags().StringVar(&installPrefix, "prefix", defaultPrefix, "Sets the install location prefix")
+}
+
+func silentUsage(cmd *cobra.Command, args []string) {
+	cmd.SilenceUsage = true
+	cmd.SilenceErrors = true
+}
diff --git a/cmd/podman-mac-helper/service.go b/cmd/podman-mac-helper/service.go
new file mode 100644
index 000000000..65cd89f34
--- /dev/null
+++ b/cmd/podman-mac-helper/service.go
@@ -0,0 +1,85 @@
+//go:build darwin
+// +build darwin
+
+package main
+
+import (
+	"fmt"
+	"io"
+	"io/fs"
+	"os"
+	"time"
+
+	"github.com/spf13/cobra"
+)
+
+const (
+	trigger = "GO\n"
+	fail    = "NO"
+	success = "OK"
+)
+
+var serviceCmd = &cobra.Command{
+	Use:    "service",
+	Short:  "services requests",
+	Long:   "services requests",
+	PreRun: silentUsage,
+	Run:    serviceRun,
+	Hidden: true,
+}
+
+func init() {
+	rootCmd.AddCommand(serviceCmd)
+}
+
+func serviceRun(cmd *cobra.Command, args []string) {
+	info, err := os.Stdin.Stat()
+	if err != nil || info.Mode()&fs.ModeSocket == 0 {
+		fmt.Fprintln(os.Stderr, "This is an internal command that is not intended for standard terminal usage")
+		os.Exit(1)
+	}
+
+	os.Exit(service())
+}
+
+func service() int {
+	defer os.Stdout.Close()
+	defer os.Stdin.Close()
+	defer os.Stderr.Close()
+	if len(os.Args) < 3 {
+		fmt.Print(fail)
+		return 1
+	}
+	target := os.Args[2]
+
+	request := make(chan bool)
+	go func() {
+		buf := make([]byte, 3)
+		_, err := io.ReadFull(os.Stdin, buf)
+		request <- err == nil && string(buf) == trigger
+	}()
+
+	valid := false
+	select {
+	case valid = <-request:
+	case <-time.After(5 * time.Second):
+	}
+
+	if !valid {
+		fmt.Println(fail)
+		return 2
+	}
+
+	err := os.Remove(dockerSock)
+	if err == nil || os.IsNotExist(err) {
+		err = os.Symlink(target, dockerSock)
+	}
+
+	if err != nil {
+		fmt.Print(fail)
+		return 3
+	}
+
+	fmt.Print(success)
+	return 0
+}
diff --git a/cmd/podman-mac-helper/uninstall.go b/cmd/podman-mac-helper/uninstall.go
new file mode 100644
index 000000000..f72d0efd1
--- /dev/null
+++ b/cmd/podman-mac-helper/uninstall.go
@@ -0,0 +1,60 @@
+//go:build darwin
+// +build darwin
+
+package main
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+
+	"github.com/pkg/errors"
+	"github.com/spf13/cobra"
+)
+
+var uninstallCmd = &cobra.Command{
+	Use:    "uninstall",
+	Short:  "uninstalls the podman helper agent",
+	Long:   "uninstalls the podman helper agent, which manages the /var/run/docker.sock link",
+	PreRun: silentUsage,
+	RunE:   uninstall,
+}
+
+func init() {
+	addPrefixFlag(uninstallCmd)
+	rootCmd.AddCommand(uninstallCmd)
+}
+
+func uninstall(cmd *cobra.Command, args []string) error {
+	userName, _, _, err := getUser()
+	if err != nil {
+		return err
+	}
+
+	labelName := fmt.Sprintf("com.github.containers.podman.helper-%s", userName)
+	fileName := filepath.Join("/Library", "LaunchDaemons", labelName+".plist")
+
+	if err = runDetectErr("launchctl", "unload", fileName); err != nil {
+		// Try removing the service by label in case the service is half uninstalled
+		if rerr := runDetectErr("launchctl", "remove", labelName); rerr != nil {
+			// Exit code 3 = no service to remove
+			if exitErr, ok := rerr.(*exec.ExitError); !ok || exitErr.ExitCode() != 3 {
+				fmt.Fprintf(os.Stderr, "Warning: service unloading failed: %s\n", err.Error())
+				fmt.Fprintf(os.Stderr, "Warning: remove also failed: %s\n", rerr.Error())
+			}
+		}
+	}
+
+	if err := os.Remove(fileName); err != nil {
+		if !os.IsNotExist(err) {
+			return errors.Errorf("could not remove plist file: %s", fileName)
+		}
+	}
+
+	helperPath := filepath.Join(installPrefix, "podman", "helper", userName)
+	if err := os.RemoveAll(helperPath); err != nil {
+		return errors.Errorf("could not remove helper binary path: %s", helperPath)
+	}
+	return nil
+}