[client, management] implement certificate posture check (#7535)

Co-authored-by: mlsmaycon <mlsmaycon@gmail.com>

client/internal/certproof/consoleuser_darwin.go

@@ -0,0 +1,113 @@
+package certproof
+
+import (
+	"bytes"
+	"fmt"
+	"sync"
+
+	"github.com/ebitengine/purego"
+	log "github.com/sirupsen/logrus"
+)
+
+const (
+	systemConfigurationFramework = "/System/Library/Frameworks/SystemConfiguration.framework/SystemConfiguration"
+
+	encodingUTF8       = 0x08000100
+	consoleNameBufSize = 256
+)
+
+var (
+	consoleOnce sync.Once
+	consoleErr  error
+
+	scDynamicStoreCopyConsoleUser func(store uintptr, uid, gid *uint32) uintptr
+	cfStringGetCString            func(str uintptr, buffer *byte, size int, encoding uint32) bool
+)
+
+// ConsoleUser is the account whose desktop session owns the display. Its login keychain
+// is the only user keychain a NetBird daemon can reach, and only while it is logged in.
+type ConsoleUser struct {
+	Name string
+	UID  uint32
+	GID  uint32
+}
+
+// CurrentConsoleUser reports the user sitting at the desktop. The second return value is
+// false when nobody is: at the login window macOS either reports no console user at all
+// or attributes the session to root, and neither has a login keychain to offer.
+func CurrentConsoleUser() (ConsoleUser, bool) {
+	if err := loadConsoleUser(); err != nil {
+		log.Infof("console user lookup unavailable: %v", err)
+		return ConsoleUser{}, false
+	}
+
+	var uid, gid uint32
+	name := scDynamicStoreCopyConsoleUser(0, &uid, &gid)
+	if name == 0 {
+		log.Info("no console user is logged in, no login keychain is reachable")
+		return ConsoleUser{}, false
+	}
+	defer cfRelease(name)
+
+	user := ConsoleUser{Name: cfString(name), UID: uid, GID: gid}
+	if !user.hasDesktop() {
+		log.Infof("console session belongs to %q uid=%d, which is not a desktop login, no login keychain is reachable", user.Name, user.UID)
+		return ConsoleUser{}, false
+	}
+	return user, true
+}
+
+// hasDesktop reports whether the console session is a real user desktop. The login
+// window runs as root and some macOS releases name it "loginwindow" instead.
+func (u ConsoleUser) hasDesktop() bool {
+	switch u.Name {
+	case "", "root", "loginwindow":
+		return false
+	}
+	return u.UID != 0
+}
+
+func cfString(str uintptr) string {
+	buf := make([]byte, consoleNameBufSize)
+	if !cfStringGetCString(str, &buf[0], len(buf), encodingUTF8) {
+		return ""
+	}
+	if end := bytes.IndexByte(buf, 0); end >= 0 {
+		return string(buf[:end])
+	}
+	return string(buf)
+}
+
+// loadConsoleUser resolves the console user symbols. It loads the keychain bindings
+// first because CFRelease is resolved there and released strings depend on it.
+func loadConsoleUser() error {
+	if err := loadKeychain(); err != nil {
+		return err
+	}
+	consoleOnce.Do(func() { consoleErr = resolveConsoleUser() })
+	return consoleErr
+}
+
+func resolveConsoleUser() error {
+	systemConfiguration, err := purego.Dlopen(systemConfigurationFramework, purego.RTLD_LAZY|purego.RTLD_GLOBAL)
+	if err != nil {
+		return fmt.Errorf("open %s: %w", systemConfigurationFramework, err)
+	}
+	coreFoundation, err := purego.Dlopen(coreFoundationFramework, purego.RTLD_LAZY|purego.RTLD_GLOBAL)
+	if err != nil {
+		return fmt.Errorf("open %s: %w", coreFoundationFramework, err)
+	}
+
+	symbol, err := purego.Dlsym(systemConfiguration, "SCDynamicStoreCopyConsoleUser")
+	if err != nil {
+		return fmt.Errorf("resolve SCDynamicStoreCopyConsoleUser: %w", err)
+	}
+	purego.RegisterFunc(&scDynamicStoreCopyConsoleUser, symbol)
+
+	symbol, err = purego.Dlsym(coreFoundation, "CFStringGetCString")
+	if err != nil {
+		return fmt.Errorf("resolve CFStringGetCString: %w", err)
+	}
+	purego.RegisterFunc(&cfStringGetCString, symbol)
+	return nil
+}