netbird/client/internal/certproof/collect_darwin.go

//go:build !ios

package certproof

import (
	"context"
	"errors"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"strconv"
	"time"

	log "github.com/sirupsen/logrus"

	"github.com/netbirdio/netbird/shared/management/certposture"
	"github.com/netbirdio/netbird/shared/management/proto"
)

const helperTimeout = 30 * time.Second

// userHelperBackoff holds off asking a user's keychain again after it proved nothing.
var userHelperBackoff = newHelperBackoff()

// CollectProofs answers the certificate challenges in checks from every store this Mac
// can reach. The root daemon reads the System keychain itself, which is where MDM
// installs device identities, and reaches the console user's login keychain only by
// launching a helper into that user's session. A Mac sitting at the login window
// therefore yields device proofs alone.
func CollectProofs(ctx context.Context, checks []*proto.Checks, peerKey []byte, cfg Config) []certposture.Proof {
	challenges := certificateChallenges(checks)
	if len(challenges) == 0 {
		logNoChallenges(checks)
		return nil
	}

	// A helper already runs inside the user's session, so it reads its own keychain
	// directly and must never launch another one.
	if os.Geteuid() != 0 {
		return CollectChallenges(ctx, DefaultStore(), challenges, peerKey)
	}

	proofs := CollectChallenges(ctx, DefaultStore(), challenges, peerKey)
	if cfg.OwnerUnknown {
		return proofs
	}

	userProofs, err := collectAsConsoleUser(ctx, cfg.ProfileOwner, challenges, peerKey)
	if err != nil {
		log.Debugf("certificate posture: console user keychain unavailable: %v", err)
	}
	return mergeProofs(proofs, userProofs)
}

// UserContext identifies the user whose keychain a collection would include: the console
// user when it owns the active profile, or empty when no user keychain would be asked. A
// change means a collection made earlier no longer reflects what this Mac can prove.
func UserContext(cfg Config) string {
	if os.Geteuid() != 0 || cfg.OwnerUnknown {
		return ""
	}
	user, ok := currentConsoleUser()
	if !ok || !user.isOwner(cfg.ProfileOwner) {
		return ""
	}
	return strconv.FormatUint(uint64(user.UID), 10) + ":" + user.Name
}

// collectAsConsoleUser runs the helper inside the desktop session of the logged-in
// user. Dropping to their uid is not enough: keychain access is an XPC call to a
// per-session securityd, so the helper has to enter their Mach bootstrap namespace,
// which is what launchctl asuser does.
func collectAsConsoleUser(ctx context.Context, owner string, challenges []*proto.CertificateChallenge, peerKey []byte) ([]certposture.Proof, error) {
	user, ok := currentConsoleUser()
	if !ok {
		return nil, nil
	}
	if !user.isOwner(owner) {
		log.Debugf("certificate posture: console user %s does not own the active profile, no user keychain is asked", user.Name)
		return nil, nil
	}

	uid := strconv.FormatUint(uint64(user.UID), 10)
	backoffKey := helperBackoffKey(uid, challenges)
	if !userHelperBackoff.allow(backoffKey, time.Now()) {
		log.Debugf("certificate posture: the keychain of uid %s proved nothing recently, not asking again yet", uid)
		return nil, nil
	}

	binary, err := os.Executable()
	if err != nil {
		return nil, fmt.Errorf("resolve own binary: %w", err)
	}

	parent := ctx
	ctx, cancel := context.WithTimeout(ctx, helperTimeout)
	defer cancel()

	// Absolute paths, because the daemon's PATH is configurable through the service
	// environment, and sudo selects the user by uid so the name never has to round-trip.
	cmd := exec.CommandContext(ctx, "/bin/launchctl", "asuser", uid, "/usr/bin/sudo", "-u", "#"+uid, "-H", "--", binary, "posture", "cert-proof")
	killHelperGroupOnCancel(cmd)

	log.Debugf("certificate posture: asking the desktop session of uid %s to answer %d challenges", uid, len(challenges))
	proofs, err := runHelperCmd(cmd, helperRequest(challenges, peerKey))
	// A run that completed, or ran into the timeout waiting on a prompt nobody answered,
	// tells whether the keychain proves anything. A launch or output failure, or a run the
	// caller cut short, says nothing about it and must not hold off the next one.
	timedOut := errors.Is(ctx.Err(), context.DeadlineExceeded) && parent.Err() == nil
	if err == nil || timedOut {
		userHelperBackoff.record(backoffKey, err == nil && len(proofs) > 0, time.Now())
	}
	if err != nil {
		return nil, fmt.Errorf("run helper as uid %s: %w", uid, err)
	}
	log.Debugf("certificate posture: desktop session of uid %s returned %d proofs", uid, len(proofs))
	return proofs, nil
}

// helperStore is the store the helper reads: the user's login keychain alone. The
// session's search list also holds the System keychain, which the daemon reads itself,
// and using a System keychain key from the user's session would ask for an
// administrator's approval.
func helperStore() Store {
	home, err := os.UserHomeDir()
	if err != nil {
		log.Debugf("certificate posture: no home directory, searching the default keychain list: %v", err)
		return newKeychainStore()
	}
	login := filepath.Join(home, "Library", "Keychains", "login.keychain-db")
	if _, err := os.Stat(login); err != nil {
		// Keychains created before macOS 10.12 keep the old file name.
		login = filepath.Join(home, "Library", "Keychains", "login.keychain")
	}
	return newKeychainStore(login)
}