[client] Fail closed in InvokingUser when the sudo user lookup fails

A previous change made baseConfigDir fail closed when SUDO_USER cannot be
resolved, but InvokingUser still fell through to user.Current(). Those two
guards disagreed: the active-profile mirror and the email state refused to
read root's directory, while every profile-path caller happily resolved as
root.

The consequence of a transient NSS failure under sudo was that
Profile.FilePath resolved through getConfigDirForUser("root"), creating
/var/lib/netbird/root and reading the profile JSON from there, and the CLI
sent Username "root" to the daemon in SetConfig and ListProfiles, so the
daemon resolved the same phantom namespace. The invoking user was silently
moved onto a root-owned profile instead of being told the lookup failed.

Fail closed at the single source of the fallback. getConfigDirForUser is
left alone on purpose: it is a pure path helper that also serves
daemon-supplied usernames, and under sudo with a successful lookup it must
still create the invoking user's own profile directory.

client/internal/profilemanager/invoking_user.go

@@ -28,6 +28,13 @@ func InvokingUser() (*user.User, error) {
 	if u, ok := sudoInvokingUser(); ok {
 		return u, nil
 	}
+	// Fail closed instead of falling through to root: every caller feeds this
+	// username into profile-path resolution, so a lookup failure would resolve
+	// (and create) a root-owned profile namespace and switch the daemon onto it
+	// behind the invoking user's back.
+	if sudoActive() {
+		return nil, fmt.Errorf("resolve sudo invoking user %q: refusing to fall back to root", os.Getenv(envSudoUser))
+	}
 	return user.Current()
 }
 

client/internal/profilemanager/invoking_user_test.go

@@ -56,6 +56,30 @@ func TestSudoInvokingUserResolvesInvokingUser(t *testing.T) {
 	assert.False(t, IsPlainRoot())
 }
 
+func TestInvokingUserFailsClosedWhenSudoLookupFails(t *testing.T) {
+	fakeSudo(t, filepath.Join("/home", "misha"))
+	lookupUser = func(string) (*user.User, error) { return nil, errors.New("nss unavailable") }
+
+	got, err := InvokingUser()
+	require.Error(t, err)
+	assert.Nil(t, got, "must not resolve to the root process user")
+}
+
+func TestProfileFilePathFailsClosedWhenSudoLookupFails(t *testing.T) {
+	profilesRoot := t.TempDir()
+	fakeSudo(t, filepath.Join("/home", "misha"))
+	lookupUser = func(string) (*user.User, error) { return nil, errors.New("nss unavailable") }
+
+	origDir := DefaultConfigPathDir
+	DefaultConfigPathDir = profilesRoot
+	t.Cleanup(func() { DefaultConfigPathDir = origDir })
+
+	p := &Profile{ID: "0123456789abcdef0123456789abcdef"}
+	_, err := p.FilePath()
+	require.Error(t, err)
+	assertNoEntries(t, profilesRoot)
+}
+
 func TestSudoActiveSurvivesLookupFailure(t *testing.T) {
 	fakeSudo(t, filepath.Join("/home", "misha"))
 	lookupUser = func(string) (*user.User, error) { return nil, errors.New("nss unavailable") }