rootless: enable linger if /run/user/UID not exists

at least on Fedora 30 it creates the /run/user/UID directory for the
user logged in via ssh.

This needs to be done very early so that every other check when we
create the default configuration file will point to the correct
location.

Closes: https://github.com/containers/libpod/issues/3410

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

cmd/podman/main.go

@@ -100,7 +100,7 @@ func initConfig() {
 }
 
 func before(cmd *cobra.Command, args []string) error {
-	if err := libpod.SetXdgRuntimeDir(""); err != nil {
+	if err := libpod.SetXdgRuntimeDir(); err != nil {
 		logrus.Errorf(err.Error())
 		os.Exit(1)
 	}

libpod/runtime.go

@@ -10,6 +10,7 @@ import (
 	"strings"
 	"sync"
 	"syscall"
+	"time"
 
 	"github.com/BurntSushi/toml"
 	is "github.com/containers/image/storage"
@@ -312,18 +313,39 @@ func defaultRuntimeConfig() (RuntimeConfig, error) {
 
 // SetXdgRuntimeDir ensures the XDG_RUNTIME_DIR env variable is set
 // containers/image uses XDG_RUNTIME_DIR to locate the auth file.
-func SetXdgRuntimeDir(val string) error {
+// It internally calls EnableLinger() so that the user's processes are not
+// killed once the session is terminated.  EnableLinger() also attempts to
+// get the runtime directory when XDG_RUNTIME_DIR is not specified.
+func SetXdgRuntimeDir() error {
 	if !rootless.IsRootless() {
 		return nil
 	}
-	if val == "" {
+
+	runtimeDir := os.Getenv("XDG_RUNTIME_DIR")
+
+	runtimeDirLinger, err := rootless.EnableLinger()
+	if err != nil {
+		return errors.Wrapf(err, "error enabling user session")
+	}
+	if runtimeDir == "" && runtimeDirLinger != "" {
+		if _, err := os.Stat(runtimeDirLinger); err != nil && os.IsNotExist(err) {
+			chWait := make(chan error)
+			defer close(chWait)
+			if _, err := WaitForFile(runtimeDirLinger, chWait, time.Second*10); err != nil {
+				return errors.Wrapf(err, "waiting for directory '%s'", runtimeDirLinger)
+			}
+		}
+		runtimeDir = runtimeDirLinger
+	}
+
+	if runtimeDir == "" {
 		var err error
-		val, err = util.GetRootlessRuntimeDir()
+		runtimeDir, err = util.GetRootlessRuntimeDir()
 		if err != nil {
 			return err
 		}
 	}
-	if err := os.Setenv("XDG_RUNTIME_DIR", val); err != nil {
+	if err := os.Setenv("XDG_RUNTIME_DIR", runtimeDir); err != nil {
 		return errors.Wrapf(err, "cannot set XDG_RUNTIME_DIR")
 	}
 	return nil
@@ -479,18 +501,6 @@ func newRuntimeFromConfig(ctx context.Context, userConfigPath string, options ..
 				runtime.config.SignaturePolicyPath = newPath
 			}
 		}
-
-		runtimeDir, err := util.GetRootlessRuntimeDir()
-		if err != nil {
-			return nil, err
-		}
-
-		// containers/image uses XDG_RUNTIME_DIR to locate the auth file.
-		// So make sure the env variable is set.
-		if err := SetXdgRuntimeDir(runtimeDir); err != nil {
-			return nil, errors.Wrapf(err, "cannot set XDG_RUNTIME_DIR")
-		}
-
 	}
 
 	if userConfigPath != "" {

pkg/rootless/rootless_linux.go

@@ -9,14 +9,17 @@ import (
 	"os/exec"
 	gosignal "os/signal"
 	"os/user"
+	"path/filepath"
 	"runtime"
 	"strconv"
+	"strings"
 	"sync"
 	"syscall"
 	"unsafe"
 
 	"github.com/containers/storage/pkg/idtools"
 	"github.com/docker/docker/pkg/signal"
+	"github.com/godbus/dbus"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
 )
@@ -198,24 +201,90 @@ func getUserNSFirstChild(fd uintptr) (*os.File, error) {
 	}
 }
 
-func enableLinger(pausePid string) {
-	if pausePid == "" {
-		return
+// EnableLinger configures the system to not kill the user processes once the session
+// terminates
+func EnableLinger() (string, error) {
+	uid := fmt.Sprintf("%d", GetRootlessUID())
+
+	conn, err := dbus.SystemBus()
+	if err == nil {
+		defer conn.Close()
 	}
-	// If we are trying to write a pause pid file, make sure we can leave processes
-	// running longer than the user session.
-	err := exec.Command("loginctl", "enable-linger", fmt.Sprintf("%d", GetRootlessUID())).Run()
+
+	lingerEnabled := false
+
+	// If we have a D-BUS connection, attempt to read the LINGER property from it.
+	if conn != nil {
+		path := dbus.ObjectPath((fmt.Sprintf("/org/freedesktop/login1/user/_%s", uid)))
+		ret, err := conn.Object("org.freedesktop.login1", path).GetProperty("org.freedesktop.login1.User.Linger")
+		if err == nil && ret.Value().(bool) {
+			lingerEnabled = true
+		}
+	}
+
+	xdgRuntimeDir := os.Getenv("XDG_RUNTIME_DIR")
+	lingerFile := ""
+	if xdgRuntimeDir != "" && !lingerEnabled {
+		lingerFile = filepath.Join(xdgRuntimeDir, "libpod/linger")
+		_, err := os.Stat(lingerFile)
+		if err == nil {
+			lingerEnabled = true
+		}
+	}
+
+	if !lingerEnabled {
+		// First attempt with D-BUS, if it fails, then attempt with "loginctl enable-linger"
+		if conn != nil {
+			o := conn.Object("org.freedesktop.login1", "/org/freedesktop/login1")
+			ret := o.Call("org.freedesktop.login1.Manager.SetUserLinger", 0, uint32(GetRootlessUID()), true, true)
+			if ret.Err == nil {
+				lingerEnabled = true
+			}
+		}
+		if !lingerEnabled {
+			err := exec.Command("loginctl", "enable-linger", uid).Run()
+			if err == nil {
+				lingerEnabled = true
+			} else {
+				logrus.Debugf("cannot run `loginctl enable-linger` for the current user: %v", err)
+			}
+		}
+		if lingerEnabled && lingerFile != "" {
+			f, err := os.Create(lingerFile)
+			if err == nil {
+				f.Close()
+			} else {
+				logrus.Debugf("could not create linger file: %v", err)
+			}
+		}
+	}
+
+	if !lingerEnabled {
+		return "", nil
+	}
+
+	// If we have a D-BUS connection, attempt to read the RUNTIME PATH from it.
+	if conn != nil {
+		path := dbus.ObjectPath((fmt.Sprintf("/org/freedesktop/login1/user/_%s", uid)))
+		ret, err := conn.Object("org.freedesktop.login1", path).GetProperty("org.freedesktop.login1.User.RuntimePath")
+		if err == nil {
+			return strings.Trim(ret.String(), "\"\n"), nil
+		}
+	}
+
+	// If XDG_RUNTIME_DIR is not set and the D-BUS call didn't work, try to get the runtime path with "loginctl"
+	output, err := exec.Command("loginctl", "-pRuntimePath", "show-user", uid).Output()
 	if err != nil {
-		logrus.Warnf("cannot run `loginctl enable-linger` for the current user: %v", err)
+		logrus.Debugf("could not get RuntimePath using loginctl: %v", err)
+		return "", nil
 	}
+	return strings.Trim(strings.Replace(string(output), "RuntimePath=", "", -1), "\"\n"), nil
 }
 
 // joinUserAndMountNS re-exec podman in a new userNS and join the user and mount
 // namespace of the specified PID without looking up its parent.  Useful to join directly
 // the conmon process.
 func joinUserAndMountNS(pid uint, pausePid string) (bool, int, error) {
-	enableLinger(pausePid)
-
 	if os.Geteuid() == 0 || os.Getenv("_CONTAINERS_USERNS_CONFIGURED") != "" {
 		return false, -1, nil
 	}
@@ -406,7 +475,6 @@ func becomeRootInUserNS(pausePid, fileToRead string, fileOutput *os.File) (bool,
 // If podman was re-executed the caller needs to propagate the error code returned by the child
 // process.
 func BecomeRootInUserNS(pausePid string) (bool, int, error) {
-	enableLinger(pausePid)
 	return becomeRootInUserNS(pausePid, "", nil)
 }
 

pkg/rootless/rootless_unsupported.go

@@ -29,6 +29,12 @@ func GetRootlessGID() int {
 	return -1
 }
 
+// EnableLinger configures the system to not kill the user processes once the session
+// terminates
+func EnableLinger() (string, error) {
+	return "", nil
+}
+
 // TryJoinFromFilePaths attempts to join the namespaces of the pid files in paths.
 // This is useful when there are already running containers and we
 // don't have a pause process yet.  We can use the paths to the conmon