From e7ee15f8c39122e0d2b343ce9a3c0b577af45f40 Mon Sep 17 00:00:00 2001
From: flouthoc <flouthoc.git@gmail.com>
Date: Thu, 12 Aug 2021 18:48:39 +0530
Subject: cgroup-manager-systemd:Fail early if user:rootless and relevent
 session is not present.

[NO TESTS NEEDED]

Signed-off-by: flouthoc <flouthoc.git@gmail.com>
---
 libpod/runtime.go   | 10 ++++++
 pkg/systemd/dbus.go | 98 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 108 insertions(+)

diff --git a/libpod/runtime.go b/libpod/runtime.go
index 30659a3d4..1f403790f 100644
--- a/libpod/runtime.go
+++ b/libpod/runtime.go
@@ -30,6 +30,7 @@ import (
 	"github.com/containers/podman/v3/libpod/shutdown"
 	"github.com/containers/podman/v3/pkg/cgroups"
 	"github.com/containers/podman/v3/pkg/rootless"
+	"github.com/containers/podman/v3/pkg/systemd"
 	"github.com/containers/podman/v3/pkg/util"
 	"github.com/containers/storage"
 	"github.com/containers/storage/pkg/unshare"
@@ -500,6 +501,15 @@ func makeRuntime(ctx context.Context, runtime *Runtime) (retErr error) {
 		// no containers running.  Create immediately a namespace, as
 		// we will need to access the storage.
 		if needsUserns {
+			// warn users if mode is rootless and cgroup manager is systemd
+			// and no valid systemd session is present
+			// warn only whenever new namespace is created
+			if runtime.config.Engine.CgroupManager == config.SystemdCgroupsManager {
+				unified, _ := cgroups.IsCgroup2UnifiedMode()
+				if unified && rootless.IsRootless() && !systemd.IsSystemdSessionValid(rootless.GetRootlessUID()) {
+					logrus.Debug("Invalid systemd user session for current user")
+				}
+			}
 			aliveLock.Unlock() // Unlock to avoid deadlock as BecomeRootInUserNS will reexec.
 			pausePid, err := util.GetRootlessPauseProcessPidPathGivenDir(runtime.config.Engine.TmpDir)
 			if err != nil {
diff --git a/pkg/systemd/dbus.go b/pkg/systemd/dbus.go
index 718082526..c49f537b6 100644
--- a/pkg/systemd/dbus.go
+++ b/pkg/systemd/dbus.go
@@ -9,8 +9,106 @@ import (
 	"github.com/containers/podman/v3/pkg/rootless"
 	"github.com/coreos/go-systemd/v22/dbus"
 	godbus "github.com/godbus/dbus/v5"
+	"github.com/sirupsen/logrus"
 )
 
+// IsSystemdSessionValid checks if sessions is valid for provided rootless uid.
+func IsSystemdSessionValid(uid int) bool {
+	var conn *godbus.Conn
+	var err error
+	var object godbus.BusObject
+	var seat0Path godbus.ObjectPath
+	dbusDest := "org.freedesktop.login1"
+	dbusInterface := "org.freedesktop.login1.Manager"
+	dbusPath := "/org/freedesktop/login1"
+
+	if rootless.IsRootless() {
+		conn, err = GetLogindConnection(rootless.GetRootlessUID())
+		object = conn.Object(dbusDest, godbus.ObjectPath(dbusPath))
+		if err != nil {
+			//unable to fetch systemd object for logind
+			logrus.Debugf("systemd-logind: %s", err)
+			return false
+		}
+		object = conn.Object(dbusDest, godbus.ObjectPath(dbusPath))
+		if err := object.Call(dbusInterface+".GetSeat", 0, "seat0").Store(&seat0Path); err != nil {
+			//unable to get seat0 path.
+			logrus.Debugf("systemd-logind: %s", err)
+			return false
+		}
+		seat0Obj := conn.Object(dbusDest, seat0Path)
+		activeSession, err := seat0Obj.GetProperty(dbusDest + ".Seat.ActiveSession")
+		if err != nil {
+			//unable to get active sessions.
+			logrus.Debugf("systemd-logind: %s", err)
+			return false
+		}
+		activeSessionMap, ok := activeSession.Value().([]interface{})
+		if !ok || len(activeSessionMap) < 2 {
+			//unable to get active session map.
+			logrus.Debugf("systemd-logind: %s", err)
+			return false
+		}
+		activeSessionPath, ok := activeSessionMap[1].(godbus.ObjectPath)
+		if !ok {
+			//unable to fetch active session path.
+			logrus.Debugf("systemd-logind: %s", err)
+			return false
+		}
+		activeSessionObj := conn.Object(dbusDest, activeSessionPath)
+		sessionUser, err := activeSessionObj.GetProperty(dbusDest + ".Session.User")
+		if err != nil {
+			//unable to fetch session user from activeSession path.
+			logrus.Debugf("systemd-logind: %s", err)
+			return false
+		}
+		dbusUser, ok := sessionUser.Value().([]interface{})
+		if !ok {
+			// not a valid user.
+			return false
+		}
+		if len(dbusUser) < 2 {
+			// not a valid session user.
+			return false
+		}
+		activeUID, ok := dbusUser[0].(uint32)
+		if !ok {
+			return false
+		}
+		//active session found which belongs to following rootless user
+		if activeUID == uint32(uid) {
+			return true
+		}
+		return false
+	}
+	return true
+}
+
+// GetDbusConnection returns an user connection to D-BUS
+func GetLogindConnection(uid int) (*godbus.Conn, error) {
+	return dbusAuthConnectionLogind(uid)
+}
+
+func dbusAuthConnectionLogind(uid int) (*godbus.Conn, error) {
+	var conn *godbus.Conn
+	var err error
+	conn, err = godbus.SystemBusPrivate()
+	if err != nil {
+		return nil, err
+	}
+	methods := []godbus.Auth{godbus.AuthExternal(strconv.Itoa(uid))}
+	if err = conn.Auth(methods); err != nil {
+		conn.Close()
+		return nil, err
+	}
+	err = conn.Hello()
+	if err != nil {
+		conn.Close()
+		return nil, err
+	}
+	return conn, nil
+}
+
 func dbusAuthRootlessConnection(createBus func(opts ...godbus.ConnOption) (*godbus.Conn, error)) (*godbus.Conn, error) {
 	conn, err := createBus()
 	if err != nil {
-- 
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