Merge pull request #3865 from poettering/remove-ipc

add RemoveIPC= service file setting

24 files changed, 1029 insertions, 162 deletions

diff --git a/src/core/dbus-execute.c b/src/core/dbus-execute.c
index e35d3ccd2e..7e33a2d201 100644
--- a/src/core/dbus-execute.c
+++ b/src/core/dbus-execute.c
@@ -695,6 +695,7 @@ const sd_bus_vtable bus_exec_vtable[] = {
         SD_BUS_PROPERTY("User", "s", NULL, offsetof(ExecContext, user), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("Group", "s", NULL, offsetof(ExecContext, group), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("DynamicUser", "b", bus_property_get_bool, offsetof(ExecContext, dynamic_user), SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("RemoveIPC", "b", bus_property_get_bool, offsetof(ExecContext, remove_ipc), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("SupplementaryGroups", "as", NULL, offsetof(ExecContext, supplementary_groups), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("PAMName", "s", NULL, offsetof(ExecContext, pam_name), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("ReadWriteDirectories", "as", NULL, offsetof(ExecContext, read_write_paths), SD_BUS_VTABLE_PROPERTY_CONST|SD_BUS_VTABLE_HIDDEN),
@@ -1071,7 +1072,7 @@ int bus_exec_context_set_transient_property(
                               "IgnoreSIGPIPE", "TTYVHangup", "TTYReset",
                               "PrivateTmp", "PrivateDevices", "PrivateNetwork", "PrivateUsers",
                               "NoNewPrivileges", "SyslogLevelPrefix", "MemoryDenyWriteExecute",
-                              "RestrictRealtime", "DynamicUser")) {
+                              "RestrictRealtime", "DynamicUser", "RemoveIPC")) {
                 int b;
 
                 r = sd_bus_message_read(message, "b", &b);
@@ -1103,6 +1104,8 @@ int bus_exec_context_set_transient_property(
                                 c->restrict_realtime = b;
                         else if (streq(name, "DynamicUser"))
                                 c->dynamic_user = b;
+                        else if (streq(name, "RemoveIPC"))
+                                c->remove_ipc = b;
 
                         unit_write_drop_in_private_format(u, mode, name, "%s=%s", name, yes_no(b));
                 }
diff --git a/src/core/dbus-mount.c b/src/core/dbus-mount.c
index b4bbee0648..3c6bda4073 100644
--- a/src/core/dbus-mount.c
+++ b/src/core/dbus-mount.c
@@ -117,6 +117,8 @@ const sd_bus_vtable bus_mount_vtable[] = {
         SD_BUS_PROPERTY("DirectoryMode", "u", bus_property_get_mode, offsetof(Mount, directory_mode), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("SloppyOptions", "b", bus_property_get_bool, offsetof(Mount, sloppy_options), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("Result", "s", property_get_result, offsetof(Mount, result), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
+        SD_BUS_PROPERTY("UID", "u", NULL, offsetof(Unit, ref_uid), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
+        SD_BUS_PROPERTY("GID", "u", NULL, offsetof(Unit, ref_gid), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         BUS_EXEC_COMMAND_VTABLE("ExecMount", offsetof(Mount, exec_command[MOUNT_EXEC_MOUNT]), SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION),
         BUS_EXEC_COMMAND_VTABLE("ExecUnmount", offsetof(Mount, exec_command[MOUNT_EXEC_UNMOUNT]), SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION),
         BUS_EXEC_COMMAND_VTABLE("ExecRemount", offsetof(Mount, exec_command[MOUNT_EXEC_REMOUNT]), SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION),
diff --git a/src/core/dbus-service.c b/src/core/dbus-service.c
index fab3677a01..3c55e0f7fe 100644
--- a/src/core/dbus-service.c
+++ b/src/core/dbus-service.c
@@ -50,11 +50,6 @@ const sd_bus_vtable bus_service_vtable[] = {
         SD_BUS_PROPERTY("RuntimeMaxUSec", "t", bus_property_get_usec, offsetof(Service, runtime_max_usec), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("WatchdogUSec", "t", bus_property_get_usec, offsetof(Service, watchdog_usec), SD_BUS_VTABLE_PROPERTY_CONST),
         BUS_PROPERTY_DUAL_TIMESTAMP("WatchdogTimestamp", offsetof(Service, watchdog_timestamp), 0),
-        /* The following four are obsolete, and thus marked hidden here. They moved into the Unit interface */
-        SD_BUS_PROPERTY("StartLimitInterval", "t", bus_property_get_usec, offsetof(Unit, start_limit.interval), SD_BUS_VTABLE_PROPERTY_CONST|SD_BUS_VTABLE_HIDDEN),
-        SD_BUS_PROPERTY("StartLimitBurst", "u", bus_property_get_unsigned, offsetof(Unit, start_limit.burst), SD_BUS_VTABLE_PROPERTY_CONST|SD_BUS_VTABLE_HIDDEN),
-        SD_BUS_PROPERTY("StartLimitAction", "s", property_get_failure_action, offsetof(Unit, start_limit_action), SD_BUS_VTABLE_PROPERTY_CONST|SD_BUS_VTABLE_HIDDEN),
-        SD_BUS_PROPERTY("RebootArgument", "s", NULL, offsetof(Unit, reboot_arg), SD_BUS_VTABLE_PROPERTY_CONST|SD_BUS_VTABLE_HIDDEN),
         SD_BUS_PROPERTY("FailureAction", "s", property_get_failure_action, offsetof(Service, failure_action), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("PermissionsStartOnly", "b", bus_property_get_bool, offsetof(Service, permissions_start_only), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("RootDirectoryStartOnly", "b", bus_property_get_bool, offsetof(Service, root_directory_start_only), SD_BUS_VTABLE_PROPERTY_CONST),
@@ -70,6 +65,9 @@ const sd_bus_vtable bus_service_vtable[] = {
         SD_BUS_PROPERTY("Result", "s", property_get_result, offsetof(Service, result), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         SD_BUS_PROPERTY("USBFunctionDescriptors", "s", NULL, offsetof(Service, usb_function_descriptors), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         SD_BUS_PROPERTY("USBFunctionStrings", "s", NULL, offsetof(Service, usb_function_strings), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
+        SD_BUS_PROPERTY("UID", "u", NULL, offsetof(Unit, ref_uid), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
+        SD_BUS_PROPERTY("GID", "u", NULL, offsetof(Unit, ref_gid), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
+
         BUS_EXEC_STATUS_VTABLE("ExecMain", offsetof(Service, main_exec_status), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         BUS_EXEC_COMMAND_LIST_VTABLE("ExecStartPre", offsetof(Service, exec_command[SERVICE_EXEC_START_PRE]), SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION),
         BUS_EXEC_COMMAND_LIST_VTABLE("ExecStart", offsetof(Service, exec_command[SERVICE_EXEC_START]), SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION),
@@ -77,6 +75,12 @@ const sd_bus_vtable bus_service_vtable[] = {
         BUS_EXEC_COMMAND_LIST_VTABLE("ExecReload", offsetof(Service, exec_command[SERVICE_EXEC_RELOAD]), SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION),
         BUS_EXEC_COMMAND_LIST_VTABLE("ExecStop", offsetof(Service, exec_command[SERVICE_EXEC_STOP]), SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION),
         BUS_EXEC_COMMAND_LIST_VTABLE("ExecStopPost", offsetof(Service, exec_command[SERVICE_EXEC_STOP_POST]), SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION),
+
+        /* The following four are obsolete, and thus marked hidden here. They moved into the Unit interface */
+        SD_BUS_PROPERTY("StartLimitInterval", "t", bus_property_get_usec, offsetof(Unit, start_limit.interval), SD_BUS_VTABLE_PROPERTY_CONST|SD_BUS_VTABLE_HIDDEN),
+        SD_BUS_PROPERTY("StartLimitBurst", "u", bus_property_get_unsigned, offsetof(Unit, start_limit.burst), SD_BUS_VTABLE_PROPERTY_CONST|SD_BUS_VTABLE_HIDDEN),
+        SD_BUS_PROPERTY("StartLimitAction", "s", property_get_failure_action, offsetof(Unit, start_limit_action), SD_BUS_VTABLE_PROPERTY_CONST|SD_BUS_VTABLE_HIDDEN),
+        SD_BUS_PROPERTY("RebootArgument", "s", NULL, offsetof(Unit, reboot_arg), SD_BUS_VTABLE_PROPERTY_CONST|SD_BUS_VTABLE_HIDDEN),
         SD_BUS_VTABLE_END
 };
 
diff --git a/src/core/dbus-socket.c b/src/core/dbus-socket.c
index 9a071a1355..21adb64e15 100644
--- a/src/core/dbus-socket.c
+++ b/src/core/dbus-socket.c
@@ -152,6 +152,8 @@ const sd_bus_vtable bus_socket_vtable[] = {
         SD_BUS_PROPERTY("SocketProtocol", "i", bus_property_get_int, offsetof(Socket, socket_protocol), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("TriggerLimitIntervalUSec", "t", bus_property_get_usec, offsetof(Socket, trigger_limit.interval), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("TriggerLimitBurst", "u", bus_property_get_unsigned, offsetof(Socket, trigger_limit.burst), SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("UID", "u", NULL, offsetof(Unit, ref_uid), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
+        SD_BUS_PROPERTY("GID", "u", NULL, offsetof(Unit, ref_gid), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         BUS_EXEC_COMMAND_LIST_VTABLE("ExecStartPre", offsetof(Socket, exec_command[SOCKET_EXEC_START_PRE]), SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION),
         BUS_EXEC_COMMAND_LIST_VTABLE("ExecStartPost", offsetof(Socket, exec_command[SOCKET_EXEC_START_POST]), SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION),
         BUS_EXEC_COMMAND_LIST_VTABLE("ExecStopPre", offsetof(Socket, exec_command[SOCKET_EXEC_STOP_PRE]), SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION),
diff --git a/src/core/dbus-swap.c b/src/core/dbus-swap.c
index 292f8738c6..85a2c26b98 100644
--- a/src/core/dbus-swap.c
+++ b/src/core/dbus-swap.c
@@ -84,6 +84,8 @@ const sd_bus_vtable bus_swap_vtable[] = {
         SD_BUS_PROPERTY("TimeoutUSec", "t", bus_property_get_usec, offsetof(Swap, timeout_usec), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("ControlPID", "u", bus_property_get_pid, offsetof(Swap, control_pid), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         SD_BUS_PROPERTY("Result", "s", property_get_result, offsetof(Swap, result), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
+        SD_BUS_PROPERTY("UID", "u", NULL, offsetof(Unit, ref_uid), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
+        SD_BUS_PROPERTY("GID", "u", NULL, offsetof(Unit, ref_gid), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         BUS_EXEC_COMMAND_VTABLE("ExecActivate", offsetof(Swap, exec_command[SWAP_EXEC_ACTIVATE]), SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION),
         BUS_EXEC_COMMAND_VTABLE("ExecDeactivate", offsetof(Swap, exec_command[SWAP_EXEC_DEACTIVATE]), SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION),
         SD_BUS_VTABLE_END
diff --git a/src/core/dbus-unit.c b/src/core/dbus-unit.c
index b55d2cf735..89e56a2e51 100644
--- a/src/core/dbus-unit.c
+++ b/src/core/dbus-unit.c
@@ -660,10 +660,6 @@ const sd_bus_vtable bus_unit_vtable[] = {
         SD_BUS_PROPERTY("PropagatesReloadTo", "as", property_get_dependencies, offsetof(Unit, dependencies[UNIT_PROPAGATES_RELOAD_TO]), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("ReloadPropagatedFrom", "as", property_get_dependencies, offsetof(Unit, dependencies[UNIT_RELOAD_PROPAGATED_FROM]), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("JoinsNamespaceOf", "as", property_get_dependencies, offsetof(Unit, dependencies[UNIT_JOINS_NAMESPACE_OF]), SD_BUS_VTABLE_PROPERTY_CONST),
-        SD_BUS_PROPERTY("RequiresOverridable", "as", property_get_obsolete_dependencies, 0, SD_BUS_VTABLE_HIDDEN),
-        SD_BUS_PROPERTY("RequisiteOverridable", "as", property_get_obsolete_dependencies, 0, SD_BUS_VTABLE_HIDDEN),
-        SD_BUS_PROPERTY("RequiredByOverridable", "as", property_get_obsolete_dependencies, 0, SD_BUS_VTABLE_HIDDEN),
-        SD_BUS_PROPERTY("RequisiteOfOverridable", "as", property_get_obsolete_dependencies, 0, SD_BUS_VTABLE_HIDDEN),
         SD_BUS_PROPERTY("RequiresMountsFor", "as", NULL, offsetof(Unit, requires_mounts_for), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("Documentation", "as", NULL, offsetof(Unit, documentation), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("Description", "s", property_get_description, 0, SD_BUS_VTABLE_PROPERTY_CONST),
@@ -705,7 +701,6 @@ const sd_bus_vtable bus_unit_vtable[] = {
         SD_BUS_PROPERTY("LoadError", "(ss)", property_get_load_error, 0, SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("Transient", "b", bus_property_get_bool, offsetof(Unit, transient), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("StartLimitIntervalSec", "t", bus_property_get_usec, offsetof(Unit, start_limit.interval), SD_BUS_VTABLE_PROPERTY_CONST),
-        SD_BUS_PROPERTY("StartLimitInterval", "t", bus_property_get_usec, offsetof(Unit, start_limit.interval), SD_BUS_VTABLE_PROPERTY_CONST|SD_BUS_VTABLE_HIDDEN), /* obsolete alias name */
         SD_BUS_PROPERTY("StartLimitBurst", "u", bus_property_get_unsigned, offsetof(Unit, start_limit.burst), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("StartLimitAction", "s", property_get_failure_action, offsetof(Unit, start_limit_action), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("RebootArgument", "s", NULL, offsetof(Unit, reboot_arg), SD_BUS_VTABLE_PROPERTY_CONST),
@@ -721,6 +716,12 @@ const sd_bus_vtable bus_unit_vtable[] = {
         SD_BUS_METHOD("ResetFailed", NULL, NULL, bus_unit_method_reset_failed, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("SetProperties", "ba(sv)", NULL, bus_unit_method_set_properties, SD_BUS_VTABLE_UNPRIVILEGED),
 
+        /* Obsolete properties or obsolete alias names */
+        SD_BUS_PROPERTY("RequiresOverridable", "as", property_get_obsolete_dependencies, 0, SD_BUS_VTABLE_HIDDEN),
+        SD_BUS_PROPERTY("RequisiteOverridable", "as", property_get_obsolete_dependencies, 0, SD_BUS_VTABLE_HIDDEN),
+        SD_BUS_PROPERTY("RequiredByOverridable", "as", property_get_obsolete_dependencies, 0, SD_BUS_VTABLE_HIDDEN),
+        SD_BUS_PROPERTY("RequisiteOfOverridable", "as", property_get_obsolete_dependencies, 0, SD_BUS_VTABLE_HIDDEN),
+        SD_BUS_PROPERTY("StartLimitInterval", "t", bus_property_get_usec, offsetof(Unit, start_limit.interval), SD_BUS_VTABLE_PROPERTY_CONST|SD_BUS_VTABLE_HIDDEN),
         SD_BUS_VTABLE_END
 };
 
diff --git a/src/core/dynamic-user.c b/src/core/dynamic-user.c
index 8035bee231..185d0e5f00 100644
--- a/src/core/dynamic-user.c
+++ b/src/core/dynamic-user.c
@@ -150,6 +150,42 @@ int dynamic_user_acquire(Manager *m, const char *name, DynamicUser** ret) {
         return 1;
 }
 
+static int make_uid_symlinks(uid_t uid, const char *name, bool b) {
+
+        char path1[strlen("/run/systemd/dynamic-uid/direct:") + DECIMAL_STR_MAX(uid_t) + 1];
+        const char *path2;
+        int r = 0;
+
+        /* Add direct additional symlinks for direct lookups of dynamic UIDs and their names by userspace code. The
+         * only reason we have this is because dbus-daemon cannot use D-Bus for resolving users and groups (since it
+         * would be its own client then). We hence keep these world-readable symlinks in place, so that the
+         * unprivileged dbus user can read the mappings when it needs them via these symlinks instead of having to go
+         * via the bus. Ideally, we'd use the lock files we keep for this anyway, but we can't since we use BSD locks
+         * on them and as those may be taken by any user with read access we can't make them world-readable. */
+
+        xsprintf(path1, "/run/systemd/dynamic-uid/direct:" UID_FMT, uid);
+        if (unlink(path1) < 0) {
+                if (errno != ENOENT)
+                        r = -errno;
+        }
+        if (b) {
+                if (symlink(name, path1) < 0)
+                        r = -errno;
+        }
+
+        path2 = strjoina("/run/systemd/dynamic-uid/direct:", name);
+        if (unlink(path2) < 0) {
+                if (errno != ENOENT)
+                        r = -errno;
+        }
+        if (b) {
+                if (symlink(path1 + strlen("/run/systemd/dynamic-uid/direct:"), path2) < 0)
+                        r = -errno;
+        }
+
+        return r;
+}
+
 static int pick_uid(const char *name, uid_t *ret_uid) {
 
         static const uint8_t hash_key[] = {
@@ -223,6 +259,7 @@ static int pick_uid(const char *name, uid_t *ret_uid) {
                 }
 
                 (void) ftruncate(lock_fd, l);
+                (void) make_uid_symlinks(candidate, name, true); /* also add direct lookup symlinks */
 
                 *ret_uid = candidate;
                 r = lock_fd;
@@ -324,14 +361,16 @@ static int dynamic_user_push(DynamicUser *d, uid_t uid, int lock_fd) {
         return 0;
 }
 
-static void unlink_uid_lock(int lock_fd, uid_t uid) {
+static void unlink_uid_lock(int lock_fd, uid_t uid, const char *name) {
         char lock_path[strlen("/run/systemd/dynamic-uid/") + DECIMAL_STR_MAX(uid_t) + 1];
 
         if (lock_fd < 0)
                 return;
 
         xsprintf(lock_path, "/run/systemd/dynamic-uid/" UID_FMT, uid);
-        (void) unlink_noerrno(lock_path);
+        (void) unlink(lock_path);
+
+        (void) make_uid_symlinks(uid, name, false); /* remove direct lookup symlinks */
 }
 
 int dynamic_user_realize(DynamicUser *d, uid_t *ret) {
@@ -399,7 +438,7 @@ int dynamic_user_realize(DynamicUser *d, uid_t *ret) {
 
                 /* So, we found a working UID/lock combination. Let's see if we actually still need it. */
                 if (lockf(d->storage_socket[0], F_LOCK, 0) < 0) {
-                        unlink_uid_lock(uid_lock_fd, uid);
+                        unlink_uid_lock(uid_lock_fd, uid, d->name);
                         return -errno;
                 }
 
@@ -407,7 +446,7 @@ int dynamic_user_realize(DynamicUser *d, uid_t *ret) {
                 if (r < 0) {
                         if (r != -EAGAIN) {
                                 /* OK, something bad happened, let's get rid of the bits we acquired. */
-                                unlink_uid_lock(uid_lock_fd, uid);
+                                unlink_uid_lock(uid_lock_fd, uid, d->name);
                                 goto finish;
                         }
 
@@ -416,7 +455,7 @@ int dynamic_user_realize(DynamicUser *d, uid_t *ret) {
                         /* Hmm, so as it appears there's now something stored in the storage socket. Throw away what we
                          * acquired, and use what's stored now. */
 
-                        unlink_uid_lock(uid_lock_fd, uid);
+                        unlink_uid_lock(uid_lock_fd, uid, d->name);
                         safe_close(uid_lock_fd);
 
                         uid = new_uid;
@@ -513,7 +552,7 @@ static int dynamic_user_close(DynamicUser *d) {
                 goto finish;
 
         /* This dynamic user was realized and dynamically allocated. In this case, let's remove the lock file. */
-        unlink_uid_lock(lock_fd, uid);
+        unlink_uid_lock(lock_fd, uid, d->name);
         r = 1;
 
 finish:
diff --git a/src/core/execute.c b/src/core/execute.c
index 6019df7ea6..0af8eb5a02 100644
--- a/src/core/execute.c
+++ b/src/core/execute.c
@@ -91,6 +91,7 @@
 #include "selinux-util.h"
 #include "signal-util.h"
 #include "smack-util.h"
+#include "special.h"
 #include "string-table.h"
 #include "string-util.h"
 #include "strv.h"
@@ -1384,6 +1385,7 @@ static void do_idle_pipe_dance(int idle_pipe[4]) {
 }
 
 static int build_environment(
+                Unit *u,
                 const ExecContext *c,
                 const ExecParameters *p,
                 unsigned n_fds,
@@ -1401,7 +1403,7 @@ static int build_environment(
         assert(c);
         assert(ret);
 
-        our_env = new0(char*, 12);
+        our_env = new0(char*, 13);
         if (!our_env)
                 return -ENOMEM;
 
@@ -1436,6 +1438,16 @@ static int build_environment(
                 our_env[n_env++] = x;
         }
 
+        /* If this is D-Bus, tell the nss-systemd module, since it relies on being able to use D-Bus look up dynamic
+         * users via PID 1, possibly dead-locking the dbus daemon. This way it will not use D-Bus to resolve names, but
+         * check the database directly. */
+        if (unit_has_name(u, SPECIAL_DBUS_SERVICE)) {
+                x = strdup("SYSTEMD_NSS_BYPASS_BUS=1");
+                if (!x)
+                        return -ENOMEM;
+                our_env[n_env++] = x;
+        }
+
         if (home) {
                 x = strappend("HOME=", home);
                 if (!x)
@@ -1723,11 +1735,12 @@ static int close_remaining_fds(
                 const ExecParameters *params,
                 ExecRuntime *runtime,
                 DynamicCreds *dcreds,
+                int user_lookup_fd,
                 int socket_fd,
                 int *fds, unsigned n_fds) {
 
         unsigned n_dont_close = 0;
-        int dont_close[n_fds + 11];
+        int dont_close[n_fds + 12];
 
         assert(params);
 
@@ -1755,9 +1768,40 @@ static int close_remaining_fds(
                         append_socket_pair(dont_close, &n_dont_close, dcreds->group->storage_socket);
         }
 
+        if (user_lookup_fd >= 0)
+                dont_close[n_dont_close++] = user_lookup_fd;
+
         return close_all_fds(dont_close, n_dont_close);
 }
 
+static int send_user_lookup(
+                Unit *unit,
+                int user_lookup_fd,
+                uid_t uid,
+                gid_t gid) {
+
+        assert(unit);
+
+        /* Send the resolved UID/GID to PID 1 after we learnt it. We send a single datagram, containing the UID/GID
+         * data as well as the unit name. Note that we suppress sending this if no user/group to resolve was
+         * specified. */
+
+        if (user_lookup_fd < 0)
+                return 0;
+
+        if (!uid_is_valid(uid) && !gid_is_valid(gid))
+                return 0;
+
+        if (writev(user_lookup_fd,
+               (struct iovec[]) {
+                           { .iov_base = &uid, .iov_len = sizeof(uid) },
+                           { .iov_base = &gid, .iov_len = sizeof(gid) },
+                           { .iov_base = unit->id, .iov_len = strlen(unit->id) }}, 3) < 0)
+                return -errno;
+
+        return 0;
+}
+
 static int exec_child(
                 Unit *unit,
                 ExecCommand *command,
@@ -1769,6 +1813,7 @@ static int exec_child(
                 int socket_fd,
                 int *fds, unsigned n_fds,
                 char **files_env,
+                int user_lookup_fd,
                 int *exit_status) {
 
         _cleanup_strv_free_ char **our_env = NULL, **pass_env = NULL, **accum_env = NULL, **final_argv = NULL;
@@ -1815,7 +1860,7 @@ static int exec_child(
 
         log_forget_fds();
 
-        r = close_remaining_fds(params, runtime, dcreds, socket_fd, fds, n_fds);
+        r = close_remaining_fds(params, runtime, dcreds, user_lookup_fd, socket_fd, fds, n_fds);
         if (r < 0) {
                 *exit_status = EXIT_FDS;
                 return r;
@@ -1862,7 +1907,7 @@ static int exec_child(
                         return r;
                 }
 
-                if (uid == UID_INVALID || gid == GID_INVALID) {
+                if (!uid_is_valid(uid) || !gid_is_valid(gid)) {
                         *exit_status = EXIT_USER;
                         return -ESRCH;
                 }
@@ -1902,6 +1947,14 @@ static int exec_child(
                 }
         }
 
+        r = send_user_lookup(unit, user_lookup_fd, uid, gid);
+        if (r < 0) {
+                *exit_status = EXIT_USER;
+                return r;
+        }
+
+        user_lookup_fd = safe_close(user_lookup_fd);
+
         /* If a socket is connected to STDIN/STDOUT/STDERR, we
          * must sure to drop O_NONBLOCK */
         if (socket_fd >= 0)
@@ -2059,6 +2112,7 @@ static int exec_child(
         }
 
         r = build_environment(
+                        unit,
                         context,
                         params,
                         n_fds,
@@ -2501,6 +2555,7 @@ int exec_spawn(Unit *unit,
                                socket_fd,
                                fds, n_fds,
                                files_env,
+                               unit->manager->user_lookup_fds[1],
                                &exit_status);
                 if (r < 0) {
                         log_open();
diff --git a/src/core/execute.h b/src/core/execute.h
index 106154f81a..6082c42aba 100644
--- a/src/core/execute.h
+++ b/src/core/execute.h
@@ -178,6 +178,7 @@ struct ExecContext {
         bool no_new_privileges;
 
         bool dynamic_user;
+        bool remove_ipc;
 
         /* This is not exposed to the user but available
          * internally. We need it to make sure that whenever we spawn
diff --git a/src/core/manager.c b/src/core/manager.c
index c20e185d78..6f2477eef4 100644
--- a/src/core/manager.c
+++ b/src/core/manager.c
@@ -45,6 +45,7 @@
 #include "bus-error.h"
 #include "bus-kernel.h"
 #include "bus-util.h"
+#include "clean-ipc.h"
 #include "dbus-job.h"
 #include "dbus-manager.h"
 #include "dbus-unit.h"
@@ -81,6 +82,7 @@
 #include "transaction.h"
 #include "umask-util.h"
 #include "unit-name.h"
+#include "user-util.h"
 #include "util.h"
 #include "virt.h"
 #include "watchdog.h"
@@ -98,6 +100,7 @@ static int manager_dispatch_cgroups_agent_fd(sd_event_source *source, int fd, ui
 static int manager_dispatch_signal_fd(sd_event_source *source, int fd, uint32_t revents, void *userdata);
 static int manager_dispatch_time_change_fd(sd_event_source *source, int fd, uint32_t revents, void *userdata);
 static int manager_dispatch_idle_pipe_fd(sd_event_source *source, int fd, uint32_t revents, void *userdata);
+static int manager_dispatch_user_lookup_fd(sd_event_source *source, int fd, uint32_t revents, void *userdata);
 static int manager_dispatch_jobs_in_progress(sd_event_source *source, usec_t usec, void *userdata);
 static int manager_dispatch_run_queue(sd_event_source *source, void *userdata);
 static int manager_run_generators(Manager *m);
@@ -590,6 +593,8 @@ int manager_new(UnitFileScope scope, bool test_run, Manager **_m) {
                 m->dev_autofs_fd = m->private_listen_fd = m->kdbus_fd = m->cgroup_inotify_fd =
                 m->ask_password_inotify_fd = -1;
 
+        m->user_lookup_fds[0] = m->user_lookup_fds[1] = -1;
+
         m->current_job_id = 1; /* start as id #1, so that we can leave #0 around as "null-like" value */
 
         m->have_ask_password = -EINVAL; /* we don't know */
@@ -812,6 +817,59 @@ static int manager_setup_cgroups_agent(Manager *m) {
         return 0;
 }
 
+static int manager_setup_user_lookup_fd(Manager *m) {
+        int r;
+
+        assert(m);
+
+        /* Set up the socket pair used for passing UID/GID resolution results from forked off processes to PID
+         * 1. Background: we can't do name lookups (NSS) from PID 1, since it might involve IPC and thus activation,
+         * and we might hence deadlock on ourselves. Hence we do all user/group lookups asynchronously from the forked
+         * off processes right before executing the binaries to start. In order to be able to clean up any IPC objects
+         * created by a unit (see RemoveIPC=) we need to know in PID 1 the used UID/GID of the executed processes,
+         * hence we establish this communication channel so that forked off processes can pass their UID/GID
+         * information back to PID 1. The forked off processes send their resolved UID/GID to PID 1 in a simple
+         * datagram, along with their unit name, so that we can share one communication socket pair among all units for
+         * this purpose.
+         *
+         * You might wonder why we need a communication channel for this that is independent of the usual notification
+         * socket scheme (i.e. $NOTIFY_SOCKET). The primary difference is about trust: data sent via the $NOTIFY_SOCKET
+         * channel is only accepted if it originates from the right unit and if reception was enabled for it. The user
+         * lookup socket OTOH is only accessible by PID 1 and its children until they exec(), and always available.
+         *
+         * Note that this function is called under two circumstances: when we first initialize (in which case we
+         * allocate both the socket pair and the event source to listen on it), and when we deserialize after a reload
+         * (in which case the socket pair already exists but we still need to allocate the event source for it). */
+
+        if (m->user_lookup_fds[0] < 0) {
+
+                /* Free all secondary fields */
+                safe_close_pair(m->user_lookup_fds);
+                m->user_lookup_event_source = sd_event_source_unref(m->user_lookup_event_source);
+
+                if (socketpair(AF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0, m->user_lookup_fds) < 0)
+                        return log_error_errno(errno, "Failed to allocate user lookup socket: %m");
+
+                (void) fd_inc_rcvbuf(m->user_lookup_fds[0], NOTIFY_RCVBUF_SIZE);
+        }
+
+        if (!m->user_lookup_event_source) {
+                r = sd_event_add_io(m->event, &m->user_lookup_event_source, m->user_lookup_fds[0], EPOLLIN, manager_dispatch_user_lookup_fd, m);
+                if (r < 0)
+                        return log_error_errno(errno, "Failed to allocate user lookup event source: %m");
+
+                /* Process even earlier than the notify event source, so that we always know first about valid UID/GID
+                 * resolutions */
+                r = sd_event_source_set_priority(m->user_lookup_event_source, SD_EVENT_PRIORITY_NORMAL-8);
+                if (r < 0)
+                        return log_error_errno(errno, "Failed to set priority ot user lookup event source: %m");
+
+                (void) sd_event_source_set_description(m->user_lookup_event_source, "user-lookup");
+        }
+
+        return 0;
+}
+
 static int manager_connect_bus(Manager *m, bool reexecuting) {
         bool try_bus_connect;
 
@@ -853,8 +911,7 @@ enum {
         _GC_OFFSET_MAX
 };
 
-static void unit_gc_mark_good(Unit *u, unsigned gc_marker)
-{
+static void unit_gc_mark_good(Unit *u, unsigned gc_marker) {
         Iterator i;
         Unit *other;
 
@@ -1021,12 +1078,14 @@ Manager* manager_free(Manager *m) {
         sd_event_source_unref(m->time_change_event_source);
         sd_event_source_unref(m->jobs_in_progress_event_source);
         sd_event_source_unref(m->run_queue_event_source);
+        sd_event_source_unref(m->user_lookup_event_source);
 
         safe_close(m->signal_fd);
         safe_close(m->notify_fd);
         safe_close(m->cgroups_agent_fd);
         safe_close(m->time_change_fd);
         safe_close(m->kdbus_fd);
+        safe_close_pair(m->user_lookup_fds);
 
         manager_close_ask_password(m);
 
@@ -1052,6 +1111,9 @@ Manager* manager_free(Manager *m) {
         assert(hashmap_isempty(m->units_requiring_mounts_for));
         hashmap_free(m->units_requiring_mounts_for);
 
+        hashmap_free(m->uid_refs);
+        hashmap_free(m->gid_refs);
+
         free(m);
         return NULL;
 }
@@ -1221,6 +1283,10 @@ int manager_startup(Manager *m, FILE *serialization, FDSet *fds) {
         if (q < 0 && r == 0)
                 r = q;
 
+        q = manager_setup_user_lookup_fd(m);
+        if (q < 0 && r == 0)
+                r = q;
+
         /* We might have deserialized the kdbus control fd, but if we
          * didn't, then let's create the bus now. */
         manager_connect_bus(m, !!serialization);
@@ -1232,6 +1298,10 @@ int manager_startup(Manager *m, FILE *serialization, FDSet *fds) {
         /* Release any dynamic users no longer referenced */
         dynamic_user_vacuum(m, true);
 
+        /* Release any references to UIDs/GIDs no longer referenced, and destroy any IPC owned by them */
+        manager_vacuum_uid_refs(m);
+        manager_vacuum_gid_refs(m);
+
         if (serialization) {
                 assert(m->n_reloading > 0);
                 m->n_reloading--;
@@ -2396,6 +2466,20 @@ int manager_serialize(Manager *m, FILE *f, FDSet *fds, bool switching_root) {
                 fprintf(f, "cgroups-agent-fd=%i\n", copy);
         }
 
+        if (m->user_lookup_fds[0] >= 0) {
+                int copy0, copy1;
+
+                copy0 = fdset_put_dup(fds, m->user_lookup_fds[0]);
+                if (copy0 < 0)
+                        return copy0;
+
+                copy1 = fdset_put_dup(fds, m->user_lookup_fds[1]);
+                if (copy1 < 0)
+                        return copy1;
+
+                fprintf(f, "user-lookup=%i %i\n", copy0, copy1);
+        }
+
         if (m->kdbus_fd >= 0) {
                 int copy;
 
@@ -2412,6 +2496,9 @@ int manager_serialize(Manager *m, FILE *f, FDSet *fds, bool switching_root) {
         if (r < 0)
                 return r;
 
+        manager_serialize_uid_refs(m, f);
+        manager_serialize_gid_refs(m, f);
+
         fputc('\n', f);
 
         HASHMAP_FOREACH_KEY(u, t, m->units, i) {
@@ -2578,6 +2665,18 @@ int manager_deserialize(Manager *m, FILE *f, FDSet *fds) {
                                 m->cgroups_agent_fd = fdset_remove(fds, fd);
                         }
 
+                } else if (startswith(l, "user-lookup=")) {
+                        int fd0, fd1;
+
+                        if (sscanf(l + 12, "%i %i", &fd0, &fd1) != 2 || fd0 < 0 || fd1 < 0 || fd0 == fd1 || !fdset_contains(fds, fd0) || !fdset_contains(fds, fd1))
+                                log_debug("Failed to parse user lookup fd: %s", l + 12);
+                        else {
+                                m->user_lookup_event_source = sd_event_source_unref(m->user_lookup_event_source);
+                                safe_close_pair(m->user_lookup_fds);
+                                m->user_lookup_fds[0] = fdset_remove(fds, fd0);
+                                m->user_lookup_fds[1] = fdset_remove(fds, fd1);
+                        }
+
                 } else if (startswith(l, "kdbus-fd=")) {
                         int fd;
 
@@ -2590,6 +2689,10 @@ int manager_deserialize(Manager *m, FILE *f, FDSet *fds) {
 
                 } else if (startswith(l, "dynamic-user="))
                         dynamic_user_deserialize_one(m, l + 13, fds);
+                else if (startswith(l, "destroy-ipc-uid="))
+                        manager_deserialize_uid_refs_one(m, l + 16);
+                else if (startswith(l, "destroy-ipc-gid="))
+                        manager_deserialize_gid_refs_one(m, l + 16);
                 else {
                         int k;
 
@@ -2672,6 +2775,8 @@ int manager_reload(Manager *m) {
         lookup_paths_flush_generator(&m->lookup_paths);
         lookup_paths_free(&m->lookup_paths);
         dynamic_user_vacuum(m, false);
+        m->uid_refs = hashmap_free(m->uid_refs);
+        m->gid_refs = hashmap_free(m->gid_refs);
 
         q = lookup_paths_init(&m->lookup_paths, m->unit_file_scope, 0, NULL);
         if (q < 0 && r >= 0)
@@ -2705,12 +2810,20 @@ int manager_reload(Manager *m) {
         if (q < 0 && r >= 0)
                 r = q;
 
+        q = manager_setup_user_lookup_fd(m);
+        if (q < 0 && r >= 0)
+                r = q;
+
         /* Third, fire things up! */
         manager_coldplug(m);
 
         /* Release any dynamic users no longer referenced */
         dynamic_user_vacuum(m, true);
 
+        /* Release any references to UIDs/GIDs no longer referenced, and destroy any IPC owned by them */
+        manager_vacuum_uid_refs(m);
+        manager_vacuum_gid_refs(m);
+
         /* Sync current state of bus names with our set of listening units */
         if (m->api_bus)
                 manager_sync_bus_names(m, m->api_bus);
@@ -3144,6 +3257,300 @@ ManagerState manager_state(Manager *m) {
         return MANAGER_RUNNING;
 }
 
+#define DESTROY_IPC_FLAG (UINT32_C(1) << 31)
+
+static void manager_unref_uid_internal(
+                Manager *m,
+                Hashmap **uid_refs,
+                uid_t uid,
+                bool destroy_now,
+                int (*_clean_ipc)(uid_t uid)) {
+
+        uint32_t c, n;
+
+        assert(m);
+        assert(uid_refs);
+        assert(uid_is_valid(uid));
+        assert(_clean_ipc);
+
+        /* A generic implementation, covering both manager_unref_uid() and manager_unref_gid(), under the assumption
+         * that uid_t and gid_t are actually defined the same way, with the same validity rules.
+         *
+         * We store a hashmap where the UID/GID is they key and the value is a 32bit reference counter, whose highest
+         * bit is used as flag for marking UIDs/GIDs whose IPC objects to remove when the last reference to the UID/GID
+         * is dropped. The flag is set to on, once at least one reference from a unit where RemoveIPC= is set is added
+         * on a UID/GID. It is reset when the UID's/GID's reference counter drops to 0 again. */
+
+        assert_cc(sizeof(uid_t) == sizeof(gid_t));
+        assert_cc(UID_INVALID == (uid_t) GID_INVALID);
+
+        if (uid == 0) /* We don't keep track of root, and will never destroy it */
+                return;
+
+        c = PTR_TO_UINT32(hashmap_get(*uid_refs, UID_TO_PTR(uid)));
+
+        n = c & ~DESTROY_IPC_FLAG;
+        assert(n > 0);
+        n--;
+
+        if (destroy_now && n == 0) {
+                hashmap_remove(*uid_refs, UID_TO_PTR(uid));
+
+                if (c & DESTROY_IPC_FLAG) {
+                        log_debug("%s " UID_FMT " is no longer referenced, cleaning up its IPC.",
+                                  _clean_ipc == clean_ipc_by_uid ? "UID" : "GID",
+                                  uid);
+                        (void) _clean_ipc(uid);
+                }
+        } else {
+                c = n | (c & DESTROY_IPC_FLAG);
+                assert_se(hashmap_update(*uid_refs, UID_TO_PTR(uid), UINT32_TO_PTR(c)) >= 0);
+        }
+}
+
+void manager_unref_uid(Manager *m, uid_t uid, bool destroy_now) {
+        manager_unref_uid_internal(m, &m->uid_refs, uid, destroy_now, clean_ipc_by_uid);
+}
+
+void manager_unref_gid(Manager *m, gid_t gid, bool destroy_now) {
+        manager_unref_uid_internal(m, &m->gid_refs, (uid_t) gid, destroy_now, clean_ipc_by_gid);
+}
+
+static int manager_ref_uid_internal(
+                Manager *m,
+                Hashmap **uid_refs,
+                uid_t uid,
+                bool clean_ipc) {
+
+        uint32_t c, n;
+        int r;
+
+        assert(m);
+        assert(uid_refs);
+        assert(uid_is_valid(uid));
+
+        /* A generic implementation, covering both manager_ref_uid() and manager_ref_gid(), under the assumption
+         * that uid_t and gid_t are actually defined the same way, with the same validity rules. */
+
+        assert_cc(sizeof(uid_t) == sizeof(gid_t));
+        assert_cc(UID_INVALID == (uid_t) GID_INVALID);
+
+        if (uid == 0) /* We don't keep track of root, and will never destroy it */
+                return 0;
+
+        r = hashmap_ensure_allocated(uid_refs, &trivial_hash_ops);
+        if (r < 0)
+                return r;
+
+        c = PTR_TO_UINT32(hashmap_get(*uid_refs, UID_TO_PTR(uid)));
+
+        n = c & ~DESTROY_IPC_FLAG;
+        n++;
+
+        if (n & DESTROY_IPC_FLAG) /* check for overflow */
+                return -EOVERFLOW;
+
+        c = n | (c & DESTROY_IPC_FLAG) | (clean_ipc ? DESTROY_IPC_FLAG : 0);
+
+        return hashmap_replace(*uid_refs, UID_TO_PTR(uid), UINT32_TO_PTR(c));
+}
+
+int manager_ref_uid(Manager *m, uid_t uid, bool clean_ipc) {
+        return manager_ref_uid_internal(m, &m->uid_refs, uid, clean_ipc);
+}
+
+int manager_ref_gid(Manager *m, gid_t gid, bool clean_ipc) {
+        return manager_ref_uid_internal(m, &m->gid_refs, (uid_t) gid, clean_ipc);
+}
+
+static void manager_vacuum_uid_refs_internal(
+                Manager *m,
+                Hashmap **uid_refs,
+                int (*_clean_ipc)(uid_t uid)) {
+
+        Iterator i;
+        void *p, *k;
+
+        assert(m);
+        assert(uid_refs);
+        assert(_clean_ipc);
+
+        HASHMAP_FOREACH_KEY(p, k, *uid_refs, i) {
+                uint32_t c, n;
+                uid_t uid;
+
+                uid = PTR_TO_UID(k);
+                c = PTR_TO_UINT32(p);
+
+                n = c & ~DESTROY_IPC_FLAG;
+                if (n > 0)
+                        continue;
+
+                if (c & DESTROY_IPC_FLAG) {
+                        log_debug("Found unreferenced %s " UID_FMT " after reload/reexec. Cleaning up.",
+                                  _clean_ipc == clean_ipc_by_uid ? "UID" : "GID",
+                                  uid);
+                        (void) _clean_ipc(uid);
+                }
+
+                assert_se(hashmap_remove(*uid_refs, k) == p);
+        }
+}
+
+void manager_vacuum_uid_refs(Manager *m) {
+        manager_vacuum_uid_refs_internal(m, &m->uid_refs, clean_ipc_by_uid);
+}
+
+void manager_vacuum_gid_refs(Manager *m) {
+        manager_vacuum_uid_refs_internal(m, &m->gid_refs, clean_ipc_by_gid);
+}
+
+static void manager_serialize_uid_refs_internal(
+                Manager *m,
+                FILE *f,
+                Hashmap **uid_refs,
+                const char *field_name) {
+
+        Iterator i;
+        void *p, *k;
+
+        assert(m);
+        assert(f);
+        assert(uid_refs);
+        assert(field_name);
+
+        /* Serialize the UID reference table. Or actually, just the IPC destruction flag of it, as the actual counter
+         * of it is better rebuild after a reload/reexec. */
+
+        HASHMAP_FOREACH_KEY(p, k, *uid_refs, i) {
+                uint32_t c;
+                uid_t uid;
+
+                uid = PTR_TO_UID(k);
+                c = PTR_TO_UINT32(p);
+
+                if (!(c & DESTROY_IPC_FLAG))
+                        continue;
+
+                fprintf(f, "%s=" UID_FMT "\n", field_name, uid);
+        }
+}
+
+void manager_serialize_uid_refs(Manager *m, FILE *f) {
+        manager_serialize_uid_refs_internal(m, f, &m->uid_refs, "destroy-ipc-uid");
+}
+
+void manager_serialize_gid_refs(Manager *m, FILE *f) {
+        manager_serialize_uid_refs_internal(m, f, &m->gid_refs, "destroy-ipc-gid");
+}
+
+static void manager_deserialize_uid_refs_one_internal(
+                Manager *m,
+                Hashmap** uid_refs,
+                const char *value) {
+
+        uid_t uid;
+        uint32_t c;
+        int r;
+
+        assert(m);
+        assert(uid_refs);
+        assert(value);
+
+        r = parse_uid(value, &uid);
+        if (r < 0 || uid == 0) {
+                log_debug("Unable to parse UID reference serialization");
+                return;
+        }
+
+        r = hashmap_ensure_allocated(uid_refs, &trivial_hash_ops);
+        if (r < 0) {
+                log_oom();
+                return;
+        }
+
+        c = PTR_TO_UINT32(hashmap_get(*uid_refs, UID_TO_PTR(uid)));
+        if (c & DESTROY_IPC_FLAG)
+                return;
+
+        c |= DESTROY_IPC_FLAG;
+
+        r = hashmap_replace(*uid_refs, UID_TO_PTR(uid), UINT32_TO_PTR(c));
+        if (r < 0) {
+                log_debug("Failed to add UID reference entry");
+                return;
+        }
+}
+
+void manager_deserialize_uid_refs_one(Manager *m, const char *value) {
+        manager_deserialize_uid_refs_one_internal(m, &m->uid_refs, value);
+}
+
+void manager_deserialize_gid_refs_one(Manager *m, const char *value) {
+        manager_deserialize_uid_refs_one_internal(m, &m->gid_refs, value);
+}
+
+int manager_dispatch_user_lookup_fd(sd_event_source *source, int fd, uint32_t revents, void *userdata) {
+        struct buffer {
+                uid_t uid;
+                gid_t gid;
+                char unit_name[UNIT_NAME_MAX+1];
+        } _packed_ buffer;
+
+        Manager *m = userdata;
+        ssize_t l;
+        size_t n;
+        Unit *u;
+
+        assert_se(source);
+        assert_se(m);
+
+        /* Invoked whenever a child process succeeded resolving its user/group to use and sent us the resulting UID/GID
+         * in a datagram. We parse the datagram here and pass it off to the unit, so that it can add a reference to the
+         * UID/GID so that it can destroy the UID/GID's IPC objects when the reference counter drops to 0. */
+
+        l = recv(fd, &buffer, sizeof(buffer), MSG_DONTWAIT);
+        if (l < 0) {
+                if (errno == EINTR || errno == EAGAIN)
+                        return 0;
+
+                return log_error_errno(errno, "Failed to read from user lookup fd: %m");
+        }
+
+        if ((size_t) l <= offsetof(struct buffer, unit_name)) {
+                log_warning("Received too short user lookup message, ignoring.");
+                return 0;
+        }
+
+        if ((size_t) l > offsetof(struct buffer, unit_name) + UNIT_NAME_MAX) {
+                log_warning("Received too long user lookup message, ignoring.");
+                return 0;
+        }
+
+        if (!uid_is_valid(buffer.uid) && !gid_is_valid(buffer.gid)) {
+                log_warning("Got user lookup message with invalid UID/GID pair, ignoring.");
+                return 0;
+        }
+
+        n = (size_t) l - offsetof(struct buffer, unit_name);
+        if (memchr(buffer.unit_name, 0, n)) {
+                log_warning("Received lookup message with embedded NUL character, ignoring.");
+                return 0;
+        }
+
+        buffer.unit_name[n] = 0;
+        u = manager_get_unit(m, buffer.unit_name);
+        if (!u) {
+                log_debug("Got user lookup message but unit doesn't exist, ignoring.");
+                return 0;
+        }
+
+        log_unit_debug(u, "User lookup succeeded: uid=" UID_FMT " gid=" GID_FMT, buffer.uid, buffer.gid);
+
+        unit_notify_user_lookup(u, buffer.uid, buffer.gid);
+        return 0;
+}
+
 static const char *const manager_state_table[_MANAGER_STATE_MAX] = {
         [MANAGER_INITIALIZING] = "initializing",
         [MANAGER_STARTING] = "starting",
diff --git a/src/core/manager.h b/src/core/manager.h
index c681d5dc46..b9f2e4b5a1 100644
--- a/src/core/manager.h
+++ b/src/core/manager.h
@@ -143,6 +143,9 @@ struct Manager {
 
         sd_event_source *jobs_in_progress_event_source;
 
+        int user_lookup_fds[2];
+        sd_event_source *user_lookup_event_source;
+
         UnitFileScope unit_file_scope;
         LookupPaths lookup_paths;
         Set *unit_path_cache;
@@ -234,7 +237,6 @@ struct Manager {
         bool dispatching_dbus_queue:1;
 
         bool taint_usr:1;
-
         bool test_run:1;
 
         /* If non-zero, exit with the following value when the systemd
@@ -301,6 +303,10 @@ struct Manager {
         /* Dynamic users/groups, indexed by their name */
         Hashmap *dynamic_users;
 
+        /* Keep track of all UIDs and GIDs any of our services currently use. This is useful for the RemoveIPC= logic. */
+        Hashmap *uid_refs;
+        Hashmap *gid_refs;
+
         /* When the user hits C-A-D more than 7 times per 2s, reboot immediately... */
         RateLimit ctrl_alt_del_ratelimit;
 
@@ -378,5 +384,20 @@ ManagerState manager_state(Manager *m);
 
 int manager_update_failed_units(Manager *m, Unit *u, bool failed);
 
+void manager_unref_uid(Manager *m, uid_t uid, bool destroy_now);
+int manager_ref_uid(Manager *m, uid_t uid, bool clean_ipc);
+
+void manager_unref_gid(Manager *m, gid_t gid, bool destroy_now);
+int manager_ref_gid(Manager *m, gid_t gid, bool destroy_now);
+
+void manager_vacuum_uid_refs(Manager *m);
+void manager_vacuum_gid_refs(Manager *m);
+
+void manager_serialize_uid_refs(Manager *m, FILE *f);
+void manager_deserialize_uid_refs_one(Manager *m, const char *value);
+
+void manager_serialize_gid_refs(Manager *m, FILE *f);
+void manager_deserialize_gid_refs_one(Manager *m, const char *value);
+
 const char *manager_state_to_string(ManagerState m) _const_;
 ManagerState manager_state_from_string(const char *s) _pure_;
diff --git a/src/core/mount.c b/src/core/mount.c
index f3ccf6d48a..f2ac8d171f 100644
--- a/src/core/mount.c
+++ b/src/core/mount.c
@@ -769,6 +769,8 @@ static void mount_enter_dead(Mount *m, MountResult f) {
 
         exec_context_destroy_runtime_directory(&m->exec_context, manager_get_runtime_prefix(UNIT(m)->manager));
 
+        unit_unref_uid_gid(UNIT(m), true);
+
         dynamic_creds_destroy(&m->dynamic_creds);
 }
 
diff --git a/src/core/service.c b/src/core/service.c
index 4a37702f52..1951ba9222 100644
--- a/src/core/service.c
+++ b/src/core/service.c
@@ -1471,6 +1471,9 @@ static void service_enter_dead(Service *s, ServiceResult f, bool allow_restart)
         /* Also, remove the runtime directory */
         exec_context_destroy_runtime_directory(&s->exec_context, manager_get_runtime_prefix(UNIT(s)->manager));
 
+        /* Get rid of the IPC bits of the user */
+        unit_unref_uid_gid(UNIT(s), true);
+
         /* Release the user, and destroy it if we are the only remaining owner */
         dynamic_creds_destroy(&s->dynamic_creds);
 
diff --git a/src/core/socket.c b/src/core/socket.c
index 50872e8366..70d55dd9ed 100644
--- a/src/core/socket.c
+++ b/src/core/socket.c
@@ -1905,6 +1905,8 @@ static void socket_enter_dead(Socket *s, SocketResult f) {
 
         exec_context_destroy_runtime_directory(&s->exec_context, manager_get_runtime_prefix(UNIT(s)->manager));
 
+        unit_unref_uid_gid(UNIT(s), true);
+
         dynamic_creds_destroy(&s->dynamic_creds);
 }
 
diff --git a/src/core/swap.c b/src/core/swap.c
index 2c802da3b5..fb222b6858 100644
--- a/src/core/swap.c
+++ b/src/core/swap.c
@@ -683,6 +683,8 @@ static void swap_enter_dead(Swap *s, SwapResult f) {
 
         exec_context_destroy_runtime_directory(&s->exec_context, manager_get_runtime_prefix(UNIT(s)->manager));
 
+        unit_unref_uid_gid(UNIT(s), true);
+
         dynamic_creds_destroy(&s->dynamic_creds);
 }
 
diff --git a/src/core/unit.c b/src/core/unit.c
index 952604e0db..4b8d81c3f1 100644
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -100,7 +100,8 @@ Unit *unit_new(Manager *m, size_t size) {
         u->on_failure_job_mode = JOB_REPLACE;
         u->cgroup_inotify_wd = -1;
         u->job_timeout = USEC_INFINITY;
-        u->sigchldgen = 0;
+        u->ref_uid = UID_INVALID;
+        u->ref_gid = GID_INVALID;
 
         RATELIMIT_INIT(u->start_limit, m->default_start_limit_interval, m->default_start_limit_burst);
         RATELIMIT_INIT(u->auto_stop_ratelimit, 10 * USEC_PER_SEC, 16);
@@ -550,6 +551,8 @@ void unit_free(Unit *u) {
 
         unit_release_cgroup(u);
 
+        unit_unref_uid_gid(u, false);
+
         (void) manager_update_failed_units(u->manager, u, false);
         set_remove(u->manager->startup_units, u);
 
@@ -2614,6 +2617,11 @@ int unit_serialize(Unit *u, FILE *f, FDSet *fds, bool serialize_jobs) {
                 unit_serialize_item(u, f, "cgroup", u->cgroup_path);
         unit_serialize_item(u, f, "cgroup-realized", yes_no(u->cgroup_realized));
 
+        if (uid_is_valid(u->ref_uid))
+                unit_serialize_item_format(u, f, "ref-uid", UID_FMT, u->ref_uid);
+        if (gid_is_valid(u->ref_gid))
+                unit_serialize_item_format(u, f, "ref-gid", GID_FMT, u->ref_gid);
+
         if (serialize_jobs) {
                 if (u->job) {
                         fprintf(f, "job\n");
@@ -2851,6 +2859,28 @@ int unit_deserialize(Unit *u, FILE *f, FDSet *fds) {
                                 u->cgroup_realized = b;
 
                         continue;
+
+                } else if (streq(l, "ref-uid")) {
+                        uid_t uid;
+
+                        r = parse_uid(v, &uid);
+                        if (r < 0)
+                                log_unit_debug(u, "Failed to parse referenced UID %s, ignoring.", v);
+                        else
+                                unit_ref_uid_gid(u, uid, GID_INVALID);
+
+                        continue;
+
+                } else if (streq(l, "ref-gid")) {
+                        gid_t gid;
+
+                        r = parse_gid(v, &gid);
+                        if (r < 0)
+                                log_unit_debug(u, "Failed to parse referenced GID %s, ignoring.", v);
+                        else
+                                unit_ref_uid_gid(u, UID_INVALID, gid);
+
+                        continue;
                 }
 
                 if (unit_can_serialize(u)) {
@@ -3310,6 +3340,7 @@ int unit_patch_contexts(Unit *u) {
                         }
 
                         ec->private_tmp = true;
+                        ec->remove_ipc = true;
                 }
         }
 
@@ -3932,3 +3963,144 @@ pid_t unit_main_pid(Unit *u) {
 
         return 0;
 }
+
+static void unit_unref_uid_internal(
+                Unit *u,
+                uid_t *ref_uid,
+                bool destroy_now,
+                void (*_manager_unref_uid)(Manager *m, uid_t uid, bool destroy_now)) {
+
+        assert(u);
+        assert(ref_uid);
+        assert(_manager_unref_uid);
+
+        /* Generic implementation of both unit_unref_uid() and unit_unref_gid(), under the assumption that uid_t and
+         * gid_t are actually the same time, with the same validity rules.
+         *
+         * Drops a reference to UID/GID from a unit. */
+
+        assert_cc(sizeof(uid_t) == sizeof(gid_t));
+        assert_cc(UID_INVALID == (uid_t) GID_INVALID);
+
+        if (!uid_is_valid(*ref_uid))
+                return;
+
+        _manager_unref_uid(u->manager, *ref_uid, destroy_now);
+        *ref_uid = UID_INVALID;
+}
+
+void unit_unref_uid(Unit *u, bool destroy_now) {
+        unit_unref_uid_internal(u, &u->ref_uid, destroy_now, manager_unref_uid);
+}
+
+void unit_unref_gid(Unit *u, bool destroy_now) {
+        unit_unref_uid_internal(u, (uid_t*) &u->ref_gid, destroy_now, manager_unref_gid);
+}
+
+static int unit_ref_uid_internal(
+                Unit *u,
+                uid_t *ref_uid,
+                uid_t uid,
+                bool clean_ipc,
+                int (*_manager_ref_uid)(Manager *m, uid_t uid, bool clean_ipc)) {
+
+        int r;
+
+        assert(u);
+        assert(ref_uid);
+        assert(uid_is_valid(uid));
+        assert(_manager_ref_uid);
+
+        /* Generic implementation of both unit_ref_uid() and unit_ref_guid(), under the assumption that uid_t and gid_t
+         * are actually the same type, and have the same validity rules.
+         *
+         * Adds a reference on a specific UID/GID to this unit. Each unit referencing the same UID/GID maintains a
+         * reference so that we can destroy the UID/GID's IPC resources as soon as this is requested and the counter
+         * drops to zero. */
+
+        assert_cc(sizeof(uid_t) == sizeof(gid_t));
+        assert_cc(UID_INVALID == (uid_t) GID_INVALID);
+
+        if (*ref_uid == uid)
+                return 0;
+
+        if (uid_is_valid(*ref_uid)) /* Already set? */
+                return -EBUSY;
+
+        r = _manager_ref_uid(u->manager, uid, clean_ipc);
+        if (r < 0)
+                return r;
+
+        *ref_uid = uid;
+        return 1;
+}
+
+int unit_ref_uid(Unit *u, uid_t uid, bool clean_ipc) {
+        return unit_ref_uid_internal(u, &u->ref_uid, uid, clean_ipc, manager_ref_uid);
+}
+
+int unit_ref_gid(Unit *u, gid_t gid, bool clean_ipc) {
+        return unit_ref_uid_internal(u, (uid_t*) &u->ref_gid, (uid_t) gid, clean_ipc, manager_ref_gid);
+}
+
+static int unit_ref_uid_gid_internal(Unit *u, uid_t uid, gid_t gid, bool clean_ipc) {
+        int r = 0, q = 0;
+
+        assert(u);
+
+        /* Reference both a UID and a GID in one go. Either references both, or neither. */
+
+        if (uid_is_valid(uid)) {
+                r = unit_ref_uid(u, uid, clean_ipc);
+                if (r < 0)
+                        return r;
+        }
+
+        if (gid_is_valid(gid)) {
+                q = unit_ref_gid(u, gid, clean_ipc);
+                if (q < 0) {
+                        if (r > 0)
+                                unit_unref_uid(u, false);
+
+                        return q;
+                }
+        }
+
+        return r > 0 || q > 0;
+}
+
+int unit_ref_uid_gid(Unit *u, uid_t uid, gid_t gid) {
+        ExecContext *c;
+        int r;
+
+        assert(u);
+
+        c = unit_get_exec_context(u);
+
+        r = unit_ref_uid_gid_internal(u, uid, gid, c ? c->remove_ipc : false);
+        if (r < 0)
+                return log_unit_warning_errno(u, r, "Couldn't add UID/GID reference to unit, proceeding without: %m");
+
+        return r;
+}
+
+void unit_unref_uid_gid(Unit *u, bool destroy_now) {
+        assert(u);
+
+        unit_unref_uid(u, destroy_now);
+        unit_unref_gid(u, destroy_now);
+}
+
+void unit_notify_user_lookup(Unit *u, uid_t uid, gid_t gid) {
+        int r;
+
+        assert(u);
+
+        /* This is invoked whenever one of the forked off processes let's us know the UID/GID its user name/group names
+         * resolved to. We keep track of which UID/GID is currently assigned in order to be able to destroy its IPC
+         * objects when no service references the UID/GID anymore. */
+
+        r = unit_ref_uid_gid(u, uid, gid);
+        if (r > 0)
+                bus_unit_send_change_signal(u);
+}
diff --git a/src/core/unit.h b/src/core/unit.h
index a6c69938dd..53875653d7 100644
--- a/src/core/unit.h
+++ b/src/core/unit.h
@@ -180,6 +180,10 @@ struct Unit {
         /* Make sure we never enter endless loops with the check unneeded logic, or the BindsTo= logic */
         RateLimit auto_stop_ratelimit;
 
+        /* Reference to a specific UID/GID */
+        uid_t ref_uid;
+        gid_t ref_gid;
+
         /* Cached unit file state and preset */
         UnitFileState unit_file_state;
         int unit_file_preset;
@@ -195,8 +199,6 @@ struct Unit {
         CGroupMask cgroup_members_mask;
         int cgroup_inotify_wd;
 
-        uint32_t cgroup_netclass_id;
-
         /* How to start OnFailure units */
         JobMode on_failure_job_mode;
 
@@ -373,8 +375,7 @@ struct UnitVTable {
         /* Called whenever a process of this unit sends us a message */
         void (*notify_message)(Unit *u, pid_t pid, char **tags, FDSet *fds);
 
-        /* Called whenever a name this Unit registered for comes or
-         * goes away. */
+        /* Called whenever a name this Unit registered for comes or goes away. */
         void (*bus_name_owner_change)(Unit *u, const char *name, const char *old_owner, const char *new_owner);
 
         /* Called for each property that is being set */
@@ -623,6 +624,17 @@ int unit_fail_if_symlink(Unit *u, const char* where);
 
 int unit_start_limit_test(Unit *u);
 
+void unit_unref_uid(Unit *u, bool destroy_now);
+int unit_ref_uid(Unit *u, uid_t uid, bool clean_ipc);
+
+void unit_unref_gid(Unit *u, bool destroy_now);
+int unit_ref_gid(Unit *u, gid_t gid, bool clean_ipc);
+
+int unit_ref_uid_gid(Unit *u, uid_t uid, gid_t gid);
+void unit_unref_uid_gid(Unit *u, bool destroy_now);
+
+void unit_notify_user_lookup(Unit *u, uid_t uid, gid_t gid);
+
 /* Macros which append UNIT= or USER_UNIT= to the message */
 
 #define log_unit_full(unit, level, error, ...)                          \
diff --git a/src/login/logind-user.c b/src/login/logind-user.c
index 63363035e7..11951aca5b 100644
--- a/src/login/logind-user.c
+++ b/src/login/logind-user.c
@@ -612,9 +612,14 @@ int user_finalize(User *u) {
         if (k < 0)
                 r = k;
 
-        /* Clean SysV + POSIX IPC objects */
-        if (u->manager->remove_ipc) {
-                k = clean_ipc(u->uid);
+        /* Clean SysV + POSIX IPC objects, but only if this is not a system user. Background: in many setups cronjobs
+         * are run in full PAM and thus logind sessions, even if the code run doesn't belong to actual users but to
+         * system components. Since enable RemoveIPC= globally for all users, we need to be a bit careful with such
+         * cases, as we shouldn't accidentally remove a system service's IPC objects while it is running, just because
+         * a cronjob running as the same user just finished. Hence: exclude system users generally from IPC clean-up,
+         * and do it only for normal users. */
+        if (u->manager->remove_ipc && u->uid > SYSTEM_UID_MAX) {
+                k = clean_ipc_by_uid(u->uid);
                 if (k < 0)
                         r = k;
         }
diff --git a/src/nss-mymachines/nss-mymachines.c b/src/nss-mymachines/nss-mymachines.c
index 8d57b26cbc..895f61c462 100644
--- a/src/nss-mymachines/nss-mymachines.c
+++ b/src/nss-mymachines/nss-mymachines.c
@@ -25,6 +25,7 @@
 
 #include "alloc-util.h"
 #include "bus-common-errors.h"
+#include "env-util.h"
 #include "hostname-util.h"
 #include "in-addr-util.h"
 #include "macro.h"
@@ -434,6 +435,12 @@ enum nss_status _nss_mymachines_getpwnam_r(
         if (!machine_name_is_valid(machine))
                 goto not_found;
 
+        if (getenv_bool("SYSTEMD_NSS_BYPASS_BUS") > 0)
+                /* Make sure we can't deadlock if we are invoked by dbus-daemon. This way, it won't be able to resolve
+                 * these UIDs, but that should be unproblematic as containers should never be able to connect to a bus
+                 * running on the host. */
+                goto not_found;
+
         r = sd_bus_open_system(&bus);
         if (r < 0)
                 goto fail;
@@ -514,6 +521,9 @@ enum nss_status _nss_mymachines_getpwuid_r(
         if (uid < HOST_UID_LIMIT)
                 goto not_found;
 
+        if (getenv_bool("SYSTEMD_NSS_BYPASS_BUS") > 0)
+                goto not_found;
+
         r = sd_bus_open_system(&bus);
         if (r < 0)
                 goto fail;
@@ -605,6 +615,9 @@ enum nss_status _nss_mymachines_getgrnam_r(
         if (!machine_name_is_valid(machine))
                 goto not_found;
 
+        if (getenv_bool("SYSTEMD_NSS_BYPASS_BUS") > 0)
+                goto not_found;
+
         r = sd_bus_open_system(&bus);
         if (r < 0)
                 goto fail;
@@ -682,6 +695,9 @@ enum nss_status _nss_mymachines_getgrgid_r(
         if (gid < HOST_GID_LIMIT)
                 goto not_found;
 
+        if (getenv_bool("SYSTEMD_NSS_BYPASS_BUS") > 0)
+                goto not_found;
+
         r = sd_bus_open_system(&bus);
         if (r < 0)
                 goto fail;
diff --git a/src/nss-systemd/nss-systemd.c b/src/nss-systemd/nss-systemd.c
index 7078c0c50c..17d04e958d 100644
--- a/src/nss-systemd/nss-systemd.c
+++ b/src/nss-systemd/nss-systemd.c
@@ -21,11 +21,14 @@
 
 #include "sd-bus.h"
 
+#include "alloc-util.h"
 #include "bus-common-errors.h"
 #include "env-util.h"
+#include "fs-util.h"
 #include "macro.h"
 #include "nss-util.h"
 #include "signal-util.h"
+#include "stdio-util.h"
 #include "string-util.h"
 #include "user-util.h"
 #include "util.h"
@@ -75,15 +78,50 @@ static const struct group nobody_group = {
 NSS_GETPW_PROTOTYPES(systemd);
 NSS_GETGR_PROTOTYPES(systemd);
 
+static int direct_lookup_name(const char *name, uid_t *ret) {
+        _cleanup_free_ char *s = NULL;
+        const char *path;
+        int r;
+
+        assert(name);
+
+        /* Normally, we go via the bus to resolve names. That has the benefit that it is available from any mount
+         * namespace and subject to proper authentication. However, there's one problem: if our module is called from
+         * dbus-daemon itself we really can't use D-Bus to communicate. In this case, resort to a client-side hack,
+         * and look for the dynamic names directly. This is pretty ugly, but breaks the cyclic dependency. */
+
+        path = strjoina("/run/systemd/dynamic-uid/direct:", name);
+        r = readlink_malloc(path, &s);
+        if (r < 0)
+                return r;
+
+        return parse_uid(s, ret);
+}
+
+static int direct_lookup_uid(uid_t uid, char **ret) {
+        char path[strlen("/run/systemd/dynamic-uid/direct:") + DECIMAL_STR_MAX(uid_t) + 1], *s;
+        int r;
+
+        xsprintf(path, "/run/systemd/dynamic-uid/direct:" UID_FMT, uid);
+
+        r = readlink_malloc(path, &s);
+        if (r < 0)
+                return r;
+        if (!valid_user_group_name(s)) { /* extra safety check */
+                free(s);
+                return -EINVAL;
+        }
+
+        *ret = s;
+        return 0;
+}
+
 enum nss_status _nss_systemd_getpwnam_r(
                 const char *name,
                 struct passwd *pwd,
                 char *buffer, size_t buflen,
                 int *errnop) {
 
-        _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
-        _cleanup_(sd_bus_message_unrefp) sd_bus_message* reply = NULL;
-        _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
         uint32_t translated;
         size_t l;
         int r;
@@ -114,30 +152,45 @@ enum nss_status _nss_systemd_getpwnam_r(
         if (getenv_bool("SYSTEMD_NSS_DYNAMIC_BYPASS") > 0)
                 goto not_found;
 
-        r = sd_bus_open_system(&bus);
-        if (r < 0)
-                goto fail;
+        if (getenv_bool("SYSTEMD_NSS_BYPASS_BUS") > 0) {
 
-        r = sd_bus_call_method(bus,
-                               "org.freedesktop.systemd1",
-                               "/org/freedesktop/systemd1",
-                               "org.freedesktop.systemd1.Manager",
-                               "LookupDynamicUserByName",
-                               &error,
-                               &reply,
-                               "s",
-                               name);
-        if (r < 0) {
-                if (sd_bus_error_has_name(&error, BUS_ERROR_NO_SUCH_DYNAMIC_USER))
+                /* Access the dynamic UID allocation directly if we are called from dbus-daemon, see above. */
+                r = direct_lookup_name(name, (uid_t*) &translated);
+                if (r == -ENOENT)
                         goto not_found;
-
-                goto fail;
+                if (r < 0)
+                        goto fail;
+
+        } else {
+                _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
+                _cleanup_(sd_bus_message_unrefp) sd_bus_message* reply = NULL;
+                _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
+
+                r = sd_bus_open_system(&bus);
+                if (r < 0)
+                        goto fail;
+
+                r = sd_bus_call_method(bus,
+                                       "org.freedesktop.systemd1",
+                                       "/org/freedesktop/systemd1",
+                                       "org.freedesktop.systemd1.Manager",
+                                       "LookupDynamicUserByName",
+                                       &error,
+                                       &reply,
+                                       "s",
+                                       name);
+                if (r < 0) {
+                        if (sd_bus_error_has_name(&error, BUS_ERROR_NO_SUCH_DYNAMIC_USER))
+                                goto not_found;
+
+                        goto fail;
+                }
+
+                r = sd_bus_message_read(reply, "u", &translated);
+                if (r < 0)
+                        goto fail;
         }
 
-        r = sd_bus_message_read(reply, "u", &translated);
-        if (r < 0)
-                goto fail;
-
         l = strlen(name);
         if (buflen < l+1) {
                 *errnop = ENOMEM;
@@ -175,6 +228,7 @@ enum nss_status _nss_systemd_getpwuid_r(
         _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
         _cleanup_(sd_bus_message_unrefp) sd_bus_message* reply = NULL;
         _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
+        _cleanup_free_ char *direct = NULL;
         const char *translated;
         size_t l;
         int r;
@@ -204,30 +258,42 @@ enum nss_status _nss_systemd_getpwuid_r(
         if (getenv_bool("SYSTEMD_NSS_DYNAMIC_BYPASS") > 0)
                 goto not_found;
 
-        r = sd_bus_open_system(&bus);
-        if (r < 0)
-                goto fail;
+        if (getenv_bool("SYSTEMD_NSS_BYPASS_BUS") > 0) {
 
-        r = sd_bus_call_method(bus,
-                               "org.freedesktop.systemd1",
-                               "/org/freedesktop/systemd1",
-                               "org.freedesktop.systemd1.Manager",
-                               "LookupDynamicUserByUID",
-                               &error,
-                               &reply,
-                               "u",
-                               (uint32_t) uid);
-        if (r < 0) {
-                if (sd_bus_error_has_name(&error, BUS_ERROR_NO_SUCH_DYNAMIC_USER))
+                r = direct_lookup_uid(uid, &direct);
+                if (r == -ENOENT)
                         goto not_found;
-
-                goto fail;
+                if (r < 0)
+                        goto fail;
+
+                translated = direct;
+
+        } else {
+                r = sd_bus_open_system(&bus);
+                if (r < 0)
+                        goto fail;
+
+                r = sd_bus_call_method(bus,
+                                       "org.freedesktop.systemd1",
+                                       "/org/freedesktop/systemd1",
+                                       "org.freedesktop.systemd1.Manager",
+                                       "LookupDynamicUserByUID",
+                                       &error,
+                                       &reply,
+                                       "u",
+                                       (uint32_t) uid);
+                if (r < 0) {
+                        if (sd_bus_error_has_name(&error, BUS_ERROR_NO_SUCH_DYNAMIC_USER))
+                                goto not_found;
+
+                        goto fail;
+                }
+
+                r = sd_bus_message_read(reply, "s", &translated);
+                if (r < 0)
+                        goto fail;
         }
 
-        r = sd_bus_message_read(reply, "s", &translated);
-        if (r < 0)
-                goto fail;
-
         l = strlen(translated) + 1;
         if (buflen < l) {
                 *errnop = ENOMEM;
@@ -262,9 +328,6 @@ enum nss_status _nss_systemd_getgrnam_r(
                 char *buffer, size_t buflen,
                 int *errnop) {
 
-        _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
-        _cleanup_(sd_bus_message_unrefp) sd_bus_message* reply = NULL;
-        _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
         uint32_t translated;
         size_t l;
         int r;
@@ -294,30 +357,45 @@ enum nss_status _nss_systemd_getgrnam_r(
         if (getenv_bool("SYSTEMD_NSS_DYNAMIC_BYPASS") > 0)
                 goto not_found;
 
-        r = sd_bus_open_system(&bus);
-        if (r < 0)
-                goto fail;
+        if (getenv_bool("SYSTEMD_NSS_BYPASS_BUS") > 0) {
 
-        r = sd_bus_call_method(bus,
-                               "org.freedesktop.systemd1",
-                               "/org/freedesktop/systemd1",
-                               "org.freedesktop.systemd1.Manager",
-                               "LookupDynamicUserByName",
-                               &error,
-                               &reply,
-                               "s",
-                               name);
-        if (r < 0) {
-                if (sd_bus_error_has_name(&error, BUS_ERROR_NO_SUCH_DYNAMIC_USER))
+                /* Access the dynamic GID allocation directly if we are called from dbus-daemon, see above. */
+                r = direct_lookup_name(name, (uid_t*) &translated);
+                if (r == -ENOENT)
                         goto not_found;
-
-                goto fail;
+                if (r < 0)
+                        goto fail;
+        } else {
+
+                _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
+                _cleanup_(sd_bus_message_unrefp) sd_bus_message* reply = NULL;
+                _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
+
+                r = sd_bus_open_system(&bus);
+                if (r < 0)
+                        goto fail;
+
+                r = sd_bus_call_method(bus,
+                                       "org.freedesktop.systemd1",
+                                       "/org/freedesktop/systemd1",
+                                       "org.freedesktop.systemd1.Manager",
+                                       "LookupDynamicUserByName",
+                                       &error,
+                                       &reply,
+                                       "s",
+                                       name);
+                if (r < 0) {
+                        if (sd_bus_error_has_name(&error, BUS_ERROR_NO_SUCH_DYNAMIC_USER))
+                                goto not_found;
+
+                        goto fail;
+                }
+
+                r = sd_bus_message_read(reply, "u", &translated);
+                if (r < 0)
+                        goto fail;
         }
 
-        r = sd_bus_message_read(reply, "u", &translated);
-        if (r < 0)
-                goto fail;
-
         l = sizeof(char*) + strlen(name) + 1;
         if (buflen < l) {
                 *errnop = ENOMEM;
@@ -353,6 +431,7 @@ enum nss_status _nss_systemd_getgrgid_r(
         _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
         _cleanup_(sd_bus_message_unrefp) sd_bus_message* reply = NULL;
         _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
+        _cleanup_free_ char *direct = NULL;
         const char *translated;
         size_t l;
         int r;
@@ -382,30 +461,41 @@ enum nss_status _nss_systemd_getgrgid_r(
         if (getenv_bool("SYSTEMD_NSS_DYNAMIC_BYPASS") > 0)
                 goto not_found;
 
-        r = sd_bus_open_system(&bus);
-        if (r < 0)
-                goto fail;
+        if (getenv_bool("SYSTEMD_NSS_BYPASS_BUS") > 0) {
 
-        r = sd_bus_call_method(bus,
-                               "org.freedesktop.systemd1",
-                               "/org/freedesktop/systemd1",
-                               "org.freedesktop.systemd1.Manager",
-                               "LookupDynamicUserByUID",
-                               &error,
-                               &reply,
-                               "u",
-                               (uint32_t) gid);
-        if (r < 0) {
-                if (sd_bus_error_has_name(&error, BUS_ERROR_NO_SUCH_DYNAMIC_USER))
+                r = direct_lookup_uid(gid, &direct);
+                if (r == -ENOENT)
                         goto not_found;
-
-                goto fail;
+                if (r < 0)
+                        goto fail;
+
+                translated = direct;
+        } else {
+                r = sd_bus_open_system(&bus);
+                if (r < 0)
+                        goto fail;
+
+                r = sd_bus_call_method(bus,
+                                       "org.freedesktop.systemd1",
+                                       "/org/freedesktop/systemd1",
+                                       "org.freedesktop.systemd1.Manager",
+                                       "LookupDynamicUserByUID",
+                                       &error,
+                                       &reply,
+                                       "u",
+                                       (uint32_t) gid);
+                if (r < 0) {
+                        if (sd_bus_error_has_name(&error, BUS_ERROR_NO_SUCH_DYNAMIC_USER))
+                                goto not_found;
+
+                        goto fail;
+                }
+
+                r = sd_bus_message_read(reply, "s", &translated);
+                if (r < 0)
+                        goto fail;
         }
 
-        r = sd_bus_message_read(reply, "s", &translated);
-        if (r < 0)
-                goto fail;
-
         l = sizeof(char*) + strlen(translated) + 1;
         if (buflen < l) {
                 *errnop = ENOMEM;
diff --git a/src/shared/bus-unit-util.c b/src/shared/bus-unit-util.c
index f9e12e0578..ab30afb527 100644
--- a/src/shared/bus-unit-util.c
+++ b/src/shared/bus-unit-util.c
@@ -204,7 +204,7 @@ int bus_append_unit_property_assignment(sd_bus_message *m, const char *assignmen
                               "IgnoreSIGPIPE", "TTYVHangup", "TTYReset", "RemainAfterExit",
                               "PrivateTmp", "PrivateDevices", "PrivateNetwork", "PrivateUsers", "NoNewPrivileges",
                               "SyslogLevelPrefix", "Delegate", "RemainAfterElapse", "MemoryDenyWriteExecute",
-                              "RestrictRealtime", "DynamicUser")) {
+                              "RestrictRealtime", "DynamicUser", "RemoveIPC")) {
 
                 r = parse_boolean(eq);
                 if (r < 0)
diff --git a/src/shared/clean-ipc.c b/src/shared/clean-ipc.c
index a3ac7aeb82..d5db604f03 100644
--- a/src/shared/clean-ipc.c
+++ b/src/shared/clean-ipc.c
@@ -41,8 +41,20 @@
 #include "macro.h"
 #include "string-util.h"
 #include "strv.h"
+#include "user-util.h"
 
-static int clean_sysvipc_shm(uid_t delete_uid) {
+static bool match_uid_gid(uid_t subject_uid, gid_t subject_gid, uid_t delete_uid, gid_t delete_gid) {
+
+        if (uid_is_valid(delete_uid) && subject_uid == delete_uid)
+                return true;
+
+        if (gid_is_valid(delete_gid) && subject_gid == delete_gid)
+                return true;
+
+        return false;
+}
+
+static int clean_sysvipc_shm(uid_t delete_uid, gid_t delete_gid) {
         _cleanup_fclose_ FILE *f = NULL;
         char line[LINE_MAX];
         bool first = true;
@@ -77,7 +89,7 @@ static int clean_sysvipc_shm(uid_t delete_uid) {
                 if (n_attached > 0)
                         continue;
 
-                if (uid != delete_uid)
+                if (!match_uid_gid(uid, gid, delete_uid, delete_gid))
                         continue;
 
                 if (shmctl(shmid, IPC_RMID, NULL) < 0) {
@@ -89,7 +101,8 @@ static int clean_sysvipc_shm(uid_t delete_uid) {
                         ret = log_warning_errno(errno,
                                                 "Failed to remove SysV shared memory segment %i: %m",
                                                 shmid);
-                }
+                } else
+                        log_debug("Removed SysV shared memory segment %i.", shmid);
         }
 
         return ret;
@@ -98,7 +111,7 @@ fail:
         return log_warning_errno(errno, "Failed to read /proc/sysvipc/shm: %m");
 }
 
-static int clean_sysvipc_sem(uid_t delete_uid) {
+static int clean_sysvipc_sem(uid_t delete_uid, gid_t delete_gid) {
         _cleanup_fclose_ FILE *f = NULL;
         char line[LINE_MAX];
         bool first = true;
@@ -128,7 +141,7 @@ static int clean_sysvipc_sem(uid_t delete_uid) {
                            &semid, &uid, &gid, &cuid, &cgid) != 5)
                         continue;
 
-                if (uid != delete_uid)
+                if (!match_uid_gid(uid, gid, delete_uid, delete_gid))
                         continue;
 
                 if (semctl(semid, 0, IPC_RMID) < 0) {
@@ -140,7 +153,8 @@ static int clean_sysvipc_sem(uid_t delete_uid) {
                         ret = log_warning_errno(errno,
                                                 "Failed to remove SysV semaphores object %i: %m",
                                                 semid);
-                }
+                } else
+                        log_debug("Removed SysV semaphore %i.", semid);
         }
 
         return ret;
@@ -149,7 +163,7 @@ fail:
         return log_warning_errno(errno, "Failed to read /proc/sysvipc/sem: %m");
 }
 
-static int clean_sysvipc_msg(uid_t delete_uid) {
+static int clean_sysvipc_msg(uid_t delete_uid, gid_t delete_gid) {
         _cleanup_fclose_ FILE *f = NULL;
         char line[LINE_MAX];
         bool first = true;
@@ -180,7 +194,7 @@ static int clean_sysvipc_msg(uid_t delete_uid) {
                            &msgid, &cpid, &lpid, &uid, &gid, &cuid, &cgid) != 7)
                         continue;
 
-                if (uid != delete_uid)
+                if (!match_uid_gid(uid, gid, delete_uid, delete_gid))
                         continue;
 
                 if (msgctl(msgid, IPC_RMID, NULL) < 0) {
@@ -192,7 +206,8 @@ static int clean_sysvipc_msg(uid_t delete_uid) {
                         ret = log_warning_errno(errno,
                                                 "Failed to remove SysV message queue %i: %m",
                                                 msgid);
-                }
+                } else
+                        log_debug("Removed SysV message queue %i.", msgid);
         }
 
         return ret;
@@ -201,13 +216,13 @@ fail:
         return log_warning_errno(errno, "Failed to read /proc/sysvipc/msg: %m");
 }
 
-static int clean_posix_shm_internal(DIR *dir, uid_t uid) {
+static int clean_posix_shm_internal(DIR *dir, uid_t uid, gid_t gid) {
         struct dirent *de;
         int ret = 0, r;
 
         assert(dir);
 
-        FOREACH_DIRENT(de, dir, goto fail) {
+        FOREACH_DIRENT_ALL(de, dir, goto fail) {
                 struct stat st;
 
                 if (STR_IN_SET(de->d_name, "..", "."))
@@ -217,12 +232,11 @@ static int clean_posix_shm_internal(DIR *dir, uid_t uid) {
                         if (errno == ENOENT)
                                 continue;
 
-                        log_warning_errno(errno, "Failed to stat() POSIX shared memory segment %s: %m", de->d_name);
-                        ret = -errno;
+                        ret = log_warning_errno(errno, "Failed to stat() POSIX shared memory segment %s: %m", de->d_name);
                         continue;
                 }
 
-                if (st.st_uid != uid)
+                if (!match_uid_gid(st.st_uid, st.st_gid, uid, gid))
                         continue;
 
                 if (S_ISDIR(st.st_mode)) {
@@ -230,12 +244,10 @@ static int clean_posix_shm_internal(DIR *dir, uid_t uid) {
 
                         kid = xopendirat(dirfd(dir), de->d_name, O_NOFOLLOW|O_NOATIME);
                         if (!kid) {
-                                if (errno != ENOENT) {
-                                        log_warning_errno(errno, "Failed to enter shared memory directory %s: %m", de->d_name);
-                                        ret = -errno;
-                                }
+                                if (errno != ENOENT)
+                                        ret = log_warning_errno(errno, "Failed to enter shared memory directory %s: %m", de->d_name);
                         } else {
-                                r = clean_posix_shm_internal(kid, uid);
+                                r = clean_posix_shm_internal(kid, uid, gid);
                                 if (r < 0)
                                         ret = r;
                         }
@@ -245,9 +257,9 @@ static int clean_posix_shm_internal(DIR *dir, uid_t uid) {
                                 if (errno == ENOENT)
                                         continue;
 
-                                log_warning_errno(errno, "Failed to remove POSIX shared memory directory %s: %m", de->d_name);
-                                ret = -errno;
-                        }
+                                ret = log_warning_errno(errno, "Failed to remove POSIX shared memory directory %s: %m", de->d_name);
+                        } else
+                                log_debug("Removed POSIX shared memory directory %s", de->d_name);
                 } else {
 
                         if (unlinkat(dirfd(dir), de->d_name, 0) < 0) {
@@ -255,20 +267,19 @@ static int clean_posix_shm_internal(DIR *dir, uid_t uid) {
                                 if (errno == ENOENT)
                                         continue;
 
-                                log_warning_errno(errno, "Failed to remove POSIX shared memory segment %s: %m", de->d_name);
-                                ret = -errno;
-                        }
+                                ret = log_warning_errno(errno, "Failed to remove POSIX shared memory segment %s: %m", de->d_name);
+                        } else
+                                log_debug("Removed POSIX shared memory segment %s", de->d_name);
                 }
         }
 
         return ret;
 
 fail:
-        log_warning_errno(errno, "Failed to read /dev/shm: %m");
-        return -errno;
+        return log_warning_errno(errno, "Failed to read /dev/shm: %m");
 }
 
-static int clean_posix_shm(uid_t uid) {
+static int clean_posix_shm(uid_t uid, gid_t gid) {
         _cleanup_closedir_ DIR *dir = NULL;
 
         dir = opendir("/dev/shm");
@@ -279,10 +290,10 @@ static int clean_posix_shm(uid_t uid) {
                 return log_warning_errno(errno, "Failed to open /dev/shm: %m");
         }
 
-        return clean_posix_shm_internal(dir, uid);
+        return clean_posix_shm_internal(dir, uid, gid);
 }
 
-static int clean_posix_mq(uid_t uid) {
+static int clean_posix_mq(uid_t uid, gid_t gid) {
         _cleanup_closedir_ DIR *dir = NULL;
         struct dirent *de;
         int ret = 0;
@@ -295,7 +306,7 @@ static int clean_posix_mq(uid_t uid) {
                 return log_warning_errno(errno, "Failed to open /dev/mqueue: %m");
         }
 
-        FOREACH_DIRENT(de, dir, goto fail) {
+        FOREACH_DIRENT_ALL(de, dir, goto fail) {
                 struct stat st;
                 char fn[1+strlen(de->d_name)+1];
 
@@ -312,7 +323,7 @@ static int clean_posix_mq(uid_t uid) {
                         continue;
                 }
 
-                if (st.st_uid != uid)
+                if (!match_uid_gid(st.st_uid, st.st_gid, uid, gid))
                         continue;
 
                 fn[0] = '/';
@@ -325,7 +336,8 @@ static int clean_posix_mq(uid_t uid) {
                         ret = log_warning_errno(errno,
                                                 "Failed to unlink POSIX message queue %s: %m",
                                                 fn);
-                }
+                } else
+                        log_debug("Removed POSIX message queue %s", fn);
         }
 
         return ret;
@@ -334,32 +346,44 @@ fail:
         return log_warning_errno(errno, "Failed to read /dev/mqueue: %m");
 }
 
-int clean_ipc(uid_t uid) {
+int clean_ipc(uid_t uid, gid_t gid) {
         int ret = 0, r;
 
-        /* Refuse to clean IPC of the root and system users */
-        if (uid <= SYSTEM_UID_MAX)
+        /* Anything to do? */
+        if (!uid_is_valid(uid) && !gid_is_valid(gid))
+                return 0;
+
+        /* Refuse to clean IPC of the root user */
+        if (uid == 0 && gid == 0)
                 return 0;
 
-        r = clean_sysvipc_shm(uid);
+        r = clean_sysvipc_shm(uid, gid);
         if (r < 0)
                 ret = r;
 
-        r = clean_sysvipc_sem(uid);
+        r = clean_sysvipc_sem(uid, gid);
         if (r < 0)
                 ret = r;
 
-        r = clean_sysvipc_msg(uid);
+        r = clean_sysvipc_msg(uid, gid);
         if (r < 0)
                 ret = r;
 
-        r = clean_posix_shm(uid);
+        r = clean_posix_shm(uid, gid);
         if (r < 0)
                 ret = r;
 
-        r = clean_posix_mq(uid);
+        r = clean_posix_mq(uid, gid);
         if (r < 0)
                 ret = r;
 
         return ret;
 }
+
+int clean_ipc_by_uid(uid_t uid) {
+        return clean_ipc(uid, GID_INVALID);
+}
+
+int clean_ipc_by_gid(gid_t gid) {
+        return clean_ipc(UID_INVALID, gid);
+}
diff --git a/src/shared/clean-ipc.h b/src/shared/clean-ipc.h
index 44a83afcf7..6ca57f44fd 100644
--- a/src/shared/clean-ipc.h
+++ b/src/shared/clean-ipc.h
@@ -21,4 +21,6 @@
 
 #include <sys/types.h>
 
-int clean_ipc(uid_t uid);
+int clean_ipc(uid_t uid, gid_t gid);
+int clean_ipc_by_uid(uid_t uid);
+int clean_ipc_by_gid(gid_t gid);
diff --git a/src/test/test-ipcrm.c b/src/test/test-ipcrm.c
index c5bcaf47bb..551eba7215 100644
--- a/src/test/test-ipcrm.c
+++ b/src/test/test-ipcrm.c
@@ -32,5 +32,5 @@ int main(int argc, char *argv[]) {
                 return EXIT_FAILURE;
         }
 
-        return clean_ipc(uid) < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
+        return clean_ipc_by_uid(uid) < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
 }