Merge c1875023b9 into 69af4849aa

This separates the preparatory checks that generate D-Bus errors from
the code that actually allocates the session. This make the logic easier
to follow and prepares ground so that we can reuse the 2nd part later
when exposing session creation via Varlink.

src/basic/cgroup-util.c

@@ -1418,6 +1418,26 @@ int cg_pid_get_session(pid_t pid, char **ret_session) {
         return cg_path_get_session(cgroup, ret_session);
 }
 
+int cg_pidref_get_session(const PidRef *pidref, char **ret) {
+        int r;
+
+        if (!pidref_is_set(pidref))
+                return -ESRCH;
+
+        _cleanup_free_ char *session = NULL;
+        r = cg_pid_get_session(pidref->pid, &session);
+        if (r < 0)
+                return r;
+
+        r = pidref_verify(pidref);
+        if (r < 0)
+                return r;
+
+        if (ret)
+                *ret = TAKE_PTR(session);
+        return 0;
+}
+
 int cg_path_get_owner_uid(const char *path, uid_t *ret_uid) {
         _cleanup_free_ char *slice = NULL;
         char *start, *end;
@@ -1455,6 +1475,27 @@ int cg_pid_get_owner_uid(pid_t pid, uid_t *ret_uid) {
         return cg_path_get_owner_uid(cgroup, ret_uid);
 }
 
+int cg_pidref_get_owner_uid(const PidRef *pidref, uid_t *ret) {
+        int r;
+
+        if (!pidref_is_set(pidref))
+                return -ESRCH;
+
+        uid_t uid;
+        r = cg_pid_get_owner_uid(pidref->pid, &uid);
+        if (r < 0)
+                return r;
+
+        r = pidref_verify(pidref);
+        if (r < 0)
+                return r;
+
+        if (ret)
+                *ret = uid;
+
+        return 0;
+}
+
 int cg_path_get_slice(const char *p, char **ret_slice) {
         const char *e = NULL;
 

src/basic/cgroup-util.h

@@ -280,7 +280,9 @@ int cg_shift_path(const char *cgroup, const char *cached_root, const char **ret_
 int cg_pid_get_path_shifted(pid_t pid, const char *cached_root, char **ret_cgroup);
 
 int cg_pid_get_session(pid_t pid, char **ret_session);
+int cg_pidref_get_session(const PidRef *pidref, char **ret_session);
 int cg_pid_get_owner_uid(pid_t pid, uid_t *ret_uid);
+int cg_pidref_get_owner_uid(const PidRef *pidref, uid_t *ret_uid);
 int cg_pid_get_unit(pid_t pid, char **ret_unit);
 int cg_pidref_get_unit(const PidRef *pidref, char **ret);
 int cg_pid_get_user_unit(pid_t pid, char **ret_unit);

src/basic/pidref.c

@@ -429,7 +429,7 @@ int pidref_wait(const PidRef *pidref, siginfo_t *ret, int options) {
         if (pidref_is_remote(pidref))
                 return -EREMOTE;
 
-        if (pidref->pid == 1 || pidref->pid == getpid_cached())
+        if (pidref->pid == 1 || pidref_is_self(pidref))
                 return -ECHILD;
 
         siginfo_t si = {};

src/basic/socket-util.c

@@ -975,6 +975,28 @@ int getpeerpidfd(int fd) {
         return pidfd;
 }
 
+int getpeerpidref(int fd, PidRef *ret) {
+        int r;
+
+        assert(fd >= 0);
+        assert(ret);
+
+        int pidfd = getpeerpidfd(fd);
+        if (pidfd < 0)  {
+                if (!ERRNO_IS_NEG_NOT_SUPPORTED(pidfd))
+                        return pidfd;
+
+                struct ucred ucred;
+                r = getpeercred(fd, &ucred);
+                if (r < 0)
+                        return r;
+
+                return pidref_set_pid(ret, ucred.pid);
+        }
+
+        return pidref_set_pidfd_consume(ret, pidfd);
+}
+
 ssize_t send_many_fds_iov_sa(
                 int transport_fd,
                 int *fds_array, size_t n_fds_array,

src/basic/socket-util.h

@@ -20,6 +20,7 @@
 #include "macro.h"
 #include "missing_network.h"
 #include "missing_socket.h"
+#include "pidref.h"
 #include "sparse-endian.h"
 
 union sockaddr_union {
@@ -154,6 +155,7 @@ int getpeercred(int fd, struct ucred *ucred);
 int getpeersec(int fd, char **ret);
 int getpeergroups(int fd, gid_t **ret);
 int getpeerpidfd(int fd);
+int getpeerpidref(int fd, PidRef *ret);
 
 ssize_t send_many_fds_iov_sa(
                 int transport_fd,

src/basic/terminal-util.c

@@ -761,26 +761,24 @@ bool tty_is_console(const char *tty) {
 }
 
 int vtnr_from_tty(const char *tty) {
-        int i, r;
+        int r;
 
         assert(tty);
 
         tty = skip_dev_prefix(tty);
 
-        if (!startswith(tty, "tty") )
+        const char *e = startswith(tty, "tty");
+        if (!e)
                 return -EINVAL;
 
-        if (!ascii_isdigit(tty[3]))
-                return -EINVAL;
-
-        r = safe_atoi(tty+3, &i);
+        unsigned u;
+        r = safe_atou(e, &u);
         if (r < 0)
                 return r;
+        if (!vtnr_is_valid(u))
+                return -ERANGE;
 
-        if (i < 0 || i > 63)
-                return -EINVAL;
-
-        return i;
+        return (int) u;
 }
 
 int resolve_dev_console(char **ret) {

src/basic/terminal-util.h

@@ -157,3 +157,7 @@ int terminal_is_pty_fd(int fd);
 
 int pty_open_peer_racefree(int fd, int mode);
 int pty_open_peer(int fd, int mode);
+
+static inline bool vtnr_is_valid(unsigned n) {
+        return n >= 1 && n <= 63;
+}

src/libsystemd/sd-bus/test-bus-peersockaddr.c

@@ -81,7 +81,7 @@ static void *server(void *p) {
                 _cleanup_(pidref_done) PidRef pidref = PIDREF_NULL;
 
                 assert_se(pidref_set_pidfd_take(&pidref, pidfd) >= 0);
-                assert_se(pidref.pid == getpid_cached());
+                assert_se(pidref_is_self(&pidref));
         }
 
         const gid_t *gl = NULL;

src/libsystemd/sd-json/json-util.c

@@ -125,14 +125,13 @@ int json_dispatch_in_addr(const char *name, sd_json_variant *variant, sd_json_di
         return 0;
 }
 
-int json_dispatch_path(const char *name, sd_json_variant *variant, sd_json_dispatch_flags_t flags, void *userdata) {
-        char **p = ASSERT_PTR(userdata);
-        const char *path;
+int json_dispatch_const_path(const char *name, sd_json_variant *variant, sd_json_dispatch_flags_t flags, void *userdata) {
+        const char **p = ASSERT_PTR(userdata), *path;
 
         assert(variant);
 
         if (sd_json_variant_is_null(variant)) {
-                *p = mfree(*p);
+                *p = NULL;
                 return 0;
         }
 
@@ -145,8 +144,24 @@ int json_dispatch_path(const char *name, sd_json_variant *variant, sd_json_dispa
         if (!path_is_absolute(path))
                 return json_log(variant, flags, SYNTHETIC_ERRNO(EINVAL), "JSON field '%s' is not an absolute file system path.", strna(name));
 
-        if (free_and_strdup(p, path) < 0)
-                return json_log_oom(variant, flags);
+        *p = path;
+        return 0;
+}
+
+int json_dispatch_path(const char *name, sd_json_variant *variant, sd_json_dispatch_flags_t flags, void *userdata) {
+        char **s = ASSERT_PTR(userdata);
+        const char *p;
+        int r;
+
+        assert_return(variant, -EINVAL);
+
+        r = json_dispatch_const_path(name, variant, flags, &p);
+        if (r < 0)
+                return r;
+
+        r = free_and_strdup(s, p);
+        if (r < 0)
+                return json_log(variant, flags, r, "Failed to allocate path string: %m");
 
         return 0;
 }

src/libsystemd/sd-json/json-util.h

@@ -113,6 +113,7 @@ int json_dispatch_user_group_name(const char *name, sd_json_variant *variant, sd
 int json_dispatch_const_user_group_name(const char *name, sd_json_variant *variant, sd_json_dispatch_flags_t flags, void *userdata);
 int json_dispatch_in_addr(const char *name, sd_json_variant *variant, sd_json_dispatch_flags_t flags, void *userdata);
 int json_dispatch_path(const char *name, sd_json_variant *variant, sd_json_dispatch_flags_t flags, void *userdata);
+int json_dispatch_const_path(const char *name, sd_json_variant *variant, sd_json_dispatch_flags_t flags, void *userdata);
 int json_dispatch_pidref(const char *name, sd_json_variant *variant, sd_json_dispatch_flags_t flags, void *userdata);
 int json_dispatch_devnum(const char *name, sd_json_variant *variant, sd_json_dispatch_flags_t flags, void *userdata);
 int json_dispatch_ifindex(const char *name, sd_json_variant *variant, sd_json_dispatch_flags_t flags, void *userdata);

src/libsystemd/sd-login/sd-login.c

@@ -334,46 +334,46 @@ _public_ int sd_pidfd_get_cgroup(int pidfd, char **ret_cgroup) {
         return 0;
 }
 
-_public_ int sd_peer_get_session(int fd, char **session) {
-        struct ucred ucred = UCRED_INVALID;
+_public_ int sd_peer_get_session(int fd, char **ret) {
         int r;
 
         assert_return(fd >= 0, -EBADF);
-        assert_return(session, -EINVAL);
+        assert_return(ret, -EINVAL);
 
-        r = getpeercred(fd, &ucred);
+        _cleanup_(pidref_done) PidRef pidref = PIDREF_NULL;
+        r = getpeerpidref(fd, &pidref);
         if (r < 0)
                 return r;
 
-        return cg_pid_get_session(ucred.pid, session);
+        return cg_pidref_get_session(&pidref, ret);
 }
 
-_public_ int sd_peer_get_owner_uid(int fd, uid_t *uid) {
-        struct ucred ucred;
+_public_ int sd_peer_get_owner_uid(int fd, uid_t *ret) {
         int r;
 
         assert_return(fd >= 0, -EBADF);
-        assert_return(uid, -EINVAL);
+        assert_return(ret, -EINVAL);
 
-        r = getpeercred(fd, &ucred);
+        _cleanup_(pidref_done) PidRef pidref = PIDREF_NULL;
+        r = getpeerpidref(fd, &pidref);
         if (r < 0)
                 return r;
 
-        return cg_pid_get_owner_uid(ucred.pid, uid);
+        return cg_pidref_get_owner_uid(&pidref, ret);
 }
 
-_public_ int sd_peer_get_unit(int fd, char **unit) {
-        struct ucred ucred;
+_public_ int sd_peer_get_unit(int fd, char **ret) {
         int r;
 
         assert_return(fd >= 0, -EBADF);
-        assert_return(unit, -EINVAL);
+        assert_return(ret, -EINVAL);
 
-        r = getpeercred(fd, &ucred);
+        _cleanup_(pidref_done) PidRef pidref = PIDREF_NULL;
+        r = getpeerpidref(fd, &pidref);
         if (r < 0)
                 return r;
 
-        return cg_pid_get_unit(ucred.pid, unit);
+        return cg_pidref_get_unit(&pidref, ret);
 }
 
 _public_ int sd_peer_get_user_unit(int fd, char **unit) {

src/libsystemd/sd-varlink/sd-varlink.c

@@ -1698,7 +1698,8 @@ _public_ int sd_varlink_get_events(sd_varlink *v) {
                 ret |= EPOLLIN;
 
         if (!v->write_disconnected &&
-            v->output_buffer_size > 0)
+            (v->output_queue ||
+             v->output_buffer_size > 0))
                 ret |= EPOLLOUT;
 
         return ret;
@@ -3218,7 +3219,13 @@ _public_ int sd_varlink_server_new(sd_varlink_server **ret, sd_varlink_server_fl
         int r;
 
         assert_return(ret, -EINVAL);
-        assert_return((flags & ~(SD_VARLINK_SERVER_ROOT_ONLY|SD_VARLINK_SERVER_MYSELF_ONLY|SD_VARLINK_SERVER_ACCOUNT_UID|SD_VARLINK_SERVER_INHERIT_USERDATA|SD_VARLINK_SERVER_INPUT_SENSITIVE)) == 0, -EINVAL);
+        assert_return((flags & ~(SD_VARLINK_SERVER_ROOT_ONLY|
+                                 SD_VARLINK_SERVER_MYSELF_ONLY|
+                                 SD_VARLINK_SERVER_ACCOUNT_UID|
+                                 SD_VARLINK_SERVER_INHERIT_USERDATA|
+                                 SD_VARLINK_SERVER_INPUT_SENSITIVE|
+                                 SD_VARLINK_SERVER_ALLOW_FD_PASSING_INPUT|
+                                 SD_VARLINK_SERVER_ALLOW_FD_PASSING_OUTPUT)) == 0, -EINVAL);
 
         s = new(sd_varlink_server, 1);
         if (!s)
@@ -3399,6 +3406,9 @@ _public_ int sd_varlink_server_add_connection_pair(
         if (asprintf(&desc, "%s-%i-%i", varlink_server_description(server), input_fd, output_fd) >= 0)
                 v->description = TAKE_PTR(desc);
 
+        (void) sd_varlink_set_allow_fd_passing_input(v, FLAGS_SET(server->flags, SD_VARLINK_SERVER_ALLOW_FD_PASSING_INPUT));
+        (void) sd_varlink_set_allow_fd_passing_output(v, FLAGS_SET(server->flags, SD_VARLINK_SERVER_ALLOW_FD_PASSING_OUTPUT));
+
         /* Link up the server and the connection, and take reference in both directions. Note that the
          * reference on the connection is left dangling. It will be dropped when the connection is closed,
          * which happens in varlink_close(), including in the event loop quit callback. */

src/login/logind-dbus.c

@@ -85,6 +85,8 @@ static int get_sender_session(
         const char *name;
         int r;
 
+        assert(m);
+
         /* Acquire the sender's session. This first checks if the sending process is inside a session itself,
          * and returns that. If not and 'consult_display' is true, this returns the display session of the
          * owning user of the caller. */
@@ -827,186 +829,18 @@ static int method_list_inhibitors(sd_bus_message *message, void *userdata, sd_bu
         return sd_bus_send(NULL, reply, NULL);
 }
 
-static int create_session(
-                sd_bus_message *message,
-                void *userdata,
-                sd_bus_error *error,
-                uid_t uid,
-                pid_t leader_pid,
-                int leader_pidfd,
-                const char *service,
-                const char *type,
-                const char *class,
-                const char *desktop,
-                const char *cseat,
-                uint32_t vtnr,
-                const char *tty,
-                const char *display,
-                int remote,
-                const char *remote_user,
-                const char *remote_host,
-                uint64_t flags) {
+static int manager_choose_session_id(
+                Manager *m,
+                PidRef *leader,
+                char **ret_id) {
+
+        assert(m);
+        assert(pidref_is_set(leader));
+        assert(ret_id);
 
-        _cleanup_(pidref_done) PidRef leader = PIDREF_NULL;
-        Manager *m = ASSERT_PTR(userdata);
         _cleanup_free_ char *id = NULL;
-        Session *session = NULL;
         uint32_t audit_id = 0;
-        User *user = NULL;
-        Seat *seat = NULL;
-        SessionType t;
-        SessionClass c;
-        int r;
-
-        assert(message);
-
-        if (!uid_is_valid(uid))
-                return sd_bus_error_set(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid UID");
-
-        if (flags != 0)
-                return sd_bus_error_set(error, SD_BUS_ERROR_INVALID_ARGS, "Flags must be zero.");
-
-        if (leader_pidfd >= 0)
-                r = pidref_set_pidfd(&leader, leader_pidfd);
-        else if (leader_pid == 0)
-                r = bus_query_sender_pidref(message, &leader);
-        else {
-                if (leader_pid < 0)
-                        return sd_bus_error_set(error, SD_BUS_ERROR_INVALID_ARGS, "Leader PID is not valid");
-
-                r = pidref_set_pid(&leader, leader_pid);
-        }
-        if (r < 0)
-                return r;
-
-        if (leader.pid == 1 || leader.pid == getpid_cached())
-                return sd_bus_error_set(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid leader PID");
-
-        if (isempty(type))
-                t = _SESSION_TYPE_INVALID;
-        else {
-                t = session_type_from_string(type);
-                if (t < 0)
-                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS,
-                                                 "Invalid session type %s", type);
-        }
-
-        if (isempty(class))
-                c = _SESSION_CLASS_INVALID;
-        else {
-                c = session_class_from_string(class);
-                if (c < 0)
-                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS,
-                                                 "Invalid session class %s", class);
-        }
-
-        if (isempty(desktop))
-                desktop = NULL;
-        else {
-                if (!string_is_safe(desktop))
-                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS,
-                                                 "Invalid desktop string %s", desktop);
-        }
-
-        if (isempty(cseat))
-                seat = NULL;
-        else {
-                seat = hashmap_get(m->seats, cseat);
-                if (!seat)
-                        return sd_bus_error_setf(error, BUS_ERROR_NO_SUCH_SEAT,
-                                                 "No seat '%s' known", cseat);
-        }
-
-        if (tty_is_vc(tty)) {
-                int v;
-
-                if (!seat)
-                        seat = m->seat0;
-                else if (seat != m->seat0)
-                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS,
-                                                 "TTY %s is virtual console but seat %s is not seat0", tty, seat->id);
-
-                v = vtnr_from_tty(tty);
-                if (v <= 0)
-                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS,
-                                                 "Cannot determine VT number from virtual console TTY %s", tty);
-
-                if (vtnr == 0)
-                        vtnr = (uint32_t) v;
-                else if (vtnr != (uint32_t) v)
-                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS,
-                                                 "Specified TTY and VT number do not match");
-
-        } else if (tty_is_console(tty)) {
-
-                if (!seat)
-                        seat = m->seat0;
-                else if (seat != m->seat0)
-                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS,
-                                                 "Console TTY specified but seat is not seat0");
-
-                if (vtnr != 0)
-                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS,
-                                                 "Console TTY specified but VT number is not 0");
-        }
-
-        if (seat) {
-                if (seat_has_vts(seat)) {
-                        if (vtnr <= 0 || vtnr > 63)
-                                return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS,
-                                                         "VT number out of range");
-                } else {
-                        if (vtnr != 0)
-                                return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS,
-                                                         "Seat has no VTs but VT number not 0");
-                }
-        }
-
-        if (t == _SESSION_TYPE_INVALID) {
-                if (!isempty(display))
-                        t = SESSION_X11;
-                else if (!isempty(tty))
-                        t = SESSION_TTY;
-                else
-                        t = SESSION_UNSPECIFIED;
-        }
-
-        if (c == _SESSION_CLASS_INVALID) {
-                if (t == SESSION_UNSPECIFIED)
-                        c = SESSION_BACKGROUND;
-                else
-                        c = SESSION_USER;
-        }
-
-        /* Check if we are already in a logind session, and if so refuse. */
-        r = manager_get_session_by_pidref(m, &leader, /* ret_session= */ NULL);
-        if (r < 0)
-                return log_debug_errno(
-                                r,
-                                "Failed to check if process " PID_FMT " is already in a session: %m",
-                                leader.pid);
-        if (r > 0)
-                return sd_bus_error_setf(error, BUS_ERROR_SESSION_BUSY,
-                                         "Already running in a session or user slice");
-
-        /* Old gdm and lightdm start the user-session on the same VT as the greeter session. But they destroy
-         * the greeter session after the user-session and want the user-session to take over the VT. We need
-         * to support this for backwards-compatibility, so make sure we allow new sessions on a VT that a
-         * greeter is running on. Furthermore, to allow re-logins, we have to allow a greeter to take over a
-         * used VT for the exact same reasons. */
-        if (c != SESSION_GREETER &&
-            vtnr > 0 &&
-            vtnr < MALLOC_ELEMENTSOF(m->seat0->positions) &&
-            m->seat0->positions[vtnr] &&
-            m->seat0->positions[vtnr]->class != SESSION_GREETER)
-                return sd_bus_error_set(error, BUS_ERROR_SESSION_BUSY, "Already occupied by a session");
-
-        if (hashmap_size(m->sessions) >= m->sessions_max)
-                return sd_bus_error_setf(error, SD_BUS_ERROR_LIMITS_EXCEEDED,
-                                         "Maximum number of sessions (%" PRIu64 ") reached, refusing further sessions.",
-                                         m->sessions_max);
-
-        (void) audit_session_from_pid(&leader, &audit_id);
+        (void) audit_session_from_pid(leader, &audit_id);
         if (audit_session_is_valid(audit_id)) {
                 /* Keep our session IDs and the audit session IDs in sync */
 
@@ -1022,7 +856,7 @@ static int create_session(
                 }
         }
 
-        if (!id) {
+        if (!id)
                 do {
                         id = mfree(id);
 
@@ -1030,15 +864,97 @@ static int create_session(
                                 return -ENOMEM;
 
                 } while (hashmap_contains(m->sessions, id));
-        }
 
         /* The generated names should not clash with 'auto' or 'self' */
         assert(!SESSION_IS_SELF(id));
         assert(!SESSION_IS_AUTO(id));
 
+        *ret_id = TAKE_PTR(id);
+        return 0;
+}
+
+int manager_create_session(
+                Manager *m,
+                uid_t uid,
+                PidRef *leader, /* consumed */
+                const char *service,
+                SessionType type,
+                SessionClass class,
+                const char *desktop,
+                Seat *seat,
+                unsigned vtnr,
+                const char *tty,
+                const char *display,
+                bool remote,
+                const char *remote_user,
+                const char *remote_host,
+                Session **ret_session) {
+
+        int r;
+
+        assert(m);
+        assert(uid_is_valid(uid));
+        assert(pidref_is_set(leader));
+        assert(ret_session);
+
+        /* Returns:
+         *    -EBUSY         → client is already in a session
+         *    -EADDRNOTAVAIL → VT is already taken
+         *    -EUSERS        → limit of sessions reached
+         */
+
+        if (type == _SESSION_TYPE_INVALID) {
+                if (!isempty(display))
+                        type = SESSION_X11;
+                else if (!isempty(tty))
+                        type = SESSION_TTY;
+                else
+                        type = SESSION_UNSPECIFIED;
+        }
+
+        if (class == _SESSION_CLASS_INVALID) {
+                if (type == SESSION_UNSPECIFIED)
+                        class = SESSION_BACKGROUND;
+                else
+                        class = SESSION_USER;
+        }
+
+        /* Check if we are already in a logind session, and if so refuse. */
+        r = manager_get_session_by_pidref(m, leader, /* ret_session= */ NULL);
+        if (r < 0)
+                return log_debug_errno(
+                                r,
+                                "Failed to check if process " PID_FMT " is already in a session: %m",
+                                leader->pid);
+        if (r > 0)
+                return log_debug_errno(SYNTHETIC_ERRNO(EBUSY), "Client is already in a session.");
+
+        /* Old gdm and lightdm start the user-session on the same VT as the greeter session. But they destroy
+         * the greeter session after the user-session and want the user-session to take over the VT. We need
+         * to support this for backwards-compatibility, so make sure we allow new sessions on a VT that a
+         * greeter is running on. Furthermore, to allow re-logins, we have to allow a greeter to take over a
+         * used VT for the exact same reasons. */
+        if (class != SESSION_GREETER &&
+            vtnr > 0 &&
+            vtnr < MALLOC_ELEMENTSOF(m->seat0->positions) &&
+            m->seat0->positions[vtnr] &&
+            m->seat0->positions[vtnr]->class != SESSION_GREETER)
+                return log_debug_errno(SYNTHETIC_ERRNO(EADDRNOTAVAIL), "VT already occupied by a session.");
+
+        if (hashmap_size(m->sessions) >= m->sessions_max)
+                return log_debug_errno(SYNTHETIC_ERRNO(EUSERS), "Maximum number of sessions (%" PRIu64 ") reached, refusing further sessions.", m->sessions_max);
+
+        _cleanup_free_ char *id = NULL;
+        r = manager_choose_session_id(m, leader, &id);
+        if (r < 0)
+                return r;
+
         /* If we are not watching utmp already, try again */
         manager_reconnect_utmp(m);
 
+        User *user = NULL;
+        Session *session = NULL;
+
         r = manager_add_user_by_uid(m, uid, &user);
         if (r < 0)
                 goto fail;
@@ -1048,21 +964,21 @@ static int create_session(
                 goto fail;
 
         session_set_user(session, user);
-        r = session_set_leader_consume(session, TAKE_PIDREF(leader));
+        r = session_set_leader_consume(session, TAKE_PIDREF(*leader));
         if (r < 0)
                 goto fail;
 
-        session->original_type = session->type = t;
+        session->original_type = session->type = type;
         session->remote = remote;
         session->vtnr = vtnr;
-        session->class = c;
+        session->class = class;
 
         /* Once the first session that is of a pinning class shows up we'll change the GC mode for the user
          * from USER_GC_BY_ANY to USER_GC_BY_PIN, so that the user goes away once the last pinning session
          * goes away. Background: we want that user@.service – when started manually – remains around (which
          * itself is a non-pinning session), but gets stopped when the last pinning session goes away. */
 
-        if (SESSION_CLASS_PIN_USER(c))
+        if (SESSION_CLASS_PIN_USER(class))
                 user->gc_mode = USER_GC_BY_PIN;
 
         if (!isempty(tty)) {
@@ -1109,14 +1025,184 @@ static int create_session(
                         goto fail;
         }
 
+        *ret_session = session;
+        return 0;
+
+fail:
+        if (session)
+                session_add_to_gc_queue(session);
+
+        if (user)
+                user_add_to_gc_queue(user);
+
+        return r;
+}
+
+static int manager_create_session_by_bus(
+                Manager *m,
+                sd_bus_message *message,
+                sd_bus_error *error,
+                uid_t uid,
+                pid_t leader_pid,
+                int leader_pidfd,
+                const char *service,
+                const char *type,
+                const char *class,
+                const char *desktop,
+                const char *cseat,
+                uint32_t vtnr,
+                const char *tty,
+                const char *display,
+                int remote,
+                const char *remote_user,
+                const char *remote_host,
+                uint64_t flags) {
+
+        int r;
+
+        assert(m);
+        assert(message);
+
+        if (!uid_is_valid(uid))
+                return sd_bus_error_set(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid UID");
+
+        if (flags != 0)
+                return sd_bus_error_set(error, SD_BUS_ERROR_INVALID_ARGS, "Flags must be zero.");
+
+        _cleanup_(pidref_done) PidRef leader = PIDREF_NULL;
+        if (leader_pidfd >= 0)
+                r = pidref_set_pidfd(&leader, leader_pidfd);
+        else if (leader_pid == 0)
+                r = bus_query_sender_pidref(message, &leader);
+        else {
+                if (leader_pid < 0)
+                        return sd_bus_error_set(error, SD_BUS_ERROR_INVALID_ARGS, "Leader PID is not valid");
+
+                r = pidref_set_pid(&leader, leader_pid);
+        }
+        if (r < 0)
+                return r;
+
+        if (leader.pid == 1 || pidref_is_self(&leader))
+                return sd_bus_error_set(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid leader PID");
+
+        SessionType t;
+        if (isempty(type))
+                t = _SESSION_TYPE_INVALID;
+        else {
+                t = session_type_from_string(type);
+                if (t < 0)
+                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS,
+                                                 "Invalid session type %s", type);
+        }
+
+        SessionClass c;
+        if (isempty(class))
+                c = _SESSION_CLASS_INVALID;
+        else {
+                c = session_class_from_string(class);
+                if (c < 0)
+                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS,
+                                                 "Invalid session class %s", class);
+        }
+
+        if (isempty(desktop))
+                desktop = NULL;
+        else {
+                if (!string_is_safe(desktop))
+                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS,
+                                                 "Invalid desktop string %s", desktop);
+        }
+
+        Seat *seat = NULL;
+        if (isempty(cseat))
+                seat = NULL;
+        else {
+                seat = hashmap_get(m->seats, cseat);
+                if (!seat)
+                        return sd_bus_error_setf(error, BUS_ERROR_NO_SUCH_SEAT,
+                                                 "No seat '%s' known", cseat);
+        }
+
+        if (isempty(tty))
+                tty = NULL;
+        else if (tty_is_vc(tty)) {
+                int v;
+
+                if (!seat)
+                        seat = m->seat0;
+                else if (seat != m->seat0)
+                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS,
+                                                 "TTY %s is virtual console but seat %s is not seat0", tty, seat->id);
+
+                v = vtnr_from_tty(tty);
+                if (v <= 0)
+                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS,
+                                                 "Cannot determine VT number from virtual console TTY %s", tty);
+
+                if (vtnr == 0)
+                        vtnr = (uint32_t) v;
+                else if (vtnr != (uint32_t) v)
+                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS,
+                                                 "Specified TTY and VT number do not match");
+
+        } else if (tty_is_console(tty)) {
+
+                if (!seat)
+                        seat = m->seat0;
+                else if (seat != m->seat0)
+                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS,
+                                                 "Console TTY specified but seat is not seat0");
+
+                if (vtnr != 0)
+                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS,
+                                                 "Console TTY specified but VT number is not 0");
+        }
+
+        if (seat) {
+                if (seat_has_vts(seat)) {
+                        if (!vtnr_is_valid(vtnr))
+                                return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS,
+                                                         "VT number out of range");
+                } else {
+                        if (vtnr != 0)
+                                return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS,
+                                                         "Seat has no VTs but VT number not 0");
+                }
+        }
+
+        Session *session;
+        r = manager_create_session(
+                        m,
+                        uid,
+                        &leader,
+                        service,
+                        t,
+                        c,
+                        desktop,
+                        seat,
+                        vtnr,
+                        tty,
+                        display,
+                        remote,
+                        remote_user,
+                        remote_host,
+                        &session);
+        if (r == -EBUSY)
+                return sd_bus_error_setf(error, BUS_ERROR_SESSION_BUSY, "Already running in a session or user slice");
+        if (r == -EADDRNOTAVAIL)
+                return sd_bus_error_set(error, BUS_ERROR_SESSION_BUSY, "Virtual terminal already occupied by a session");
+        if (r == -EUSERS)
+                return sd_bus_error_setf(error, SD_BUS_ERROR_LIMITS_EXCEEDED, "Maximum number of sessions (%" PRIu64 ") reached, refusing further sessions.", m->sessions_max);
+        if (r < 0)
+                return r;
+
         r = sd_bus_message_enter_container(message, 'a', "(sv)");
         if (r < 0)
                 goto fail;
-
         r = session_start(session, message, error);
         if (r < 0)
                 goto fail;
-
         r = sd_bus_message_exit_container(message);
         if (r < 0)
                 goto fail;
@@ -1130,7 +1216,7 @@ static int create_session(
          * all is complete - or wait again. */
         r = session_send_create_reply(session, /* error= */ NULL);
         if (r < 0)
-                return r;
+                goto fail;
 
         return 1;
 
@@ -1138,9 +1224,6 @@ fail:
         if (session)
                 session_add_to_gc_queue(session);
 
-        if (user)
-                user_add_to_gc_queue(user);
-
         return r;
 }
 
@@ -1175,9 +1258,9 @@ static int method_create_session(sd_bus_message *message, void *userdata, sd_bus
         if (r < 0)
                 return r;
 
-        return create_session(
-                        message,
+        return manager_create_session_by_bus(
                         userdata,
+                        message,
                         error,
                         uid,
                         leader_pid,
@@ -1223,9 +1306,9 @@ static int method_create_session_pidfd(sd_bus_message *message, void *userdata,
         if (r < 0)
                 return r;
 
-        return create_session(
-                        message,
+        return manager_create_session_by_bus(
                         userdata,
+                        message,
                         error,
                         uid,
                         /* leader_pid = */ 0,

src/login/logind-dbus.h

@@ -47,4 +47,21 @@ int manager_job_is_active(Manager *manager, const char *path, sd_bus_error *erro
 
 void manager_load_scheduled_shutdown(Manager *m);
 
+int manager_create_session(
+                Manager *m,
+                uid_t uid,
+                PidRef *leader,
+                const char *service,
+                SessionType type,
+                SessionClass class,
+                const char *desktop,
+                Seat *seat,
+                unsigned vtnr,
+                const char *tty,
+                const char *display,
+                bool remote,
+                const char *remote_user,
+                const char *remote_host,
+                Session **ret_session);
+
 extern const BusObjectImplementation manager_object;

src/login/logind-session-dbus.c

@@ -899,62 +899,40 @@ int session_send_lock_all(Manager *m, bool lock) {
         return r;
 }
 
-static bool session_job_pending(Session *s) {
-        assert(s);
-        assert(s->user);
-
-        /* Check if we have some jobs enqueued and not finished yet. Each time we get JobRemoved signal about
-         * relevant units, session_send_create_reply and hence us is called (see match_job_removed).
-         * Note that we don't care about job result here. */
-
-        return s->scope_job ||
-               s->user->runtime_dir_job ||
-               (SESSION_CLASS_WANTS_SERVICE_MANAGER(s->class) && s->user->service_manager_job);
-}
-
-int session_send_create_reply(Session *s, sd_bus_error *error) {
-        _cleanup_(sd_bus_message_unrefp) sd_bus_message *c = NULL;
-        _cleanup_close_ int fifo_fd = -EBADF;
-        _cleanup_free_ char *p = NULL;
-
+int session_send_create_reply_bus(Session *s, const sd_bus_error *error) {
         assert(s);
 
-        /* This is called after the session scope and the user service were successfully created, and finishes where
-         * bus_manager_create_session() left off. */
+        /* This is called after the session scope and the user service were successfully created, and
+         * finishes where manager_create_session() left off. */
 
-        if (!s->create_message)
+        _cleanup_(sd_bus_message_unrefp) sd_bus_message *c = TAKE_PTR(s->create_message);
+        if (!c)
                 return 0;
 
-        /* If error occurred, return it immediately. Otherwise let's wait for all jobs to finish before
-         * continuing. */
-        if (!sd_bus_error_is_set(error) && session_job_pending(s))
-                return 0;
-
-        c = TAKE_PTR(s->create_message);
-        if (error)
+        if (sd_bus_error_is_set(error))
                 return sd_bus_reply_method_error(c, error);
 
-        fifo_fd = session_create_fifo(s);
+        _cleanup_close_ int fifo_fd = session_create_fifo(s);
         if (fifo_fd < 0)
                 return fifo_fd;
 
         /* Update the session state file before we notify the client about the result. */
         session_save(s);
 
-        p = session_bus_path(s);
+        _cleanup_free_ char *p = session_bus_path(s);
         if (!p)
                 return -ENOMEM;
 
-        log_debug("Sending reply about created session: "
-                  "id=%s object_path=%s uid=%u runtime_path=%s "
+        log_debug("Sending D-Bus reply about created session: "
+                  "id=%s object_path=%s uid=" UID_FMT " runtime_path=%s "
                   "session_fd=%d seat=%s vtnr=%u",
                   s->id,
                   p,
-                  (uint32_t) s->user->user_record->uid,
+                  s->user->user_record->uid,
                   s->user->runtime_path,
                   fifo_fd,
                   s->seat ? s->seat->id : "",
-                  (uint32_t) s->vtnr);
+                  s->vtnr);
 
         return sd_bus_reply_method_return(
                         c, "soshusub",
@@ -968,7 +946,7 @@ int session_send_create_reply(Session *s, sd_bus_error *error) {
                         false);
 }
 
-int session_send_upgrade_reply(Session *s, sd_bus_error *error) {
+int session_send_upgrade_reply(Session *s, const sd_bus_error *error) {
         _cleanup_(sd_bus_message_unrefp) sd_bus_message *c = NULL;
         assert(s);
 

src/login/logind-session-dbus.h

@@ -15,8 +15,8 @@ int session_send_changed(Session *s, const char *properties, ...) _sentinel_;
 int session_send_lock(Session *s, bool lock);
 int session_send_lock_all(Manager *m, bool lock);
 
-int session_send_create_reply(Session *s, sd_bus_error *error);
-int session_send_upgrade_reply(Session *s, sd_bus_error *error);
+int session_send_create_reply_bus(Session *s, const sd_bus_error *error);
+int session_send_upgrade_reply(Session *s, const sd_bus_error *error);
 
 int bus_session_method_activate(sd_bus_message *message, void *userdata, sd_bus_error *error);
 int bus_session_method_lock(sd_bus_message *message, void *userdata, sd_bus_error *error);

src/login/logind-session.c

@@ -29,6 +29,7 @@
 #include "logind-session-dbus.h"
 #include "logind-session.h"
 #include "logind-user-dbus.h"
+#include "logind-varlink.h"
 #include "mkdir-label.h"
 #include "parse-util.h"
 #include "path-util.h"
@@ -192,6 +193,8 @@ Session* session_free(Session *s) {
         sd_bus_message_unref(s->create_message);
         sd_bus_message_unref(s->upgrade_message);
 
+        sd_varlink_unref(s->create_link);
+
         free(s->tty);
         free(s->display);
         free(s->remote_host);
@@ -1648,6 +1651,35 @@ void session_drop_controller(Session *s) {
         session_restore_vt(s);
 }
 
+bool session_job_pending(Session *s) {
+        assert(s);
+        assert(s->user);
+
+        /* Check if we have some jobs enqueued and not finished yet. Each time we get JobRemoved signal about
+         * relevant units, session_send_create_reply and hence us is called (see match_job_removed).
+         * Note that we don't care about job result here. */
+
+        return s->scope_job ||
+               s->user->runtime_dir_job ||
+               (SESSION_CLASS_WANTS_SERVICE_MANAGER(s->class) && s->user->service_manager_job);
+}
+
+int session_send_create_reply(Session *s, const sd_bus_error *error) {
+        int r;
+
+        assert(s);
+
+        /* If error occurred, return it immediately. Otherwise let's wait for all jobs to finish before
+         * continuing. */
+        if (!sd_bus_error_is_set(error) && session_job_pending(s))
+                return 0;
+
+        r = 0;
+        RET_GATHER(r, session_send_create_reply_bus(s, error));
+        RET_GATHER(r, session_send_create_reply_varlink(s, error));
+        return r;
+}
+
 static const char* const session_state_table[_SESSION_STATE_MAX] = {
         [SESSION_OPENING] = "opening",
         [SESSION_ONLINE]  = "online",

src/login/logind-session.h

@@ -150,6 +150,8 @@ struct Session {
         sd_bus_message *create_message;   /* The D-Bus message used to create the session, which we haven't responded to yet */
         sd_bus_message *upgrade_message;  /* The D-Bus message used to upgrade the session class user-incomplete → user, which we haven't responded to yet */
 
+        sd_varlink *create_link; /* The Varlink connection used to create session, which we haven't responded to yet */
+
         /* Set up when a client requested to release the session via the bus */
         sd_event_source *timer_event_source;
 
@@ -216,6 +218,10 @@ bool session_is_controller(Session *s, const char *sender);
 int session_set_controller(Session *s, const char *sender, bool force, bool prepare);
 void session_drop_controller(Session *s);
 
+bool session_job_pending(Session *s);
+
+int session_send_create_reply(Session *s, const sd_bus_error *error);
+
 static inline bool SESSION_IS_SELF(const char *name) {
         return isempty(name) || streq(name, "self");
 }

src/login/logind-varlink.c

@@ -0,0 +1,373 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include "cgroup-util.h"
+#include "fd-util.h"
+#include "json-util.h"
+#include "logind.h"
+#include "logind-dbus.h"
+#include "logind-session-dbus.h"
+#include "logind-varlink.h"
+#include "terminal-util.h"
+#include "user-util.h"
+#include "varlink-io.systemd.Login.h"
+#include "varlink-util.h"
+
+static int manager_varlink_get_session_by_peer(
+                Manager *m,
+                sd_varlink *link,
+                bool consult_display,
+                Session **ret) {
+
+        int r;
+
+        assert(m);
+        assert(link);
+        assert(ret);
+
+        /* Determines the session of the peer. If the peer is not part of a session, but consult_display is
+         * true, then will return the display session of the peer's owning user */
+
+        _cleanup_(pidref_done) PidRef pidref = PIDREF_NULL;
+        r = varlink_get_peer_pidref(link, &pidref);
+        if (r < 0)
+                return log_error_errno(r, "Failed to acquire peer PID: %m");
+
+        Session *session = NULL;
+        _cleanup_free_ char *name = NULL;
+        r = cg_pidref_get_session(&pidref, &name);
+        if (r < 0) {
+                if (!consult_display)
+                        log_debug_errno(r, "Failed to acquire session of peer, giving up: %m");
+                else {
+                        log_debug_errno(r, "Failed to acquire session of peer, trying to find owner UID: %m");
+
+                        uid_t uid;
+                        r = cg_pidref_get_owner_uid(&pidref, &uid);
+                        if (r < 0)
+                                log_debug_errno(r, "Failed to acquire owning UID of peer, giving up: %m");
+                        else {
+                                User *user = hashmap_get(m->users, UID_TO_PTR(uid));
+                                if (user)
+                                        session = user->display;
+                         }
+                }
+        } else
+                session = hashmap_get(m->sessions, name);
+
+        if (!session)
+                return sd_varlink_error(link, "io.systemd.Login.NoSuchSession", /* parameters= */ NULL);
+
+        *ret = session;
+        return 0;
+}
+
+static int manager_varlink_get_session_by_name(
+                Manager *m,
+                sd_varlink *link,
+                const char *name,
+                Session **ret) {
+
+        assert(m);
+        assert(link);
+        assert(ret);
+
+        /* Resolves a session name to a session object. Supports resolving the special names "self" and "auto". */
+
+        if (SESSION_IS_SELF(name))
+                return manager_varlink_get_session_by_peer(m, link, /* consult_display= */ false, ret);
+        if (SESSION_IS_AUTO(name))
+                return manager_varlink_get_session_by_peer(m, link, /* consult_display= */ true, ret);
+
+        Session *session = hashmap_get(m->sessions, name);
+        if (!session)
+                return sd_varlink_error(link, "io.systemd.Login.NoSuchSession", /* parameters= */ NULL);
+
+        *ret = session;
+        return 0;
+}
+
+int session_send_create_reply_varlink(Session *s, const sd_bus_error *error) {
+        assert(s);
+
+        /* This is called after the session scope and the user service were successfully created, and
+         * finishes where manager_create_session() left off. */
+
+        _cleanup_(sd_varlink_unrefp) sd_varlink *vl = TAKE_PTR(s->create_link);
+        if (!vl)
+                return 0;
+
+        if (sd_bus_error_is_set(error))
+                return sd_varlink_error(vl, "io.systemd.Login.UnitAllocationFailed", /* parameters= */ NULL);
+
+        _cleanup_close_ int fifo_fd = session_create_fifo(s);
+        if (fifo_fd < 0)
+                return fifo_fd;
+
+        /* Update the session state file before we notify the client about the result. */
+        session_save(s);
+
+        log_debug("Sending Varlink reply about created session: "
+                  "id=%s uid=" UID_FMT " runtime_path=%s "
+                  "session_fd=%d seat=%s vtnr=%u",
+                  s->id,
+                  s->user->user_record->uid,
+                  s->user->runtime_path,
+                  fifo_fd,
+                  s->seat ? s->seat->id : "",
+                  s->vtnr);
+
+        int fifo_fd_idx = sd_varlink_push_fd(vl, fifo_fd);
+        if (fifo_fd_idx < 0) {
+                log_error_errno(fifo_fd_idx, "Failed to push FIFO fd to Varlink: %m");
+                return sd_varlink_error_errno(vl, fifo_fd_idx);
+        }
+
+        TAKE_FD(fifo_fd);
+
+        return sd_varlink_replybo(
+                        vl,
+                        SD_JSON_BUILD_PAIR_STRING("Id", s->id),
+                        SD_JSON_BUILD_PAIR_STRING("RuntimePath", s->user->runtime_path),
+                        SD_JSON_BUILD_PAIR_UNSIGNED("SessionFileDescriptor", fifo_fd_idx),
+                        SD_JSON_BUILD_PAIR_UNSIGNED("UID", s->user->user_record->uid),
+                        SD_JSON_BUILD_PAIR_CONDITION(!!s->seat, "Seat", SD_JSON_BUILD_STRING(s->seat ? s->seat->id : NULL)),
+                        SD_JSON_BUILD_PAIR_CONDITION(s->vtnr > 0, "VTNr", SD_JSON_BUILD_UNSIGNED(s->vtnr)));
+}
+
+static JSON_DISPATCH_ENUM_DEFINE(json_dispatch_session_class, SessionClass, session_class_from_string);
+static JSON_DISPATCH_ENUM_DEFINE(json_dispatch_session_type, SessionType, session_type_from_string);
+
+static int vl_method_create_session(sd_varlink *link, sd_json_variant *parameters, sd_varlink_method_flags_t flags, void *userdata) {
+        Manager *m = ASSERT_PTR(userdata);
+        int r;
+
+        struct {
+                uid_t uid;
+                const char *service;
+                SessionType type;
+                SessionClass class;
+                const char *desktop;
+                const char *seat;
+                unsigned vtnr;
+                const char *tty;
+                const char *display;
+                int remote;
+                const char *remote_user;
+                const char *remote_host;
+        } p = {
+                .uid = UID_INVALID,
+                .class = _SESSION_CLASS_INVALID,
+                .type = _SESSION_TYPE_INVALID,
+                .remote = -1,
+        };
+
+        static const sd_json_dispatch_field dispatch_table[] = {
+                { "UID",        _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_uid_gid,      voffsetof(p, uid),         SD_JSON_MANDATORY },
+                { "Service",    SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string, voffsetof(p, service),     0                 },
+                { "Type",       SD_JSON_VARIANT_STRING,        json_dispatch_session_type,    voffsetof(p, type),        SD_JSON_MANDATORY },
+                { "Class",      SD_JSON_VARIANT_STRING,        json_dispatch_session_class,   voffsetof(p, class),       SD_JSON_MANDATORY },
+                { "Desktop",    SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string, voffsetof(p, desktop),     SD_JSON_STRICT    },
+                { "Seat",       SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string, voffsetof(p, seat),        0                 },
+                { "VTNr",       _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_uint,         voffsetof(p, vtnr),        0                 },
+                { "TTY",        SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string, voffsetof(p, tty),         0                 },
+                { "Display",    SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string, voffsetof(p, display),     0                 },
+                { "Remote",     SD_JSON_VARIANT_BOOLEAN,       sd_json_dispatch_tristate,     voffsetof(p, remote),      0                 },
+                { "RemoteUser", SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string, voffsetof(p, remote_user), 0                 },
+                { "RemoteHost", SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string, voffsetof(p, remote_host), 0                 },
+                {}
+        };
+
+        r = sd_varlink_dispatch(link, parameters, dispatch_table, &p);
+        if (r != 0)
+                return r;
+
+        Seat *seat = NULL;
+        if (p.seat) {
+                seat = hashmap_get(m->seats, p.seat);
+                if (!seat)
+                        return sd_varlink_replyb(link, "io.systemd.Login.NoSuchSeat", /* parameters= */ NULL);
+        }
+
+        if (p.tty) {
+                if (tty_is_vc(p.tty)) {
+                        if (!seat)
+                                seat = m->seat0;
+                        else if (seat != m->seat0)
+                                return sd_varlink_error_invalid_parameter_name(link, "Seat");
+
+                        int v = vtnr_from_tty(p.tty);
+                        if (v <= 0)
+                                return sd_varlink_error_invalid_parameter_name(link, "TTY");
+
+                        if (p.vtnr == 0)
+                                p.vtnr = v;
+                        else if (p.vtnr != (unsigned) v)
+                                return sd_varlink_error_invalid_parameter_name(link, "VTNr");
+
+                } else if (tty_is_console(p.tty)) {
+                        if (!seat)
+                                seat = m->seat0;
+                        else if (seat != m->seat0)
+                                return sd_varlink_error_invalid_parameter_name(link, "Seat");
+
+                        if (p.vtnr != 0)
+                                return sd_varlink_error_invalid_parameter_name(link, "VTNr");
+                }
+        }
+
+        if (seat) {
+                if (seat_has_vts(seat)) {
+                        if (!vtnr_is_valid(p.vtnr))
+                                return sd_varlink_error_invalid_parameter_name(link, "VTNr");
+                } else {
+                        if (p.vtnr != 0)
+                                return sd_varlink_error_invalid_parameter_name(link, "VTNr");
+                }
+        }
+
+        if (p.remote < 0)
+                p.remote = p.remote_user || p.remote_host;
+
+        /* Before we continue processing this, let's ensure the peer is privileged */
+        uid_t peer_uid;
+        r = sd_varlink_get_peer_uid(link, &peer_uid);
+        if (r < 0)
+                return log_debug_errno(r, "Failed to get peer UID: %m");
+        if (peer_uid != 0)
+                return sd_varlink_error(link, SD_VARLINK_ERROR_PERMISSION_DENIED, /* parameters= */ NULL);
+
+        _cleanup_(pidref_done) PidRef leader = PIDREF_NULL;
+        r = varlink_get_peer_pidref(link, &leader);
+        if (r < 0)
+                return log_debug_errno(r, "Failed to get peer pidref: %m");
+
+        Session *session;
+        r = manager_create_session(
+                        m,
+                        p.uid,
+                        &leader,
+                        p.service,
+                        p.type,
+                        p.class,
+                        p.desktop,
+                        seat,
+                        p.vtnr,
+                        p.tty,
+                        p.display,
+                        p.remote,
+                        p.remote_user,
+                        p.remote_host,
+                        &session);
+        if (r == -EBUSY)
+                return sd_varlink_error(link, "io.systemd.Login.AlreadySessionMember", /* parameters= */ NULL);
+        if (r == -EADDRNOTAVAIL)
+                return sd_varlink_error(link, "io.systemd.Login.VirtualTerminalAlreadyTaken", /* parameters= */ NULL);
+        if (r == -EUSERS)
+                return sd_varlink_error(link, "io.systemd.Login.TooManySessions", /* parameters= */ NULL);
+        if (r < 0)
+                return r;
+
+        r = session_start(session, /* properties= */ NULL, /* error= */ NULL);
+        if (r < 0)
+                goto fail;
+
+        session->create_link = sd_varlink_ref(link);
+
+        /* Let's check if this is complete now */
+        r = session_send_create_reply(session, /* error= */ NULL);
+        if (r < 0)
+                goto fail;
+
+        return 1;
+
+fail:
+        if (session)
+                session_add_to_gc_queue(session);
+
+        return r;
+}
+
+static int vl_method_release_session(sd_varlink *link, sd_json_variant *parameters, sd_varlink_method_flags_t flags, void *userdata) {
+        Manager *m = ASSERT_PTR(userdata);
+        int r;
+
+        struct {
+                const char *id;
+        } p;
+
+        static const sd_json_dispatch_field dispatch_table[] = {
+                { "Id", SD_JSON_VARIANT_STRING, sd_json_dispatch_const_string, voffsetof(p, id), SD_JSON_MANDATORY },
+                {}
+        };
+
+        r = sd_varlink_dispatch(link, parameters, dispatch_table, &p);
+        if (r != 0)
+                return r;
+
+        Session *session;
+        r = manager_varlink_get_session_by_name(m, link, p.id, &session);
+        if (r != 0)
+                return r;
+
+        Session *peer_session;
+        r = manager_varlink_get_session_by_peer(m, link, /* consult_display= */ false, &peer_session);
+        if (r != 0)
+                return r;
+
+        if (session != peer_session)
+                return sd_varlink_error(link, SD_VARLINK_ERROR_PERMISSION_DENIED, /* parameters= */ NULL);
+
+        r = session_release(session);
+        if (r < 0)
+                return r;
+
+        return sd_varlink_replyb(link, SD_JSON_BUILD_EMPTY_OBJECT);
+}
+
+int manager_varlink_init(Manager *m) {
+        _cleanup_(sd_varlink_server_unrefp) sd_varlink_server *s = NULL;
+        int r;
+
+        assert(m);
+
+        if (m->varlink_server)
+                return 0;
+
+        r = sd_varlink_server_new(
+                        &s,
+                        SD_VARLINK_SERVER_ACCOUNT_UID|
+                        SD_VARLINK_SERVER_INHERIT_USERDATA|
+                        SD_VARLINK_SERVER_ALLOW_FD_PASSING_OUTPUT);
+        if (r < 0)
+                return log_error_errno(r, "Failed to allocate varlink server object: %m");
+
+        sd_varlink_server_set_userdata(s, m);
+
+        r = sd_varlink_server_add_interface(s, &vl_interface_io_systemd_Login);
+        if (r < 0)
+                return log_error_errno(r, "Failed to add Login interface to varlink server: %m");
+
+        r = sd_varlink_server_bind_method_many(
+                        s,
+                        "io.systemd.Login.CreateSession",  vl_method_create_session,
+                        "io.systemd.Login.ReleaseSession", vl_method_release_session);
+        if (r < 0)
+                return log_error_errno(r, "Failed to register varlink methods: %m");
+
+        r = sd_varlink_server_listen_address(s, "/run/systemd/io.systemd.Login", 0666);
+        if (r < 0)
+                return log_error_errno(r, "Failed to bind to varlink socket: %m");
+
+        r = sd_varlink_server_attach_event(s, m->event, SD_EVENT_PRIORITY_NORMAL);
+        if (r < 0)
+                return log_error_errno(r, "Failed to attach varlink connection to event loop: %m");
+
+        m->varlink_server = TAKE_PTR(s);
+        return 0;
+}
+
+void manager_varlink_done(Manager *m) {
+        assert(m);
+
+        m->varlink_server = sd_varlink_server_unref(m->varlink_server);
+}

src/login/logind-varlink.h

@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include "sd-bus.h"
+
+#include "logind.h"
+#include "logind-session.h"
+
+int manager_varlink_init(Manager *m);
+void manager_varlink_done(Manager *m);
+
+int session_send_create_reply_varlink(Session *s, const sd_bus_error *error);

src/login/logind.c

@@ -24,11 +24,12 @@
 #include "fd-util.h"
 #include "format-util.h"
 #include "fs-util.h"
+#include "logind.h"
 #include "logind-dbus.h"
 #include "logind-seat-dbus.h"
 #include "logind-session-dbus.h"
 #include "logind-user-dbus.h"
-#include "logind.h"
+#include "logind-varlink.h"
 #include "main-func.h"
 #include "mkdir-label.h"
 #include "parse-util.h"
@@ -153,6 +154,8 @@ static Manager* manager_free(Manager *m) {
 
         hashmap_free(m->polkit_registry);
 
+        manager_varlink_done(m);
+
         sd_bus_flush_close_unref(m->bus);
         sd_event_unref(m->event);
 
@@ -1114,6 +1117,10 @@ static int manager_startup(Manager *m) {
         if (r < 0)
                 return r;
 
+        r = manager_varlink_init(m);
+        if (r < 0)
+                return r;
+
         /* Instantiate magic seat 0 */
         r = manager_add_seat(m, "seat0", &m->seat0);
         if (r < 0)

src/login/logind.h

@@ -7,6 +7,7 @@
 #include "sd-bus.h"
 #include "sd-device.h"
 #include "sd-event.h"
+#include "sd-varlink.h"
 
 #include "calendarspec.h"
 #include "conf-parser.h"
@@ -145,6 +146,8 @@ struct Manager {
         struct stat efi_loader_entry_one_shot_stat;
 
         CalendarSpec *maintenance_time;
+
+        sd_varlink_server *varlink_server;
 };
 
 void manager_reset_config(Manager *m);

src/login/meson.build

@@ -26,6 +26,7 @@ liblogind_core_sources = files(
         'logind-session.c',
         'logind-user-dbus.c',
         'logind-user.c',
+        'logind-varlink.c',
         'logind-wall.c',
 )
 

src/shared/meson.build

@@ -182,6 +182,7 @@ shared_sources = files(
         'varlink-io.systemd.Hostname.c',
         'varlink-io.systemd.Import.c',
         'varlink-io.systemd.Journal.c',
+        'varlink-io.systemd.Login.c',
         'varlink-io.systemd.Machine.c',
         'varlink-io.systemd.MachineImage.c',
         'varlink-io.systemd.ManagedOOM.c',

src/shared/pam-util.c

@@ -253,17 +253,17 @@ int pam_get_item_many_internal(pam_handle_t *handle, ...) {
         va_list ap;
         int r;
 
+        assert(handle);
+
         va_start(ap, handle);
         for (;;) {
                 int item_type = va_arg(ap, int);
-
                 if (item_type <= 0) {
                         r = PAM_SUCCESS;
                         break;
                 }
 
                 const void **value = ASSERT_PTR(va_arg(ap, const void **));
-
                 r = pam_get_item(handle, item_type, value);
                 if (!IN_SET(r, PAM_BAD_ITEM, PAM_SUCCESS))
                         break;
@@ -273,6 +273,30 @@ int pam_get_item_many_internal(pam_handle_t *handle, ...) {
         return r;
 }
 
+int pam_get_data_many_internal(pam_handle_t *handle, ...) {
+        va_list ap;
+        int r;
+
+        assert(handle);
+
+        va_start(ap, handle);
+        for (;;) {
+                const char *data_name = va_arg(ap, const char *);
+                if (!data_name) {
+                        r = PAM_SUCCESS;
+                        break;
+                }
+
+                const void **value = ASSERT_PTR(va_arg(ap, const void **));
+                r = pam_get_data(handle, data_name, value);
+                if (!IN_SET(r, PAM_NO_MODULE_DATA, PAM_SUCCESS))
+                        break;
+        }
+        va_end(ap);
+
+        return r;
+}
+
 int pam_prompt_graceful(pam_handle_t *handle, int style, char **ret_response, const char *fmt, ...) {
         va_list args;
         int r;

src/shared/pam-util.h

@@ -44,7 +44,9 @@ int pam_get_bus_data(pam_handle_t *handle, const char *module_name, PamBusData *
 void pam_cleanup_free(pam_handle_t *handle, void *data, int error_status);
 
 int pam_get_item_many_internal(pam_handle_t *handle, ...);
-
 #define pam_get_item_many(handle, ...) pam_get_item_many_internal(handle, __VA_ARGS__, -1)
 
+int pam_get_data_many_internal(pam_handle_t *handle, ...);
+#define pam_get_data_many(handle, ...) pam_get_data_many_internal(handle, __VA_ARGS__, NULL)
+
 int pam_prompt_graceful(pam_handle_t *handle, int style, char **ret_response, const char *fmt, ...) _printf_(4,5);

src/shared/varlink-io.systemd.Login.c

@@ -0,0 +1,92 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include "bus-polkit.h"
+#include "varlink-io.systemd.Login.h"
+
+static SD_VARLINK_DEFINE_ENUM_TYPE(
+                SessionType,
+                SD_VARLINK_DEFINE_ENUM_VALUE(unspecified),
+                SD_VARLINK_DEFINE_ENUM_VALUE(tty),
+                SD_VARLINK_DEFINE_ENUM_VALUE(x11),
+                SD_VARLINK_DEFINE_ENUM_VALUE(wayland),
+                SD_VARLINK_DEFINE_ENUM_VALUE(mir),
+                SD_VARLINK_DEFINE_ENUM_VALUE(web));
+
+static SD_VARLINK_DEFINE_ENUM_TYPE(
+                SessionClass,
+                SD_VARLINK_DEFINE_ENUM_VALUE(user),
+                SD_VARLINK_DEFINE_ENUM_VALUE(user_early),
+                SD_VARLINK_DEFINE_ENUM_VALUE(user_incomplete),
+                SD_VARLINK_DEFINE_ENUM_VALUE(greeter),
+                SD_VARLINK_DEFINE_ENUM_VALUE(lock_screen),
+                SD_VARLINK_DEFINE_ENUM_VALUE(background),
+                SD_VARLINK_DEFINE_ENUM_VALUE(background_light),
+                SD_VARLINK_DEFINE_ENUM_VALUE(manager),
+                SD_VARLINK_DEFINE_ENUM_VALUE(manager_early));
+
+static SD_VARLINK_DEFINE_METHOD(
+                CreateSession,
+                SD_VARLINK_FIELD_COMMENT("Numeric UNIX UID of the user this session shall be owned by"),
+                SD_VARLINK_DEFINE_INPUT(UID, SD_VARLINK_INT, 0),
+                SD_VARLINK_FIELD_COMMENT("PAM service name of the program requesting the session"),
+                SD_VARLINK_DEFINE_INPUT(Service, SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
+                SD_VARLINK_FIELD_COMMENT("The type of session"),
+                SD_VARLINK_DEFINE_INPUT_BY_TYPE(Type, SessionType, 0),
+                SD_VARLINK_DEFINE_INPUT_BY_TYPE(Class, SessionClass, 0),
+                SD_VARLINK_DEFINE_INPUT(Desktop, SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
+                SD_VARLINK_DEFINE_INPUT(Seat, SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
+                SD_VARLINK_DEFINE_INPUT(VTNr, SD_VARLINK_INT, SD_VARLINK_NULLABLE),
+                SD_VARLINK_DEFINE_INPUT(TTY, SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
+                SD_VARLINK_DEFINE_INPUT(Display, SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
+                SD_VARLINK_DEFINE_INPUT(Remote, SD_VARLINK_BOOL, SD_VARLINK_NULLABLE),
+                SD_VARLINK_DEFINE_INPUT(RemoteUser, SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
+                SD_VARLINK_DEFINE_INPUT(RemoteHost, SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
+                SD_VARLINK_FIELD_COMMENT("The identifier string of the session of the user."),
+                SD_VARLINK_DEFINE_OUTPUT(Id, SD_VARLINK_STRING, 0),
+                SD_VARLINK_FIELD_COMMENT("The runtime path ($XDG_RUNTIME_DIR) of the user."),
+                SD_VARLINK_DEFINE_OUTPUT(RuntimePath, SD_VARLINK_STRING, 0),
+                SD_VARLINK_FIELD_COMMENT("Index into the file descriptor table of this reply with the session tracking fd for this session."),
+                SD_VARLINK_DEFINE_OUTPUT(SessionFileDescriptor, SD_VARLINK_INT, 0),
+                SD_VARLINK_FIELD_COMMENT("The original UID of this session."),
+                SD_VARLINK_DEFINE_OUTPUT(UID, SD_VARLINK_INT, 0),
+                SD_VARLINK_FIELD_COMMENT("The seat this session has been assigned to"),
+                SD_VARLINK_DEFINE_OUTPUT(Seat, SD_VARLINK_STRING, SD_VARLINK_NULLABLE),
+                SD_VARLINK_FIELD_COMMENT("The virtual terminal number the session has been assigned to"),
+                SD_VARLINK_DEFINE_OUTPUT(VTNr, SD_VARLINK_INT, SD_VARLINK_NULLABLE));
+
+static SD_VARLINK_DEFINE_METHOD(
+                ReleaseSession,
+                SD_VARLINK_FIELD_COMMENT("The identifier string of the session to release. If unspecified or 'self', will return the callers session."),
+                SD_VARLINK_DEFINE_INPUT(Id, SD_VARLINK_STRING, SD_VARLINK_NULLABLE));
+
+static SD_VARLINK_DEFINE_ERROR(NoSuchSession);
+static SD_VARLINK_DEFINE_ERROR(NoSuchSeat);
+static SD_VARLINK_DEFINE_ERROR(AlreadySessionMember);
+static SD_VARLINK_DEFINE_ERROR(VirtualTerminalAlreadyTaken);
+static SD_VARLINK_DEFINE_ERROR(TooManySessions);
+static SD_VARLINK_DEFINE_ERROR(UnitAllocationFailed);
+
+SD_VARLINK_DEFINE_INTERFACE(
+                io_systemd_Login,
+                "io.systemd.Login",
+                SD_VARLINK_INTERFACE_COMMENT("APIs for managing login sessions."),
+                SD_VARLINK_SYMBOL_COMMENT("Various types of sessions"),
+                &vl_type_SessionType,
+                SD_VARLINK_SYMBOL_COMMENT("Various classes of sessions"),
+                &vl_type_SessionClass,
+                SD_VARLINK_SYMBOL_COMMENT("Allocates a new session."),
+                &vl_method_CreateSession,
+                SD_VARLINK_SYMBOL_COMMENT("Releases an existing session. Currently, will be refuses unless originating from the session to release itself."),
+                &vl_method_ReleaseSession,
+                SD_VARLINK_SYMBOL_COMMENT("No session by this name found"),
+                &vl_error_NoSuchSession,
+                SD_VARLINK_SYMBOL_COMMENT("No seat by this name found"),
+                &vl_error_NoSuchSeat,
+                SD_VARLINK_SYMBOL_COMMENT("Process already member of a session"),
+                &vl_error_AlreadySessionMember,
+                SD_VARLINK_SYMBOL_COMMENT("The specified virtual terminal (VT) is already taken by another session"),
+                &vl_error_VirtualTerminalAlreadyTaken,
+                SD_VARLINK_SYMBOL_COMMENT("Maximum number of sessions reached"),
+                &vl_error_TooManySessions,
+                SD_VARLINK_SYMBOL_COMMENT("Failed to allocate a unit for the session"),
+                &vl_error_UnitAllocationFailed);

src/shared/varlink-io.systemd.Login.h

@@ -0,0 +1,6 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include "sd-varlink-idl.h"
+
+extern const sd_varlink_interface vl_interface_io_systemd_Login;

src/systemd/sd-varlink.h

@@ -65,11 +65,13 @@ __extension__ typedef enum _SD_ENUM_TYPE_S64(sd_varlink_method_flags_t) {
 } sd_varlink_method_flags_t;
 
 __extension__ typedef enum _SD_ENUM_TYPE_S64(sd_varlink_server_flags_t) {
-        SD_VARLINK_SERVER_ROOT_ONLY        = 1 << 0, /* Only accessible by root */
-        SD_VARLINK_SERVER_MYSELF_ONLY      = 1 << 1, /* Only accessible by our own UID */
-        SD_VARLINK_SERVER_ACCOUNT_UID      = 1 << 2, /* Do per user accounting */
-        SD_VARLINK_SERVER_INHERIT_USERDATA = 1 << 3, /* Initialize Varlink connection userdata from sd_varlink_server userdata */
-        SD_VARLINK_SERVER_INPUT_SENSITIVE  = 1 << 4, /* Automatically mark all connection input as sensitive */
+        SD_VARLINK_SERVER_ROOT_ONLY               = 1 << 0, /* Only accessible by root */
+        SD_VARLINK_SERVER_MYSELF_ONLY             = 1 << 1, /* Only accessible by our own UID */
+        SD_VARLINK_SERVER_ACCOUNT_UID             = 1 << 2, /* Do per user accounting */
+        SD_VARLINK_SERVER_INHERIT_USERDATA        = 1 << 3, /* Initialize Varlink connection userdata from sd_varlink_server userdata */
+        SD_VARLINK_SERVER_INPUT_SENSITIVE         = 1 << 4, /* Automatically mark all connection input as sensitive */
+        SD_VARLINK_SERVER_ALLOW_FD_PASSING_INPUT  = 1 << 5, /* Allow receiving fds over all connections */
+        SD_VARLINK_SERVER_ALLOW_FD_PASSING_OUTPUT = 1 << 6, /* Allow sending fds over all connections */
         _SD_ENUM_FORCE_S64(SD_VARLINK_SERVER)
 } sd_varlink_server_flags_t;
 

src/test/test-cgroup-util.c

@@ -212,8 +212,8 @@ TEST(proc) {
 
                 cg_pid_get_path(SYSTEMD_CGROUP_CONTROLLER, pid.pid, &path);
                 cg_pid_get_path_shifted(pid.pid, NULL, &path_shifted);
-                cg_pid_get_owner_uid(pid.pid, &uid);
-                cg_pid_get_session(pid.pid, &session);
+                cg_pidref_get_owner_uid(&pid, &uid);
+                cg_pidref_get_session(&pid, &session);
                 cg_pid_get_unit(pid.pid, &unit);
                 cg_pid_get_user_unit(pid.pid, &user_unit);
                 cg_pid_get_machine_name(pid.pid, &machine);

src/test/test-varlink-idl.c

@@ -14,6 +14,7 @@
 #include "varlink-io.systemd.Credentials.h"
 #include "varlink-io.systemd.Import.h"
 #include "varlink-io.systemd.Journal.h"
+#include "varlink-io.systemd.Login.h"
 #include "varlink-io.systemd.Machine.h"
 #include "varlink-io.systemd.MachineImage.h"
 #include "varlink-io.systemd.ManagedOOM.h"
@@ -193,6 +194,8 @@ TEST(parse_format) {
         print_separator();
         test_parse_format_one(&vl_interface_io_systemd_MachineImage);
         print_separator();
+        test_parse_format_one(&vl_interface_io_systemd_Login);
+        print_separator();
         test_parse_format_one(&vl_interface_xyz_test);
 }