From d897789b4dc7d115c915842eabf33ed3de20110a Mon Sep 17 00:00:00 2001

From: Lennart Poettering <lennart@poettering.net>

Date: Tue, 7 Aug 2018 13:49:34 +0200

Subject: [PATCH] logind: optionally watch utmp for login data

This allows us to determine the TTY an ssh session is for, which is

useful to to proper idle detection for ssh sessions.

Fixes: #9622

(cherry picked from commit 3d0ef5c7e00155bc74f6f71c34cad518a4ff56ba)

Related: #2122288

---

 src/login/logind-core.c    | 143 +++++++++++++++++++++++++++++++++++++

 src/login/logind-dbus.c    |   5 ++

 src/login/logind-session.c |  24 +++++++

 src/login/logind-session.h |  14 +++-

 src/login/logind.c         |  10 +++

 src/login/logind.h         |   8 +++

 6 files changed, 203 insertions(+), 1 deletion(-)

diff --git a/src/login/logind-core.c b/src/login/logind-core.c

index 0ed812a2c8..7e33f8e6aa 100644

--- a/src/login/logind-core.c

+++ b/src/login/logind-core.c

@@ -5,6 +5,9 @@

 #include <sys/ioctl.h>

 #include <sys/types.h>

 #include <linux/vt.h>

+#if ENABLE_UTMP

+#include <utmpx.h>

+#endif

 #include "alloc-util.h"

 #include "bus-error.h"

@@ -14,6 +17,7 @@

 #include "fd-util.h"

 #include "logind.h"

 #include "parse-util.h"

+#include "path-util.h"

 #include "process-util.h"

 #include "strv.h"

 #include "terminal-util.h"

@@ -692,3 +696,142 @@ bool manager_all_buttons_ignored(Manager *m) {

         return true;

 }

+

+int manager_read_utmp(Manager *m) {

+#if ENABLE_UTMP

+        int r;

+

+        assert(m);

+

+        if (utmpxname(_PATH_UTMPX) < 0)

+                return log_error_errno(errno, "Failed to set utmp path to " _PATH_UTMPX ": %m");

+

+        setutxent();

+

+        for (;;) {

+                _cleanup_free_ char *t = NULL;

+                struct utmpx *u;

+                const char *c;

+                Session *s;

+

+                errno = 0;

+                u = getutxent();

+                if (!u) {

+                        if (errno != 0)

+                                log_warning_errno(errno, "Failed to read " _PATH_UTMPX ", ignoring: %m");

+                        r = 0;

+                        break;

+                }

+

+                if (u->ut_type != USER_PROCESS)

+                        continue;

+

+                if (!pid_is_valid(u->ut_pid))

+                        continue;

+

+                t = strndup(u->ut_line, sizeof(u->ut_line));

+                if (!t) {

+                        r = log_oom();

+                        break;

+                }

+

+                c = path_startswith(t, "/dev/");

+                if (c) {

+                        r = free_and_strdup(&t, c);

+                        if (r < 0) {

+                                log_oom();

+                                break;

+                        }

+                }

+

+                if (isempty(t))

+                        continue;

+

+                s = hashmap_get(m->sessions_by_leader, PID_TO_PTR(u->ut_pid));

+                if (!s)

+                        continue;

+

+                if (s->tty_validity == TTY_FROM_UTMP && !streq_ptr(s->tty, t)) {

+                        /* This may happen on multiplexed SSH connection (i.e. 'SSH connection sharing'). In

+                         * this case PAM and utmp sessions don't match. In such a case let's invalidate the TTY

+                         * information and never acquire it again. */

+

+                        s->tty = mfree(s->tty);

+                        s->tty_validity = TTY_UTMP_INCONSISTENT;

+                        log_debug("Session '%s' has inconsistent TTY information, dropping TTY information.", s->id);

+                        continue;

+                }

+

+                /* Never override what we figured out once */

+                if (s->tty || s->tty_validity >= 0)

+                        continue;

+

+                s->tty = TAKE_PTR(t);

+                s->tty_validity = TTY_FROM_UTMP;

+                log_debug("Acquired TTY information '%s' from utmp for session '%s'.", s->tty, s->id);

+        }

+

+        endutxent();

+        return r;

+#else

+        return 0

+#endif

+}

+

+#if ENABLE_UTMP

+static int manager_dispatch_utmp(sd_event_source *s, const struct inotify_event *event, void *userdata) {

+        Manager *m = userdata;

+

+        assert(m);

+

+        /* If there's indication the file itself might have been removed or became otherwise unavailable, then let's

+         * reestablish the watch on whatever there's now. */

+        if ((event->mask & (IN_ATTRIB|IN_DELETE_SELF|IN_MOVE_SELF|IN_Q_OVERFLOW|IN_UNMOUNT)) != 0)

+                manager_connect_utmp(m);

+

+        (void) manager_read_utmp(m);

+        return 0;

+}

+#endif

+

+void manager_connect_utmp(Manager *m) {

+#if ENABLE_UTMP

+        sd_event_source *s = NULL;

+        int r;

+

+        assert(m);

+

+        /* Watch utmp for changes via inotify. We do this to deal with tools such as ssh, which will register the PAM

+         * session early, and acquire a TTY only much later for the connection. Thus during PAM the TTY won't be known

+         * yet. ssh will register itself with utmp when it finally acquired the TTY. Hence, let's make use of this, and

+         * watch utmp for the TTY asynchronously. We use the PAM session's leader PID as key, to find the right entry.

+         *

+         * Yes, relying on utmp is pretty ugly, but it's good enough for informational purposes, as well as idle

+         * detection (which, for tty sessions, relies on the TTY used) */

+

+        r = sd_event_add_inotify(m->event, &s, _PATH_UTMPX, IN_MODIFY|IN_MOVE_SELF|IN_DELETE_SELF|IN_ATTRIB, manager_dispatch_utmp, m);

+        if (r < 0)

+                log_full_errno(r == -ENOENT ? LOG_DEBUG: LOG_WARNING, r, "Failed to create inotify watch on " _PATH_UTMPX ", ignoring: %m");

+        else {

+                r = sd_event_source_set_priority(s, SD_EVENT_PRIORITY_IDLE);

+                if (r < 0)

+                        log_warning_errno(r, "Failed to adjust utmp event source priority, ignoring: %m");

+

+                (void) sd_event_source_set_description(s, "utmp");

+        }

+

+        sd_event_source_unref(m->utmp_event_source);

+        m->utmp_event_source = s;

+#endif

+}

+

+void manager_reconnect_utmp(Manager *m) {

+#if ENABLE_UTMP

+        assert(m);

+

+        if (m->utmp_event_source)

+                return;

+

+        manager_connect_utmp(m);

+#endif

+}

diff --git a/src/login/logind-dbus.c b/src/login/logind-dbus.c

index 1bb152bc20..0248042308 100644

--- a/src/login/logind-dbus.c

+++ b/src/login/logind-dbus.c

@@ -772,6 +772,9 @@ static int method_create_session(sd_bus_message *message, void *userdata, sd_bus

                 } while (hashmap_get(m->sessions, id));

         }

+        /* If we are not watching utmp aleady, try again */

+        manager_reconnect_utmp(m);

+

         r = manager_add_user_by_uid(m, uid, &user);

         if (r < 0)

                 goto fail;

@@ -795,6 +798,8 @@ static int method_create_session(sd_bus_message *message, void *userdata, sd_bus

                         r = -ENOMEM;

                         goto fail;

                 }

+

+                session->tty_validity = TTY_FROM_PAM;

         }

         if (!isempty(display)) {

diff --git a/src/login/logind-session.c b/src/login/logind-session.c

index 1143a834a4..d666f86d3f 100644

--- a/src/login/logind-session.c

+++ b/src/login/logind-session.c

@@ -56,6 +56,7 @@ int session_new(Session **ret, Manager *m, const char *id) {

                 .fifo_fd = -1,

                 .vtfd = -1,

                 .audit_id = AUDIT_SESSION_INVALID,

+                .tty_validity = _TTY_VALIDITY_INVALID,

         };

         s->state_file = strappend("/run/systemd/sessions/", id);

@@ -219,6 +220,9 @@ int session_save(Session *s) {

         if (s->tty)

                 fprintf(f, "TTY=%s\n", s->tty);

+        if (s->tty_validity >= 0)

+                fprintf(f, "TTY_VALIDITY=%s\n", tty_validity_to_string(s->tty_validity));

+

         if (s->display)

                 fprintf(f, "DISPLAY=%s\n", s->display);

@@ -355,6 +359,7 @@ static int session_load_devices(Session *s, const char *devices) {

 int session_load(Session *s) {

         _cleanup_free_ char *remote = NULL,

                 *seat = NULL,

+                *tty_validity = NULL,

                 *vtnr = NULL,

                 *state = NULL,

                 *position = NULL,

@@ -380,6 +385,7 @@ int session_load(Session *s) {

                            "FIFO",           &s->fifo_path,

                            "SEAT",           &seat,

                            "TTY",            &s->tty,

+                           "TTY_VALIDITY",   &tty_validity,

                            "DISPLAY",        &s->display,

                            "REMOTE_HOST",    &s->remote_host,

                            "REMOTE_USER",    &s->remote_user,

@@ -456,6 +462,16 @@ int session_load(Session *s) {

                 seat_claim_position(s->seat, s, npos);

         }

+        if (tty_validity) {

+                TTYValidity v;

+

+                v = tty_validity_from_string(tty_validity);

+                if (v < 0)

+                        log_debug("Failed to parse TTY validity: %s", tty_validity);

+                else

+                        s->tty_validity = v;

+        }

+

         if (leader) {

                 if (parse_pid(leader, &s->leader) >= 0)

                         (void) audit_session_from_pid(s->leader, &s->audit_id);

@@ -1368,3 +1384,11 @@ static const char* const kill_who_table[_KILL_WHO_MAX] = {

 };

 DEFINE_STRING_TABLE_LOOKUP(kill_who, KillWho);

+

+static const char* const tty_validity_table[_TTY_VALIDITY_MAX] = {

+        [TTY_FROM_PAM] = "from-pam",

+        [TTY_FROM_UTMP] = "from-utmp",

+        [TTY_UTMP_INCONSISTENT] = "utmp-inconsistent",

+};

+

+DEFINE_STRING_TABLE_LOOKUP(tty_validity, TTYValidity);

diff --git a/src/login/logind-session.h b/src/login/logind-session.h

index 9bd0c96a03..7da845cea3 100644

--- a/src/login/logind-session.h

+++ b/src/login/logind-session.h

@@ -46,6 +46,14 @@ enum KillWho {

         _KILL_WHO_INVALID = -1

 };

+typedef enum TTYValidity {

+        TTY_FROM_PAM,

+        TTY_FROM_UTMP,

+        TTY_UTMP_INCONSISTENT, /* may happen on ssh sessions with multiplexed TTYs */

+        _TTY_VALIDITY_MAX,

+        _TTY_VALIDITY_INVALID = -1,

+} TTYValidity;

+

 struct Session {

         Manager *manager;

@@ -60,8 +68,9 @@ struct Session {

         dual_timestamp timestamp;

-        char *tty;

         char *display;

+        char *tty;

+        TTYValidity tty_validity;

         bool remote;

         char *remote_user;

@@ -159,6 +168,9 @@ SessionClass session_class_from_string(const char *s) _pure_;

 const char *kill_who_to_string(KillWho k) _const_;

 KillWho kill_who_from_string(const char *s) _pure_;

+const char* tty_validity_to_string(TTYValidity t) _const_;

+TTYValidity tty_validity_from_string(const char *s) _pure_;

+

 int session_prepare_vt(Session *s);

 void session_restore_vt(Session *s);

 void session_leave_vt(Session *s);

diff --git a/src/login/logind.c b/src/login/logind.c

index 6c208c8e89..25de9a6ab2 100644

--- a/src/login/logind.c

+++ b/src/login/logind.c

@@ -132,6 +132,10 @@ static Manager* manager_unref(Manager *m) {

         sd_event_source_unref(m->udev_button_event_source);

         sd_event_source_unref(m->lid_switch_ignore_event_source);

+#if ENABLE_UTMP

+        sd_event_source_unref(m->utmp_event_source);

+#endif

+

         safe_close(m->console_active_fd);

         udev_monitor_unref(m->udev_seat_monitor);

@@ -1095,6 +1099,9 @@ static int manager_startup(Manager *m) {

         if (r < 0)

                 return log_error_errno(r, "Failed to register SIGHUP handler: %m");

+        /* Connect to utmp */

+        manager_connect_utmp(m);

+

         /* Connect to console */

         r = manager_connect_console(m);

         if (r < 0)

@@ -1150,6 +1157,9 @@ static int manager_startup(Manager *m) {

         /* Reserve the special reserved VT */

         manager_reserve_vt(m);

+        /* Read in utmp if it exists */

+        manager_read_utmp(m);

+

         /* And start everything */

         HASHMAP_FOREACH(seat, m->seats, i)

                 seat_start(seat);

diff --git a/src/login/logind.h b/src/login/logind.h

index d29b01c75b..bb127bf4a5 100644

--- a/src/login/logind.h

+++ b/src/login/logind.h

@@ -43,6 +43,10 @@ struct Manager {

         sd_event_source *udev_vcsa_event_source;

         sd_event_source *udev_button_event_source;

+#if ENABLE_UTMP

+        sd_event_source *utmp_event_source;

+#endif

+

         int console_active_fd;

         unsigned n_autovts;

@@ -150,6 +154,10 @@ bool manager_is_docked_or_external_displays(Manager *m);

 bool manager_is_on_external_power(void);

 bool manager_all_buttons_ignored(Manager *m);

+int manager_read_utmp(Manager *m);

+void manager_connect_utmp(Manager *m);

+void manager_reconnect_utmp(Manager *m);

+

 extern const sd_bus_vtable manager_vtable[];

 int match_job_removed(sd_bus_message *message, void *userdata, sd_bus_error *error);