Use logind instead of utmp because of Y2038

Bi-arch systems line x86-64 present the Y2038 problem, where an overflow
can be produced because some glibc compatibility decissions (see
https://github.com/thkukuk/utmpx/blob/main/Y2038.md for more
information)

This patch uses logind from systemd instead of utmp on Linux systems, if
the systemd version is support the new API (>= 254).

Signed-off-by: Alberto Planas <aplanas@suse.com>

psutil/_psutil_linux.c

@@ -14,6 +14,9 @@
 #include <stdlib.h>
 #include <mntent.h>
 #include <features.h>
+#ifdef SYSTEMD_LINUX
+    #include <dlfcn.h>
+#endif
 #include <utmp.h>
 #include <sched.h>
 #include <linux/version.h>
@@ -357,12 +360,152 @@ psutil_proc_cpu_affinity_set(PyObject *self, PyObject *args) {
 }
 #endif  /* PSUTIL_HAVE_CPU_AFFINITY */
 
+#ifdef SYSTEMD_LINUX
+
+/* Systemd function signatures that will be loaded */
+int (*sd_booted)(void);
+int (*sd_get_sessions)(char ***);
+int (*sd_session_get_leader)(const char *, pid_t *);
+int (*sd_session_get_remote_host)(const char *,char **);
+int (*sd_session_get_start_time)(const char *, uint64_t *);
+int (*sd_session_get_tty)(const char *, char **);
+int (*sd_session_get_username)(const char *, char **);
+
+#define dlsym_check(__h, __fn) do {           \
+    __fn = dlsym(__h, #__fn);                 \
+    if (dlerror() != NULL || __fn == NULL) {  \
+        dlclose(__h);                         \
+        return NULL;                          \
+    }                                         \
+} while (0)
+
+void *
+load_systemd() {
+    void *handle = dlopen("libsystemd.so.0", RTLD_LAZY);
+    if (dlerror() != NULL || handle == NULL)
+        return NULL;
+
+    dlsym_check(handle, sd_booted);
+    dlsym_check(handle, sd_get_sessions);
+    dlsym_check(handle, sd_session_get_leader);
+    dlsym_check(handle, sd_session_get_remote_host);
+    dlsym_check(handle, sd_session_get_start_time);
+    dlsym_check(handle, sd_session_get_tty);
+    dlsym_check(handle, sd_session_get_username);
+
+    return handle;
+}
+
+/*
+ * Return currently connected users as a list of tuples.
+ */
+static PyObject *
+psutil_users_systemd(PyObject *self, PyObject *args) {
+    char **sessions_list = NULL;
+    PyObject *py_retlist = PyList_New(0);
+    PyObject *py_tuple = NULL;
+    PyObject *py_username = NULL;
+    PyObject *py_tty = NULL;
+    PyObject *py_hostname = NULL;
+    PyObject *py_user_proc = NULL;
+    double tstamp = 0.0;
+    pid_t pid = 0;
+
+    if (py_retlist == NULL)
+        return NULL;
+    int sessions = sd_get_sessions(&sessions_list);
+    for (int i = 0; i < sessions; i++) {
+        const char *session_id = sessions_list[i];
+        py_tuple = NULL;
+        py_user_proc = NULL;
+        py_user_proc = Py_True;
+
+        char *username = NULL;
+        if (sd_session_get_username(session_id, &username) < 0)
+            goto error;
+        py_username = PyUnicode_DecodeFSDefault(username);
+        free(username);
+        if (! py_username)
+            goto error;
+
+        char *tty = NULL;
+        if (sd_session_get_tty(session_id, &tty) < 0) {
+            py_tty = PyUnicode_DecodeFSDefault("n/a");
+        } else {
+            py_tty = PyUnicode_DecodeFSDefault(tty);
+            free(tty);
+        }
+        if (! py_tty)
+            goto error;
+
+        char *hostname = NULL;
+        if (sd_session_get_remote_host(session_id, &hostname) < 0)
+            goto error;
+        py_hostname = PyUnicode_DecodeFSDefault(hostname);
+        free(hostname);
+        if (! py_hostname)
+            goto error;
+
+        uint64_t usec = 0;
+        if (sd_session_get_start_time(session_id, &usec) < 0)
+           goto error;
+        tstamp = (double)usec / 1000000.0;
+
+        if (sd_session_get_leader(session_id, &pid) < 0)
+           goto error;
+
+        py_tuple = Py_BuildValue(
+            "OOOdO" _Py_PARSE_PID,
+            py_username,              // username
+            py_tty,                   // tty
+            py_hostname,              // hostname
+            tstamp,                   // tstamp
+            py_user_proc,             // (bool) user process
+            pid                       // process id
+        );
+        if (! py_tuple)
+            goto error;
+        if (PyList_Append(py_retlist, py_tuple))
+            goto error;
+        Py_CLEAR(py_username);
+        Py_CLEAR(py_tty);
+        Py_CLEAR(py_hostname);
+        Py_CLEAR(py_tuple);
+        free (sessions_list[i]);
+    }
+    free(sessions_list);
+    return py_retlist;
+
+error:
+    Py_XDECREF(py_username);
+    Py_XDECREF(py_tty);
+    Py_XDECREF(py_hostname);
+    Py_XDECREF(py_tuple);
+    Py_DECREF(py_retlist);
+    free(sessions_list);
+    return NULL;
+}
+
+static PyObject *psutil_users_utmp(PyObject *, PyObject *);
+
+static PyObject *
+psutil_users(PyObject *self, PyObject *args) {
+  void *handle = load_systemd();
+  if (handle && sd_booted())
+      return psutil_users_systemd(self, args);
+  else
+    return psutil_users_utmp(self, args);
+}
 
 /*
  * Return currently connected users as a list of tuples.
  */
 static PyObject *
+psutil_users_utmp(PyObject *self, PyObject *args) {
+#else
+static PyObject *
 psutil_users(PyObject *self, PyObject *args) {
+#endif
     struct utmp *ut;
     PyObject *py_retlist = PyList_New(0);
     PyObject *py_tuple = NULL;

setup.py

@@ -193,6 +193,23 @@ def unix_can_compile(c_code):
         shutil.rmtree(tempdir)
 
 
+def get_systemd_version():
+    try:
+        r = subprocess.run(["systemctl", "--version"], capture_output=True)
+    except FileNotFoundError:
+        return 0
+    if r.returncode != 0:
+        return 0
+    out = r.stdout.split()
+    if len(out) < 2:
+        return 0
+    version = out[1]
+    try:
+        return int(version)
+    except ValueError:
+        return 0
+
+
 if WINDOWS:
     def get_winver():
         maj, min = sys.getwindowsversion()[0:2]
@@ -294,6 +311,11 @@ def get_winver():
     if not unix_can_compile("#include <linux/ethtool.h>"):
         macros.append(("PSUTIL_ETHTOOL_MISSING_TYPES", 1))
 
+    # Systemd >= 254 can replace utmp. See:
+    # https://github.com/thkukuk/utmpx/blob/main/utmp-to-logind.md
+    if get_systemd_version() >= 254:
+        macros.append(("SYSTEMD_LINUX", 1))
+
     macros.append(("PSUTIL_LINUX", 1))
     ext = Extension(
         'psutil._psutil_linux',