libmisc: implement get_session_host()

Implement `get_session_host()` in `utmp.c` and `logind.c`.

Signed-off-by: Iker Pedrosa <ipedrosa@redhat.com>

lib/prototypes.h

@@ -472,7 +472,19 @@ extern int set_filesize_limit (int blocks);
 /* user_busy.c */
 extern int user_busy (const char *name, uid_t uid);
 
-/* utmp.c */
+/*
+ * Session management: utmp.c or logind.c
+ */
+
+/**
+ * @brief Get host for the current session
+ *
+ * @param[out] out Host name
+ *
+ * @return 0 or a positive integer if the host was obtained properly,
+ *         another value on error.
+ */
+extern int get_session_host (char **out);
 extern /*@null@*/struct utmp *get_current_utmp (void);
 extern struct utmp *prepare_utmp (const char *name,
                                   const char *line,

libmisc/Makefile.am

@@ -94,4 +94,4 @@ endif
 
 if ENABLE_LASTLOG
 libmisc_la_SOURCES += log.c
-endif
+endif

libmisc/logind.c

@@ -0,0 +1,36 @@
+/*
+ * SPDX-FileCopyrightText:  2023, Iker Pedrosa <ipedrosa@redhat.com>
+ *
+ * SPDX-License-Identifier:  BSD-3-Clause
+ */
+
+#include <config.h>
+
+#ident "$Id$"
+
+#include "defines.h"
+#include "prototypes.h"
+
+#include <systemd/sd-login.h>
+
+int get_session_host (char **out)
+{
+    char *host = NULL;
+    char *session = NULL;
+    int ret;
+
+    ret = sd_pid_get_session (getpid(), &session);
+    if (ret < 0) {
+        return ret;
+    }
+    ret = sd_session_get_remote_host (session, &host);
+    if (ret < 0) {
+        goto done;
+    }
+
+    *out = host;
+
+done:
+    free (session);
+    return ret;
+}

libmisc/utmp.c

@@ -101,6 +101,32 @@ static bool is_my_tty (const char tty[UT_LINESIZE])
 	return ret;
 }
 
+int get_session_host (char **out)
+{
+	char *hostname = NULL;
+	struct utmp *ut = NULL;
+	int ret = 0;
+
+	ut = get_current_utmp();
+
+#ifdef HAVE_STRUCT_UTMP_UT_HOST
+	if ((ut != NULL) && (ut->ut_host[0] != '\0')) {
+		hostname = XMALLOC(sizeof(ut->ut_host) + 1, char);
+		strncpy (hostname, ut->ut_host, sizeof (ut->ut_host));
+		hostname[sizeof (ut->ut_host)] = '\0';
+		*out = hostname;
+		free (ut);
+	} else {
+		*out = NULL;
+		ret = -2;
+	}
+#else
+	*out = NULL;
+	ret = -2;
+#endif /* HAVE_STRUCT_UTMP_UT_HOST */
+
+	return ret;
+}
 
 #ifndef USE_PAM
 /*