Add code to drop privileges of xrdp daemon

common/os_calls.c

@@ -3167,6 +3167,48 @@ g_setgid(int pid)
 #endif
 }
 
+/*****************************************************************************/
+/* Used by daemonizing code */
+/* returns error, zero is success, non zero is error */
+int
+g_drop_privileges(const char *user, const char *group)
+{
+    int rv = 1;
+    int uid;
+    int gid;
+    if (g_getuser_info_by_name(user, &uid, NULL, NULL, NULL, NULL) != 0)
+    {
+        LOG(LOG_LEVEL_ERROR, "Unable to get UID for user '%s' [%s]", user,
+            g_get_strerror());
+    }
+    else if (g_getgroup_info(group, &gid) != 0)
+    {
+        LOG(LOG_LEVEL_ERROR, "Unable to get GID for group '%s' [%s]", group,
+            g_get_strerror());
+    }
+    else if (initgroups(user, gid) != 0)
+    {
+        LOG(LOG_LEVEL_ERROR, "Unable to init groups for '%s' [%s]", user,
+            g_get_strerror());
+    }
+    else if (g_setgid(gid) != 0)
+    {
+        LOG(LOG_LEVEL_ERROR, "Unable to set group to '%s' [%s]", group,
+            g_get_strerror());
+    }
+    else if (g_setuid(uid) != 0)
+    {
+        LOG(LOG_LEVEL_ERROR, "Unable to set user to '%s' [%s]", user,
+            g_get_strerror());
+    }
+    else
+    {
+        rv = 0;
+    }
+
+    return rv;
+}
+
 /*****************************************************************************/
 /* returns error, zero is success, non zero is error */
 /* does not work in win32 */

common/os_calls.h

@@ -338,6 +338,7 @@ void     g_signal_pipe(void (*func)(int));
 void     g_signal_usr1(void (*func)(int));
 int      g_fork(void);
 int      g_setgid(int pid);
+int      g_drop_privileges(const char *user, const char *group);
 int      g_initgroups(const char *user);
 int      g_getuid(void);
 int      g_getgid(void);

xrdp/xrdp.c

@@ -416,6 +416,38 @@ xrdp_sanity_check(void)
     return 0;
 }
 
+/*****************************************************************************/
+static int
+check_drop_privileges(struct xrdp_startup_params *startup_params)
+{
+    int rv = 1;
+    const char *user = startup_params->runtime_user;
+    const char *group = startup_params->runtime_group;
+
+    if (user[0] == '\0' && group[0] == '\0')
+    {
+        // Allow this for now
+        LOG(LOG_LEVEL_ALWAYS,
+            "You are running xrdp as root. This is not safe.");
+        rv = 0;
+    }
+    else if (user[0] == '\0' || group[0] == '\0')
+    {
+        LOG(LOG_LEVEL_ERROR,
+            "Both a runtime_user and a runtime_group MUST be specified");
+    }
+    else
+    {
+        rv = g_drop_privileges(user, group);
+        if (rv == 0)
+        {
+            LOG(LOG_LEVEL_INFO, "Switched user:group to %s:%s", user, group);
+        }
+    }
+
+    return rv;
+}
+
 /*****************************************************************************/
 int
 main(int argc, char **argv)
@@ -548,7 +580,7 @@ main(int argc, char **argv)
         g_exit(1);
     }
 
-    if (!read_xrdp_ini_startup_params(&startup_params))
+    if (read_xrdp_ini_startup_params(&startup_params) != 0)
     {
         log_end();
         g_deinit();
@@ -653,7 +685,7 @@ main(int argc, char **argv)
         LOG(LOG_LEVEL_ALWAYS, "Failed to start xrdp daemon, "
             "possibly address already in use.");
     }
-    else
+    else if (check_drop_privileges(&startup_params) == 0)
     {
         g_set_threadid(tc_get_threadid());
         g_signal_user_interrupt(xrdp_shutdown); /* SIGINT */