From 0329e09b6934bd1d707f48271353fc4a9527542d Mon Sep 17 00:00:00 2001
From: Matthew Leeds <matthew.leeds@endlessm.com>
Date: Wed, 24 Jul 2019 14:45:16 -0700
Subject: [PATCH] service: Allow services to be run as root

This commit adds a GssService:allow-root property to allow subclasses to
let themselves be run as root.

The specific situation this is meant for is a service running as root to
avoid being killed when systemd gains control after the pivot to the
final root filesystem (all non-root processes are killed at that
point).[1]

[1] https://www.freedesktop.org/wiki/Software/systemd/RootStorageDaemons/
---
 libgsystemservice/service.c | 43 +++++++++++++++++++++++++++++++------
 1 file changed, 36 insertions(+), 7 deletions(-)

diff --git a/libgsystemservice/service.c b/libgsystemservice/service.c
index 28e8ab1..84e7a9d 100644
--- a/libgsystemservice/service.c
+++ b/libgsystemservice/service.c
@@ -91,6 +91,7 @@ typedef struct
   GError *run_error;  /* (nullable) (owned) */
   gboolean run_exited;
   int run_exit_signal;
+  gboolean allow_root;
 
   GMainContext *context;  /* (owned) */
 
@@ -110,6 +111,7 @@ typedef enum
   PROP_BUS_TYPE,
   PROP_SERVICE_ID,
   PROP_INACTIVITY_TIMEOUT,
+  PROP_ALLOW_ROOT,
 } GssServiceProperty;
 
 G_DEFINE_ABSTRACT_TYPE_WITH_PRIVATE (GssService, gss_service, G_TYPE_OBJECT)
@@ -118,7 +120,7 @@ static void
 gss_service_class_init (GssServiceClass *klass)
 {
   GObjectClass *object_class = (GObjectClass *) klass;
-  GParamSpec *props[PROP_INACTIVITY_TIMEOUT + 1] = { NULL, };
+  GParamSpec *props[PROP_ALLOW_ROOT + 1] = { NULL, };
 
   object_class->dispose = gss_service_dispose;
   object_class->get_property = gss_service_get_property;
@@ -231,6 +233,23 @@ gss_service_class_init (GssServiceClass *klass)
                          G_PARAM_READWRITE |
                          G_PARAM_STATIC_STRINGS);
 
+  /**
+   * GssService:allow-root:
+   *
+   * If %TRUE, the service can be run by root. Otherwise, and by default,
+   * gss_service_run() will fail if the UID or effective UID is zero.
+   *
+   * Since: 0.1.0
+   */
+  props[PROP_ALLOW_ROOT] =
+      g_param_spec_boolean ("allow-root", "Allow Root",
+                            "Whether the service should be allowed to run "
+                            "as root (UID 0).",
+                            FALSE,
+                            G_PARAM_READWRITE |
+                            G_PARAM_CONSTRUCT_ONLY |
+                            G_PARAM_STATIC_STRINGS);
+
   g_object_class_install_properties (object_class, G_N_ELEMENTS (props), props);
 }
 
@@ -309,6 +328,9 @@ gss_service_get_property (GObject    *object,
     case PROP_INACTIVITY_TIMEOUT:
       g_value_set_uint (value, priv->inactivity_timeout_ms);
       break;
+    case PROP_ALLOW_ROOT:
+      g_value_set_boolean (value, priv->allow_root);
+      break;
     default:
       g_assert_not_reached ();
     }
@@ -352,6 +374,10 @@ gss_service_set_property (GObject      *object,
     case PROP_INACTIVITY_TIMEOUT:
       gss_service_set_inactivity_timeout (self, g_value_get_uint (value));
       break;
+    case PROP_ALLOW_ROOT:
+      /* Construct only. */
+      priv->allow_root = g_value_get_boolean (value);
+      break;
     default:
       g_assert_not_reached ();
     }
@@ -560,13 +586,16 @@ gss_service_run (GssService  *self,
   bind_textdomain_codeset (GETTEXT_PACKAGE, "UTF-8");
   textdomain (GETTEXT_PACKAGE);
 
-  /* Ensure we are not running as root — we don’t need those privileges. */
-  if (getuid () == 0 || geteuid () == 0)
+  if (!priv->allow_root)
     {
-      g_set_error_literal (error, GSS_SERVICE_ERROR,
-                           GSS_SERVICE_ERROR_INVALID_ENVIRONMENT,
-                           _("This daemon must not be run as root."));
-      return;
+      /* Ensure we are not running as root — we don’t need those privileges. */
+      if (getuid () == 0 || geteuid () == 0)
+        {
+          g_set_error_literal (error, GSS_SERVICE_ERROR,
+                               GSS_SERVICE_ERROR_INVALID_ENVIRONMENT,
+                               _("This daemon must not be run as root."));
+          return;
+        }
     }
 
   gss_service_hold (self);
-- 
GitLab