commit e58597b091dc48ef81ecd361e6f0f9ae3561a44c
Author: Amey Deshpande <ameyd@google.com>
Date:   Wed Feb 17 12:08:40 2016 -0800

    hostnamed: allow systemd-network user to call SetHostname
    
    systemd-networkd runs as a non-root user and does not have CAP_SYS_ADMIN.
    systemd-hostnamed requires that for SetHostname method, either the
    caller should have CAP_SYS_ADMIN or a PolKit rule should whitelist the
    caller uid.
    
    Lakitu doesn't ship with PolKit.  This patch tweaks systemd-hostnamed to
    whitelist the well-known user of systemd-networkd to call SetHostname
    method.  All other Set methods remain unchanged.

diff --git a/src/hostname/hostnamed.c b/src/hostname/hostnamed.c
index a78516c..1a12509 100644
--- a/src/hostname/hostnamed.c
+++ b/src/hostname/hostnamed.c
@@ -37,6 +37,8 @@
 
 #define VALID_DEPLOYMENT_CHARS (DIGITS LETTERS "-.:")
 
+#define ALLOW_NETWORKD_TO_SET_HOSTNAME 1
+
 enum {
         PROP_HOSTNAME,
         PROP_STATIC_HOSTNAME,
@@ -404,6 +406,19 @@ static int property_get_chassis(
         return sd_bus_message_append(reply, "s", name);
 }
 
+static uid_t get_good_user_uid(void) {
+#ifdef ALLOW_NETWORKD_TO_SET_HOSTNAME
+        const char *username = "systemd-network";
+        uid_t uid;
+        if (get_user_creds(&username, &uid, NULL, NULL, NULL)) {
+                return UID_INVALID;
+        }
+        return uid;
+#else
+        return UID_INVALID;
+#endif
+}
+
 static int method_set_hostname(sd_bus_message *m, void *userdata, sd_bus_error *error) {
         Context *c = userdata;
         const char *name;
@@ -435,7 +450,7 @@ static int method_set_hostname(sd_bus_message *m, void *userdata, sd_bus_error *
                         CAP_SYS_ADMIN,
                         "org.freedesktop.hostname1.set-hostname",
                         interactive,
-                        UID_INVALID,
+                        get_good_user_uid(),
                         &c->polkit_registry,
                         error);
         if (r < 0)