networkd: add bus property exposing network namepace ID we run in

This is useful for clients to determine whether they are running in the
same network namespace as networkd.

Note that access to /proc/$PID/ns/ is restricted and only permitted to
equally privileged programs. This new bus property is primarily a way to
work around this, so that unprivileged clients can determine the
networkd netns, too.

diff --git a/src/network/networkd-manager-bus.c b/src/network/networkd-manager-bus.c
index 23c1fb57c68055dc6c304521c351c0cbbd5c45da..1c6230b393235870253397717ca37b7e878bc906 100644 (file)
--- a/src/network/networkd-manager-bus.c
+++ b/src/network/networkd-manager-bus.c
@@ -263,6 +263,34 @@ static int bus_method_describe(sd_bus_message *message, void *userdata, sd_bus_e
         return sd_bus_send(NULL, reply, NULL);
 }
 
+static int property_get_namespace_id(
+                sd_bus *bus,
+                const char *path,
+                const char *interface,
+                const char *property,
+                sd_bus_message *reply,
+                void *userdata,
+                sd_bus_error *error) {
+
+        uint64_t id = 0;
+        struct stat st;
+
+        assert(bus);
+        assert(reply);
+
+        /* Returns our own network namespace ID, i.e. the inode number of /proc/self/ns/net. This allows
+         * unprivileged clients to determine whether they are in the same network namespace as us (note that
+         * access to that path is restricted, thus they can't check directly unless privileged). */
+
+        if (stat("/proc/self/ns/net", &st) < 0) {
+                log_warning_errno(errno, "Failed to stat network namespace, ignoring: %m");
+                id = 0;
+        } else
+                id = st.st_ino;
+
+        return sd_bus_message_append(reply, "t", id);
+}
+
 const sd_bus_vtable manager_vtable[] = {
         SD_BUS_VTABLE_START(0),
 
@@ -272,6 +300,7 @@ const sd_bus_vtable manager_vtable[] = {
         SD_BUS_PROPERTY("IPv4AddressState", "s", property_get_address_state, offsetof(Manager, ipv4_address_state), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         SD_BUS_PROPERTY("IPv6AddressState", "s", property_get_address_state, offsetof(Manager, ipv6_address_state), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         SD_BUS_PROPERTY("OnlineState", "s", property_get_online_state, offsetof(Manager, online_state), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
+        SD_BUS_PROPERTY("NamespaceId", "t", property_get_namespace_id, 0, SD_BUS_VTABLE_PROPERTY_CONST),
 
         SD_BUS_METHOD_WITH_ARGS("ListLinks",
                                 SD_BUS_NO_ARGS,