GNetworkMonitorNetlink: Fix check for non-kernel messages

This code used to look at the SCM_CREDENTIALS and ignore every message
not from uid 0. However, when user namespaces are in use this does not
work, as if uid 0 is not mapped you get overflowuid instead. Right now
this means we ignore all messages in such user namespaces and glib
apps hang on startup.

We can't look at pids either, as pid 0 is returned for processes
outside your pid namespace.

Instead the correct approach is to look at the sending sockaddr and
if the port id (nl_pid) is zero, then its from the kernel.

Source:
http://lists.linuxfoundation.org/pipermail/containers/2015-May/036032.html

https://bugzilla.gnome.org/show_bug.cgi?id=750203

diff --git a/gio/gnetworkmonitornetlink.c b/gio/gnetworkmonitornetlink.c
index 21a7ad5..b9ff011 100644 (file)
--- a/gio/gnetworkmonitornetlink.c
+++ b/gio/gnetworkmonitornetlink.c
@@ -293,14 +293,13 @@ read_netlink_messages (GSocket      *socket,
   GNetworkMonitorNetlink *nl = user_data;
   GInputVector iv;
   gssize len;
-  GSocketControlMessage **cmsgs = NULL;
-  gint num_cmsgs = 0, i, flags;
+  gint flags;
   GError *error = NULL;
-  GCredentials *creds;
-  uid_t sender;
+  GSocketAddress *addr;
   struct nlmsghdr *msg;
   struct rtmsg *rtmsg;
   struct rtattr *attr;
+  struct sockaddr_nl source_sockaddr;
   gsize attrlen;
   guint8 *dest, *gateway, *oif;
   gboolean retval = TRUE;
@@ -322,8 +321,8 @@ read_netlink_messages (GSocket      *socket,
 
   iv.buffer = g_malloc (len);
   iv.size = len;
-  len = g_socket_receive_message (nl->priv->sock, NULL, &iv, 1,
-                                  &cmsgs, &num_cmsgs, NULL, NULL, &error);
+  len = g_socket_receive_message (nl->priv->sock, &addr, &iv, 1,
+                                  NULL, NULL, NULL, NULL, &error);
   if (len < 0)
     {
       g_warning ("Error on netlink socket: %s", error->message);
@@ -333,12 +332,17 @@ read_netlink_messages (GSocket      *socket,
       return FALSE;
     }
 
-  if (num_cmsgs != 1 || !G_IS_UNIX_CREDENTIALS_MESSAGE (cmsgs[0]))
-    goto done;
+  if (!g_socket_address_to_native (addr, &source_sockaddr, sizeof (source_sockaddr), &error))
+    {
+      g_warning ("Error on netlink socket: %s", error->message);
+      g_error_free (error);
+      if (nl->priv->dump_networks)
+        finish_dump (nl);
+      return FALSE;
+    }
 
-  creds = g_unix_credentials_message_get_credentials (G_UNIX_CREDENTIALS_MESSAGE (cmsgs[0]));
-  sender = g_credentials_get_unix_user (creds, NULL);
-  if (sender != 0)
+  /* If the sender port id is 0 (not fakeable) then the message is from the kernel */
+  if (source_sockaddr.nl_pid != 0)
     goto done;
 
   msg = (struct nlmsghdr *) iv.buffer;
@@ -420,10 +424,6 @@ read_netlink_messages (GSocket      *socket,
     }
 
  done:
-  for (i = 0; i < num_cmsgs; i++)
-    g_object_unref (cmsgs[i]);
-  g_free (cmsgs);
-
   g_free (iv.buffer);
 
   if (!retval && nl->priv->dump_networks)