2 files changed, 22 insertions, 4 deletions

diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index 0efc5028ba9d..46ee488c0015 100644
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -106,6 +106,10 @@ static struct sk_buff *reset_per_cpu_data(struct per_cpu_dm_data *data)
         return skb;
 }
 
+static struct genl_multicast_group dm_mcgrp = {
+        .name = "events",
+};
+
 static void send_dm_alert(struct work_struct *work)
 {
         struct sk_buff *skb;
@@ -116,7 +120,7 @@ static void send_dm_alert(struct work_struct *work)
         skb = reset_per_cpu_data(data);
 
         if (skb)
-                genlmsg_multicast(skb, 0, NET_DM_GRP_ALERT, GFP_KERNEL);
+                genlmsg_multicast(skb, 0, dm_mcgrp.id, GFP_KERNEL);
 }
 
 /*
@@ -371,6 +375,13 @@ static int __init init_net_drop_monitor(void)
                 return rc;
         }
 
+        rc = genl_register_mc_group(&net_drop_monitor_family, &dm_mcgrp);
+        if (rc) {
+                pr_err("Failed to register drop monitor mcast group\n");
+                goto out_unreg;
+        }
+        WARN_ON(dm_mcgrp.id != NET_DM_GRP_ALERT);
+
         rc = register_netdevice_notifier(&dropmon_net_notifier);
         if (rc < 0) {
                 pr_crit("Failed to register netdevice notifier\n");
diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index c68ce73619b5..353909d46dda 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -65,8 +65,12 @@ static struct list_head family_ht[GENL_FAM_TAB_SIZE];
  * To avoid an allocation at boot of just one unsigned long,
  * declare it global instead.
  * Bit 0 is marked as already used since group 0 is invalid.
+ * Bit 1 is marked as already used since the drop-monitor code
+ * abuses the API and thinks it can statically use group 1.
+ * That group will typically conflict with other groups that
+ * any proper users use.
  */
-static unsigned long mc_group_start = 0x1;
+static unsigned long mc_group_start = 0x3;
 static unsigned long *mc_groups = &mc_group_start;
 static unsigned long mc_groups_longs = 1;
 
@@ -160,9 +164,11 @@ int genl_register_mc_group(struct genl_family *family,
 
         genl_lock_all();
 
-        /* special-case our own group */
+        /* special-case our own group and hacks */
         if (grp == &notify_grp)
                 id = GENL_ID_CTRL;
+        else if (strcmp(family->name, "NET_DM") == 0)
+                id = 1;
         else
                 id = find_first_zero_bit(mc_groups,
                                          mc_groups_longs * BITS_PER_LONG);
@@ -245,7 +251,8 @@ static void __genl_unregister_mc_group(struct genl_family *family,
         rcu_read_unlock();
         netlink_table_ungrab();
 
-        clear_bit(grp->id, mc_groups);
+        if (grp->id != 1)
+                clear_bit(grp->id, mc_groups);
         list_del(&grp->list);
         genl_ctrl_event(CTRL_CMD_DELMCAST_GRP, grp);
         grp->id = 0;