genetlink: make multicast groups const, prevent abuse

Register generic netlink multicast groups as an array with
the family and give them contiguous group IDs. Then instead
of passing the global group ID to the various functions that
send messages, pass the ID relative to the family - for most
families that's just 0 because the only have one group.

This avoids the list_head and ID in each group, adding a new
field for the mcast group ID offset to the family.

At the same time, this allows us to prevent abusing groups
again like the quota and dropmon code did, since we can now
check that a family only uses a group it owns.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 12 deletions

diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index 1eab1dc48821..95897183226e 100644
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -106,8 +106,8 @@ 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 struct genl_multicast_group dropmon_mcgrps[] = {
+	{ .name = "events", },
 };
 
 static void send_dm_alert(struct work_struct *work)
@@ -121,7 +121,7 @@ static void send_dm_alert(struct work_struct *work)
 
 	if (skb)
 		genlmsg_multicast(&net_drop_monitor_family, skb, 0,
-				  dm_mcgrp.id, GFP_KERNEL);
+				  0, GFP_KERNEL);
 }
 
 /*
@@ -369,19 +369,13 @@ static int __init init_net_drop_monitor(void)
 		return -ENOSPC;
 	}
 
-	rc = genl_register_family_with_ops(&net_drop_monitor_family,
-					   dropmon_ops);
+	rc = genl_register_family_with_ops_groups(&net_drop_monitor_family,
+						  dropmon_ops, dropmon_mcgrps);
 	if (rc) {
 		pr_err("Could not create drop monitor netlink family\n");
 		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);
+	WARN_ON(net_drop_monitor_family.mcgrp_offset != NET_DM_GRP_ALERT);
 
 	rc = register_netdevice_notifier(&dropmon_net_notifier);
 	if (rc < 0) {