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, 20 insertions, 29 deletions

diff --git a/include/linux/genl_magic_func.h b/include/linux/genl_magic_func.h
index 5b9b8ae6748b..c0894dd8827b 100644
--- a/include/linux/genl_magic_func.h
+++ b/include/linux/genl_magic_func.h
@@ -273,49 +273,40 @@ static struct genl_family ZZZ_genl_family __read_mostly = {
  * Magic: define multicast groups
  * Magic: define multicast group registration helper
  */
+#define ZZZ_genl_mcgrps		CONCAT_(GENL_MAGIC_FAMILY, _genl_mcgrps)
+static const struct genl_multicast_group ZZZ_genl_mcgrps[] = {
+#undef GENL_mc_group
+#define GENL_mc_group(group) { .name = #group, },
+#include GENL_MAGIC_INCLUDE_FILE
+};
+
+enum CONCAT_(GENL_MAGIC_FAMILY, group_ids) {
+#undef GENL_mc_group
+#define GENL_mc_group(group) CONCAT_(GENL_MAGIC_FAMILY, _group_ ## group),
+#include GENL_MAGIC_INCLUDE_FILE
+};
+
 #undef GENL_mc_group
 #define GENL_mc_group(group)						\
-static struct genl_multicast_group					\
-CONCAT_(GENL_MAGIC_FAMILY, _mcg_ ## group) __read_mostly = {		\
-	.name = #group,							\
-};									\
 static int CONCAT_(GENL_MAGIC_FAMILY, _genl_multicast_ ## group)(	\
 	struct sk_buff *skb, gfp_t flags)				\
 {									\
 	unsigned int group_id =						\
-		CONCAT_(GENL_MAGIC_FAMILY, _mcg_ ## group).id;	\
-	if (!group_id)							\
-		return -EINVAL;						\
+		CONCAT_(GENL_MAGIC_FAMILY, _group_ ## group);		\
 	return genlmsg_multicast(&ZZZ_genl_family, skb, 0,		\
 				 group_id, flags);			\
 }
 
 #include GENL_MAGIC_INCLUDE_FILE
 
-int CONCAT_(GENL_MAGIC_FAMILY, _genl_register)(void)
-{
-	int err = genl_register_family_with_ops(&ZZZ_genl_family, ZZZ_genl_ops);
-	if (err)
-		return err;
-#undef GENL_mc_group
-#define GENL_mc_group(group)						\
-	err = genl_register_mc_group(&ZZZ_genl_family,			\
-		&CONCAT_(GENL_MAGIC_FAMILY, _mcg_ ## group));		\
-	if (err)							\
-		goto fail;						\
-	else								\
-		pr_info("%s: mcg %s: %u\n", #group,			\
-			__stringify(GENL_MAGIC_FAMILY),			\
-			CONCAT_(GENL_MAGIC_FAMILY, _mcg_ ## group).id);
-
-#include GENL_MAGIC_INCLUDE_FILE
-
 #undef GENL_mc_group
 #define GENL_mc_group(group)
-	return 0;
-fail:
-	genl_unregister_family(&ZZZ_genl_family);
-	return err;
+
+int CONCAT_(GENL_MAGIC_FAMILY, _genl_register)(void)
+{
+	return genl_register_family_with_ops_groups(&ZZZ_genl_family,	\
+						    ZZZ_genl_ops,	\
+						    ZZZ_genl_mcgrps);
 }
 
 void CONCAT_(GENL_MAGIC_FAMILY, _genl_unregister)(void)