netfilter: nf_tables: add userdata support for nft_object

Enables storing userdata for nft_object. Initially this will store an
optional comment but can be extended in the future as needed.

Adds new attribute NFTA_OBJ_USERDATA to nft_object.
Signed-off-by: Jose M. Guisado Gomez <guigom@riseup.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_tables.h

@@ -1123,6 +1123,8 @@ struct nft_object {
 	u32				genmask:2,
 					use:30;
 	u64				handle;
+	u16				udlen;
+	u8				*udata;
 	/* runtime data below here */
 	const struct nft_object_ops	*ops ____cacheline_aligned;
 	unsigned char			data[]

include/uapi/linux/netfilter/nf_tables.h

@@ -1559,6 +1559,7 @@ enum nft_ct_expectation_attributes {
  * @NFTA_OBJ_DATA: stateful object data (NLA_NESTED)
  * @NFTA_OBJ_USE: number of references to this expression (NLA_U32)
  * @NFTA_OBJ_HANDLE: object handle (NLA_U64)
+ * @NFTA_OBJ_USERDATA: user data (NLA_BINARY)
  */
 enum nft_object_attributes {
 	NFTA_OBJ_UNSPEC,
@@ -1569,6 +1570,7 @@ enum nft_object_attributes {
 	NFTA_OBJ_USE,
 	NFTA_OBJ_HANDLE,
 	NFTA_OBJ_PAD,
+	NFTA_OBJ_USERDATA,
 	__NFTA_OBJ_MAX
 };
 #define NFTA_OBJ_MAX		(__NFTA_OBJ_MAX - 1)

net/netfilter/nf_tables_api.c

@@ -5755,6 +5755,8 @@ static const struct nla_policy nft_obj_policy[NFTA_OBJ_MAX + 1] = {
 	[NFTA_OBJ_TYPE]		= { .type = NLA_U32 },
 	[NFTA_OBJ_DATA]		= { .type = NLA_NESTED },
 	[NFTA_OBJ_HANDLE]	= { .type = NLA_U64},
+	[NFTA_OBJ_USERDATA]	= { .type = NLA_BINARY,
+				    .len = NFT_USERDATA_MAXLEN },
 };
 
 static struct nft_object *nft_obj_init(const struct nft_ctx *ctx,
@@ -5902,6 +5904,7 @@ static int nf_tables_newobj(struct net *net, struct sock *nlsk,
 	struct nft_object *obj;
 	struct nft_ctx ctx;
 	u32 objtype;
+	u16 udlen;
 	int err;
 
 	if (!nla[NFTA_OBJ_TYPE] ||
@@ -5946,7 +5949,7 @@ static int nf_tables_newobj(struct net *net, struct sock *nlsk,
 	obj = nft_obj_init(&ctx, type, nla[NFTA_OBJ_DATA]);
 	if (IS_ERR(obj)) {
 		err = PTR_ERR(obj);
-		goto err1;
+		goto err_init;
 	}
 	obj->key.table = table;
 	obj->handle = nf_tables_alloc_handle(table);
@@ -5954,32 +5957,44 @@ static int nf_tables_newobj(struct net *net, struct sock *nlsk,
 	obj->key.name = nla_strdup(nla[NFTA_OBJ_NAME], GFP_KERNEL);
 	if (!obj->key.name) {
 		err = -ENOMEM;
-		goto err2;
+		goto err_strdup;
+	}
+
+	if (nla[NFTA_OBJ_USERDATA]) {
+		udlen = nla_len(nla[NFTA_OBJ_USERDATA]);
+		obj->udata = kzalloc(udlen, GFP_KERNEL);
+		if (obj->udata == NULL)
+			goto err_userdata;
+
+		nla_memcpy(obj->udata, nla[NFTA_OBJ_USERDATA], udlen);
+		obj->udlen = udlen;
 	}
 
 	err = nft_trans_obj_add(&ctx, NFT_MSG_NEWOBJ, obj);
 	if (err < 0)
-		goto err3;
+		goto err_trans;
 
 	err = rhltable_insert(&nft_objname_ht, &obj->rhlhead,
 			      nft_objname_ht_params);
 	if (err < 0)
-		goto err4;
+		goto err_obj_ht;
 
 	list_add_tail_rcu(&obj->list, &table->objects);
 	table->use++;
 	return 0;
-err4:
+err_obj_ht:
 	/* queued in transaction log */
 	INIT_LIST_HEAD(&obj->list);
 	return err;
-err3:
+err_trans:
 	kfree(obj->key.name);
-err2:
+err_userdata:
+	kfree(obj->udata);
+err_strdup:
 	if (obj->ops->destroy)
 		obj->ops->destroy(&ctx, obj);
 	kfree(obj);
-err1:
+err_init:
 	module_put(type->owner);
 	return err;
 }
@@ -6011,6 +6026,10 @@ static int nf_tables_fill_obj_info(struct sk_buff *skb, struct net *net,
 			 NFTA_OBJ_PAD))
 		goto nla_put_failure;
 
+	if (obj->udata &&
+	    nla_put(skb, NFTA_OBJ_USERDATA, obj->udlen, obj->udata))
+		goto nla_put_failure;
+
 	nlmsg_end(skb, nlh);
 	return 0;