netfilter: nf_tables: support optional userdata for set elements

Add an userdata set extension and allow the user to attach arbitrary
data to set elements. This is intended to hold TLV encoded data like
comments or DNS annotations that have no meaning to the kernel.

Signed-off-by: Patrick McHardy <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

include/net/netfilter/nf_tables.h

···
  *	@NFT_SET_EXT_FLAGS: element flags
  *	@NFT_SET_EXT_TIMEOUT: element timeout
  *	@NFT_SET_EXT_EXPIRATION: element expiration time
+ *	@NFT_SET_EXT_USERDATA: user data associated with the element
  *	@NFT_SET_EXT_NUM: number of extension types
  */
 enum nft_set_extensions {
···
 	NFT_SET_EXT_FLAGS,
 	NFT_SET_EXT_TIMEOUT,
 	NFT_SET_EXT_EXPIRATION,
+	NFT_SET_EXT_USERDATA,
 	NFT_SET_EXT_NUM
 };
 
···
 static inline unsigned long *nft_set_ext_expiration(const struct nft_set_ext *ext)
 {
 	return nft_set_ext(ext, NFT_SET_EXT_EXPIRATION);
+}
+
+static inline struct nft_userdata *nft_set_ext_userdata(const struct nft_set_ext *ext)
+{
+	return nft_set_ext(ext, NFT_SET_EXT_USERDATA);
 }
 
 static inline bool nft_set_elem_expired(const struct nft_set_ext *ext)

include/uapi/linux/netfilter/nf_tables.h

···
  * @NFTA_SET_ELEM_FLAGS: bitmask of nft_set_elem_flags (NLA_U32)
  * @NFTA_SET_ELEM_TIMEOUT: timeout value (NLA_U64)
  * @NFTA_SET_ELEM_EXPIRATION: expiration time (NLA_U64)
+ * @NFTA_SET_ELEM_USERDATA: user data (NLA_BINARY)
  */
 enum nft_set_elem_attributes {
 	NFTA_SET_ELEM_UNSPEC,
···
 	NFTA_SET_ELEM_FLAGS,
 	NFTA_SET_ELEM_TIMEOUT,
 	NFTA_SET_ELEM_EXPIRATION,
+	NFTA_SET_ELEM_USERDATA,
 	__NFTA_SET_ELEM_MAX
 };
 #define NFTA_SET_ELEM_MAX	(__NFTA_SET_ELEM_MAX - 1)

net/netfilter/nf_tables_api.c

···
 		.len	= sizeof(unsigned long),
 		.align	= __alignof__(unsigned long),
 	},
+	[NFT_SET_EXT_USERDATA]		= {
+		.len	= sizeof(struct nft_userdata),
+		.align	= __alignof__(struct nft_userdata),
+	},
 };
 EXPORT_SYMBOL_GPL(nft_set_ext_types);
 
···
 	[NFTA_SET_ELEM_DATA]		= { .type = NLA_NESTED },
 	[NFTA_SET_ELEM_FLAGS]		= { .type = NLA_U32 },
 	[NFTA_SET_ELEM_TIMEOUT]		= { .type = NLA_U64 },
+	[NFTA_SET_ELEM_USERDATA]	= { .type = NLA_BINARY,
+					    .len = NFT_USERDATA_MAXLEN },
 };
 
 static const struct nla_policy nft_set_elem_list_policy[NFTA_SET_ELEM_LIST_MAX + 1] = {
···
 
 		if (nla_put_be64(skb, NFTA_SET_ELEM_EXPIRATION,
 				 cpu_to_be64(jiffies_to_msecs(expires))))
+			goto nla_put_failure;
+	}
+
+	if (nft_set_ext_exists(ext, NFT_SET_EXT_USERDATA)) {
+		struct nft_userdata *udata;
+
+		udata = nft_set_ext_userdata(ext);
+		if (nla_put(skb, NFTA_SET_ELEM_USERDATA,
+			    udata->len + 1, udata->data))
 			goto nla_put_failure;
 	}
 
···
 	struct nft_set_ext *ext;
 	struct nft_set_elem elem;
 	struct nft_set_binding *binding;
+	struct nft_userdata *udata;
 	struct nft_data data;
 	enum nft_registers dreg;
 	struct nft_trans *trans;
 	u64 timeout;
 	u32 flags;
+	u8 ulen;
 	int err;
 
 	err = nla_parse_nested(nla, NFTA_SET_ELEM_MAX, attr,
···
 		nft_set_ext_add(&tmpl, NFT_SET_EXT_DATA);
 	}
 
+	/* The full maximum length of userdata can exceed the maximum
+	 * offset value (U8_MAX) for following extensions, therefor it
+	 * must be the last extension added.
+	 */
+	ulen = 0;
+	if (nla[NFTA_SET_ELEM_USERDATA] != NULL) {
+		ulen = nla_len(nla[NFTA_SET_ELEM_USERDATA]);
+		if (ulen > 0)
+			nft_set_ext_add_length(&tmpl, NFT_SET_EXT_USERDATA,
+					       ulen);
+	}
+
 	err = -ENOMEM;
 	elem.priv = nft_set_elem_init(set, &tmpl, &elem.key, &data,
 				      timeout, GFP_KERNEL);
···
 	ext = nft_set_elem_ext(set, elem.priv);
 	if (flags)
 		*nft_set_ext_flags(ext) = flags;
+	if (ulen > 0) {
+		udata = nft_set_ext_userdata(ext);
+		udata->len = ulen - 1;
+		nla_memcpy(&udata->data, nla[NFTA_SET_ELEM_USERDATA], ulen);
+	}
 
 	trans = nft_trans_elem_alloc(ctx, NFT_MSG_NEWSETELEM, set);
 	if (trans == NULL)