netfilter: nf_tables: export rule-set generation ID

This patch exposes the ruleset generation ID in three ways:

1) The new command NFT_MSG_GETGEN that exposes the 32-bits ruleset
   generation ID. This ID is incremented in every commit and it
   should be large enough to avoid wraparound problems.

2) The less significant 16-bits of the generation ID are exposed through
   the nfgenmsg->res_id header field. This allows us to quickly catch
   if the ruleset has change between two consecutive list dumps from
   different object lists (in this specific case I think the risk of
   wraparound is unlikely).

3) Userspace subscribers may receive notifications of new rule-set
   generation after every commit. This also provides an alternative
   way to monitor the generation ID. If the events are lost, the
   userspace process hits a overrun error, so it knows that it is
   working with a stale ruleset anyway.

Patrick spotted that rule-set transformations in userspace may take
quite some time. In that case, it annotates the 32-bits generation ID
before fetching the rule-set, then:

1) it compares it to what we obtain after the transformation to
   make sure it is not working with a stale rule-set and no wraparound
   has ocurred.

2) it subscribes to ruleset notifications, so it can watch for new
   generation ID.

This is complementary to the NLM_F_DUMP_INTR approach, which allows
us to detect an interference in the middle one single list dumping.
There is no way to explicitly check that an interference has occurred
between two list dumps from the kernel, since it doesn't know how
many lists the userspace client is actually going to dump.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/uapi/linux/netfilter/nf_tables.h

@@ -51,6 +51,8 @@ enum nft_verdicts {
  * @NFT_MSG_NEWSETELEM: create a new set element (enum nft_set_elem_attributes)
  * @NFT_MSG_GETSETELEM: get a set element (enum nft_set_elem_attributes)
  * @NFT_MSG_DELSETELEM: delete a set element (enum nft_set_elem_attributes)
+ * @NFT_MSG_NEWGEN: announce a new generation, only for events (enum nft_gen_attributes)
+ * @NFT_MSG_GETGEN: get the rule-set generation (enum nft_gen_attributes)
  */
 enum nf_tables_msg_types {
 	NFT_MSG_NEWTABLE,
@@ -68,6 +70,8 @@ enum nf_tables_msg_types {
 	NFT_MSG_NEWSETELEM,
 	NFT_MSG_GETSETELEM,
 	NFT_MSG_DELSETELEM,
+	NFT_MSG_NEWGEN,
+	NFT_MSG_GETGEN,
 	NFT_MSG_MAX,
 };
 
@@ -812,4 +816,16 @@ enum nft_masq_attributes {
 };
 #define NFTA_MASQ_MAX		(__NFTA_MASQ_MAX - 1)
 
+/**
+ * enum nft_gen_attributes - nf_tables ruleset generation attributes
+ *
+ * @NFTA_GEN_ID: Ruleset generation ID (NLA_U32)
+ */
+enum nft_gen_attributes {
+	NFTA_GEN_UNSPEC,
+	NFTA_GEN_ID,
+	__NFTA_GEN_MAX
+};
+#define NFTA_GEN_MAX		(__NFTA_GEN_MAX - 1)
+
 #endif /* _LINUX_NF_TABLES_H */

net/netfilter/nf_tables_api.c

@@ -405,9 +405,9 @@ static const struct nla_policy nft_table_policy[NFTA_TABLE_MAX + 1] = {
 	[NFTA_TABLE_FLAGS]	= { .type = NLA_U32 },
 };
 
-static int nf_tables_fill_table_info(struct sk_buff *skb, u32 portid, u32 seq,
-				     int event, u32 flags, int family,
-				     const struct nft_table *table)
+static int nf_tables_fill_table_info(struct sk_buff *skb, struct net *net,
+				     u32 portid, u32 seq, int event, u32 flags,
+				     int family, const struct nft_table *table)
 {
 	struct nlmsghdr *nlh;
 	struct nfgenmsg *nfmsg;
@@ -420,7 +420,7 @@ static int nf_tables_fill_table_info(struct sk_buff *skb, u32 portid, u32 seq,
 	nfmsg = nlmsg_data(nlh);
 	nfmsg->nfgen_family	= family;
 	nfmsg->version		= NFNETLINK_V0;
-	nfmsg->res_id		= 0;
+	nfmsg->res_id		= htons(net->nft.base_seq & 0xffff);
 
 	if (nla_put_string(skb, NFTA_TABLE_NAME, table->name) ||
 	    nla_put_be32(skb, NFTA_TABLE_FLAGS, htonl(table->flags)) ||
@@ -448,8 +448,8 @@ static int nf_tables_table_notify(const struct nft_ctx *ctx, int event)
 	if (skb == NULL)
 		goto err;
 
-	err = nf_tables_fill_table_info(skb, ctx->portid, ctx->seq, event, 0,
-					ctx->afi->family, ctx->table);
+	err = nf_tables_fill_table_info(skb, ctx->net, ctx->portid, ctx->seq,
+					event, 0, ctx->afi->family, ctx->table);
 	if (err < 0) {
 		kfree_skb(skb);
 		goto err;
@@ -488,7 +488,7 @@ static int nf_tables_dump_tables(struct sk_buff *skb,
 			if (idx > s_idx)
 				memset(&cb->args[1], 0,
 				       sizeof(cb->args) - sizeof(cb->args[0]));
-			if (nf_tables_fill_table_info(skb,
+			if (nf_tables_fill_table_info(skb, net,
 						      NETLINK_CB(cb->skb).portid,
 						      cb->nlh->nlmsg_seq,
 						      NFT_MSG_NEWTABLE,
@@ -540,7 +540,7 @@ static int nf_tables_gettable(struct sock *nlsk, struct sk_buff *skb,
 	if (!skb2)
 		return -ENOMEM;
 
-	err = nf_tables_fill_table_info(skb2, NETLINK_CB(skb).portid,
+	err = nf_tables_fill_table_info(skb2, net, NETLINK_CB(skb).portid,
 					nlh->nlmsg_seq, NFT_MSG_NEWTABLE, 0,
 					family, table);
 	if (err < 0)
@@ -914,9 +914,9 @@ nla_put_failure:
 	return -ENOSPC;
 }
 
-static int nf_tables_fill_chain_info(struct sk_buff *skb, u32 portid, u32 seq,
-				     int event, u32 flags, int family,
-				     const struct nft_table *table,
+static int nf_tables_fill_chain_info(struct sk_buff *skb, struct net *net,
+				     u32 portid, u32 seq, int event, u32 flags,
+				     int family, const struct nft_table *table,
 				     const struct nft_chain *chain)
 {
 	struct nlmsghdr *nlh;
@@ -930,7 +930,7 @@ static int nf_tables_fill_chain_info(struct sk_buff *skb, u32 portid, u32 seq,
 	nfmsg = nlmsg_data(nlh);
 	nfmsg->nfgen_family	= family;
 	nfmsg->version		= NFNETLINK_V0;
-	nfmsg->res_id		= 0;
+	nfmsg->res_id		= htons(net->nft.base_seq & 0xffff);
 
 	if (nla_put_string(skb, NFTA_CHAIN_TABLE, table->name))
 		goto nla_put_failure;
@@ -988,8 +988,8 @@ static int nf_tables_chain_notify(const struct nft_ctx *ctx, int event)
 	if (skb == NULL)
 		goto err;
 
-	err = nf_tables_fill_chain_info(skb, ctx->portid, ctx->seq, event, 0,
-					ctx->afi->family, ctx->table,
+	err = nf_tables_fill_chain_info(skb, ctx->net, ctx->portid, ctx->seq,
+					event, 0, ctx->afi->family, ctx->table,
 					ctx->chain);
 	if (err < 0) {
 		kfree_skb(skb);
@@ -1031,7 +1031,8 @@ static int nf_tables_dump_chains(struct sk_buff *skb,
 				if (idx > s_idx)
 					memset(&cb->args[1], 0,
 					       sizeof(cb->args) - sizeof(cb->args[0]));
-				if (nf_tables_fill_chain_info(skb, NETLINK_CB(cb->skb).portid,
+				if (nf_tables_fill_chain_info(skb, net,
+							      NETLINK_CB(cb->skb).portid,
 							      cb->nlh->nlmsg_seq,
 							      NFT_MSG_NEWCHAIN,
 							      NLM_F_MULTI,
@@ -1090,7 +1091,7 @@ static int nf_tables_getchain(struct sock *nlsk, struct sk_buff *skb,
 	if (!skb2)
 		return -ENOMEM;
 
-	err = nf_tables_fill_chain_info(skb2, NETLINK_CB(skb).portid,
+	err = nf_tables_fill_chain_info(skb2, net, NETLINK_CB(skb).portid,
 					nlh->nlmsg_seq, NFT_MSG_NEWCHAIN, 0,
 					family, table, chain);
 	if (err < 0)
@@ -1647,8 +1648,9 @@ static const struct nla_policy nft_rule_policy[NFTA_RULE_MAX + 1] = {
 				    .len = NFT_USERDATA_MAXLEN },
 };
 
-static int nf_tables_fill_rule_info(struct sk_buff *skb, u32 portid, u32 seq,
-				    int event, u32 flags, int family,
+static int nf_tables_fill_rule_info(struct sk_buff *skb, struct net *net,
+				    u32 portid, u32 seq, int event,
+				    u32 flags, int family,
 				    const struct nft_table *table,
 				    const struct nft_chain *chain,
 				    const struct nft_rule *rule)
@@ -1668,7 +1670,7 @@ static int nf_tables_fill_rule_info(struct sk_buff *skb, u32 portid, u32 seq,
 	nfmsg = nlmsg_data(nlh);
 	nfmsg->nfgen_family	= family;
 	nfmsg->version		= NFNETLINK_V0;
-	nfmsg->res_id		= 0;
+	nfmsg->res_id		= htons(net->nft.base_seq & 0xffff);
 
 	if (nla_put_string(skb, NFTA_RULE_TABLE, table->name))
 		goto nla_put_failure;
@@ -1724,8 +1726,8 @@ static int nf_tables_rule_notify(const struct nft_ctx *ctx,
 	if (skb == NULL)
 		goto err;
 
-	err = nf_tables_fill_rule_info(skb, ctx->portid, ctx->seq, event, 0,
-				       ctx->afi->family, ctx->table,
+	err = nf_tables_fill_rule_info(skb, ctx->net, ctx->portid, ctx->seq,
+				       event, 0, ctx->afi->family, ctx->table,
 				       ctx->chain, rule);
 	if (err < 0) {
 		kfree_skb(skb);
@@ -1771,7 +1773,7 @@ static int nf_tables_dump_rules(struct sk_buff *skb,
 					if (idx > s_idx)
 						memset(&cb->args[1], 0,
 						       sizeof(cb->args) - sizeof(cb->args[0]));
-					if (nf_tables_fill_rule_info(skb, NETLINK_CB(cb->skb).portid,
+					if (nf_tables_fill_rule_info(skb, net, NETLINK_CB(cb->skb).portid,
 								      cb->nlh->nlmsg_seq,
 								      NFT_MSG_NEWRULE,
 								      NLM_F_MULTI | NLM_F_APPEND,
@@ -1837,7 +1839,7 @@ static int nf_tables_getrule(struct sock *nlsk, struct sk_buff *skb,
 	if (!skb2)
 		return -ENOMEM;
 
-	err = nf_tables_fill_rule_info(skb2, NETLINK_CB(skb).portid,
+	err = nf_tables_fill_rule_info(skb2, net, NETLINK_CB(skb).portid,
 				       nlh->nlmsg_seq, NFT_MSG_NEWRULE, 0,
 				       family, table, chain, rule);
 	if (err < 0)
@@ -2321,7 +2323,7 @@ static int nf_tables_fill_set(struct sk_buff *skb, const struct nft_ctx *ctx,
 	nfmsg = nlmsg_data(nlh);
 	nfmsg->nfgen_family	= ctx->afi->family;
 	nfmsg->version		= NFNETLINK_V0;
-	nfmsg->res_id		= 0;
+	nfmsg->res_id		= htons(ctx->net->nft.base_seq & 0xffff);
 
 	if (nla_put_string(skb, NFTA_SET_TABLE, ctx->table->name))
 		goto nla_put_failure;
@@ -2925,7 +2927,7 @@ static int nf_tables_dump_set(struct sk_buff *skb, struct netlink_callback *cb)
 	nfmsg = nlmsg_data(nlh);
 	nfmsg->nfgen_family = ctx.afi->family;
 	nfmsg->version      = NFNETLINK_V0;
-	nfmsg->res_id       = 0;
+	nfmsg->res_id	    = htons(ctx.net->nft.base_seq & 0xffff);
 
 	if (nla_put_string(skb, NFTA_SET_ELEM_LIST_TABLE, ctx.table->name))
 		goto nla_put_failure;
@@ -3006,7 +3008,7 @@ static int nf_tables_fill_setelem_info(struct sk_buff *skb,
 	nfmsg = nlmsg_data(nlh);
 	nfmsg->nfgen_family	= ctx->afi->family;
 	nfmsg->version		= NFNETLINK_V0;
-	nfmsg->res_id		= 0;
+	nfmsg->res_id		= htons(ctx->net->nft.base_seq & 0xffff);
 
 	if (nla_put_string(skb, NFTA_SET_TABLE, ctx->table->name))
 		goto nla_put_failure;
@@ -3293,6 +3295,87 @@ static int nf_tables_delsetelem(struct sock *nlsk, struct sk_buff *skb,
 	return err;
 }
 
+static int nf_tables_fill_gen_info(struct sk_buff *skb, struct net *net,
+				   u32 portid, u32 seq)
+{
+	struct nlmsghdr *nlh;
+	struct nfgenmsg *nfmsg;
+	int event = (NFNL_SUBSYS_NFTABLES << 8) | NFT_MSG_NEWGEN;
+
+	nlh = nlmsg_put(skb, portid, seq, event, sizeof(struct nfgenmsg), 0);
+	if (nlh == NULL)
+		goto nla_put_failure;
+
+	nfmsg = nlmsg_data(nlh);
+	nfmsg->nfgen_family	= AF_UNSPEC;
+	nfmsg->version		= NFNETLINK_V0;
+	nfmsg->res_id		= htons(net->nft.base_seq & 0xffff);
+
+	if (nla_put_be32(skb, NFTA_GEN_ID, htonl(net->nft.base_seq)))
+		goto nla_put_failure;
+
+	return nlmsg_end(skb, nlh);
+
+nla_put_failure:
+	nlmsg_trim(skb, nlh);
+	return -EMSGSIZE;
+}
+
+static int nf_tables_gen_notify(struct net *net, struct sk_buff *skb, int event)
+{
+	struct nlmsghdr *nlh = nlmsg_hdr(skb);
+	struct sk_buff *skb2;
+	int err;
+
+	if (nlmsg_report(nlh) &&
+	    !nfnetlink_has_listeners(net, NFNLGRP_NFTABLES))
+		return 0;
+
+	err = -ENOBUFS;
+	skb2 = nlmsg_new(NLMSG_GOODSIZE, GFP_KERNEL);
+	if (skb2 == NULL)
+		goto err;
+
+	err = nf_tables_fill_gen_info(skb2, net, NETLINK_CB(skb).portid,
+				      nlh->nlmsg_seq);
+	if (err < 0) {
+		kfree_skb(skb2);
+		goto err;
+	}
+
+	err = nfnetlink_send(skb2, net, NETLINK_CB(skb).portid,
+			     NFNLGRP_NFTABLES, nlmsg_report(nlh), GFP_KERNEL);
+err:
+	if (err < 0) {
+		nfnetlink_set_err(net, NETLINK_CB(skb).portid, NFNLGRP_NFTABLES,
+				  err);
+	}
+	return err;
+}
+
+static int nf_tables_getgen(struct sock *nlsk, struct sk_buff *skb,
+			    const struct nlmsghdr *nlh,
+			    const struct nlattr * const nla[])
+{
+	struct net *net = sock_net(skb->sk);
+	struct sk_buff *skb2;
+	int err;
+
+	skb2 = alloc_skb(NLMSG_GOODSIZE, GFP_KERNEL);
+	if (skb2 == NULL)
+		return -ENOMEM;
+
+	err = nf_tables_fill_gen_info(skb2, net, NETLINK_CB(skb).portid,
+				      nlh->nlmsg_seq);
+	if (err < 0)
+		goto err;
+
+	return nlmsg_unicast(nlsk, skb2, NETLINK_CB(skb).portid);
+err:
+	kfree_skb(skb2);
+	return err;
+}
+
 static const struct nfnl_callback nf_tables_cb[NFT_MSG_MAX] = {
 	[NFT_MSG_NEWTABLE] = {
 		.call_batch	= nf_tables_newtable,
@@ -3369,6 +3452,9 @@ static const struct nfnl_callback nf_tables_cb[NFT_MSG_MAX] = {
 		.attr_count	= NFTA_SET_ELEM_LIST_MAX,
 		.policy		= nft_set_elem_list_policy,
 	},
+	[NFT_MSG_GETGEN] = {
+		.call		= nf_tables_getgen,
+	},
 };
 
 static void nft_chain_commit_update(struct nft_trans *trans)
@@ -3526,6 +3612,8 @@ static int nf_tables_commit(struct sk_buff *skb)
 		call_rcu(&trans->rcu_head, nf_tables_commit_release_rcu);
 	}
 
+	nf_tables_gen_notify(net, skb, NFT_MSG_NEWGEN);
+
 	return 0;
 }