netfilter: nf_tables: fix chain binding transaction logic

Add bound flag to rule and chain transactions as in 6a0a8d10a366
("netfilter: nf_tables: use-after-free in failing rule with bound set")
to skip them in case that the chain is already bound from the abort
path.

This patch fixes an imbalance in the chain use refcnt that triggers a
WARN_ON on the table and chain destroy path.

This patch also disallows nested chain bindings, which is not
supported from userspace.

The logic to deal with chain binding in nft_data_hold() and
nft_data_release() is not correct. The NFT_TRANS_PREPARE state needs a
special handling in case a chain is bound but next expressions in the
same rule fail to initialize as described by 1240eb93f061 ("netfilter:
nf_tables: incorrect error path handling with NFT_MSG_NEWRULE").

The chain is left bound if rule construction fails, so the objects
stored in this chain (and the chain itself) are released by the
transaction records from the abort path, follow up patch ("netfilter:
nf_tables: add NFT_TRANS_PREPARE_ERROR to deal with bound set/chain")
completes this error handling.

When deleting an existing rule, chain bound flag is set off so the
rule expression .destroy path releases the objects.

Fixes: d0e2c7de92c7 ("netfilter: nf_tables: add NFT_CHAIN_BINDING")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

2 files changed, 133 insertions, 40 deletions

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index 69bceefaa5c8..5e4965b98528 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -193,6 +193,48 @@ static void nft_set_trans_bind(const struct nft_ctx *ctx, struct nft_set *set)
 	}
 }
 
+static void nft_chain_trans_bind(const struct nft_ctx *ctx, struct nft_chain *chain)
+{
+	struct nftables_pernet *nft_net;
+	struct net *net = ctx->net;
+	struct nft_trans *trans;
+
+	if (!nft_chain_binding(chain))
+		return;
+
+	nft_net = nft_pernet(net);
+	list_for_each_entry_reverse(trans, &nft_net->commit_list, list) {
+		switch (trans->msg_type) {
+		case NFT_MSG_NEWCHAIN:
+			if (nft_trans_chain(trans) == chain)
+				nft_trans_chain_bound(trans) = true;
+			break;
+		case NFT_MSG_NEWRULE:
+			if (trans->ctx.chain == chain)
+				nft_trans_rule_bound(trans) = true;
+			break;
+		}
+	}
+}
+
+int nf_tables_bind_chain(const struct nft_ctx *ctx, struct nft_chain *chain)
+{
+	if (!nft_chain_binding(chain))
+		return 0;
+
+	if (nft_chain_binding(ctx->chain))
+		return -EOPNOTSUPP;
+
+	if (chain->bound)
+		return -EBUSY;
+
+	chain->bound = true;
+	chain->use++;
+	nft_chain_trans_bind(ctx, chain);
+
+	return 0;
+}
+
 static int nft_netdev_register_hooks(struct net *net,
 				     struct list_head *hook_list)
 {
@@ -338,8 +380,9 @@ static struct nft_trans *nft_trans_chain_add(struct nft_ctx *ctx, int msg_type)
 				ntohl(nla_get_be32(ctx->nla[NFTA_CHAIN_ID]));
 		}
 	}
-
+	nft_trans_chain(trans) = ctx->chain;
 	nft_trans_commit_list_add_tail(ctx->net, trans);
+
 	return trans;
 }
 
@@ -357,8 +400,7 @@ static int nft_delchain(struct nft_ctx *ctx)
 	return 0;
 }
 
-static void nft_rule_expr_activate(const struct nft_ctx *ctx,
-				   struct nft_rule *rule)
+void nft_rule_expr_activate(const struct nft_ctx *ctx, struct nft_rule *rule)
 {
 	struct nft_expr *expr;
 
@@ -371,9 +413,8 @@ static void nft_rule_expr_activate(const struct nft_ctx *ctx,
 	}
 }
 
-static void nft_rule_expr_deactivate(const struct nft_ctx *ctx,
-				     struct nft_rule *rule,
-				     enum nft_trans_phase phase)
+void nft_rule_expr_deactivate(const struct nft_ctx *ctx, struct nft_rule *rule,
+			      enum nft_trans_phase phase)
 {
 	struct nft_expr *expr;
 
@@ -2226,7 +2267,7 @@ static int nft_basechain_init(struct nft_base_chain *basechain, u8 family,
 	return 0;
 }
 
-static int nft_chain_add(struct nft_table *table, struct nft_chain *chain)
+int nft_chain_add(struct nft_table *table, struct nft_chain *chain)
 {
 	int err;
 
@@ -3490,8 +3531,7 @@ err_fill_rule_info:
 	return err;
 }
 
-static void nf_tables_rule_destroy(const struct nft_ctx *ctx,
-				   struct nft_rule *rule)
+void nf_tables_rule_destroy(const struct nft_ctx *ctx, struct nft_rule *rule)
 {
 	struct nft_expr *expr, *next;
 
@@ -3508,7 +3548,7 @@ static void nf_tables_rule_destroy(const struct nft_ctx *ctx,
 	kfree(rule);
 }
 
-void nf_tables_rule_release(const struct nft_ctx *ctx, struct nft_rule *rule)
+static void nf_tables_rule_release(const struct nft_ctx *ctx, struct nft_rule *rule)
 {
 	nft_rule_expr_deactivate(ctx, rule, NFT_TRANS_RELEASE);
 	nf_tables_rule_destroy(ctx, rule);
@@ -6638,7 +6678,6 @@ static int nf_tables_newsetelem(struct sk_buff *skb,
 void nft_data_hold(const struct nft_data *data, enum nft_data_types type)
 {
 	struct nft_chain *chain;
-	struct nft_rule *rule;
 
 	if (type == NFT_DATA_VERDICT) {
 		switch (data->verdict.code) {
@@ -6646,15 +6685,6 @@ void nft_data_hold(const struct nft_data *data, enum nft_data_types type)
 		case NFT_GOTO:
 			chain = data->verdict.chain;
 			chain->use++;
-
-			if (!nft_chain_is_bound(chain))
-				break;
-
-			chain->table->use++;
-			list_for_each_entry(rule, &chain->rules, list)
-				chain->use++;
-
-			nft_chain_add(chain->table, chain);
 			break;
 		}
 	}
@@ -9677,7 +9707,7 @@ static int __nf_tables_abort(struct net *net, enum nfnl_abort_action action)
 				kfree(nft_trans_chain_name(trans));
 				nft_trans_destroy(trans);
 			} else {
-				if (nft_chain_is_bound(trans->ctx.chain)) {
+				if (nft_trans_chain_bound(trans)) {
 					nft_trans_destroy(trans);
 					break;
 				}
@@ -9700,6 +9730,10 @@ static int __nf_tables_abort(struct net *net, enum nfnl_abort_action action)
 			nft_trans_destroy(trans);
 			break;
 		case NFT_MSG_NEWRULE:
+			if (nft_trans_rule_bound(trans)) {
+				nft_trans_destroy(trans);
+				break;
+			}
 			trans->ctx.chain->use--;
 			list_del_rcu(&nft_trans_rule(trans)->list);
 			nft_rule_expr_deactivate(&trans->ctx,
@@ -10263,22 +10297,12 @@ static int nft_verdict_init(const struct nft_ctx *ctx, struct nft_data *data,
 static void nft_verdict_uninit(const struct nft_data *data)
 {
 	struct nft_chain *chain;
-	struct nft_rule *rule;
 
 	switch (data->verdict.code) {
 	case NFT_JUMP:
 	case NFT_GOTO:
 		chain = data->verdict.chain;
 		chain->use--;
-
-		if (!nft_chain_is_bound(chain))
-			break;
-
-		chain->table->use--;
-		list_for_each_entry(rule, &chain->rules, list)
-			chain->use--;
-
-		nft_chain_del(chain);
 		break;
 	}
 }
diff --git a/net/netfilter/nft_immediate.c b/net/netfilter/nft_immediate.c
index c9d2f7c29f53..0492a04064f1 100644
--- a/net/netfilter/nft_immediate.c
+++ b/net/netfilter/nft_immediate.c
@@ -76,11 +76,9 @@ static int nft_immediate_init(const struct nft_ctx *ctx,
 		switch (priv->data.verdict.code) {
 		case NFT_JUMP:
 		case NFT_GOTO:
-			if (nft_chain_is_bound(chain)) {
-				err = -EBUSY;
-				goto err1;
-			}
-			chain->bound = true;
+			err = nf_tables_bind_chain(ctx, chain);
+			if (err < 0)
+				return err;
 			break;
 		default:
 			break;
@@ -98,6 +96,31 @@ static void nft_immediate_activate(const struct nft_ctx *ctx,
 				   const struct nft_expr *expr)
 {
 	const struct nft_immediate_expr *priv = nft_expr_priv(expr);
+	const struct nft_data *data = &priv->data;
+	struct nft_ctx chain_ctx;
+	struct nft_chain *chain;
+	struct nft_rule *rule;
+
+	if (priv->dreg == NFT_REG_VERDICT) {
+		switch (data->verdict.code) {
+		case NFT_JUMP:
+		case NFT_GOTO:
+			chain = data->verdict.chain;
+			if (!nft_chain_binding(chain))
+				break;
+
+			chain_ctx = *ctx;
+			chain_ctx.chain = chain;
+
+			list_for_each_entry(rule, &chain->rules, list)
+				nft_rule_expr_activate(&chain_ctx, rule);
+
+			nft_clear(ctx->net, chain);
+			break;
+		default:
+			break;
+		}
+	}
 
 	return nft_data_hold(&priv->data, nft_dreg_to_type(priv->dreg));
 }
@@ -107,6 +130,40 @@ static void nft_immediate_deactivate(const struct nft_ctx *ctx,
 				     enum nft_trans_phase phase)
 {
 	const struct nft_immediate_expr *priv = nft_expr_priv(expr);
+	const struct nft_data *data = &priv->data;
+	struct nft_ctx chain_ctx;
+	struct nft_chain *chain;
+	struct nft_rule *rule;
+
+	if (priv->dreg == NFT_REG_VERDICT) {
+		switch (data->verdict.code) {
+		case NFT_JUMP:
+		case NFT_GOTO:
+			chain = data->verdict.chain;
+			if (!nft_chain_binding(chain))
+				break;
+
+			chain_ctx = *ctx;
+			chain_ctx.chain = chain;
+
+			list_for_each_entry(rule, &chain->rules, list)
+				nft_rule_expr_deactivate(&chain_ctx, rule, phase);
+
+			switch (phase) {
+			case NFT_TRANS_PREPARE:
+				nft_deactivate_next(ctx->net, chain);
+				break;
+			default:
+				nft_chain_del(chain);
+				chain->bound = false;
+				chain->table->use--;
+				break;
+			}
+			break;
+		default:
+			break;
+		}
+	}
 
 	if (phase == NFT_TRANS_COMMIT)
 		return;
@@ -131,15 +188,27 @@ static void nft_immediate_destroy(const struct nft_ctx *ctx,
 	case NFT_GOTO:
 		chain = data->verdict.chain;
 
-		if (!nft_chain_is_bound(chain))
+		if (!nft_chain_binding(chain))
+			break;
+
+		/* Rule construction failed, but chain is already bound:
+		 * let the transaction records release this chain and its rules.
+		 */
+		if (chain->bound) {
+			chain->use--;
 			break;
+		}
 
+		/* Rule has been deleted, release chain and its rules. */
 		chain_ctx = *ctx;
 		chain_ctx.chain = chain;
 
-		list_for_each_entry_safe(rule, n, &chain->rules, list)
-			nf_tables_rule_release(&chain_ctx, rule);
-
+		chain->use--;
+		list_for_each_entry_safe(rule, n, &chain->rules, list) {
+			chain->use--;
+			list_del(&rule->list);
+			nf_tables_rule_destroy(&chain_ctx, rule);
+		}
 		nf_tables_chain_destroy(&chain_ctx);
 		break;
 	default: