netfilter: nf_tables: Always allocate nft_rule_dump_ctx

It will move into struct netlink_callback's scratch area later, just put
nf_tables_dump_rules_start in shape to reduce churn later.
Suggested-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Florian Westphal <fw@strlen.de>

net/netfilter/nf_tables_api.c

@@ -3521,10 +3521,10 @@ static int nf_tables_dump_rules(struct sk_buff *skb,
 		if (family != NFPROTO_UNSPEC && family != table->family)
 			continue;
 
-		if (ctx && ctx->table && strcmp(ctx->table, table->name) != 0)
+		if (ctx->table && strcmp(ctx->table, table->name) != 0)
 			continue;
 
-		if (ctx && ctx->table && ctx->chain) {
+		if (ctx->table && ctx->chain) {
 			struct rhlist_head *list, *tmp;
 
 			list = rhltable_lookup(&table->chains_ht, ctx->chain,
@@ -3548,7 +3548,7 @@ static int nf_tables_dump_rules(struct sk_buff *skb,
 				goto done;
 		}
 
-		if (ctx && ctx->table)
+		if (ctx->table)
 			break;
 	}
 done:
@@ -3563,27 +3563,23 @@ static int nf_tables_dump_rules_start(struct netlink_callback *cb)
 	const struct nlattr * const *nla = cb->data;
 	struct nft_rule_dump_ctx *ctx = NULL;
 
-	if (nla[NFTA_RULE_TABLE] || nla[NFTA_RULE_CHAIN]) {
-		ctx = kzalloc(sizeof(*ctx), GFP_ATOMIC);
-		if (!ctx)
-			return -ENOMEM;
+	ctx = kzalloc(sizeof(*ctx), GFP_ATOMIC);
+	if (!ctx)
+		return -ENOMEM;
 
-		if (nla[NFTA_RULE_TABLE]) {
-			ctx->table = nla_strdup(nla[NFTA_RULE_TABLE],
-							GFP_ATOMIC);
-			if (!ctx->table) {
-				kfree(ctx);
-				return -ENOMEM;
-			}
+	if (nla[NFTA_RULE_TABLE]) {
+		ctx->table = nla_strdup(nla[NFTA_RULE_TABLE], GFP_ATOMIC);
+		if (!ctx->table) {
+			kfree(ctx);
+			return -ENOMEM;
 		}
-		if (nla[NFTA_RULE_CHAIN]) {
-			ctx->chain = nla_strdup(nla[NFTA_RULE_CHAIN],
-						GFP_ATOMIC);
-			if (!ctx->chain) {
-				kfree(ctx->table);
-				kfree(ctx);
-				return -ENOMEM;
-			}
+	}
+	if (nla[NFTA_RULE_CHAIN]) {
+		ctx->chain = nla_strdup(nla[NFTA_RULE_CHAIN], GFP_ATOMIC);
+		if (!ctx->chain) {
+			kfree(ctx->table);
+			kfree(ctx);
+			return -ENOMEM;
 		}
 	}
 
@@ -3595,11 +3591,9 @@ static int nf_tables_dump_rules_done(struct netlink_callback *cb)
 {
 	struct nft_rule_dump_ctx *ctx = cb->data;
 
-	if (ctx) {
-		kfree(ctx->table);
-		kfree(ctx->chain);
-		kfree(ctx);
-	}
+	kfree(ctx->table);
+	kfree(ctx->chain);
+	kfree(ctx);
 	return 0;
 }