netfilter: nf_tables: initialize set before expression setup

nft_set_elem_expr_alloc() needs an initialized set if expression sets on
the NFT_EXPR_GC flag. Move set fields initialization before expression
setup.

[4512935.019450] ==================================================================
[4512935.019456] BUG: KASAN: null-ptr-deref in nft_set_elem_expr_alloc+0x84/0xd0 [nf_tables]
[4512935.019487] Read of size 8 at addr 0000000000000070 by task nft/23532
[4512935.019494] CPU: 1 PID: 23532 Comm: nft Not tainted 5.12.0-rc4+ #48
[...]
[4512935.019502] Call Trace:
[4512935.019505]  dump_stack+0x89/0xb4
[4512935.019512]  ? nft_set_elem_expr_alloc+0x84/0xd0 [nf_tables]
[4512935.019536]  ? nft_set_elem_expr_alloc+0x84/0xd0 [nf_tables]
[4512935.019560]  kasan_report.cold.12+0x5f/0xd8
[4512935.019566]  ? nft_set_elem_expr_alloc+0x84/0xd0 [nf_tables]
[4512935.019590]  nft_set_elem_expr_alloc+0x84/0xd0 [nf_tables]
[4512935.019615]  nf_tables_newset+0xc7f/0x1460 [nf_tables]

Reported-by: syzbot+ce96ca2b1d0b37c6422d@syzkaller.appspotmail.com
Fixes: 65038428b2 ("netfilter: nf_tables: allow to specify stateful expression in set definition")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -4364,44 +4364,7 @@ static int nf_tables_newset(struct sk_buff *skb, const struct nfnl_info *info,
 	err = nf_tables_set_alloc_name(&ctx, set, name);
 	kfree(name);
 	if (err < 0)
-		goto err_set_alloc_name;
+		goto err_set_name;
-
-	if (nla[NFTA_SET_EXPR]) {
-		expr = nft_set_elem_expr_alloc(&ctx, set, nla[NFTA_SET_EXPR]);
-		if (IS_ERR(expr)) {
-			err = PTR_ERR(expr);
-			goto err_set_alloc_name;
-		}
-		set->exprs[0] = expr;
-		set->num_exprs++;
-	} else if (nla[NFTA_SET_EXPRESSIONS]) {
-		struct nft_expr *expr;
-		struct nlattr *tmp;
-		int left;
-
-		if (!(flags & NFT_SET_EXPR)) {
-			err = -EINVAL;
-			goto err_set_alloc_name;
-		}
-		i = 0;
-		nla_for_each_nested(tmp, nla[NFTA_SET_EXPRESSIONS], left) {
-			if (i == NFT_SET_EXPR_MAX) {
-				err = -E2BIG;
-				goto err_set_init;
-			}
-			if (nla_type(tmp) != NFTA_LIST_ELEM) {
-				err = -EINVAL;
-				goto err_set_init;
-			}
-			expr = nft_set_elem_expr_alloc(&ctx, set, tmp);
-			if (IS_ERR(expr)) {
-				err = PTR_ERR(expr);
-				goto err_set_init;
-			}
-			set->exprs[i++] = expr;
-			set->num_exprs++;
-		}
-	}
 
 	udata = NULL;
 	if (udlen) {
@@ -4413,20 +4376,19 @@ static int nf_tables_newset(struct sk_buff *skb, const struct nfnl_info *info,
 	INIT_LIST_HEAD(&set->catchall_list);
 	set->table = table;
 	write_pnet(&set->net, net);
-	set->ops   = ops;
+	set->ops = ops;
 	set->ktype = ktype;
-	set->klen  = desc.klen;
+	set->klen = desc.klen;
 	set->dtype = dtype;
 	set->objtype = objtype;
-	set->dlen  = desc.dlen;
+	set->dlen = desc.dlen;
 	set->flags = flags;
-	set->size  = desc.size;
+	set->size = desc.size;
 	set->policy = policy;
-	set->udlen  = udlen;
+	set->udlen = udlen;
-	set->udata  = udata;
+	set->udata = udata;
 	set->timeout = timeout;
 	set->gc_int = gc_int;
-	set->handle = nf_tables_alloc_handle(table);
 
 	set->field_count = desc.field_count;
 	for (i = 0; i < desc.field_count; i++)
@@ -4436,20 +4398,59 @@ static int nf_tables_newset(struct sk_buff *skb, const struct nfnl_info *info,
 	if (err < 0)
 		goto err_set_init;
 
+	if (nla[NFTA_SET_EXPR]) {
+		expr = nft_set_elem_expr_alloc(&ctx, set, nla[NFTA_SET_EXPR]);
+		if (IS_ERR(expr)) {
+			err = PTR_ERR(expr);
+			goto err_set_expr_alloc;
+		}
+		set->exprs[0] = expr;
+		set->num_exprs++;
+	} else if (nla[NFTA_SET_EXPRESSIONS]) {
+		struct nft_expr *expr;
+		struct nlattr *tmp;
+		int left;
+
+		if (!(flags & NFT_SET_EXPR)) {
+			err = -EINVAL;
+			goto err_set_expr_alloc;
+		}
+		i = 0;
+		nla_for_each_nested(tmp, nla[NFTA_SET_EXPRESSIONS], left) {
+			if (i == NFT_SET_EXPR_MAX) {
+				err = -E2BIG;
+				goto err_set_expr_alloc;
+			}
+			if (nla_type(tmp) != NFTA_LIST_ELEM) {
+				err = -EINVAL;
+				goto err_set_expr_alloc;
+			}
+			expr = nft_set_elem_expr_alloc(&ctx, set, tmp);
+			if (IS_ERR(expr)) {
+				err = PTR_ERR(expr);
+				goto err_set_expr_alloc;
+			}
+			set->exprs[i++] = expr;
+			set->num_exprs++;
+		}
+	}
+
+	set->handle = nf_tables_alloc_handle(table);
+
 	err = nft_trans_set_add(&ctx, NFT_MSG_NEWSET, set);
 	if (err < 0)
-		goto err_set_trans;
+		goto err_set_expr_alloc;
 
 	list_add_tail_rcu(&set->list, &table->sets);
 	table->use++;
 	return 0;
 
-err_set_trans:
+err_set_expr_alloc:
-	ops->destroy(set);
-err_set_init:
 	for (i = 0; i < set->num_exprs; i++)
 		nft_expr_destroy(&ctx, set->exprs[i]);
-err_set_alloc_name:
+
+	ops->destroy(set);
+err_set_init:
 	kfree(set->name);
 err_set_name:
 	kvfree(set);