netfilter: nf_tables: bail out on mismatching dynset and set expressions

If dynset expressions provided by userspace is larger than the declared
set expressions, then bail out.

Fixes: 48b0ae046ee9 ("netfilter: nftables: netlink support for several set element expressions")
Reported-by: Xingyuan Mo <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

net/netfilter/nft_dynset.c

···
 			priv->expr_array[i] = dynset_expr;
 			priv->num_exprs++;
 
-			if (set->num_exprs &&
-			    dynset_expr->ops != set->exprs[i]->ops) {
-				err = -EOPNOTSUPP;
-				goto err_expr_free;
+			if (set->num_exprs) {
+				if (i >= set->num_exprs) {
+					err = -EINVAL;
+					goto err_expr_free;
+				}
+				if (dynset_expr->ops != set->exprs[i]->ops) {
+					err = -EOPNOTSUPP;
+					goto err_expr_free;
+				}
 			}
 			i++;
 		}