Re: [PATCH] netfilter: Set expressions out of range in nft_add_set_elem()

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Mon, Sep 08, 2025 at 10:08:44PM +0800, Chen Yufeng wrote:
> The number of `expr` expressions provided by userspace may exceed the 
> declared set expressions, potentially leading to errors or undefined behavior. 
> This patch addresses the issue by validating whether i exceeds 
> set->num_exprs.

        } else if (nla[NFTA_SET_ELEM_EXPRESSIONS]) {
                struct nft_expr *expr;
                struct nlattr *tmp;
                int left;

                i = 0;
                nla_for_each_nested(tmp, nla[NFTA_SET_ELEM_EXPRESSIONS], left) {
                        if (i == NFT_SET_EXPR_MAX ||
                            (set->num_exprs && set->num_exprs == i)) {

There is this a upfront check to validate what you describe.

Are you reporting a different issue?

> This patch is inspired by commit 3701cd390fd7("netfilter: nf_tables: 
>  bail out on mismatching dynset and set expressions").
>
> Signed-off-by: Chen Yufeng <chenyufeng@iie.ac.cn>
> ---
>  net/netfilter/nf_tables_api.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
> index 58c5425d61c2..958a7c8b0b4c 100644
> --- a/net/netfilter/nf_tables_api.c
> +++ b/net/netfilter/nf_tables_api.c
> @@ -7338,9 +7338,15 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
>  			expr_array[i] = expr;
>  			num_exprs++;
>  
> -			if (set->num_exprs && expr->ops != set->exprs[i]->ops) {
> -				err = -EOPNOTSUPP;
> -				goto err_set_elem_expr;
> +			if (set->num_exprs) {
> +				if (i >= set->num_exprs) {
> +					err = -EINVAL;
> +					goto err_set_elem_expr;
> +				}
> +				if (expr->ops != set->exprs[i]->ops) {
> +					err = -EOPNOTSUPP;
> +					goto err_set_elem_expr;
> +				}
>  			}
>  			i++;
>  		}
> -- 
> 2.34.1
>