Commit message: netfilter: nf_tables_offload: incorrect flow offload action array size

immediate verdict expression needs to allocate one slot in the flow offload
action array, however, immediate data expression does not need to do so.

fwd and dup expression need to allocate one slot, this is missing.

Add a new offload_action interface to report if this expression needs to
allocate one slot in the flow offload action array.

Fixes: be2861dc36d7 ("netfilter: nft_{fwd,dup}_netdev: add offload support")
Reported-and-tested-by: Nick Gregory <Nick.Gregory@Sophos.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
CVE: CVE-2022-25636
CWE: CWE-269
Vulnerability description: net/netfilter/nf_dup_netdev.c in the Linux kernel 5.4 through 5.6.10 allows local users to gain privileges because of a heap out-of-bounds write. This is related to nf_tables_offload.

Project: nf
File: nf_tables_offload.c

struct nft_flow_rule *nft_flow_rule_create(struct net *net,
					   const struct nft_rule *rule)
{
	struct nft_offload_ctx *ctx;
	struct nft_flow_rule *flow;
	int num_actions = 0, err;
	struct nft_expr *expr;

	expr = nft_expr_first(rule);
	while (nft_expr_more(rule, expr)) {
		if (expr->ops->offload_flags & NFT_OFFLOAD_F_ACTION)
			num_actions++;

		expr = nft_expr_next(expr);
	}

	if (num_actions == 0)
		return ERR_PTR(-EOPNOTSUPP);

	flow = nft_flow_rule_alloc(num_actions);
	if (!flow)
		return ERR_PTR(-ENOMEM);

	expr = nft_expr_first(rule);

	ctx = kzalloc(sizeof(struct nft_offload_ctx), GFP_KERNEL);
	if (!ctx) {
		err = -ENOMEM;
		goto err_out;
	}
	ctx->net = net;
	ctx->dep.type = NFT_OFFLOAD_DEP_UNSPEC;

	while (nft_expr_more(rule, expr)) {
		if (!expr->ops->offload) {
			err = -EOPNOTSUPP;
			goto err_out;
		}
		err = expr->ops->offload(ctx, flow, expr);
		if (err < 0)
			goto err_out;

		expr = nft_expr_next(expr);
	}
	nft_flow_rule_transfer_vlan(ctx, flow);

	flow->proto = ctx->dep.l3num;
	kfree(ctx);

	return flow;
err_out:
	kfree(ctx);
	nft_flow_rule_destroy(flow);

	return ERR_PTR(err);
}

Project: nf
File: nf_tables_offload.c

struct nft_flow_rule *nft_flow_rule_create(struct net *net,
					   const struct nft_rule *rule)
{
	struct nft_offload_ctx *ctx;
	struct nft_flow_rule *flow;
	int num_actions = 0, err;
	struct nft_expr *expr;

	expr = nft_expr_first(rule);
	while (nft_expr_more(rule, expr)) {
		if (expr->ops->offload_action &&
		    expr->ops->offload_action(expr))
			num_actions++;

		expr = nft_expr_next(expr);
	}

	if (num_actions == 0)
		return ERR_PTR(-EOPNOTSUPP);

	flow = nft_flow_rule_alloc(num_actions);
	if (!flow)
		return ERR_PTR(-ENOMEM);

	expr = nft_expr_first(rule);

	ctx = kzalloc(sizeof(struct nft_offload_ctx), GFP_KERNEL);
	if (!ctx) {
		err = -ENOMEM;
		goto err_out;
	}
	ctx->net = net;
	ctx->dep.type = NFT_OFFLOAD_DEP_UNSPEC;

	while (nft_expr_more(rule, expr)) {
		if (!expr->ops->offload) {
			err = -EOPNOTSUPP;
			goto err_out;
		}
		err = expr->ops->offload(ctx, flow, expr);
		if (err < 0)
			goto err_out;

		expr = nft_expr_next(expr);
	}
	nft_flow_rule_transfer_vlan(ctx, flow);

	flow->proto = ctx->dep.l3num;
	kfree(ctx);

	return flow;
err_out:
	kfree(ctx);
	nft_flow_rule_destroy(flow);

	return ERR_PTR(err);
}