netdev - Re: [PATCH net-next v4 1/4] net/sched: Introduce action ct

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Message-ID: <20190707120455.6li4tfb5ppht4xy7@breakpoint.cc>
Date:   Sun, 7 Jul 2019 14:04:55 +0200
From:   Florian Westphal <fw@...len.de>
To:     Paul Blakey <paulb@...lanox.com>
Cc:     Jiri Pirko <jiri@...lanox.com>, Roi Dayan <roid@...lanox.com>,
        Yossi Kuperman <yossiku@...lanox.com>,
        Oz Shlomo <ozsh@...lanox.com>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        netdev@...r.kernel.org, David Miller <davem@...emloft.net>,
        Aaron Conole <aconole@...hat.com>,
        Zhike Wang <wangzhike@...com>,
        Rony Efraim <ronye@...lanox.com>, nst-kernel@...hat.com,
        John Hurley <john.hurley@...ronome.com>,
        Simon Horman <simon.horman@...ronome.com>,
        Justin Pettit <jpettit@....org>
Subject: Re: [PATCH net-next v4 1/4] net/sched: Introduce action ct

Paul Blakey <paulb@...lanox.com> wrote:
> +/* Determine whether skb->_nfct is equal to the result of conntrack lookup. */
> +static bool tcf_ct_skb_nfct_cached(struct net *net, struct sk_buff *skb,
> +				   u16 zone_id, bool force)
> +{
> +	enum ip_conntrack_info ctinfo;
> +	struct nf_conn *ct;
> +
> +	ct = nf_ct_get(skb, &ctinfo);
> +	if (!ct)
> +		return false;
> +	if (!net_eq(net, read_pnet(&ct->ct_net)))
> +		return false;
> +	if (nf_ct_zone(ct)->id != zone_id)
> +		return false;
> +
> +	/* Force conntrack entry direction. */
> +	if (force && CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL) {
> +		nf_conntrack_put(&ct->ct_general);
> +		nf_ct_set(skb, NULL, IP_CT_UNTRACKED);
> +
> +		if (nf_ct_is_confirmed(ct))
> +			nf_ct_kill(ct);

This looks like a possible UAF:
nf_conntrack_put() may free the conntrack entry.

It seems better to do do:
	if (nf_ct_is_confirmed(ct))
		nf_ct_kill(ct);

	nf_conntrack_put(&ct->ct_general);
	nf_ct_set(skb, ...