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Message-ID: <CAM0EoMkDHQYdL+0cgOzbEemAOfFXPJSe-z0Bgez=YbyQ56iLoQ@mail.gmail.com>
Date: Thu, 8 Jun 2023 13:08:23 -0400
From: Jamal Hadi Salim <jhs@...atatu.com>
To: Florian Westphal <fw@...len.de>
Cc: netdev@...r.kernel.org, kuba@...nel.org, edumazet@...gle.com,
davem@...emloft.net, pabeni@...hat.com, xiyou.wangcong@...il.com,
jiri@...nulli.us, Simon Horman <simon.horman@...igine.com>
Subject: Re: [PATCH net v2 2/3] net/sched: act_ipt: add sanity checks on skb
before calling target
On Thu, Jun 8, 2023 at 10:03 AM Florian Westphal <fw@...len.de> wrote:
>
> Netfilter targets make assumptions on the skb state, for example
> iphdr is supposed to be in the linear area.
>
> This is normally done by IP stack, but in act_ipt case no
> such checks are made.
>
> Some targets can even assume that skb_dst will be valid.
> Make a minimum effort to check for this:
>
> - Don't call the targets eval function for non-ipv4 skbs.
> - Don't call the targets eval function for POSTROUTING
> emulation when the skb has no dst set.
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Florian Westphal <fw@...len.de>
> Reviewed-by: Simon Horman <simon.horman@...igine.com>
Other than the comment from Davide (which makes sense) I would say:
Acked-by: Jamal Hadi Salim <jhs@...atatu.com>
cheers,
jamal
> ---
> v2: add Fixes tag, diff unchanged.
>
> net/sched/act_ipt.c | 33 +++++++++++++++++++++++++++++++++
> 1 file changed, 33 insertions(+)
>
> diff --git a/net/sched/act_ipt.c b/net/sched/act_ipt.c
> index ea7f151e7dd2..2f0b39cc4e37 100644
> --- a/net/sched/act_ipt.c
> +++ b/net/sched/act_ipt.c
> @@ -230,6 +230,26 @@ static int tcf_xt_init(struct net *net, struct nlattr *nla,
> a, &act_xt_ops, tp, flags);
> }
>
> +static bool tcf_ipt_act_check(struct sk_buff *skb)
> +{
> + const struct iphdr *iph;
> + unsigned int nhoff, len;
> +
> + if (!pskb_may_pull(skb, sizeof(struct iphdr)))
> + return false;
> +
> + nhoff = skb_network_offset(skb);
> + iph = ip_hdr(skb);
> + if (iph->ihl < 5 || iph->version != 4)
> + return false;
> +
> + len = skb_ip_totlen(skb);
> + if (skb->len < nhoff + len || len < (iph->ihl * 4u))
> + return false;
> +
> + return pskb_may_pull(skb, iph->ihl * 4u);
> +}
> +
> TC_INDIRECT_SCOPE int tcf_ipt_act(struct sk_buff *skb,
> const struct tc_action *a,
> struct tcf_result *res)
> @@ -244,9 +264,22 @@ TC_INDIRECT_SCOPE int tcf_ipt_act(struct sk_buff *skb,
> .pf = NFPROTO_IPV4,
> };
>
> + if (skb->protocol != htons(ETH_P_IP))
> + return TC_ACT_UNSPEC;
> +
> if (skb_unclone(skb, GFP_ATOMIC))
> return TC_ACT_UNSPEC;
>
> + if (!tcf_ipt_act_check(skb))
> + return TC_ACT_UNSPEC;
> +
> + if (state.hook == NF_INET_POST_ROUTING) {
> + if (!skb_dst(skb))
> + return TC_ACT_UNSPEC;
> +
> + state.out = skb->dev;
> + }
> +
> spin_lock(&ipt->tcf_lock);
>
> tcf_lastuse_update(&ipt->tcf_tm);
> --
> 2.40.1
>
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