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 <CAN1Lvyo1CVopsB7iV=e-dAN9JDFg-SmQ8g6H6RrgD7qACAd4hQ@mail.gmail.com> <20190422093502.36da6z3qf7zxpwny@breakpoint.cc>
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From:   Rundong Ge <rdong.ge@gmail.com>
Date:   Mon, 22 Apr 2019 17:51:28 +0800
Message-ID: <CAN1LvyrSWPbNSvzLquQAeK9kYK=YyqyJEm7zodd3O-QWAVTC4Q@mail.gmail.com>
Subject: Re: [PATCH] netfilter: fix dangling pointer access of fake_rtable
To:     Florian Westphal <fw@strlen.de>
Cc:     Pablo Neira Ayuso <pablo@netfilter.org>, kadlec@blackhole.kfki.hu,
        Roopa Prabhu <roopa@cumulusnetworks.com>, davem@davemloft.net,
        netfilter-devel@vger.kernel.org, coreteam@netfilter.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
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Sender: linux-kernel-owner@vger.kernel.org
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skb->dev is munged in setup_prerouting() to be bridge or vlan device on
top of bridge.
--Yes, but  br_nf_pre_routing_finish will set the skb->dev back to the phyi=
ndev.

Florian Westphal <fw@strlen.de> =E4=BA=8E2019=E5=B9=B44=E6=9C=8822=E6=97=A5=
=E5=91=A8=E4=B8=80 =E4=B8=8B=E5=8D=885:35=E5=86=99=E9=81=93=EF=BC=9A
>
> Rundong Ge <rdong.ge@gmail.com> wrote:
> > br_nf_pre_routing will call the NF_INET_PRE_ROUTING hooks, at this
> > time both entry->state.in and entry->state.out are not bridge device.
> >
> > NF_HOOK(NFPROTO_IPV4, NF_INET_PRE_ROUTING, state->net, state->sk, skb,
> > skb->dev, NULL,
> > br_nf_pre_routing_finish);
>
> skb->dev is munged in setup_prerouting() to be bridge or vlan device on
> top of bridge.
>
> That being said, I think we need this fix at least:
>
> diff --git a/net/netfilter/nf_queue.c b/net/netfilter/nf_queue.c
> --- a/net/netfilter/nf_queue.c
> +++ b/net/netfilter/nf_queue.c
> @@ -197,8 +197,15 @@ static int __nf_queue(struct sk_buff *skb, const str=
uct nf_hook_state *state,
>                 .size   =3D sizeof(*entry) + route_key_size,
>         };
>
> +       if (skb_dst(skb)) {
> +               skb_dst_force(skb);
> +               if (!skb_dst(skb)) {
> +                       status =3D -EHOSTUNREACH;
> +                       goto err;
> +               }
> +       }
> +
>         nf_queue_entry_get_refs(entry);
> -       skb_dst_force(skb);
>
>         switch (entry->state.pf) {
>         case AF_INET:
>
>
> Then, why not add, in dev_cmp:
>
>         dst =3D skb_dst(skb);
>         if (dst && dst->dev->index =3D=3D index ...
>
> ?