linux-kernel - Re: [PATCH] netfilter: fix dangling pointer access of fake

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Date:   Mon, 22 Apr 2019 18:10:06 +0800
From:   Rundong Ge <rdong.ge@...il.com>
To:     Florian Westphal <fw@...len.de>
Cc:     Pablo Neira Ayuso <pablo@...filter.org>, kadlec@...ckhole.kfki.hu,
        Roopa Prabhu <roopa@...ulusnetworks.com>, davem@...emloft.net,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] netfilter: fix dangling pointer access of fake_rtable

The hook in my testcase is at NF_BR_FORWARD, and priority is -2.
And at this hook point both the entry->out  and entry->in  are not
bridge device.
But the dst was set to the bridge's fake_rtable.

Rundong Ge <rdong.ge@...il.com> 于2019年4月22日周一 下午5:51写道：
>
> 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 phyindev.
>
> Florian Westphal <fw@...len.de> 于2019年4月22日周一 下午5:35写道：
> >
> > Rundong Ge <rdong.ge@...il.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 struct nf_hook_state *state,
> >                 .size   = sizeof(*entry) + route_key_size,
> >         };
> >
> > +       if (skb_dst(skb)) {
> > +               skb_dst_force(skb);
> > +               if (!skb_dst(skb)) {
> > +                       status = -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 = skb_dst(skb);
> >         if (dst && dst->dev->index == index ...
> >
> > ?