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SubjectRe: [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@gmail.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@strlen.de> 于2019年4月22日周一 下午5:35写道:
> >
> > 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 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 ...
> >
> > ?

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