Re: [PATCH] netfilter: fix dangling pointer access of fake_rtable

[Rundong Ge]

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@xxxxxxxxx> ä2019å4æ22æåä äå5:35åéï
>
> Rundong Ge <rdong.ge@xxxxxxxxx> 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 ...
>
> ?