On Sat, Jan 07, 2017 at 08:49:18PM +0800, Liping Zhang wrote: > From: Liping Zhang <[email protected]> > > Currently, we check the existing rtable in PREROUTING hook, if RTCF_LOCAL > is set, we assume that the packet is loopback. > > But this assumption is incorrect, for example, a packet encapsulated > in ipsec transport mode was received and routed to local, after > decapsulation, it would be delivered to local again, and the rtable > was not dropped, so RTCF_LOCAL check would trigger. But actually, the > packet was not loopback. > > So for these normal loopback packets, we can check whether the in device > is IFF_LOOPBACK or not. For these locally generated broadcast/multicast, > we can check whether the skb->pkt_type is PACKET_LOOPBACK or not. > > Finally, there's a subtle difference between nft fib expr and xtables > rpfilter extension, user can add the following nft rule to do strict > rpfilter check: > # nft add rule x y meta iif eth0 fib saddr . iif oif != eth0 drop > > So when the packet is loopback, it's better to store the in device > instead of the LOOPBACK_IFINDEX, otherwise, after adding the above > nft rule, locally generated broad/multicast packets will be dropped > incorrectly.
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