netdev - Re: [PATCH net] ipv6: fix neighbour resolution with raw socket

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Date:   Sat, 22 Jun 2019 17:07:12 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     nicolas.dichtel@...nd.com
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net] ipv6: fix neighbour resolution with raw socket

From: Nicolas Dichtel <nicolas.dichtel@...nd.com>
Date: Thu, 20 Jun 2019 14:34:34 +0200

> The scenario is the following: the user uses a raw socket to send an ipv6
> packet, destinated to a not-connected network, and specify a connected nh.
> Here is the corresponding python script to reproduce this scenario:
 ...
> fd00:175::/64 is a connected route and fd00:200::fa is not a connected
> host.
> 
> With this scenario, the kernel starts by sending a NS to resolve
> fd00:175::2. When it receives the NA, it flushes its queue and try to send
> the initial packet. But instead of sending it, it sends another NS to
> resolve fd00:200::fa, which obvioulsy fails, thus the packet is dropped. If
> the user sends again the packet, it now uses the right nh (fd00:175::2).
> 
> The problem is that ip6_dst_lookup_neigh() uses the rt6i_gateway, which is
> :: because the associated route is a connected route, thus it uses the dst
> addr of the packet. Let's use rt6_nexthop() to choose the right nh.
> 
> Note that rt and in6addr_any are const in ip6_dst_lookup_neigh(), thus
> let's constify rt6_nexthop() to avoid ugly cast.
> 
> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>

Applied and queued up for -stable, thanks.