netdev - Re: [PATCH net-next] ipv6: blackhole

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Date:   Mon, 14 Feb 2022 09:44:02 +0200
From:   Ido Schimmel <idosch@...sch.org>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Ido Schimmel <idosch@...dia.com>,
        syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH net-next] ipv6: blackhole_netdev needs snmp6 counters

On Sun, Feb 13, 2022 at 06:10:56PM -0800, Eric Dumazet wrote:
> From: Ido Schimmel <idosch@...dia.com>
> 
> Whenever rt6_uncached_list_flush_dev() swaps rt->rt6_idev
> to the blackhole device, parts of IPv6 stack might still need
> to increment one SNMP counter.
> 
> Root cause, patch from Ido, changelog from Eric :)
> 
> This bug suggests that we need to audit rt->rt6_idev usages
> and make sure they are properly using RCU protection.
> 
> Fixes: e5f80fcf869a ("ipv6: give an IPv6 dev to blackhole_netdev")
> Signed-off-by: Ido Schimmel <idosch@...dia.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>

Thanks for taking care of this, Eric. I applied the patch to our tree
last night before logging off and regression does look fine.