netdev - Re: [PATCH v2 1/1] netfilter: nf_tables: fib: Drop IPV6 packages if IPv6 is disabled on boot

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Date:   Tue, 27 Aug 2019 14:19:50 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     leonardo@...ux.ibm.com
Cc:     pablo@...filter.org, netfilter-devel@...r.kernel.org,
        coreteam@...filter.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, kadlec@...filter.org, fw@...len.de,
        kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org
Subject: Re: [PATCH v2 1/1] netfilter: nf_tables: fib: Drop IPV6 packages
 if IPv6 is disabled on boot

From: Leonardo Bras <leonardo@...ux.ibm.com>
Date: Tue, 27 Aug 2019 14:34:14 -0300

> I could reproduce this bug on a host ('ipv6.disable=1') starting a
> guest with a virtio-net interface with 'filterref' over a virtual
> bridge. It crashes the host during guest boot (just before login).
> 
> By that I could understand that a guest IPv6 network traffic
> (viavirtio-net) may cause this kernel panic.

Really this is bad and I suspected bridging to be involved somehow.

If ipv6 is disabled ipv6 traffic should not pass through the machine
by any means whatsoever.  Otherwise there is no point to the knob
and we will keep having to add hack checks all over the tree instead
of fixing the fundamental issue.