netdev - Re: [PATCH net] ipv6: mcast: better catch silly mtu values

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Date:   Wed, 13 Dec 2017 13:17:07 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     eric.dumazet@...il.com
Cc:     lucien.xin@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH net] ipv6: mcast: better catch silly mtu values

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Mon, 11 Dec 2017 07:03:38 -0800

> From: Eric Dumazet <edumazet@...gle.com>
> 
> syzkaller reported crashes in IPv6 stack [1]
> 
> Xin Long found that lo MTU was set to silly values.
> 
> IPv6 stack reacts to changes to small MTU, by disabling itself under
> RTNL.
> 
> But there is a window where threads not using RTNL can see a wrong
> device mtu. This can lead to surprises, in mld code where it is assumed
> the mtu is suitable.
> 
> Fix this by reading device mtu once and checking IPv6 minimal MTU.
 ...
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>

Applied and queued up for -stable.