netdev - Re: [PATCH net] ipv6: fix udpv6 sendmsg crash caused by too small MTU

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Message-Id: <20180115.133026.488063576165047709.davem@davemloft.net>
Date:   Mon, 15 Jan 2018 13:30:26 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     maloneykernel@...il.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com, maloney@...gle.com
Subject: Re: [PATCH net] ipv6: fix udpv6 sendmsg crash caused by too small
 MTU

From: Mike Maloney <maloneykernel@...il.com>
Date: Wed, 10 Jan 2018 12:45:10 -0500

> From: Mike Maloney <maloney@...gle.com>
> 
> The logic in __ip6_append_data() assumes that the MTU is at least large
> enough for the headers.  A device's MTU may be adjusted after being
> added while sendmsg() is processing data, resulting in
> __ip6_append_data() seeing any MTU.  For an mtu smaller than the size of
> the fragmentation header, the math results in a negative 'maxfraglen',
> which causes problems when refragmenting any previous skb in the
> skb_write_queue, leaving it possibly malformed.
> 
> Instead sendmsg returns EINVAL when the mtu is calculated to be less
> than IPV6_MIN_MTU.
 ...
> Reported-by: syzbot <syzkaller@...glegroups.com>
> Signed-off-by: Mike Maloney <maloney@...gle.com>

Applied and queued up for -stable, thank you.