netdev - Re: [PATCH] ipv6: remove min MTU check for tunnel destinations

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Message-Id: <20180501.122223.1661453536072731491.davem@davemloft.net>
Date:   Tue, 01 May 2018 12:22:23 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     ashwanth@...eaurora.org
Cc:     netdev@...r.kernel.org, pabeni@...hat.com, dsahern@...il.com
Subject: Re: [PATCH] ipv6: remove min MTU check for tunnel destinations

From: Ashwanth Goli <ashwanth@...eaurora.org>
Date: Mon, 30 Apr 2018 00:36:47 +0530

> With 749439bfac "fix udpv6 sendmsg crash caused by too small MTU"
> tunnel dst's that report a MTU less than IPV6_MIN_MTU are broken
> even for packets that are smaller than IPV6_MIN_MTU.
> 
> According to rfc2473#section-7.1
> 
>     if the original IPv6 packet is equal or  smaller  than  the
>     IPv6 minimum link MTU, the tunnel entry-point node
>     encapsulates the original packet, and subsequently
>     fragments the resulting IPv6 tunnel packet into IPv6
>     fragments that do not exceed the Path MTU to the tunnel
>     exit-point.
> 
> This patch drops the MTU check for tunnel destinations.
> 
> Signed-off-by: Ashwanth Goli <ashwanth@...eaurora.org>

RFC 2473 is generally about ipv6 tunnels....

> -	if (mtu < IPV6_MIN_MTU)
> +	if (!(rt->dst.flags & DST_XFRM_TUNNEL) && mtu < IPV6_MIN_MTU)
>  		return -EINVAL;

But the check you are adding is specifically checking only IPSEC
tunnels.

If what you say is true in your commit message, this test must
more generally trigger for all ipv6 tunnel types, not just IPSEC
ones.

If IPSEC tunnels are being targetting in this patch intentionally,
that needs to be explained in the commit message.