netdev - Re: [PATCH ipsec] xfrm: xfrm_state_mtu should return at least 1280 for ipv6

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Date:   Tue, 20 Apr 2021 13:59:00 +0200
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Sabrina Dubroca <sd@...asysnail.net>
CC:     <netdev@...r.kernel.org>, Jianwen Ji <jiji@...hat.com>
Subject: Re: [PATCH ipsec] xfrm: xfrm_state_mtu should return at least 1280
 for ipv6

On Fri, Apr 16, 2021 at 11:27:59AM +0200, Sabrina Dubroca wrote:
> Jianwen reported that IPv6 Interoperability tests are failing in an
> IPsec case where one of the links between the IPsec peers has an MTU
> of 1280. The peer generates a packet larger than this MTU, the router
> replies with a "Packet too big" message indicating an MTU of 1280.
> When the peer tries to send another large packet, xfrm_state_mtu
> returns 1280 - ipsec_overhead, which causes ip6_setup_cork to fail
> with EINVAL.
> 
> We can fix this by forcing xfrm_state_mtu to return IPV6_MIN_MTU when
> IPv6 is used. After going through IPsec, the packet will then be
> fragmented to obey the actual network's PMTU, just before leaving the
> host.
> 
> Currently, TFC padding is capped to PMTU - overhead to avoid
> fragementation: after padding and encapsulation, we still fit within
> the PMTU. That behavior is preserved in this patch.
> 
> Fixes: 91657eafb64b ("xfrm: take net hdr len into account for esp payload size calculation")
> Reported-by: Jianwen Ji <jiji@...hat.com>
> Signed-off-by: Sabrina Dubroca <sd@...asysnail.net>

Applied, thanks Sabrina!