netdev - Re: [RFC PATCH] fix xfrm MTU regression

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Message-ID: <YIsNeUTQ7qjzhpos@hog>
Date:   Thu, 29 Apr 2021 21:48:09 +0200
From:   Sabrina Dubroca <sd@...asysnail.net>
To:     Jiri Bohac <jbohac@...e.cz>
Cc:     Mike Maloney <maloneykernel@...il.com>,
        Eric Dumazet <eric.dumazet@...il.com>, davem@...emloft.net,
        netdev@...r.kernel.org,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [RFC PATCH] fix xfrm MTU regression

2021-04-29, 19:02:54 +0200, Jiri Bohac wrote:
> Hi,
> 
> Commit 749439bfac6e1a2932c582e2699f91d329658196 ("ipv6: fix udpv6
> sendmsg crash caused by too small MTU") breaks PMTU for xfrm.
> 
> A Packet Too Big ICMPv6 message received in response to an ESP
> packet will prevent all further communication through the tunnel
> if the reported MTU minus the ESP overhead is smaller than 1280.
> 
> E.g. in a case of a tunnel-mode ESP with sha256/aes the overhead
> is 92 bytes. Receiving a PTB with MTU of 1371 or less will result
> in all further packets in the tunnel dropped. A ping through the
> tunnel fails with "ping: sendmsg: Invalid argument".
> 
> Apparently the MTU on the xfrm route is smaller than 1280 and
> fails the check inside ip6_setup_cork() added by 749439bf.
> 
> We found this by debugging USGv6/ipv6ready failures. Failing
> tests are: "Phase-2 Interoperability Test Scenario IPsec" /
> 5.3.11 and 5.4.11 (Tunnel Mode: Fragmentation).

That should be fixed with commit b515d2637276 ("xfrm: xfrm_state_mtu
should return at least 1280 for ipv6"), currently in Steffen's ipsec
tree:
https://git.kernel.org/pub/scm/linux/kernel/git/klassert/ipsec.git/commit/?id=b515d2637276

-- 
Sabrina