netdev - Re: [devel-ipsec] [PATCH ipsec] xfrm: Don't allow optional intermediate templates that changes the address family

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Date:   Fri, 31 Mar 2023 10:19:33 +0200
From:   Tobias Brunner <tobias@...ongswan.org>
To:     Steffen Klassert <steffen.klassert@...unet.com>,
        netdev@...r.kernel.org, devel@...ux-ipsec.org
Cc:     Hyunwoo Kim <v4bel@...ori.io>,
        Tudor Ambarus <tudordana@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [devel-ipsec] [PATCH ipsec] xfrm: Don't allow optional
 intermediate templates that changes the address family

> When an optional intermediate template changes the address family,
> it is unclear which family the next template should have. This can
> lead to misinterpretations of IPv4/IPv6 addresses. So reject
> optional intermediate templates on insertion time.

This change breaks the installation of IPv4-in-IPv6 (or vice-versa) 
policies with IPComp, where the optional IPComp template and SA is 
installed with tunnel mode (while the ESP template/SA that follows is 
installed in transport mode) and the address family is that of the SA 
not that of the policy.

Note that mixed-family scenarios with IPComp are currently broken due to 
an address family issue, but that's a problem in xfrm_tmpl_resolve_one() 
that occurs later when packets are actually matched against policies. 
There is a simple patch for it that I haven't got around to submit to 
the list yet.

Regards,
Tobias