linux-kernel - Re: [PATCH v2 0/6] xfrm: Add compat layer

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Message-ID: <20200907094314.GI20687@gauss3.secunet.de>
Date:   Mon, 7 Sep 2020 11:43:14 +0200
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Dmitry Safonov <dima@...sta.com>
CC:     <linux-kernel@...r.kernel.org>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Florian Westphal <fw@...len.de>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Jakub Kicinski <kuba@...nel.org>,
        Stephen Suryaputra <ssuryaextr@...il.com>,
        <netdev@...r.kernel.org>,
        "Johannes Berg" <johannes@...solutions.net>,
        Shuah Khan <shuah@...nel.org>,
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v2 0/6] xfrm: Add compat layer

On Wed, Aug 26, 2020 at 02:49:43AM +0100, Dmitry Safonov wrote:
> Changes since v1:
> - reworked patches set to use translator
> - separated the compat layer into xfrm_compat.c,
>   compiled under XFRM_USER_COMPAT config
> - 32-bit messages now being sent in frag_list (like wext-core does)
> - instead of __packed add compat_u64 members in compat structures
> - selftest reworked to kselftest lib API
> - added netlink dump testing to the selftest
> 
> XFRM is disabled for compatible users because of the UABI difference.
> The difference is in structures paddings and in the result the size
> of netlink messages differ.
> 
> Possibility for compatible application to manage xfrm tunnels was
> disabled by: the commmit 19d7df69fdb2 ("xfrm: Refuse to insert 32 bit
> userspace socket policies on 64 bit systems") and the commit 74005991b78a
> ("xfrm: Do not parse 32bits compiled xfrm netlink msg on 64bits host").
> 
> This is my second attempt to resolve the xfrm/compat problem by adding
> the 64=>32 and 32=>64 bit translators those non-visibly to a user
> provide translation between compatible user and kernel.
> Previous attempt was to interrupt the message ABI according to a syscall
> by xfrm_user, which resulted in over-complicated code [1].
> 
> Florian Westphal provided the idea of translator and some draft patches
> in the discussion. In these patches, his idea is reused and some of his
> initial code is also present.
> 
> There were a couple of attempts to solve xfrm compat problem:
> https://lkml.org/lkml/2017/1/20/733
> https://patchwork.ozlabs.org/patch/44600/
> http://netdev.vger.kernel.narkive.com/2Gesykj6/patch-net-next-xfrm-correctly-parse-netlink-msg-from-32bits-ip-command-on-64bits-host
> 
> All the discussions end in the conclusion that xfrm should have a full
> compatible layer to correctly work with 32-bit applications on 64-bit
> kernels:
> https://lkml.org/lkml/2017/1/23/413
> https://patchwork.ozlabs.org/patch/433279/
> 
> In some recent lkml discussion, Linus said that it's worth to fix this
> problem and not giving people an excuse to stay on 32-bit kernel:
> https://lkml.org/lkml/2018/2/13/752
> 
> There is also an selftest for ipsec tunnels.
> It doesn't depend on any library and compat version can be easy
> build with: make CFLAGS=-m32 net/ipsec
> 
> Patches as a .git branch:
> https://github.com/0x7f454c46/linux/tree/xfrm-compat-v2
> 
> [1]: https://lkml.kernel.org/r/20180726023144.31066-1-dima@arista.com

Thanks for the patches, looks good!

Please fix the issue reported from 'kernel test robot' and resend.

Thanks!