linux-kernel - Re: [PATCH v3 0/7] xfrm: Add compat layer

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Message-ID: <20200928093349.GJ20687@gauss3.secunet.de>
Date:   Mon, 28 Sep 2020 11:33:49 +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>,
        Johannes Berg <johannes@...solutions.net>,
        Stephen Suryaputra <ssuryaextr@...il.com>,
        <netdev@...r.kernel.org>, Shuah Khan <shuah@...nel.org>,
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v3 0/7] xfrm: Add compat layer

On Mon, Sep 21, 2020 at 03:36:50PM +0100, Dmitry Safonov wrote:
> Changes since v2:
> - added struct xfrm_translator as API to register xfrm_compat.ko with
>   xfrm_state.ko. This allows compilation of translator as a loadable
>   module
> - fixed indention and collected reviewed-by (Johannes Berg)
> - moved boilerplate from commit messages into cover-letter (Steffen
>   Klassert)
> - found on KASAN build and fixed non-initialised stack variable usage
>   in the translator
> 
> The resulting v2/v3 diff can be found here:
> https://gist.github.com/0x7f454c46/8f68311dfa1f240959fdbe7c77ed2259
> 
> Patches as a .git branch:
> https://github.com/0x7f454c46/linux/tree/xfrm-compat-v3
> 
> 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
> 
> [1]: https://lkml.kernel.org/r/20180726023144.31066-1-dima@arista.com
> 
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Florian Westphal <fw@...len.de>
> Cc: Herbert Xu <herbert@...dor.apana.org.au>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: Johannes Berg <johannes@...solutions.net>
> Cc: Steffen Klassert <steffen.klassert@...unet.com>
> Cc: Stephen Suryaputra <ssuryaextr@...il.com>
> Cc: Dmitry Safonov <0x7f454c46@...il.com>
> Cc: netdev@...r.kernel.org
> 
> Dmitry Safonov (7):
>   xfrm: Provide API to register translator module
>   xfrm/compat: Add 64=>32-bit messages translator
>   xfrm/compat: Attach xfrm dumps to 64=>32 bit translator
>   netlink/compat: Append NLMSG_DONE/extack to frag_list
>   xfrm/compat: Add 32=>64-bit messages translator
>   xfrm/compat: Translate 32-bit user_policy from sockptr
>   selftest/net/xfrm: Add test for ipsec tunnel

Series applied to ipsec-next. Thanks a lot for your work Dmitry!