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...
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
Thanks for the patches, looks good!
Please fix the issue reported from 'kernel test robot' and resend.
Thanks!