Re: [ebtables PATCH 2/2] configure.ac: add option --enable-kernel-64-userland-32

[Florian Westphal <fw@strlen.de>]

Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> > introduced with commit 47a6959fa331fe892a4fc3b48ca08e92045c6bda
> > (5.13-rc1). Before that point, it seems CONFIG_COMPAT was the relevant
> > flag.
> 
> Sorry, I got confused by this recent commit, it's indeed CONFIG_COMPAT
> the right toggle in old kernels.
> 
> > The checks on CONFIG_COMPAT were already introduced with commit
> > 81e675c227ec60a0bdcbb547dc530ebee23ff931 in 2.6.34.x.
> > 
> > I have seen this problem on Linux 4.1 and 4.9, on an Aarch64 CPU with
> > 64-bit kernel and userspace compiled as 32-bit ARM. In both kernels,
> > CONFIG_COMPAT was set.
> 
> Hm, then ebtables compat is buggy.

It was only ever tested with i686 binary on amd64 arch.

Thomas, does unmodified 32bit iptables work on those arch/kernel
combinations?

> > So I am a bit surprised that I bump into this issue after upgrading
> > ebtables from 2.0.10-4 to 2.0.11 where the padding was removed.
> > According to your mail and the commits mentioned, it is supposed to
> > work without ebtables making specific provisions for the 32/64 bit
> > type difference.

ebtables-userspace compat fixups predate the ebtables kernel side
support, it was autoenabled on sparc64 in the old makefile:

ifeq ($(shell uname -m),sparc64)
CFLAGS+=-DEBT_MIN_ALIGN=8 -DKERNEL_64_USERSPACE_32
endif

I don't even know if the ebtables compat support is compiled in on
non-amd64.