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Date:   Mon, 29 Jul 2019 12:33:17 +0200
From:   Florian Westphal <fw@strlen.de>
To:     Juliana Rodrigueiro <juliana.rodrigueiro@intra2net.com>
Cc:     pablo@netfilter.org, netfilter-devel@vger.kernel.org
Subject: Re: [PATCH] netfilter: nfacct: Fix alignment mismatch in
 xt_nfacct_match_info
Message-ID: <20190729103317.ujlx4larhtzeijp3@breakpoint.cc>
References: <2781693.KLf3iWz6jR@rocinante.m.i2n>
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Juliana Rodrigueiro <juliana.rodrigueiro@intra2net.com> wrote:
> When running a 64-bit kernel with a 32-bit iptables binary, the size of
> the xt_nfacct_match_info struct diverges.
> 
>     kernel: sizeof(struct xt_nfacct_match_info) : 40
>     iptables: sizeof(struct xt_nfacct_match_info)) : 36
> 
> Trying to append nfacct related rules results in an unhelpful message.
> Although it is suggested to look for more information in dmesg, nothing
> can be found there.
> 
>     # iptables -A <chain> -m nfacct --nfacct-name <acct-object>
>     iptables: Invalid argument. Run `dmesg' for more information.
> 
> This patch fixes the memory misalignment by enforcing 8-byte alignment
> within the struct. This solution is often used in many other uapi
> netfilter headers.

Yes, but this breaks the 32bit abi.

Its best to add a 'v1' match revision to fix this.