netdev - Re: [PATCH net-next] netfilter: xt_quota: fix the behavior of xt

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Message-ID: <20181002181546.b6zhizcl6lj2inu2@salvia>
Date:   Tue, 2 Oct 2018 20:15:46 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Chenbo Feng <fengc@...gle.com>
Cc:     zenczykowski@...il.com, Chenbo Feng <chenbofeng.kernel@...il.com>,
        netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
        kernel-team@...roid.com, Lorenzo Colitti <lorenzo@...gle.com>
Subject: Re: [PATCH net-next] netfilter: xt_quota: fix the behavior of
 xt_quota module

Hi Chenbo,

On Tue, Oct 02, 2018 at 10:45:58AM -0700, Chenbo Feng wrote:
> On Tue, Oct 2, 2018 at 3:51 AM Pablo Neira Ayuso <pablo@...filter.org> wrote:
[...]
> Do you mean the remain field will be zeroed when copying the
> xt_quota_info struct out of the kernel? I believe that is decided by
> the usersize defined in struct xt_match and this patch set it to the
> full struct size. So the whole xt_quota_info struct will be copied
> into userspace including the field stores the remaining quota. The
> userspace will not be aware of it if the ipatbles is not updated but
> it should not modify it as well. I have tested the behavior with
> net-next branch and it seems working. Am I missing something
> recently updated?

Hm, I see, I overlook that your patch removes this:

-       .usersize   = offsetof(struct xt_quota_info, master),

BTW, is iptables -D command working with your patch?

Telling this because if .usersize is removed, then IIRC userspace
compares this new remain field with userspace value and deletion will
break.

Patch that I was referring before is this one from Willem:

commit f32815d21d4d8287336fb9cef4d2d9e0866214c2
Author: Willem de Bruijn <willemb@...gle.com>
Date:   Mon Jan 2 17:19:40 2017 -0500

    xtables: add xt_match, xt_target and data copy_to_user functions

    xt_entry_target, xt_entry_match and their private data may contain
    kernel data.
[...]
    Private data is defined in xt_match and xt_target. All matches and
    targets that maintain kernel data store this at the tail of their
    private structure. Extend xt_match and xt_target with .usersize to
    limit how many bytes of data are copied. The remainder is cleared.

Let me know, thanks !