netdev - Re: [PATCH 1/3] netfilter: Fix copy_to

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Date:	Thu, 1 Mar 2012 19:21:45 +0530
From:	santosh prasad nayak <santoshprasadnayak@...il.com>
To:	Pablo Neira Ayuso <pablo@...filter.org>
Cc:	bart.de.schuymer@...dora.be, kaber@...sh.net,
	shemminger@...tta.com, davem@...emloft.net,
	netfilter-devel@...r.kernel.org, bridge@...ts.linux-foundation.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org,
	Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [PATCH 1/3] netfilter: Fix copy_to_user too small size parametre.

Thanks Pablo for clarification.
I will resend the patch.


regards
santosh

On Thu, Mar 1, 2012 at 6:33 PM, Pablo Neira Ayuso <pablo@...filter.org> wrote:
> On Thu, Mar 01, 2012 at 04:15:05PM +0530, santosh prasad nayak wrote:
>> Hi Pablo.
>>
>> copy_to_user( dest, source, length)
>>
>> Normally,  'length'  is equal to  'sizeof (source) '.
>>
>> In this case "length"   =   32
>>        "sizeof(source)"  =   29.
>>
>> Is it intentional ?
>
> ebtables expects 32 bytes names.
>
>> Won't it copy extra 3 bytes of kernel data to userspace ?
>
> You're right. We have to copy 29 bytes but we have to fill the
> remaining bytes with zeroes. I think something like:
>
> char name[EBT_FUNCTION_MAXNAMELEN] = {};
>
> /* user-space ebtables expects 32 bytes-long names, but xt_match uses
>  * 29 bytes for that. */
> sprintf(name, "%s", m->u.match->name);
> if (copy_to_user(hlp, name, EBT_FUNCTION_MAXNAMELEN))
> ...
>
> will resolve this issue.
>
> Would you resend a new patch?
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