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

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Message-ID: <20120301130311.GA7429@1984>
Date:	Thu, 1 Mar 2012 14:03:11 +0100
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	santosh prasad nayak <santoshprasadnayak@...il.com>
Cc:	bart.de.schuymer@...dora.be, kaber@...sh.net,
	shemminger@...tta.com, davem@...emloft.net,
	netfilter-devel@...r.kernel.org, netfilter@...r.kernel.org,
	coreteam@...filter.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.

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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