netdev - Re: [PATCH nf] xtables: zero padding in data_to

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Date:   Mon, 15 May 2017 18:52:22 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
        rgb@...hat.com, fwestpha@...hat.com, pmoore@...hat.com,
        pvrabec@...hat.com, davem@...emloft.net,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH nf] xtables: zero padding in data_to_user

On Tue, May 09, 2017 at 04:17:37PM -0400, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@...gle.com>
> 
> When looking up an iptables rule, the iptables binary compares the
> aligned match and target data (XT_ALIGN). In some cases this can
> exceed the actual data size to include padding bytes.
> 
> Before commit f77bc5b23fb1 ("iptables: use match, target and data
> copy_to_user helpers") the malloc()ed bytes were overwritten by the
> kernel with kzalloced contents, zeroing the padding and making the
> comparison succeed. After this patch, the kernel copies and clears
> only data, leaving the padding bytes undefined.
> 
> Extend the clear operation from data size to aligned data size to
> include the padding bytes, if any.
> 
> Padding bytes can be observed in both match and target, and the bug
> triggered, by issuing a rule with match icmp and target ACCEPT:
> 
>   iptables -t mangle -A INPUT -i lo -p icmp --icmp-type 1 -j ACCEPT
>   iptables -t mangle -D INPUT -i lo -p icmp --icmp-type 1 -j ACCEPT

Applied, thanks.