Re: [PATCH nf] xtables: zero padding in data_to_user

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Tue, May 09, 2017 at 04:17:37PM -0400, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@google.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.