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Message-ID: <20170515165222.GA3986@salvia> 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.
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