From patchwork Thu Sep 13 10:54:07 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [3/4] netfilter: Validate the sequence number of dataless ACK packets as well Date: Thu, 13 Sep 2012 00:54:07 -0000 From: Pablo Neira X-Patchwork-Id: 183598 Message-Id: <1347533648-3451-4-git-send-email-pablo@netfilter.org> To: netfilter-devel@vger.kernel.org Cc: davem@davemloft.net, netdev@vger.kernel.org From: Jozsef Kadlecsik We spare nothing by not validating the sequence number of dataless ACK packets and enabling it makes harder off-path attacks. See: "Reflection scan: an Off-Path Attack on TCP" by Jan Wrobel, http://arxiv.org/abs/1201.2074 Signed-off-by: Jozsef Kadlecsik Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_conntrack_proto_tcp.c | 10 ++-------- 1 file changed, 2 insertions(+), 8 deletions(-) diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c index aba98f9..e046b37 100644 --- a/net/netfilter/nf_conntrack_proto_tcp.c +++ b/net/netfilter/nf_conntrack_proto_tcp.c @@ -630,15 +630,9 @@ static bool tcp_in_window(const struct nf_conn *ct, ack = sack = receiver->td_end; } - if (seq == end - && (!tcph->rst - || (seq == 0 && state->state == TCP_CONNTRACK_SYN_SENT))) + if (tcph->rst && seq == 0 && state->state == TCP_CONNTRACK_SYN_SENT) /* - * Packets contains no data: we assume it is valid - * and check the ack value only. - * However RST segments are always validated by their - * SEQ number, except when seq == 0 (reset sent answering - * SYN. + * RST sent answering SYN. */ seq = end = sender->td_end;