From mboxrd@z Thu Jan 1 00:00:00 1970 From: Maxime Bizon Subject: [PATCH v2] netfilter: fix bad checksum on IPv6 when NAT is performed Date: Thu, 08 Oct 2015 22:26:12 +0200 Message-ID: <1444335972.14655.388.camel@sakura.staff.proxad.net> References: <1444141425.14655.341.camel@sakura.staff.proxad.net> <1444335587.14655.387.camel@sakura.staff.proxad.net> Reply-To: mbizon@freebox.fr Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: davem , kaber , pablo@netfilter.org, netfilter-devel To: netdev Return-path: Received: from ns.iliad.fr ([212.27.33.1]:44735 "EHLO ns.iliad.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758375AbbJHU0O (ORCPT ); Thu, 8 Oct 2015 16:26:14 -0400 In-Reply-To: <1444335587.14655.387.camel@sakura.staff.proxad.net> Sender: netfilter-devel-owner@vger.kernel.org List-ID: With this setup: * non IPv6 checksumming capable network hardware * GRO off * IPv6 SNAT I get this when I receive an UDPv6 reply: ": hw csum failure" Call trace: * nf_ip6_checksum() calls __skb_checksum_complete() * nf_nat_ipv6_csum_update() & nf_nat_ipv6_manip_pkt() * __udp6_lib_rcv() => udp6_csum_init() * __skb_checksum_validate_complete() "fastpath" fails because skb->csum is incorrect. * udpv6_recvmsg() => skb_copy_and_csum_datagram_msg() The last call computes a valid checksum despite CHECKSUM_COMPLETE and triggers the warning. When we perform NAT on IPv4, we also update the IPv4 checksum, so there is no side effect on skb->csum (since the csum over a valid IPv4 header area was already zero). But IPv6 doesn't have such checksum, so when performing NAT we need to update skb->csum. Signed-off-by: Maxime Bizon --- net/ipv6/netfilter/nf_nat_l3proto_ipv6.c | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-) diff --git a/net/ipv6/netfilter/nf_nat_l3proto_ipv6.c b/net/ipv6/netfilter/nf_nat_l3proto_ipv6.c index 70fbaed..e44af9c 100644 --- a/net/ipv6/netfilter/nf_nat_l3proto_ipv6.c +++ b/net/ipv6/netfilter/nf_nat_l3proto_ipv6.c @@ -81,6 +81,8 @@ static bool nf_nat_ipv6_manip_pkt(struct sk_buff *skb, enum nf_nat_manip_type maniptype) { struct ipv6hdr *ipv6h; + const __be32 *to; + __be32 *from; __be16 frag_off; int hdroff; u8 nexthdr; @@ -100,11 +102,24 @@ static bool nf_nat_ipv6_manip_pkt(struct sk_buff *skb, target, maniptype)) return false; manip_addr: - if (maniptype == NF_NAT_MANIP_SRC) - ipv6h->saddr = target->src.u3.in6; - else - ipv6h->daddr = target->dst.u3.in6; + if (maniptype == NF_NAT_MANIP_SRC) { + from = ipv6h->saddr.s6_addr32; + to = target->src.u3.in6.s6_addr32; + } else { + from = ipv6h->daddr.s6_addr32; + to = target->dst.u3.in6.s6_addr32; + } + + if (skb->ip_summed == CHECKSUM_COMPLETE) { + __be32 diff[] = { + ~from[0], ~from[1], ~from[2], ~from[3], + to[0], to[1], to[2], to[3], + }; + + skb->csum = ~csum_partial(diff, sizeof(diff), ~skb->csum); + } + memcpy(from, to, sizeof (struct in6_addr)); return true; } -- 1.9.1 -- Maxime