From d5608a0578a07766a97c00904d85f6a7221ddb37 Mon Sep 17 00:00:00 2001 From: Michael Zhou Date: Fri, 7 Aug 2020 01:15:25 +1000 Subject: netfilter: ip6t_NPT: rewrite addresses in ICMPv6 original packet Detect and rewrite a prefix embedded in an ICMPv6 original packet that was rewritten by a corresponding DNPT/SNPT rule so it will be recognised by the host that sent the original packet. Example Rules in effect on the 1:2:3:4::/64 + 5:6:7:8::/64 side router: * SNPT src-pfx 1:2:3:4::/64 dst-pfx 5:6:7:8::/64 * DNPT src-pfx 5:6:7:8::/64 dst-pfx 1:2:3:4::/64 No rules on the 9:a:b:c::/64 side. 1. 1:2:3:4::1 sends UDP packet to 9:a:b:c::1 2. Router applies SNPT changing src to 5:6:7:8::ffef::1 3. 9:a:b:c::1 receives packet with (src 5:6:7:8::ffef::1 dst 9:a:b:c::1) and replies with ICMPv6 port unreachable to 5:6:7:8::ffef::1, including original packet (src 5:6:7:8::ffef::1 dst 9:a:b:c::1) 4. Router forwards ICMPv6 packet with (src 9:a:b:c::1 dst 5:6:7:8::ffef::1) including original packet (src 5:6:7:8::ffef::1 dst 9:a:b:c::1) and applies DNPT changing dst to 1:2:3:4::1 5. 1:2:3:4::1 receives ICMPv6 packet with (src 9:a:b:c::1 dst 1:2:3:4::1) including original packet (src 5:6:7:8::ffef::1 dst 9:a:b:c::1). It doesn't recognise the original packet as the src doesn't match anything it originally sent With this change, at step 4, DNPT will also rewrite the original packet src to 1:2:3:4::1, so at step 5, 1:2:3:4::1 will recognise the ICMPv6 error and provide feedback to the application properly. Conversely, SNPT will help when ICMPv6 errors are sent from the translated network. 1. 9:a:b:c::1 sends UDP packet to 5:6:7:8::ffef::1 2. Router applies DNPT changing dst to 1:2:3:4::1 3. 1:2:3:4::1 receives packet with (src 9:a:b:c::1 dst 1:2:3:4::1) and replies with ICMPv6 port unreachable to 9:a:b:c::1 including original packet (src 9:a:b:c::1 dst 1:2:3:4::1) 4. Router forwards ICMPv6 packet with (src 1:2:3:4::1 dst 9:a:b:c::1) including original packet (src 9:a:b:c::1 dst 1:2:3:4::1) and applies SNPT changing src to 5:6:7:8::ffef::1 5. 9:a:b:c::1 receives ICMPv6 packet with (src 5:6:7:8::ffef::1 dst 9:a:b:c::1) including original packet (src 9:a:b:c::1 dst 1:2:3:4::1). It doesn't recognise the original packet as the dst doesn't match anything it already sent The change to SNPT means the ICMPv6 original packet dst will be rewritten to 5:6:7:8::ffef::1 in step 4, allowing the error to be properly recognised in step 5. Signed-off-by: Michael Zhou Signed-off-by: Pablo Neira Ayuso --- net/ipv6/netfilter/ip6t_NPT.c | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) (limited to 'net/ipv6') diff --git a/net/ipv6/netfilter/ip6t_NPT.c b/net/ipv6/netfilter/ip6t_NPT.c index 9ee077bf4f49..787c74aa85e3 100644 --- a/net/ipv6/netfilter/ip6t_NPT.c +++ b/net/ipv6/netfilter/ip6t_NPT.c @@ -77,16 +77,43 @@ static bool ip6t_npt_map_pfx(const struct ip6t_npt_tginfo *npt, return true; } +static struct ipv6hdr *icmpv6_bounced_ipv6hdr(struct sk_buff *skb, + struct ipv6hdr *_bounced_hdr) +{ + if (ipv6_hdr(skb)->nexthdr != IPPROTO_ICMPV6) + return NULL; + + if (!icmpv6_is_err(icmp6_hdr(skb)->icmp6_type)) + return NULL; + + return skb_header_pointer(skb, + skb_transport_offset(skb) + sizeof(struct icmp6hdr), + sizeof(struct ipv6hdr), + _bounced_hdr); +} + static unsigned int ip6t_snpt_tg(struct sk_buff *skb, const struct xt_action_param *par) { const struct ip6t_npt_tginfo *npt = par->targinfo; + struct ipv6hdr _bounced_hdr; + struct ipv6hdr *bounced_hdr; + struct in6_addr bounced_pfx; if (!ip6t_npt_map_pfx(npt, &ipv6_hdr(skb)->saddr)) { icmpv6_send(skb, ICMPV6_PARAMPROB, ICMPV6_HDR_FIELD, offsetof(struct ipv6hdr, saddr)); return NF_DROP; } + + /* rewrite dst addr of bounced packet which was sent to dst range */ + bounced_hdr = icmpv6_bounced_ipv6hdr(skb, &_bounced_hdr); + if (bounced_hdr) { + ipv6_addr_prefix(&bounced_pfx, &bounced_hdr->daddr, npt->src_pfx_len); + if (ipv6_addr_cmp(&bounced_pfx, &npt->src_pfx.in6) == 0) + ip6t_npt_map_pfx(npt, &bounced_hdr->daddr); + } + return XT_CONTINUE; } @@ -94,12 +121,24 @@ static unsigned int ip6t_dnpt_tg(struct sk_buff *skb, const struct xt_action_param *par) { const struct ip6t_npt_tginfo *npt = par->targinfo; + struct ipv6hdr _bounced_hdr; + struct ipv6hdr *bounced_hdr; + struct in6_addr bounced_pfx; if (!ip6t_npt_map_pfx(npt, &ipv6_hdr(skb)->daddr)) { icmpv6_send(skb, ICMPV6_PARAMPROB, ICMPV6_HDR_FIELD, offsetof(struct ipv6hdr, daddr)); return NF_DROP; } + + /* rewrite src addr of bounced packet which was sent from dst range */ + bounced_hdr = icmpv6_bounced_ipv6hdr(skb, &_bounced_hdr); + if (bounced_hdr) { + ipv6_addr_prefix(&bounced_pfx, &bounced_hdr->saddr, npt->src_pfx_len); + if (ipv6_addr_cmp(&bounced_pfx, &npt->src_pfx.in6) == 0) + ip6t_npt_map_pfx(npt, &bounced_hdr->saddr); + } + return XT_CONTINUE; } -- cgit v1.2.3