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authorMichael Zhou <mzhou@cse.unsw.edu.au>2020-08-07 01:15:25 +1000
committerPablo Neira Ayuso <pablo@netfilter.org>2020-08-28 19:18:48 +0200
commitd5608a0578a07766a97c00904d85f6a7221ddb37 (patch)
tree124740cbd6b74647c82b201811e654d9ce3ef439 /net/ipv6
parent0f091e43310f5c292b7094f9f115e651358e8053 (diff)
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 <mzhou@cse.unsw.edu.au> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Diffstat (limited to 'net/ipv6')
-rw-r--r--net/ipv6/netfilter/ip6t_NPT.c39
1 files changed, 39 insertions, 0 deletions
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;
}