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@xxxxxxxxxxxxxxx>
---
net/ipv6/netfilter/ip6t_NPT.c | 37 +++++++++++++++++++++++++++++++++++
1 file changed, 37 insertions(+)
diff --git a/net/ipv6/netfilter/ip6t_NPT.c b/net/ipv6/netfilter/ip6t_NPT.c
index 9ee077bf4f49..b25e786607ed 100644
--- a/net/ipv6/netfilter/ip6t_NPT.c
+++ b/net/ipv6/netfilter/ip6t_NPT.c
@@ -77,16 +77,42 @@ static bool ip6t_npt_map_pfx(const struct ip6t_npt_tginfo *npt,
return true;
}
+static struct ipv6hdr *ip6t_npt_icmpv6_bounced_ipv6hdr(struct sk_buff *skb)
+{
+ if (ipv6_hdr(skb)->nexthdr != IPPROTO_ICMPV6)
+ return NULL;
+
+ if (!icmpv6_is_err(icmp6_hdr(skb)->icmp6_type))
+ return NULL;
+
+ if ((const unsigned char *)&icmp6_hdr(skb)[1] + sizeof(struct ipv6hdr) >
+ skb_tail_pointer(skb))
+ return NULL;
+
+ return (struct ipv6hdr *)&icmp6_hdr(skb)[1];
+}
+
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 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 = ip6t_npt_icmpv6_bounced_ipv6hdr(skb);
+ 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 +120,23 @@ 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 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 = ip6t_npt_icmpv6_bounced_ipv6hdr(skb);
+ 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;
}
--
2.25.1
