If destination port is above 32k and source port below 16k
assume this might cause 'port shadowing' where a 'new' inbound
connection matches an existing one, e.g.
inbound X:41234 -> Y:53 matches existing conntrack entry
Z:53 -> X:4123, where Z got natted to X.
In this case, new packet is natted to Z:53 which is likely
unwanted.
We avoid the rewrite for connections that originate from local host:
port-shadowing is only possible with forwarded connections.
Also adjust test case.
Cc: Eric Garver <eric@xxxxxxxxxxx>
Cc: Phil Sutter <phil@xxxxxx>
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
---
v2: skip remap if local_out is set.
net/netfilter/nf_nat_core.c | 43 ++++++++++++++++++--
tools/testing/selftests/netfilter/nft_nat.sh | 5 ++-
2 files changed, 43 insertions(+), 5 deletions(-)
diff --git a/net/netfilter/nf_nat_core.c b/net/netfilter/nf_nat_core.c
index ab9f6c75524d..e890b3086417 100644
--- a/net/netfilter/nf_nat_core.c
+++ b/net/netfilter/nf_nat_core.c
@@ -494,6 +494,38 @@ static void nf_nat_l4proto_unique_tuple(struct nf_conntrack_tuple *tuple,
goto another_round;
}
+static bool tuple_force_port_remap(const struct nf_conntrack_tuple *tuple)
+{
+ u16 sp, dp;
+
+ switch (tuple->dst.protonum) {
+ case IPPROTO_TCP:
+ sp = ntohs(tuple->src.u.tcp.port);
+ dp = ntohs(tuple->dst.u.tcp.port);
+ break;
+ case IPPROTO_UDP:
+ case IPPROTO_UDPLITE:
+ sp = ntohs(tuple->src.u.udp.port);
+ dp = ntohs(tuple->dst.u.udp.port);
+ break;
+ default:
+ return false;
+ }
+
+ /* IANA: System port range: 1-1023,
+ * user port range: 1024-49151,
+ * private port range: 49152-65535.
+ *
+ * Linux default ephemeral port range is 32768-60999.
+ *
+ * Enforce port remapping if sport is significantly lower
+ * than dport to prevent NAT port shadowing, i.e.
+ * accidental match of 'new' inbound connection vs.
+ * existing outbound one.
+ */
+ return sp < 16384 && dp >= 32768;
+}
+
/* Manipulate the tuple into the range given. For NF_INET_POST_ROUTING,
* we change the source to map into the range. For NF_INET_PRE_ROUTING
* and NF_INET_LOCAL_OUT, we change the destination to map into the
@@ -507,11 +539,17 @@ get_unique_tuple(struct nf_conntrack_tuple *tuple,
struct nf_conn *ct,
enum nf_nat_manip_type maniptype)
{
+ bool random_port = range->flags & NF_NAT_RANGE_PROTO_RANDOM_ALL;
const struct nf_conntrack_zone *zone;
struct net *net = nf_ct_net(ct);
zone = nf_ct_zone(ct);
+ if (maniptype == NF_NAT_MANIP_SRC &&
+ !ct->local_origin &&
+ tuple_force_port_remap(orig_tuple))
+ random_port = true;
+
/* 1) If this srcip/proto/src-proto-part is currently mapped,
* and that same mapping gives a unique tuple within the given
* range, use that.
@@ -520,8 +558,7 @@ get_unique_tuple(struct nf_conntrack_tuple *tuple,
* So far, we don't do local source mappings, so multiple
* manips not an issue.
*/
- if (maniptype == NF_NAT_MANIP_SRC &&
- !(range->flags & NF_NAT_RANGE_PROTO_RANDOM_ALL)) {
+ if (maniptype == NF_NAT_MANIP_SRC && !random_port) {
/* try the original tuple first */
if (in_range(orig_tuple, range)) {
if (!nf_nat_used_tuple(orig_tuple, ct)) {
@@ -545,7 +582,7 @@ get_unique_tuple(struct nf_conntrack_tuple *tuple,
*/
/* Only bother mapping if it's not already in range and unique */
- if (!(range->flags & NF_NAT_RANGE_PROTO_RANDOM_ALL)) {
+ if (!random_port) {
if (range->flags & NF_NAT_RANGE_PROTO_SPECIFIED) {
if (!(range->flags & NF_NAT_RANGE_PROTO_OFFSET) &&
l4proto_in_range(tuple, maniptype,
diff --git a/tools/testing/selftests/netfilter/nft_nat.sh b/tools/testing/selftests/netfilter/nft_nat.sh
index d88867d2fed7..349a319a9e51 100755
--- a/tools/testing/selftests/netfilter/nft_nat.sh
+++ b/tools/testing/selftests/netfilter/nft_nat.sh
@@ -880,8 +880,9 @@ EOF
return $ksft_skip
fi
- # test default behaviour. Packet from ns1 to ns0 is redirected to ns2.
- test_port_shadow "default" "CLIENT"
+ # test default behaviour. Packet from ns1 to ns0 is not redirected
+ # due to automatic port translation.
+ test_port_shadow "default" "ROUTER"
# test packet filter based mitigation: prevent forwarding of
# packets claiming to come from the service port.
--
2.32.0
