UbiquitousOS
/
OpenCloudOS-Kernel
mirror of https://gitee.com/OpenCloudOS/OpenCloudOS-Kernel.git
11
0
Fork 0
Code Issues Projects Releases Wiki Activity

netfilter: nat: force port remap to prevent shadowing well-known ports 

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.

v3: no need to call tuple_force_port_remap if already in random mode (Phil)

Signed-off-by: Florian Westphal <fw@strlen.de>
Acked-by: Phil Sutter <phil@nwl.cc>
Acked-by: Eric Garver <eric@garver.life>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal 2021-12-17 11:29:57 +01:00 committed by Pablo Neira Ayuso
parent 4a6fbdd801
commit 878aed8db3
2 changed files with 43 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

43
net/netfilter/nf_nat_core.c
View File

@ -494,6 +494,38 @@ another_round:
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 &&
!random_port &&
!ct->local_origin)
random_port = tuple_force_port_remap(orig_tuple);
/* 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,

5
tools/testing/selftests/netfilter/nft_nat.sh
View File

@ -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.