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authorGuilhem Moulin <guilhem@fripost.org>2020-11-02 03:13:34 +0100
committerGuilhem Moulin <guilhem@fripost.org>2020-11-02 03:14:09 +0100
commita6b8c0b3a4758f8d84a7ad07bb9e068075d098d3 (patch)
treea7ed534b60bb89c545d3d2eb7fda1198a5d37a89
parent787652f46cce3263dac529679f290597eefb1e74 (diff)
Firewall: Move martian and bogus TCP filters early in the packet flow.
This is more efficient: the earlier we filter the crap out the less resources they consume.
-rwxr-xr-xroles/common/templates/etc/nftables.conf.j2148
1 files changed, 84 insertions, 64 deletions
diff --git a/roles/common/templates/etc/nftables.conf.j2 b/roles/common/templates/etc/nftables.conf.j2
index fc7691a..d788457 100755
--- a/roles/common/templates/etc/nftables.conf.j2
+++ b/roles/common/templates/etc/nftables.conf.j2
@@ -45,6 +45,90 @@ define out-tcp-ports = {
flush ruleset
+table netdev filter {
+{% for if in ansible_interfaces %}
+{% if if != "lo" and ansible_facts[if].active %}
+{% set addr = (ansible_facts[if].ipv4 | default({'address': '0.0.0.0'})).address %}
+ chain INGRESS-{{ if }} {
+ type filter hook ingress device {{ if }} priority -499
+ policy accept
+
+ # bogon filter (cf. RFC 6890 for non-global ip addresses)
+ define bogon = {
+ 0.0.0.0/8 # this host, on this network (RFC 1122 sec. 3.2.1.3)
+{% if not addr | ipaddr('10.0.0.0/8') %}
+ , 10.0.0.0/8 # private-use (RFC 1918)
+{% endif %}
+ , 100.64.0.0/10 # shared address space (RFC 6598)
+ , 127.0.0.0/8 # loopback (RFC 1122, sec. 3.2.1.3)
+ , 169.254.0.0/16 # link local (RFC 3927)
+{% if not addr | ipaddr('172.16.0.0/12') %}
+ , 172.16.0.0/12 # private-use (RFC 1918)
+{% endif %}
+ , 192.0.0.0/24 # IETF protocol assignments (RFC 6890 sec. 2.1)
+ , 192.0.2.0/24 # documentation (RFC 5737)
+{% if not addr | ipaddr('192.168.0.0/16') %}
+ , 192.168.0.0/16 # private-use (RFC 1918)
+{% endif %}
+ , 198.18.0.0/15 # benchmarking (RFC 2544)
+ , 198.51.100.0/24 # documentation (RFC 5737)
+ , 203.0.113.0/24 # documentation (RFC 5737)
+ , 224.0.0.0/3 # multicast - class D 224.0.0.0/4 + class E 240.0.0.0/4 (RFC 1112 sec. 4)
+ , 255.255.255.255/32 # limited broadcast (RFC 0919 sec. 7)
+ }
+
+ ip saddr $bogon counter drop
+ ip daddr $bogon counter drop
+
+ # See also https://www.team-cymru.org/Services/Bogons/fullbogons-ipv6.txt
+ define bogon6 = {
+ ::1/128 # loopback address (RFC 4291)
+ , ::/128 # unspecified (RFC 4291)
+ , ::ffff:0:0/96 # IPv4-mapped address (RFC 4291)
+ , 100::/64 # discard-only address block (RFC 6666)
+ , 2001::/23 # IETF protocol assignments (RFC 2928)
+ , 2001::/32 # TEREDO (RFC 4380)
+ , 2001:2::/48 # benchmarking (RFC 5180)
+ , 2001:db8::/32 # documentation (RFC 3849)
+ , 2001:10::/28 # ORCHID (RFC 4843)
+ , 2002::/16 # 6to4 (RFC 3056)
+ , fc00::/7 # unique-local (RFC 4193)
+ , fe80::/10 # linked-scoped unicast (RFC 4291)
+ }
+
+ ip6 saddr $bogon6 counter drop
+ ip6 saddr $bogon6 counter drop
+ }
+{% endif %}
+{% endfor %}
+}
+
+table inet raw {
+ chain PREROUTING-stateless {
+ # XXX can't add that to the ingress hook as that happens before IP defragmentation
+ # so we don't have the TCP header in later fragments (we don't want to drop IP
+ # fragments, see https://blog.cloudflare.com/ip-fragmentation-is-broken/ )
+ type filter hook prerouting priority -399 # > NF_IP_PRI_CONNTRACK_DEFRAG (-400)
+ policy accept
+
+ # stateless filter for bogus TCP packets
+ tcp flags & (fin|syn|rst|psh|ack|urg) == 0x0 counter drop # null packet
+ tcp flags & (fin|psh|urg) == fin|psh|urg counter drop # XMAS packet
+ tcp flags & (syn|rst) == syn|rst counter drop
+ tcp flags & (fin|rst) == fin|rst counter drop
+ tcp flags & (fin|syn) == fin|syn counter drop
+ tcp flags & (fin|psh|ack) == fin|psh counter drop
+ }
+
+ chain PREROUTING {
+ type filter hook prerouting priority -199 # > NF_IP_PRI_CONNTRACK (-200)
+ policy accept
+
+ # stateful filter
+ ct state invalid counter drop
+ }
+}
+
table inet filter {
# blackholes
set fail2ban { type ipv4_addr; timeout 10m; }
@@ -75,9 +159,6 @@ table inet filter {
# accept neighbour discovery for autoconfiguration, RFC 4890 sec. 4.4.1
icmpv6 type { 133,134,135,136,141,142 } ip6 hoplimit 255 counter accept
- jump martian
- jump invalid
-
udp sport 123 udp dport 123 ct state related,established accept
{% if groups.all | length > 1 %}
udp sport 500 udp dport 500 ct state new,related,established accept
@@ -116,9 +197,6 @@ table inet filter {
meta l4proto { icmp, icmpv6 } accept
- jump martian
- jump invalid
-
udp sport 123 udp dport 123 ct state new,related,established accept
{% if groups.all | length > 1 %}
udp sport 500 udp dport 500 ct state new,related,established accept
@@ -142,62 +220,4 @@ table inet filter {
meta l4proto udp counter reject
counter reject
}
-
- chain martian {
- # bogon filter (cf. RFC 6890 for non-global ip addresses)
- define invalid-ip = {
- 0.0.0.0/8 # this host, on this network (RFC 1122 sec. 3.2.1.3)
-{% if not ansible_default_ipv4.address | ipaddr('10.0.0.0/8') %}
- , 10.0.0.0/8 # private-use (RFC 1918)
-{% endif %}
- , 100.64.0.0/10 # shared address space (RFC 6598)
- , 127.0.0.0/8 # loopback (RFC 1122, sec. 3.2.1.3)
- , 169.254.0.0/16 # link local (RFC 3927)
-{% if not ansible_default_ipv4.address | ipaddr('172.16.0.0/12') %}
- , 172.16.0.0/12 # private-use (RFC 1918)
-{% endif %}
- , 192.0.0.0/24 # IETF protocol assignments (RFC 6890 sec. 2.1)
- , 192.0.2.0/24 # documentation (RFC 5737)
-{% if not ansible_default_ipv4.address | ipaddr('192.168.0.0/16') %}
- , 192.168.0.0/16 # private-use (RFC 1918)
-{% endif %}
- , 198.18.0.0/15 # benchmarking (RFC 2544)
- , 198.51.100.0/24 # documentation (RFC 5737)
- , 203.0.113.0/24 # documentation (RFC 5737)
- , 240.0.0.0/4 # reserved (RFC 1112, sec. 4)
- , 255.255.255.255/32 # limited broadcast (RFC 0919, section 7)
- }
-
- define invalid-ip6 = {
- ::1/128 # loopback address (RFC 4291)
- , ::/128 # unspecified (RFC 4291)
- , ::ffff:0:0/96 # IPv4-mapped address (RFC 4291)
- , 100::/64 # discard-only address block (RFC 6666)
- , 2001::/23 # IETF protocol assignments (RFC 2928)
- , 2001::/32 # TEREDO (RFC 4380)
- , 2001:2::/48 # benchmarking (RFC 5180)
- , 2001:db8::/32 # documentation (RFC 3849)
- , 2001:10::/28 # ORCHID (RFC 4843)
- , 2002::/16 # 6to4 (RFC 3056)
- , fc00::/7 # unique-local (RFC 4193)
- , fe80::/10 # linked-scoped unicast (RFC 4291)
- }
-
- ip saddr $invalid-ip counter drop
- ip daddr $invalid-ip counter drop
-
- ip6 saddr $invalid-ip6 counter drop
- ip6 daddr $invalid-ip6 counter drop
- }
-
- chain invalid {
- ct state invalid counter reject
-
- # drop bogus TCP packets
- tcp flags & (fin|syn|rst|psh|ack|urg) == 0x0 counter drop # null packets
- tcp flags != syn ct state new counter drop # SYN-flood attacks
- tcp flags & (fin|syn|rst|psh|ack|urg) == fin|psh|urg counter drop # XMAS packets
- tcp flags & (fin|syn) == fin|syn counter drop # bogus
- tcp flags & (syn|rst) == syn|rst counter drop # bogus
- }
}