Set up IPSec tunnels between each pair of hosts.

We use a dedicated, non-routable, IPv4 subnet for IPSec.  Furthermore
the subnet is nullrouted in the absence of xfrm lookup (i.e., when there
is no matching IPSec Security Association) to avoid data leaks.

Each host is associated with an IP in that subnet (thus only reachble
within that subnet, either by the host itself or by its IPSec peers).

The peers authenticate each other using RSA public key authentication.
Kernel traps are used to ensure that connections are only established
when traffic is detected between the peers; after 30m of inactivity
(this value needs to be less than the rekeying period) the connection is
brought down and a kernel trap is installed.

1 files changed, 32 insertions, 70 deletions

diff --git a/roles/common/files/usr/local/sbin/update-firewall.sh b/roles/common/files/usr/local/sbin/update-firewall.sh
index f25f507..065bae2 100755
--- a/roles/common/files/usr/local/sbin/update-firewall.sh
+++ b/roles/common/files/usr/local/sbin/update-firewall.sh
@@ -40,8 +40,12 @@ check=0
 verbose=0
 addrfam=
 
-secmark=0xA99   # must match that in /etc/network/if-up.d/ipsec
-secproto=esp    # must match /etc/ipsec.conf; ESP is the default (vs AH/IPComp)
+secproto=esp # must match /etc/ipsec.conf; ESP is the default (vs AH/IPComp)
+if [ -x /usr/sbin/ipsec ] && /usr/sbin/ipsec status >/dev/null; then
+    ipsec=y
+else
+    ipsec=n
+fi
 
 fail2ban_re='^(\[[0-9]+:[0-9]+\]\s+)?-A fail2ban-\S'
 IPSec_re=" -m policy --dir (in|out) --pol ipsec --reqid [0-9]+ --proto $secproto -j ACCEPT$"
@@ -152,21 +156,9 @@ run() {
     tables[$f]=filter
 
     # The default interface associated with this address.
-    local if=$( /bin/ip -$f route show to default scope global \
+    local if=$( /bin/ip -$f -o route show to default scope global \
               | sed -nr '/^default via \S+ dev (\S+).*/ {s//\1/p;q}' )
 
-    # The virtual interface reserved for IPSec.
-    local ifsec=$( /bin/ip -o -$f link show \
-                 | sed -nr "/^[0-9]+:\s+(sec[0-9]+)@$if:\s.*/ {s//\1/p;q}" )
-
-    # The (host-scoped) IP reserved for IPSec.
-    local ipsec=
-    if [ "$ifsec" -a $f = 4 ]; then
-        tables[$f]='mangle nat filter'
-        ipsec=$( /bin/ip -$f address show dev "$ifsec" scope host \
-               | sed -nr '/^\s+inet\s(\S+).*/ {s//\1/p;q}' )
-    fi
-
     # Store the old (current) ruleset
     local old=$(mktemp --tmpdir current-rules.v$f.XXXXXX) \
           new=$(mktemp --tmpdir new-rules.v$f.XXXXXX)
@@ -203,8 +195,9 @@ run() {
         grep -E -- "$fail2ban_re"       "$old" || true
     fi >> "$new"
 
-    if [ "$ipsec" ]; then
-        # (Host-to-host) IPSec tunnels come first. TODO: test IPSec with IPv6.
+    if [ "$f" = 4 -a "$ipsec" = y ]; then
+        # Our IPSec tunnels are IPv4 only.
+        # (Host-to-host) IPSec tunnels come first.
         grep -E -- "$IPSec_re" "$old" >> "$new" || true
 
         # Allow any IPsec $secproto protocol packets to be sent and received.
@@ -219,15 +212,24 @@ run() {
     #            http://baldric.net/loose-iptables-firewall-for-servers/
 
     local ip
-    if [ "$f" = 4 ]; then
+    if [ "$f" = 4 -a "$ipsec" = y ]; then
         # Private-use networks (RFC 1918) and link local (RFC 3927)
-        local MyNetwork=$( /bin/ip -4 address show dev $if scope global \
-                         | sed -nr 's/^\s+inet\s(\S+).*/\1/p')
+        local MyIPSec="$( /bin/ip -4 -o route show table 220 dev $if | sed 's/\s.*//' )"
+        local MyNetwork="$( /bin/ip -4 -o address show dev $if scope global \
+                          | sed -nr "s/^[0-9]+:\s+$if\s+inet\s(\S+).*/\1/p" \
+                          | while read ip; do
+                              for ips in $MyIPSec; do
+                                [ "$ips" = "$(/usr/bin/netmask -nc "$ip" "$ips" | sed 's/^ *//')" ] || echo "$ip"
+                              done
+                            done
+                          )"
         [ "$MyNetwork" ] && \
         for ip in 10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 169.254.0.0/16; do
             # Don't lock us out if we are behind a NAT ;-)
-            [ "$ip" = "$(/usr/bin/netmask -nc $ip $MyNetwork | sed 's/ //g')" ] \
-            || iptables -A INPUT -i $if -s "$ip" -j DROP
+            for myip in $MyNetwork; do
+                [ "$ip" = "$(/usr/bin/netmask -nc "$ip" "$myip" | sed 's/^ *//')" ] \
+                || iptables -A INPUT -i $if -s "$ip" -j DROP
+            done
         done
 
         # Other martian packets: "This" network, multicast, broadcast (RFCs
@@ -259,14 +261,14 @@ run() {
     local localhost=$(inet46 $f '127.0.0.1/8' '::1/128')
     iptables -A INPUT  -i lo -s "$localhost" -d "$localhost" -j ACCEPT
     iptables -A OUTPUT -o lo -s "$localhost" -d "$localhost" -j ACCEPT
-
-    if [ "$ipsec" ]; then
-        # ACCEPT any, *IPSec* traffic destinating to the non-routable
-        # $ipsec.  Also ACCEPT all traffic originating from $ipsec, as
-        # it is MASQUERADE'd.
-        iptables -A INPUT  -d "$ipsec" -i $if -m policy --dir in \
-            --pol ipsec --proto $secproto -j ACCEPT
-        iptables -A OUTPUT -m mark --mark "$secmark" -o $if -j ACCEPT
+    if [ "$f" = 4 -a "$ipsec" = y ]; then
+        # Allow local access to our virtual IP
+        /bin/ip -4 -o route show table 220 dev $if \
+        | sed -nr 's/.*\ssrc\s+([[:digit:].]{7,15})(\s.*)?/\1/p' \
+        | while read ipsec; do
+            iptables -A INPUT  -i lo -s "$ipsec" -d "$ipsec" -j ACCEPT
+            iptables -A OUTPUT -o lo -s "$ipsec" -d "$ipsec" -j ACCEPT
+        done
     fi
 
     # Prepare fail2ban.  We make fail2ban insert its rules in a
@@ -330,46 +332,6 @@ run() {
     ########################################################################
     commit
 
-    if [ "$ipsec" ]; then
-        # DNAT the IPSec paquets to $ipsec after decapsulation, and SNAT
-        # them before encapsulation.  We need to do the NAT'ing before
-        # packets enter the IPSec stack because they are signed
-        # afterwards, and NAT'ing would mess up the signature.
-        ipt-chains mangle PREROUTING:ACCEPT INPUT:ACCEPT \
-                          FORWARD:DROP \
-                          OUTPUT:ACCEPT POSTROUTING:ACCEPT
-
-        # Packets which destination is $ipsec *must* be associated with
-        # an IPSec policy.
-        iptables -A INPUT -d "$ipsec" -i $if -m policy --dir in \
-            --pol ipsec --proto $secproto -j ACCEPT
-        iptables -A INPUT -d "$ipsec" -i $if -j DROP
-
-        # Packets originating from our (non-routable) $ipsec are marked;
-        # if there is no xfrm lookup (i.e., no matching IPSec
-        # association), the packet will retain its mark and be null
-        # routed later on.  Otherwise, the packet is re-queued unmarked.
-        iptables -A OUTPUT -o $if -j MARK --set-mark 0x0
-        iptables -A OUTPUT -s "$ipsec" -o $if -m policy --dir out \
-            --pol none -j MARK --set-mark $secmark
-        commit
-
-        ipt-chains nat PREROUTING:ACCEPT INPUT:ACCEPT \
-                       OUTPUT:ACCEPT POSTROUTING:ACCEPT
-
-        # DNAT all marked packets after decapsulation.
-        iptables -A PREROUTING \! -d "$ipsec" -i $if -m policy --dir in \
-            --pol ipsec --proto $secproto -j DNAT --to "${ipsec%/*}"
-
-        # Packets originating from our IPSec are SNAT'ed (MASQUERADE).
-        # (And null-routed later on unless there is an xfrm
-        # association.)
-        iptables -A POSTROUTING -m mark --mark $secmark -o $if -j MASQUERADE
-        commit
-    fi
-
-    ########################################################################
-
 
     local rv1=0 rv2=0 persistent=/etc/iptables/rules.v$f
     local oldz=$(mktemp --tmpdir current-rules.v$f.XXXXXX)