meta-google: gbmc-ncsi-config: Restrict NCSI input packets

Break down packets by their incoming address and ensure that we don't
allow packets to unintended destinations. Right now this is effectively
a no-op, but it will be necessary for BMC public addressing.

Change-Id: I39c16c3b9cd4c293df42b928674e39677d7834e9
Signed-off-by: William A. Kennington III <wak@google.com>

3 files changed, 122 insertions, 3 deletions

diff --git a/meta-google/recipes-google/ncsi/files/50-gbmc-ncsi.rules.in b/meta-google/recipes-google/ncsi/files/50-gbmc-ncsi.rules.in
index 33031f0db..4ebe35128 100644
--- a/meta-google/recipes-google/ncsi/files/50-gbmc-ncsi.rules.in
+++ b/meta-google/recipes-google/ncsi/files/50-gbmc-ncsi.rules.in
@@ -3,10 +3,23 @@ table inet filter {
         type filter hook input priority 0; policy drop;
         iifname != @NCSI_IF@ accept
         ct state established accept
+        ip6 daddr ff00::/8 goto ncsi_brd_input
+        ip6 daddr fe80::/64 goto ncsi_legacy_input
+    }
+    chain ncsi_gbmc_br_pub_input {
+        jump gbmc_br_pub_input
+        reject
+    }
+    chain gbmc_br_pub_input {
+    }
+    chain ncsi_legacy_input {
+        jump ncsi_brd_input
         tcp dport 3959 accept
         udp dport 3959 accept
         tcp dport 3967 accept
         udp dport 3967 accept
+    }
+    chain ncsi_brd_input {
         icmpv6 type nd-neighbor-advert accept
         icmpv6 type nd-neighbor-solicit accept
         icmpv6 type nd-router-advert accept
diff --git a/meta-google/recipes-google/ncsi/files/gbmc-ncsi-nft.sh.in b/meta-google/recipes-google/ncsi/files/gbmc-ncsi-nft.sh.in
new file mode 100644
index 000000000..34ca4e52f
--- /dev/null
+++ b/meta-google/recipes-google/ncsi/files/gbmc-ncsi-nft.sh.in
@@ -0,0 +1,95 @@
+# Copyright 2021 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+[ -z "${gbmc_ncsi_nft_lib-}" ] || return
+
+gbmc_ncsi_nft_init=
+gbmc_ncsi_nft_lastip4=
+gbmc_ncsi_nft_lastip6=
+
+gbmc_ncsi_nft_update() {
+  [ -n "$gbmc_ncsi_nft_init" ] || return
+
+  printf 'NCSI firewall for IPv4(%s) IPv6(%s)\n' \
+    "${gbmc_ncsi_nft_lastip4:-(deleted)}" \
+    "${gbmc_ncsi_nft_lastip6:-(deleted)}" >&2
+
+  local contents=
+  contents+='table inet filter {'$'\n'
+  contents+='    chain ncsi_input {'$'\n'
+
+  local ip4="$gbmc_ncsi_nft_lastip4"
+  if [ -n "$ip4" ]; then
+    contents+="        ip daddr $ip4 goto ncsi_legacy_input"$'\n'
+  fi
+
+  local ip6="$gbmc_ncsi_nft_lastip6"
+  if [ -n "$ip6" ]; then
+    contents+="        ip6 daddr $ip6/128 goto ncsi_legacy_input"$'\n'
+
+    # Pad out to 4 hextets with no trailing semicolons
+    local pfx=
+    pfx="${ip6%::}"
+    while true; do
+      # Count `:` in `pfx` by removing them and diffing their lengths
+      local nos="${pfx//:/}"
+      (( ${#pfx} - ${#nos} >= 3 )) && break
+      pfx+=":0"
+    done
+
+    # If our address has enough spare bits for appending the BMC suffix
+    # then we add a rule that allows the BMC subnet. That is, we need a /64
+    # as input.
+    if (( ${#pfx} - ${#nos} == 3 )); then
+      contents+="        ip6 saddr != ${pfx}:fd00::/72 ip6 daddr"
+      contents+=" ${pfx}:fd00::/72 goto ncsi_gbmc_br_pub_input"$'\n'
+    fi
+  fi
+
+  contents+='    }'$'\n'
+  contents+='}'$'\n'
+
+  local rfile=/run/nftables/40-gbmc-ncsi-in.rules
+  mkdir -p -m 755 "$(dirname "$rfile")"
+  printf '%s' "$contents" >"$rfile"
+
+  echo 'Restarting nftables' >&2
+  systemctl reset-failed nftables
+  systemctl --no-block restart nftables
+}
+
+gbmc_ncsi_nft_hook() {
+  if [ "$change" = 'init' ]; then
+    gbmc_ncsi_nft_init=1
+    gbmc_ncsi_nft_update
+  elif [ "$change" = 'addr' -a "$intf" = '@NCSI_IF@' -a "$scope" = 'global' ]; then
+    if [ "$fam" = 'inet6' ]; then
+      local -n lastip='gbmc_ncsi_nft_lastip6'
+    else
+      local -n lastip='gbmc_ncsi_nft_lastip4'
+    fi
+    if [ "$action" = 'add' -a "$ip" != "$lastip" ]; then
+      lastip="$ip"
+      gbmc_ncsi_nft_update
+    fi
+    if [ "$action" = 'del' -a "$ip" = "$lastip" ]; then
+      lastip=
+      gbmc_ncsi_nft_update
+    fi
+  fi
+}
+
+GBMC_IP_MONITOR_HOOKS+=(gbmc_ncsi_nft_hook)
+
+gbmc_ncsi_nft_lib=1
diff --git a/meta-google/recipes-google/ncsi/gbmc-ncsi-config.bb b/meta-google/recipes-google/ncsi/gbmc-ncsi-config.bb
index ecdda2cb6..b833810f1 100644
--- a/meta-google/recipes-google/ncsi/gbmc-ncsi-config.bb
+++ b/meta-google/recipes-google/ncsi/gbmc-ncsi-config.bb
@@ -9,17 +9,22 @@ SRC_URI += " \
   file://50-gbmc-ncsi.rules.in \
   file://gbmc-ncsi-sslh.socket.in \
   file://gbmc-ncsi-sslh.service \
+  file://gbmc-ncsi-nft.sh.in \
   "
 
 S = "${WORKDIR}"
 
 RDEPENDS_${PN} += " \
+  gbmc-ip-monitor \
   ncsid \
   nftables-systemd \
   sslh \
   "
 
-FILES_${PN} += "${systemd_unitdir}"
+FILES_${PN} += " \
+  ${datadir}/gbmc-ip-monitor \
+  ${systemd_unitdir} \
+  "
 
 SYSTEMD_SERVICE_${PN} += " \
   gbmc-ncsi-sslh.service \
@@ -50,7 +55,7 @@ do_install_append() {
 
   nftdir=${D}${sysconfdir}/nftables
   install -d -m0755 "$nftdir"
-  sed "s,@NCSI_IF@,$if_name," ${WORKDIR}/50-gbmc-ncsi.rules.in \
+  sed "s,@NCSI_IF@,$if_name,g" ${WORKDIR}/50-gbmc-ncsi.rules.in \
     >"$nftdir"/50-gbmc-ncsi.rules
 
   wantdir=${D}${systemd_system_unitdir}/multi-user.target.wants
@@ -58,6 +63,12 @@ do_install_append() {
   ln -sv ../ncsid@.service "$wantdir"/ncsid@$if_name.service
 
   install -m 0644 ${WORKDIR}/gbmc-ncsi-sslh.service ${D}${systemd_system_unitdir}
-  sed "s,@NCSI_IF@,$if_name," ${WORKDIR}/gbmc-ncsi-sslh.socket.in \
+  sed "s,@NCSI_IF@,$if_name,g" ${WORKDIR}/gbmc-ncsi-sslh.socket.in \
     >${D}${systemd_system_unitdir}/gbmc-ncsi-sslh.socket
+
+  mondir=${D}${datadir}/gbmc-ip-monitor/
+  install -d -m0755 $mondir
+  sed "s,@NCSI_IF@,$if_name,g" ${WORKDIR}/gbmc-ncsi-nft.sh.in \
+    >${WORKDIR}/gbmc-ncsi-nft.sh
+  install -m644 ${WORKDIR}/gbmc-ncsi-nft.sh $mondir
 }