dnsmasq: add dhcp-ignore-names support - CERT VU#598349

dnsmasq v2.80test8 adds the ability to ignore dhcp client's requests for
specific hostnames.  Clients claiming certain hostnames and thus
claiming DNS namespace represent a potential security risk. e.g. a
malicious host could claim 'wpad' for itself and redirect other web
client requests to it for nefarious purpose. See CERT VU#598349 for more
details.

Some Samsung TVs are claiming the hostname 'localhost', it is believed
not (yet) for nefarious purposes.

/usr/share/dnsmasq/dhcpbogushostname.conf contains a list of hostnames
in correct syntax to be excluded. e.g.

dhcp-name-match=set:dhcp_bogus_hostname,localhost

Inclusion of this file is controlled by uci option dhcpbogushostname
which is enabled by default.

To be absolutely clear, DHCP leases to these requesting hosts are still
permitted, but they do NOT get to claim ownership of the hostname
itself and hence put into DNS for other hosts to be confused/manipulate by.

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>

3 files changed, 18 insertions, 1 deletions

diff --git a/package/network/services/dnsmasq/Makefile b/package/network/services/dnsmasq/Makefile
index f1daac397c..287edf5791 100644
--- a/package/network/services/dnsmasq/Makefile
+++ b/package/network/services/dnsmasq/Makefile
@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=dnsmasq
 PKG_VERSION:=2.80test8
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.xz
 PKG_SOURCE_URL:=http://thekelleys.org.uk/dnsmasq/test-releases
@@ -166,6 +166,7 @@ define Package/dnsmasq/install
 	$(INSTALL_DIR) $(1)/etc/hotplug.d/tftp
 	$(INSTALL_DATA) ./files/dnsmasqsec.hotplug $(1)/etc/hotplug.d/ntp/25-dnsmasqsec
 	$(INSTALL_DIR) $(1)/usr/share/dnsmasq
+	$(INSTALL_DATA) ./files/dhcpbogushostname.conf $(1)/usr/share/dnsmasq/
 	$(INSTALL_DATA) ./files/rfc6761.conf $(1)/usr/share/dnsmasq/
 	$(INSTALL_DIR) $(1)/usr/lib/dnsmasq
 	$(INSTALL_BIN) ./files/dhcp-script.sh $(1)/usr/lib/dnsmasq/dhcp-script.sh
diff --git a/package/network/services/dnsmasq/files/dhcpbogushostname.conf b/package/network/services/dnsmasq/files/dhcpbogushostname.conf
new file mode 100644
index 0000000000..e83b6975d0
--- /dev/null
+++ b/package/network/services/dnsmasq/files/dhcpbogushostname.conf
@@ -0,0 +1,8 @@
+# dhcpbogushostname.conf included configuration file for dnsmasq
+#
+# includes a list of hostnames that should not be associated with dhcp leases
+# in response to CERT VU#598349
+# file included by default, option dhcpbogushostname 0  to disable
+
+dhcp-name-match=set:dhcp_bogus_hostname,localhost
+dhcp-name-match=set:dhcp_bogus_hostname,wpad
diff --git a/package/network/services/dnsmasq/files/dnsmasq.init b/package/network/services/dnsmasq/files/dnsmasq.init
index de15552424..0c786e82c7 100644
--- a/package/network/services/dnsmasq/files/dnsmasq.init
+++ b/package/network/services/dnsmasq/files/dnsmasq.init
@@ -16,6 +16,7 @@ BASEHOSTFILE="/tmp/hosts/dhcp"
 TRUSTANCHORSFILE="/usr/share/dnsmasq/trust-anchors.conf"
 TIMEVALIDFILE="/var/state/dnsmasqsec"
 BASEDHCPSTAMPFILE="/var/run/dnsmasq"
+DHCPBOGUSHOSTNAMEFILE="/usr/share/dnsmasq/dhcpbogushostname.conf"
 RFC6761FILE="/usr/share/dnsmasq/rfc6761.conf"
 DHCPSCRIPT="/usr/lib/dnsmasq/dhcp-script.sh"
 
@@ -956,6 +957,13 @@ dnsmasq_start()
 
 	config_foreach filter_dnsmasq host dhcp_host_add "$cfg"
 	echo >> $CONFIGFILE_TMP
+
+	config_get_bool dhcpbogushostname "$cfg" dhcpbogushostname 1
+	[ "$dhcpbogushostname" -gt 0 ] && {
+		xappend "--dhcp-ignore-names=tag:dhcp_bogus_hostname"
+		[ -r "$DHCPBOGUSHOSTNAMEFILE" ] && xappend "--conf-file=$DHCPBOGUSHOSTNAMEFILE"
+	}
+
 	config_foreach filter_dnsmasq boot dhcp_boot_add "$cfg"
 	config_foreach filter_dnsmasq mac dhcp_mac_add "$cfg"
 	config_foreach filter_dnsmasq tag dhcp_tag_add "$cfg"