dnsmasq: fix more dnsmasq jail issues

 * remove superflus mounts of /dev/null and /dev/urandom
 * reset EXTRA_MOUNTS at the beginning of the script
 * add mount according to ignore_hosts_dir
 * don't add mount for file which is inside a directory already in the
   EXTRA_MOUNTS list

Fixes: 59c63224e1 ("dnsmasq: rework jail mounts")
Reported-by: Hartmut Birr <[email protected]>
Signed-off-by: Daniel Golle <[email protected]>

package/network/services/dnsmasq/files/dnsmasq.init

@@ -10,6 +10,7 @@ ADD_LOCAL_DOMAIN=1
 ADD_LOCAL_HOSTNAME=1
 ADD_WAN_FQDN=0
 ADD_LOCAL_FQDN=""
+EXTRA_MOUNT=""
 
 BASECONFIGFILE="/var/etc/dnsmasq.conf"
 BASEHOSTFILE="/tmp/hosts/dhcp"
@@ -187,8 +188,22 @@ append_notinterface() {
 	xappend "--except-interface=$ifname"
 }
 
+ismounted() {
+	local filename="$1"
+	local dirname
+	for dirname in $EXTRA_MOUNT ; do
+		case "$filename" in
+			"${dirname}/"* | "${dirname}" )
+				return 1
+				;;
+		esac
+	done
+
+	return 0
+}
+
 append_addnhosts() {
-	append EXTRA_MOUNT "$1"
+	ismounted "$1" || append EXTRA_MOUNT "$1"
 	xappend "--addn-hosts=$1"
 }
 
@@ -927,6 +942,14 @@ dnsmasq_start()
 		config_list_foreach "$cfg" "interface" append_interface
 		config_list_foreach "$cfg" "notinterface" append_notinterface
 	}
+	config_get_bool ignore_hosts_dir "$cfg" ignore_hosts_dir 0
+	if [ "$ignore_hosts_dir" = "1" ]; then
+		xappend "--addn-hosts=$HOSTFILE"
+		append EXTRA_MOUNT "$HOSTFILE"
+	else
+		xappend "--addn-hosts=$(dirname $HOSTFILE)"
+		append EXTRA_MOUNT "$(dirname $HOSTFILE)"
+	fi
 	config_list_foreach "$cfg" "addnhosts" append_addnhosts
 	config_list_foreach "$cfg" "bogusnxdomain" append_bogusnxdomain
 	append_parm "$cfg" "leasefile" "--dhcp-leasefile" "/tmp/dhcp.leases"
@@ -1022,12 +1045,6 @@ dnsmasq_start()
 
 	xappend "--dhcp-broadcast=tag:needs-broadcast"
 
-	config_get_bool ignore_hosts_dir "$cfg" ignore_hosts_dir 0
-	if [ "$ignore_hosts_dir" = "1" ]; then
-		xappend "--addn-hosts=$HOSTFILE"
-	else
-		xappend "--addn-hosts=$(dirname $HOSTFILE)"
-	fi
 
 	config_get dnsmasqconfdir "$cfg" confdir "/tmp/dnsmasq.d"
 	xappend "--conf-dir=$dnsmasqconfdir"
@@ -1121,10 +1138,9 @@ dnsmasq_start()
 	procd_set_param respawn
 
 	procd_add_jail dnsmasq ubus log
-	procd_add_jail_mount $CONFIGFILE $TRUSTANCHORSFILE $HOSTFILE $RFC6761FILE
-	procd_add_jail_mount $EXTRA_MOUNT $DHCPBOGUSHOSTNAMEFILE $DHCPSCRIPT $DHCPSCRIPT_DEPENDS
+	procd_add_jail_mount $CONFIGFILE $DHCPBOGUSHOSTNAMEFILE $DHCPSCRIPT $DHCPSCRIPT_DEPENDS
+	procd_add_jail_mount $EXTRA_MOUNT $RFC6761FILE $TRUSTANCHORSFILE
 	procd_add_jail_mount $dnsmasqconffile $dnsmasqconfdir $resolvdir $user_dhcpscript
-	procd_add_jail_mount /dev/null /dev/urandom
 	procd_add_jail_mount /etc/passwd /etc/group /etc/TZ /etc/hosts /etc/ethers
 	procd_add_jail_mount_rw /var/run/dnsmasq/ $leasefile