unbound: Test upstream name servers before using

unbound has some trouble with validating DNSSEC-enabled
domains when the upstream name server is stripping signatures
from the authoritative responses.

This script now checks that, removes any broken upstream
name servers from the list and prints a warning.

If all name servers fail the test, unbound falls back
into recursor mode.

Signed-off-by: Arne Fitzenreiter <arne_f@ipfire.org>

diff --git a/src/initscripts/init.d/unbound b/src/initscripts/init.d/unbound
index 1b2649f20c3b2303c2a85f7b7ca907f3f2498ca3..4d2b266758f29fd6055750a3d4978f6bed8afa9c 100644 (file)
--- a/src/initscripts/init.d/unbound
+++ b/src/initscripts/init.d/unbound
@@ -7,6 +7,11 @@
 . /etc/sysconfig/rc
 . ${rc_functions}
 
+TEST_DOMAIN="ipfire.org"
+
+# This domain will never validate
+TEST_DOMAIN_FAIL="dnssec-failed.org"
+
 USE_FORWARDERS=1
 
 # Cache any local zones for 60 seconds
@@ -53,18 +58,45 @@ config_header() {
 }
 
 update_forwarders() {
-       local forwarders="$(read_name_servers)"
+       if [ "${USE_FORWARDERS}" = "1" -a -e "/var/ipfire/red/active" ]; then
+               local forwarders
+               local broken_forwarders
+
+               local ns
+               for ns in $(read_name_servers); do
+                       test_name_server ${ns} &>/dev/null
+                       case "$?" in
+                               # Only use DNSSEC-validating or DNSSEC-aware name servers
+                               0|2)
+                                       forwarders="${forwarders} ${ns}"
+                                       ;;
+                               *)
+                                       broken_forwarders="${broken_forwarders} ${ns}"
+                                       ;;
+                       esac
+               done
+
+               # Show warning for any broken upstream name servers
+               if [ -n "${broken_forwarders}" ]; then
+                       boot_mesg "Ignoring broken upstream name server(s): ${broken_forwarders:1}" ${WARNING}
+                       echo_warning
+               fi
 
-       if [ "${USE_FORWARDERS}" = "1" ] && [ -n "${forwarders}" ]; then
-               boot_mesg "Using Name Server(s): ${forwarders}"
-               boot_mesg_flush
+               if [ -n "${broken_forwarders}" -a -z "${forwarders}" ]; then
+                       boot_mesg "Falling back to recursor mode" ${WARNING}
+                       echo_warning
 
-               unbound-control -q forward ${forwarders}
+               elif [ -n "${forwarders}" ]; then
+                       boot_mesg "Configuring upstream name server(s): ${forwarders:1}" ${INFO}
+                       echo_ok
 
-       # If forwarders cannot be used we run in recursor mode
-       else
-               unbound-control -q forward off
+                       unbound-control -q forward ${forwarders}
+                       return 0
+               fi
        fi
+
+       # If forwarders cannot be used we run in recursor mode
+       unbound-control -q forward off
 }
 
 update_hosts() {
@@ -179,6 +211,77 @@ get_memory_amount() {
        done < /proc/meminfo
 }
 
+test_name_server() {
+       local ns=${1}
+
+       # Return codes:
+       # 0     DNSSEC validating
+       # 1     Error: unreachable, etc.
+       # 2     DNSSEC aware
+       # 3     NOT DNSSEC-aware
+
+       # Exit when the server is not reachable
+       ns_is_online ${ns} || return 1
+
+       # Return 0 if validating
+       ns_is_validating ${ns} && return 0
+
+       local errors
+       for rr in DNSKEY DS RRSIG; do
+               if ! ns_forwards_${rr} ${ns}; then
+                       errors="${errors} ${rr}"
+               fi
+       done
+
+       if [ -n "${errors}" ]; then
+               echo >&2 "Unable to retrieve the following resource records from ${ns}: ${errors:1}"
+               return 3
+       fi
+
+       # Is DNSSEC-aware
+       return 2
+}
+
+# Sends an A query to the nameserver w/o DNSSEC
+ns_is_online() {
+       local ns=${1}
+
+       dig @${ns} +nodnssec A ${TEST_DOMAIN} >/dev/null
+}
+
+# Resolving ${TEST_DOMAIN_FAIL} will fail if the nameserver is validating
+ns_is_validating() {
+       local ns=${1}
+
+       dig @${ns} A ${TEST_DOMAIN_FAIL} | grep -q SERVFAIL
+}
+
+# Checks if we can retrieve the DNSKEY for this domain.
+# dig will print the SOA if nothing was found
+ns_forwards_DNSKEY() {
+       local ns=${1}
+
+       dig @${ns} DNSKEY ${TEST_DOMAIN} | grep -qv SOA
+}
+
+ns_forwards_DS() {
+       local ns=${1}
+
+       dig @${ns} DS ${TEST_DOMAIN} | grep -qv SOA
+}
+
+ns_forwards_RRSIG() {
+       local ns=${1}
+
+       dig @${ns} +dnssec A ${TEST_DOMAIN} | grep -q RRSIG
+}
+
+ns_supports_tcp() {
+       local ns=${1}
+
+       dig @${ns} +tcp A ${TEST_DOMAIN} >/dev/null || return 1
+}
+
 case "$1" in
        start)
                # Print a nicer messagen when unbound is already running
@@ -228,8 +331,38 @@ case "$1" in
                update_forwarders
                ;;
 
+       test-name-server)
+               ns=${2}
+
+               test_name_server ${ns}
+               ret=${?}
+
+               case "${ret}" in
+                       0)
+                               echo "${ns} is validating"
+                               ;;
+                       2)
+                               echo "${ns} is DNSSEC-aware"
+                               ;;
+                       3)
+                               echo "${ns} is NOT DNSSEC-aware"
+                               ;;
+                       *)
+                               echo "Test failed for an unknown reason"
+                               ;;
+               esac
+
+               if ns_supports_tcp ${ns}; then
+                       echo "${ns} supports TCP fallback"
+               else
+                       echo "${ns} does not support TCP fallback"
+               fi
+
+               exit ${ret}
+               ;;
+
        *)
-               echo "Usage: $0 {start|stop|restart|status|update-forwarders}"
+               echo "Usage: $0 {start|stop|restart|status|update-forwarders|test-name-server}"
                exit 1
                ;;
 esac