[PATCH] DNS: Fall back to permissive mode if recursor mode is unavailable

[Michael Tremer <michael.tremer@ipfire.org>]

[-- Attachment #1: Type: text/plain, Size: 6103 bytes --]

The tests when assigning DNS name servers has been extended so that
if no working forwarder can be found, we will test if the local recursor
mode is an option.

If not, we will configure unbound's validator module into permissive
mode so that at least some DNS functionality is available.

Signed-off-by: Michael Tremer <michael.tremer(a)ipfire.org>
---
 config/rootfiles/core/110/filelists/files          |  1 +
 lfs/unbound                                        |  1 +
 src/initscripts/init.d/unbound                     | 67 ++++++++++++++++++++--
 ...ting-validator-permissive-mode-at-runtime.patch | 43 ++++++++++++++
 4 files changed, 107 insertions(+), 5 deletions(-)
 create mode 100644 src/patches/unbound-allow-setting-validator-permissive-mode-at-runtime.patch

diff --git a/config/rootfiles/core/110/filelists/files b/config/rootfiles/core/110/filelists/files
index 670b9ae..f4ce989 100644
--- a/config/rootfiles/core/110/filelists/files
+++ b/config/rootfiles/core/110/filelists/files
@@ -1,5 +1,6 @@
 etc/system-release
 etc/issue
+etc/rc.d/init.d/unbound
 srv/web/ipfire/cgi-bin/index.cgi
 srv/web/ipfire/cgi-bin/vpnmain.cgi
 usr/lib/libssp.so.0
diff --git a/lfs/unbound b/lfs/unbound
index 2b7745c..f361f24 100644
--- a/lfs/unbound
+++ b/lfs/unbound
@@ -70,6 +70,7 @@ $(subst %,%_MD5,$(objects)) :
 $(TARGET) : $(patsubst %,$(DIR_DL)/%,$(objects))
 	@$(PREBUILD)
 	@rm -rf $(DIR_APP) && cd $(DIR_SRC) && tar axf $(DIR_DL)/$(DL_FILE)
+	cd $(DIR_APP) && patch -Np1 < $(DIR_SRC)/src/patches/unbound-allow-setting-validator-permissive-mode-at-runtime.patch
 	cd $(DIR_APP) && \
 		./configure \
 			--prefix=/usr \
diff --git a/src/initscripts/init.d/unbound b/src/initscripts/init.d/unbound
index 8802781..bbf9c00 100644
--- a/src/initscripts/init.d/unbound
+++ b/src/initscripts/init.d/unbound
@@ -114,17 +114,38 @@ update_forwarders() {
 			echo_warning
 		fi
 
-		if [ -n "${broken_forwarders}" -a -z "${forwarders}" ]; then
-			boot_mesg "Falling back to recursor mode" ${WARNING}
-			echo_warning
-
-		elif [ -n "${forwarders}" ]; then
+		if [ -n "${forwarders}" ]; then
 			boot_mesg "Configuring upstream name server(s): ${forwarders:1}" ${INFO}
 			echo_ok
 
+			# Make sure DNSSEC is activated
+			enable_dnssec
+
 			echo "${forwarders}" > /var/ipfire/red/dns
 			unbound-control -q forward ${forwarders}
 			return 0
+
+		# In case we have found no working forwarders
+		else
+			# Test if the recursor mode is available
+			if can_resolve_root +bufsize=${new_edns_buffer_size}; then
+				# Make sure DNSSEC is activated
+				enable_dnssec
+
+				boot_mesg "Falling back to recursor mode" ${WARNING}
+				echo_warning
+
+			# If not, we set DNSSEC in permissive mode and allow using all recursors
+			elif [ -n "${broken_forwarders}" ]; then
+				disable_dnssec
+
+				boot_mesg "DNSSEC has been set to permissive mode" ${FAILURE}
+				echo_failure
+
+				echo "${broken_forwarders}" > /var/ipfire/red/dns
+				unbound-control -q forward ${broken_forwarders}
+				return 0
+			fi
 		fi
 	fi
 
@@ -370,6 +391,42 @@ ns_determine_edns_buffer_size() {
 	return 1
 }
 
+get_root_nameservers() {
+	while read -r hostname ttl record address; do
+		# Searching for A records
+		[ "${record}" = "A" ] || continue
+
+		echo "${address}"
+	done < /etc/unbound/root.hints
+}
+
+can_resolve_root() {
+	local ns
+	for ns in $(get_root_nameservers); do
+		if dig @${ns} +dnssec SOA . $@ >/dev/null; then
+			return 0
+		fi
+	done
+
+	# none of the servers was reachable
+	return 1
+}
+
+enable_dnssec() {
+	local status=$(unbound-control get_option val-permissive-mode)
+
+	# Don't do anything if DNSSEC is already activated
+	[ "${status}" = "no" ] && return 0
+
+	# Activate DNSSEC and flush cache with any stale and unvalidated data
+	unbound-control -q set_option val-permissive-mode: no
+	unbound-control -q flush_zone .
+}
+
+disable_dnssec() {
+	unbound-control -q set_option val-permissive-mode: yes
+}
+
 case "$1" in
 	start)
 		# Print a nicer messagen when unbound is already running
diff --git a/src/patches/unbound-allow-setting-validator-permissive-mode-at-runtime.patch b/src/patches/unbound-allow-setting-validator-permissive-mode-at-runtime.patch
new file mode 100644
index 0000000..f476d08
--- /dev/null
+++ b/src/patches/unbound-allow-setting-validator-permissive-mode-at-runtime.patch
@@ -0,0 +1,43 @@
+diff --git a/validator/validator.c b/validator/validator.c
+index 676dcdf..7c19f3d 100644
+--- a/validator/validator.c
++++ b/validator/validator.c
+@@ -113,7 +113,7 @@ val_apply_cfg(struct module_env* env, struct val_env* val_env,
+ 	int c;
+ 	val_env->bogus_ttl = (uint32_t)cfg->bogus_ttl;
+ 	val_env->clean_additional = cfg->val_clean_additional;
+-	val_env->permissive_mode = cfg->val_permissive_mode;
++	val_env->permissive_mode = &cfg->val_permissive_mode;
+ 	if(!env->anchors)
+ 		env->anchors = anchors_create();
+ 	if(!env->anchors) {
+@@ -170,7 +170,6 @@ val_init(struct module_env* env, int id)
+ 	}
+ 	env->modinfo[id] = (void*)val_env;
+ 	env->need_to_validate = 1;
+-	val_env->permissive_mode = 0;
+ 	lock_basic_init(&val_env->bogus_lock);
+ 	lock_protect(&val_env->bogus_lock, &val_env->num_rrset_bogus,
+ 		sizeof(val_env->num_rrset_bogus));
+@@ -2084,7 +2083,7 @@ processFinished(struct module_qstate* qstate, struct val_qstate* vq,
+ 			}
+ 		}
+ 		/* If we are in permissive mode, bogus gets indeterminate */
+-		if(ve->permissive_mode)
++		if(*ve->permissive_mode)
+ 			vq->orig_msg->rep->security = sec_status_indeterminate;
+ 	}
+ 
+diff --git a/validator/validator.h b/validator/validator.h
+index 23d3072..f8464b8 100644
+--- a/validator/validator.h
++++ b/validator/validator.h
+@@ -104,7 +104,7 @@ struct val_env {
+ 	 * This allows an operator to run validation 'shadow' without
+ 	 * hurting responses to clients.
+ 	 */
+-	int permissive_mode;
++	int* permissive_mode;
+ 
+ 	/**
+ 	 * Number of entries in the NSEC3 maximum iteration count table.
-- 
2.9.3