RA: expire RDNSS and DNSSL entries

This allows us to remember N fully expired RA's which works around
an obscure issue where a received RA has no lifetime or any
prefixes with lifetimes but does have an instruction to start DHCP6.

It was harmless but filled the log with spam and now there is no
log spam!

1 files changed, 18 insertions, 18 deletions

diff --git a/hooks/20-resolv.conf b/hooks/20-resolv.conf
index 61c75e82..cf323749 100644
--- a/hooks/20-resolv.conf
+++ b/hooks/20-resolv.conf
@@ -69,30 +69,26 @@ build_resolv_conf()
 }
 
 # Extract any ND DNS options from the RA
-# For now, we ignore the lifetime of the DNS options unless they
-# are absent or zero.
-# In this case they are removed from consideration.
-# See draft-gont-6man-slaac-dns-config-issues-01 for issues
-# regarding DNS option lifetime in ND messages.
+# Obey the lifetimes
 eval_nd_dns()
 {
-	eval ltime=\$nd${i}_rdnss${j}_lifetime
-	if [ -z "$ltime" ] || [ "$ltime" = 0 ]; then
-		rdnss=
-	else
+
+	eval rdnsstime=\$nd${i}_rdnss${j}_lifetime
+	[ -z "$rdnsstime" ] && return 1
+	ltime=$(($rdnsstime - $offset))
+	if [ "$ltime" -gt 0 ]; then
 		eval rdnss=\$nd${i}_rdnss${j}_servers
+		[ -n "$rdnss" ] && new_rdnss="$new_rdnss${new_rdnss:+ }$rdnss"
 	fi
-	eval ltime=\$nd${i}_dnssl${j}_lifetime
-	if [ -z "$ltime" ] || [ "$ltime" = 0 ]; then
-		dnssl=
-	else
+
+	eval dnssltime=\$nd${i}_dnssl${j}_lifetime
+	[ -z "$dnssltime" ] && return 1
+	ltime=$(($dnssltime - $offset))
+	if [ "$ltime" -gt 0 ]; then
 		eval dnssl=\$nd${i}_dnssl${j}_search
+		[ -n "$dnssl" ] && new_dnssl="$new_dnssl${new_dnssl:+ }$dnssl"
 	fi
 
-	[ -z "${rdnss}${dnssl}" ] && return 1
-
-	[ -n "$rdnss" ] && new_rdnss="$new_rdnss${new_rdnss:+ }$rdnss"
-	[ -n "$dnssl" ] && new_dnssl="$new_dnssl${new_dnssl:+ }$dnssl"
 	j=$(($j + 1))
 	return 0
 }
@@ -106,12 +102,16 @@ add_resolv_conf()
 	i=1
 	j=1
 	while true; do
+		eval acquired=\$nd${i}_acquired
+		[ -z "$acquired" ] && break
+		eval now=\$nd${i}_now
+		[ -z "$now" ] && break
+		offset=$(($now - $acquired))
 		while true; do
 			eval_nd_dns || break
 		done
 		i=$(($i + 1))
 		j=1
-		eval_nd_dns || break
 	done
 	[ -n "$new_rdnss" ] && \
 	    new_domain_name_servers="$new_domain_name_servers${new_domain_name_servers:+ }$new_rdnss"