RFC2181 section 11 says a DNS label can be pretty much anything.

So just test overall length and label length.

Thanks to Robert Elz.

1 files changed, 2 insertions, 7 deletions

diff --git a/hooks/dhcpcd-run-hooks.in b/hooks/dhcpcd-run-hooks.in
index 076ffb2b..6c37bde6 100644
--- a/hooks/dhcpcd-run-hooks.in
+++ b/hooks/dhcpcd-run-hooks.in
@@ -198,8 +198,7 @@ syslog()
 	fi
 }
 
-# Check for a valid domain name as per RFC1123 with the exception of
-# allowing - and _ as they seem to be widely used.
+# Check for a valid domain name as per RFC2181 section 11
 valid_domainname()
 {
 	local name="$1" label
@@ -209,11 +208,7 @@ valid_domainname()
 	while [ -n "$name" ]; do
 		label="${name%%.*}"
 		[ -z "$label" -o ${#label} -gt 63 ] && return 1
-		case "$label" in
-		-*|_*|*-|*_)		return 1;;
-		*[![:alnum:]_-]*)	return 1;;
-		"$name")		return 0;;
-		esac
+		[ "$label" = "$name" ] && return 0
 		name="${name#*.}"
 	done
 	return 0