diff --git a/tools/testing/selftests/net/lib.sh b/tools/testing/selftests/net/lib.sh
index 2c371e321ee6..a186490edb4a 100644
--- a/tools/testing/selftests/net/lib.sh
+++ b/tools/testing/selftests/net/lib.sh
@@ -10,7 +10,7 @@ BUSYWAIT_TIMEOUT=$((WAIT_TIMEOUT * 1000)) # ms
 # Kselftest framework requirement - SKIP code is 4.
 ksft_skip=4
 # namespace list created by setup_ns
-NS_LIST=""
+NS_LIST=()
 
 ##############################################################################
 # Helpers
@@ -48,6 +48,7 @@ cleanup_ns()
 	fi
 
 	for ns in "$@"; do
+		[ -z "${ns}" ] && continue
 		ip netns delete "${ns}" &> /dev/null
 		if ! busywait $BUSYWAIT_TIMEOUT ip netns list \| grep -vq "^$ns$" &> /dev/null; then
 			echo "Warn: Failed to remove namespace $ns"
@@ -61,7 +62,7 @@ cleanup_ns()
 
 cleanup_all_ns()
 {
-	cleanup_ns $NS_LIST
+	cleanup_ns "${NS_LIST[@]}"
 }
 
 # setup netns with given names as prefix. e.g
@@ -70,7 +71,7 @@ setup_ns()
 {
 	local ns=""
 	local ns_name=""
-	local ns_list=""
+	local ns_list=()
 	local ns_exist=
 	for ns_name in "$@"; do
 		# Some test may setup/remove same netns multi times
@@ -86,11 +87,11 @@ setup_ns()
 
 		if ! ip netns add "$ns"; then
 			echo "Failed to create namespace $ns_name"
-			cleanup_ns "$ns_list"
+			cleanup_ns "${ns_list[@]}"
 			return $ksft_skip
 		fi
 		ip -n "$ns" link set lo up
-		! $ns_exist && ns_list="$ns_list $ns"
+		! $ns_exist && ns_list+=("$ns")
 	done
-	NS_LIST="$NS_LIST $ns_list"
+	NS_LIST+=("${ns_list[@]}")
 }