Merge pull request #815 from smallstep/herman/fix-empty-dns-init

Add check for empty DNS value in ca init

command/ca/init.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"crypto/rand"
 	"crypto/x509"
+	stderrors "errors"
 	"fmt"
 	"io"
 	"net"
@@ -823,8 +824,11 @@ func processDNSValue(dnsValue string) ([]string, error) {
 	)
 	dnsValue = strings.ReplaceAll(dnsValue, " ", ",")
 	parts := strings.Split(dnsValue, ",")
+	if allEmpty(parts) {
+		return nil, stderrors.New("dns must not be empty")
+	}
 	for _, name := range parts {
-		if name == "" {
+		if name == "" { // skip empty name
 			continue
 		}
 		if err := dnsValidator(name); err != nil {
@@ -845,3 +849,14 @@ func normalize(name string) string {
 	}
 	return name
 }
+
+// allEmpty loops through all strings in the slice and returns if
+// all are empty (length 0).
+func allEmpty(parts []string) bool {
+	for _, p := range parts {
+		if p != "" {
+			return false
+		}
+	}
+	return true
+}