dns-domain: enforce maximum DNS domain name length

src/resolve/resolved-dns-domain.c

@@ -203,6 +203,9 @@ int dns_name_normalize(const char *s, char **_ret) {
                 n += r;
         }
 
+        if (n > DNS_NAME_MAX)
+                return -EINVAL;
+
         if (!GREEDY_REALLOC(ret, allocated, n + 1))
                 return -ENOMEM;
 

src/resolve/resolved-dns-domain.h

@@ -25,6 +25,7 @@
 #include "in-addr-util.h"
 
 #define DNS_LABEL_MAX 63
+#define DNS_NAME_MAX 255
 
 int dns_label_unescape(const char **name, char *dest, size_t sz);
 int dns_label_escape(const char *p, size_t l, char **ret);