dns-domain: don't accept overly long hostnames

Make sure dns_name_normalize(), dns_name_concat(), dns_name_is_valid()
do not accept/generate invalidly long hostnames, i.e. longer than 253
characters.

2 files changed, 6 insertions, 0 deletions

diff --git a/src/shared/dns-domain.c b/src/shared/dns-domain.c
index 7a4093cc47..ab61eb3b6e 100644
--- a/src/shared/dns-domain.c
+++ b/src/shared/dns-domain.c
@@ -442,6 +442,9 @@ int dns_name_concat(const char *a, const char *b, char **_ret) {
                 n += r;
         }
 
+        if (n > DNS_HOSTNAME_MAX)
+                return -EINVAL;
+
         if (_ret) {
                 if (!GREEDY_REALLOC(ret, allocated, n + 1))
                         return -ENOMEM;
diff --git a/src/shared/dns-domain.h b/src/shared/dns-domain.h
index c68f1945e1..44a9975541 100644
--- a/src/shared/dns-domain.h
+++ b/src/shared/dns-domain.h
@@ -31,6 +31,9 @@
 /* Worst case length of a single label, with all escaping applied and room for a trailing NUL byte. */
 #define DNS_LABEL_ESCAPED_MAX (DNS_LABEL_MAX*4+1)
 
+/* Maximum length of a full hostname, consisting of a series of unescaped labels, and no trailing dot or NUL byte */
+#define DNS_HOSTNAME_MAX 253
+
 int dns_label_unescape(const char **name, char *dest, size_t sz);
 int dns_label_unescape_suffix(const char *name, const char **label_end, char *dest, size_t sz);
 int dns_label_escape(const char *p, size_t l, char *dest, size_t sz);