Empty SNI names are not valid

While empty inputs to SSL_set1_host() clear the reference identifier
list.

Reviewed-by: Rich Salz <rsalz@openssl.org>

crypto/x509/x509_vpm.c

diff --git a/crypto/x509/x509_vpm.c b/crypto/x509/x509_vpm.c
index 827360d..8826fec 100644
--- a/crypto/x509/x509_vpm.c
+++ b/crypto/x509/x509_vpm.c
@@ -92,11 +92,11 @@
      * Refuse names with embedded NUL bytes, except perhaps as final byte.
      * XXX: Do we need to push an error onto the error stack?
      */
-    if (namelen == 0)
+    if (namelen == 0 || name == NULL)
         namelen = name ? strlen(name) : 0;
     else if (name && memchr(name, '\0', namelen > 1 ? namelen - 1 : namelen))
         return 0;
-    if (name && name[namelen - 1] == '\0')
+    if (namelen > 0 && name[namelen - 1] == '\0')
         --namelen;
 
     if (mode == SET_HOST) {

ssl/s3_lib.c

diff --git a/ssl/s3_lib.c b/ssl/s3_lib.c
index de8dae2..54b8eba 100644
--- a/ssl/s3_lib.c
+++ b/ssl/s3_lib.c
@@ -3534,13 +3534,16 @@
 #endif                          /* !OPENSSL_NO_EC */
     case SSL_CTRL_SET_TLSEXT_HOSTNAME:
         if (larg == TLSEXT_NAMETYPE_host_name) {
+            size_t len;
+
             OPENSSL_free(s->tlsext_hostname);
             s->tlsext_hostname = NULL;
 
             ret = 1;
             if (parg == NULL)
                 break;
-            if (strlen((char *)parg) > TLSEXT_MAXLEN_host_name) {
+            len = strlen((char *)parg);
+            if (len == 0 || len > TLSEXT_MAXLEN_host_name) {
                 SSLerr(SSL_F_SSL3_CTRL, SSL_R_SSL3_EXT_INVALID_SERVERNAME);
                 return 0;
             }