Port gnutls.c to older (buggier?) GnuTLS

Problem reported for GnuTLS 3.2.1 by Glenn Morris in:
http://lists.gnu.org/archive/html/emacs-devel/2017-07/msg00716.html
http://lists.gnu.org/archive/html/emacs-devel/2017-07/msg00742.html
Although I don't see how this bug can occur with vanilla GnuTLS 3.2.1,
perhaps hydra was using a modified GnuTLS.
* src/gnutls.c (Fgnutls_ciphers): Don't assume GNUTLS_CIPHER_NULL
is at the end of the list returned by gnutls_cipher_list,
or that the earlier ciphers all have non-null names.

1 files changed, 7 insertions, 2 deletions

diff --git a/src/gnutls.c b/src/gnutls.c
index 9fbaea2f405..e406d665190 100644
--- a/src/gnutls.c
+++ b/src/gnutls.c
@@ -1854,12 +1854,17 @@ The alist key is the cipher name. */)
 
 #ifdef HAVE_GNUTLS3_CIPHER
   const gnutls_cipher_algorithm_t *gciphers = gnutls_cipher_list ();
-  for (ptrdiff_t pos = 0; gciphers[pos] != GNUTLS_CIPHER_NULL; pos++)
+  for (ptrdiff_t pos = 0; gciphers[pos] != 0; pos++)
     {
       gnutls_cipher_algorithm_t gca = gciphers[pos];
+      if (gca == GNUTLS_CIPHER_NULL)
+        continue;
+      char const *cipher_name = gnutls_cipher_get_name (gca);
+      if (!cipher_name)
+        continue;
 
       /* A symbol representing the GnuTLS cipher.  */
-      Lisp_Object cipher_symbol = intern (gnutls_cipher_get_name (gca));
+      Lisp_Object cipher_symbol = intern (cipher_name);
 
       ptrdiff_t cipher_tag_size = gnutls_cipher_get_tag_size (gca);