Fix CVE-2017-6891:

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-6891

Patch copied from upstream source repository:

https://git.savannah.gnu.org/cgit/libtasn1.git/commit/?id=5520704d075802df25ce4ffccc010ba1641bd484

From 5520704d075802df25ce4ffccc010ba1641bd484 Mon Sep 17 00:00:00 2001
From: Nikos Mavrogiannopoulos <nmav@redhat.com>
Date: Thu, 18 May 2017 18:03:34 +0200
Subject: [PATCH] asn1_find_node: added safety check on asn1_find_node()

This prevents a stack overflow in asn1_find_node() which
is triggered by too long variable names in the definitions
files. That means that applications have to deliberately
pass a too long 'name' constant to asn1_write_value()
and friends.  Reported by Jakub Jirasek.

Signed-off-by: Nikos Mavrogiannopoulos <nmav@redhat.com>
---
 lib/parser_aux.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/lib/parser_aux.c b/lib/parser_aux.c
index b4a7370..976ab38 100644
--- a/lib/parser_aux.c
+++ b/lib/parser_aux.c
@@ -120,6 +120,9 @@ asn1_find_node (asn1_node pointer, const char *name)
       if (n_end)
 	{
 	  nsize = n_end - n_start;
+	  if (nsize >= sizeof(n))
+		return NULL;
+
 	  memcpy (n, n_start, nsize);
 	  n[nsize] = 0;
 	  n_start = n_end;
@@ -158,6 +161,9 @@ asn1_find_node (asn1_node pointer, const char *name)
       if (n_end)
 	{
 	  nsize = n_end - n_start;
+	  if (nsize >= sizeof(n))
+		return NULL;
+
 	  memcpy (n, n_start, nsize);
 	  n[nsize] = 0;
 	  n_start = n_end;
-- 
2.13.0

