gnu: libtasn1: Fix CVE-2017-6891.

* gnu/packages/patches/libtasn1-CVE-2017-6891.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/tls.scm (libtasn1)[replacement]: New field.
(libtasn1/fixed): New variable.

gnu/local.mk

@@ -744,7 +744,8 @@ dist_patch_DATA =						\
   %D%/packages/patches/libsndfile-CVE-2017-8361-8363-8365.patch	\
   %D%/packages/patches/libsndfile-CVE-2017-8362.patch		\
   %D%/packages/patches/libssh2-fix-build-failure-with-gcrypt.patch	\
-  %D%/packages/patches/libtar-CVE-2013-4420.patch \
+  %D%/packages/patches/libtar-CVE-2013-4420.patch 		\
+  %D%/packages/patches/libtasn1-CVE-2017-6891.patch 		\
   %D%/packages/patches/libtheora-config-guess.patch		\
   %D%/packages/patches/libtiff-CVE-2016-10092.patch		\
   %D%/packages/patches/libtiff-CVE-2016-10093.patch		\

gnu/packages/patches/libtasn1-CVE-2017-6891.patch

@@ -0,0 +1,51 @@
+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
+

gnu/packages/tls.scm

@@ -52,6 +52,7 @@ (define-module (gnu packages tls)
 (define-public libtasn1
   (package
     (name "libtasn1")
+    (replacement libtasn1/fixed)
     (version "4.10")
     (source
      (origin
@@ -72,6 +73,15 @@ (define-public libtasn1
 specifications.")
     (license license:lgpl2.0+)))
 
+(define libtasn1/fixed
+  (package
+    (inherit libtasn1)
+    (source
+      (origin
+        (inherit (package-source libtasn1))
+        (patches
+          (search-patches "libtasn1-CVE-2017-6891.patch"))))))
+
 (define-public asn1c
   (package
     (name "asn1c")