Fix CVE-2018-6003:

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-6003
https://lists.gnu.org/archive/html/help-libtasn1/2018-01/msg00000.html

Patch copied from upstream source repository:

https://gitlab.com/gnutls/libtasn1/commit/c593ae84cfcde8fea45787e53950e0ac71e9ca97

From c593ae84cfcde8fea45787e53950e0ac71e9ca97 Mon Sep 17 00:00:00 2001
From: Nikos Mavrogiannopoulos <nmav@redhat.com>
Date: Thu, 4 Jan 2018 10:52:05 +0100
Subject: [PATCH] _asn1_decode_simple_ber: restrict the levels of recursion to 3

On indefinite string decoding, setting a maximum level of recursions
protects the BER decoder from a stack exhaustion due to large amounts
of recursion.

Signed-off-by: Nikos Mavrogiannopoulos <nmav@redhat.com>
---
 lib/decoding.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/lib/decoding.c b/lib/decoding.c
index 2240b09..0ee35d3 100644
--- a/lib/decoding.c
+++ b/lib/decoding.c
@@ -45,6 +45,13 @@
 
 #define DECODE_FLAG_HAVE_TAG 1
 #define DECODE_FLAG_INDEFINITE (1<<1)
+/* On indefinite string decoding, allow this maximum levels
+ * of recursion. Allowing infinite recursion, makes the BER
+ * decoder susceptible to stack exhaustion due to that recursion.
+ */
+#define DECODE_FLAG_LEVEL1 (1<<2)
+#define DECODE_FLAG_LEVEL2 (1<<3)
+#define DECODE_FLAG_LEVEL3 (1<<4)
 
 #define DECR_LEN(l, s) do { \
 	  l -= s; \
@@ -2216,7 +2223,8 @@ _asn1_decode_simple_ber (unsigned int etype, const unsigned char *der,
     }
 
   /* indefinite constructed */
-  if (((dflags & DECODE_FLAG_INDEFINITE) || class == ASN1_CLASS_STRUCTURED) && ETYPE_IS_STRING(etype))
+  if ((((dflags & DECODE_FLAG_INDEFINITE) || class == ASN1_CLASS_STRUCTURED) && ETYPE_IS_STRING(etype)) &&
+      !(dflags & DECODE_FLAG_LEVEL3))
     {
       len_len = 1;
 
@@ -2236,8 +2244,17 @@ _asn1_decode_simple_ber (unsigned int etype, const unsigned char *der,
       do
         {
           unsigned tmp_len;
+          unsigned flags = DECODE_FLAG_HAVE_TAG;
+
+          if (dflags & DECODE_FLAG_LEVEL1)
+                flags |= DECODE_FLAG_LEVEL2;
+          else if (dflags & DECODE_FLAG_LEVEL2)
+		flags |= DECODE_FLAG_LEVEL3;
+	  else
+		flags |= DECODE_FLAG_LEVEL1;
 
-          result = asn1_decode_simple_ber(etype, p, der_len, &out, &out_len, &tmp_len);
+          result = _asn1_decode_simple_ber(etype, p, der_len, &out, &out_len, &tmp_len,
+                                           flags);
           if (result != ASN1_SUCCESS)
             {
               warn();
--
libgit2 0.26.0

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