issue with octet string when tag is encoded to multiple bytes

[Tomas Petrilak]

hi,

I played with libtasn1 and observed issue when trying decode OCTET STRING
parameter with tag which is encoded to multiple bytes.
for example: parameter [200] IMPLICIT OCTET STRING

Problem seems to be in lib/decoding.c in function _asn1_get_octet_string
which assumes that tag is always only 1 byte.
Following change did fix it for me:

[root@s1 libtasn1-4.5]# diff -Naur lib/decoding.c.orig lib/decoding.c
--- lib/decoding.c.orig 2015-05-31 21:54:15.484839103 +0200
+++ lib/decoding.c      2015-05-31 22:02:18.941502144 +0200
@@ -777,7 +777,7 @@

 static int
 _asn1_get_octet_string (asn1_node node, const unsigned char *der, int
der_len,
-                        int *len, unsigned flags)
+                        int *len, unsigned flags, int tag_len)
 {
   int len2, len3, counter, tot_len, indefinite;
   int result;
@@ -785,7 +785,7 @@

   counter = 0;

-  if (*(der - 1) & ASN1_CLASS_STRUCTURED)
+  if (*(der - tag_len) & ASN1_CLASS_STRUCTURED)
     {
       tot_len = 0;

@@ -1262,7 +1262,7 @@
              move = RIGHT;
              break;
            case ASN1_ETYPE_OCTET_STRING:
-             result = _asn1_get_octet_string (p, der + counter, ider_len,
&len3, flags);
+             result = _asn1_get_octet_string (p, der + counter, ider_len,
&len3, flags, tag_len);
              if (result != ASN1_SUCCESS)
                {
                   warn();




Tomas