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:

address@hidden 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