asn1_erl_nif.c: Correct handling of tags >= 16384

Tags number above 16383 were not decoded correctly in
ber_decode_tag().

We could fix the problem, but there does not seem to be any need.

First, the only way that high tag numbers can be created is with
manual tagging; after 1994 manual tagging is no longer recommended.

Second, the ASN.1 playground (http://asn1-playground.oss.com) only
supports tags up to 16383 (the same is presumably true for OSS
Nokalva's other tools).

Therefore, clean up the existing code and make it an explicit
'invalid_tag' error when tags above 13383 are encountered
(instead of an implicit 'wrong_tag' error).

1 files changed, 21 insertions, 17 deletions

diff --git a/lib/asn1/c_src/asn1_erl_nif.c b/lib/asn1/c_src/asn1_erl_nif.c
index b29c9a7ed3..7b7e11b02d 100644
--- a/lib/asn1/c_src/asn1_erl_nif.c
+++ b/lib/asn1/c_src/asn1_erl_nif.c
@@ -901,31 +901,35 @@ static int ber_decode_tag(ErlNifEnv* env, ERL_NIF_TERM *tag, unsigned char *in_b
 
     /* then get the tag number */
     if ((tmp_tag = (int) INVMASK(in_buf[*ib_index],ASN1_CLASSFORM)) < 31) {
-	*tag = enif_make_uint(env, tag_no + tmp_tag);
+	*tag = enif_make_uint(env, tag_no | tmp_tag);
 	(*ib_index)++;
     } else {
-	int n = 0; /* n is used to check that the 64K limit is not
-	 exceeded*/
-
 	/* should check that at least three bytes are left in
 	 in-buffer,at least two tag byte and at least one length byte */
 	if ((*ib_index + 3) > in_buf_len)
 	    return ASN1_VALUE_ERROR;
 	(*ib_index)++;
-	/* The tag is in the following bytes in in_buf as
-	 1ttttttt 1ttttttt ... 0ttttttt, where the t-bits
-	 is the tag number*/
-	/* In practice is the tag size limited to 64K, i.e. 16 bits. If
-	 the tag is greater then 64K return an error */
-	while (((tmp_tag = (int) in_buf[*ib_index]) >= 128) && n < 2) {
-	    /* m.s.b. = 1 */
-	    tag_no = tag_no + (MASK(tmp_tag,ASN1_LONG_TAG) << 7);
+	/*
+         * The tag is in the following bytes in in_buf as:
+         *
+         *  1ttttttt 0ttttttt
+         *
+         * or
+         *
+         *  0ttttttt
+         *
+         * where the t-bits is the tag number. If the tag does not
+         * fit in two tag bytes (16K), return an error.
+         */
+	if ((tmp_tag = (int) in_buf[*ib_index]) >= 128) {
+	    tag_no = tag_no | (MASK(tmp_tag,ASN1_LONG_TAG) << 7);
 	    (*ib_index)++;
-	    n++;
-	};
-	if ((n == 2) && in_buf[*ib_index] > 3)
-	    return ASN1_TAG_ERROR; /* tag number > 64K */
-	tag_no = tag_no + in_buf[*ib_index];
+	}
+        tmp_tag = (int) in_buf[*ib_index];
+	if (tmp_tag >= 128) {
+	    return ASN1_TAG_ERROR; /* tag number > 16K */
+        }
+	tag_no = tag_no | tmp_tag;
 	(*ib_index)++;
 	*tag = enif_make_uint(env, tag_no);
     }