Use the ASN1_LONG_TAG and ASN1_INDEFINITE_LENGTH constants in the ASN.1
general decoder instead of the equivalent numbers.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>

Fix an error in asn1_find_indefinite_length() whereby small definite length
elements of size 0x7f are incorrecly classified as non-small.  Without this
fix, an error will be given as the length of the length will be perceived as
being very much greater than the maximum supported size.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>

asn1_find_indefinite_length() returns an error indicator of -1, which the
caller asn1_ber_decoder() places in a size_t (which is usually unsigned) and
then checks to see whether it is less than 0 (which it can't be).  This can
lead to the following warning:

	lib/asn1_decoder.c:320 asn1_ber_decoder()
		warn: unsigned 'len' is never less than zero.

Instead, asn1_find_indefinite_length() update the caller's idea of the data
cursor and length separately from returning the error code.
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>

Add an ASN.1 BER/DER/CER decoder.  This uses the bytecode from the ASN.1
compiler in the previous patch to inform it as to what to expect to find in the
encoded byte stream.  The output from the compiler also tells it what functions
to call on what tags, thus allowing the caller to retrieve information.

The decoder is called as follows:

	int asn1_decoder(const struct asn1_decoder *decoder,
			 void *context,
			 const unsigned char *data,
			 size_t datalen);

The decoder argument points to the bytecode from the ASN.1 compiler.  context
is the caller's context and is passed to the action functions.  data and
datalen define the byte stream to be decoded.

Note that the decoder is currently limited to datalen being less than 64K.
This reduces the amount of stack space used by the decoder because ASN.1 is a
nested construct.  Similarly, the decoder is limited to a maximum of 10 levels
of constructed data outside of a leaf node also in an effort to keep stack
usage down.

These restrictions can be raised if necessary.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>