rose: Add length checks to CALL_REQUEST parsing

Define some constant offsets for CALL_REQUEST based on the description
at <http://www.techfest.com/networking/wan/x25plp.htm> and the
definition of ROSE as using 10-digit (5-byte) addresses.  Use them
consistently.  Validate all implicit and explicit facilities lengths.
Validate the address length byte rather than either trusting or
assuming its value.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
char *rose2asc(char *buf, const rose_address *addr)
{
	if (addr->rose_addr[0] == 0x00 && addr->rose_addr[1] == 0x00 &&
	    addr->rose_addr[2] == 0x00 && addr->rose_addr[3] == 0x00 &&
	    addr->rose_addr[4] == 0x00) {
		strcpy(buf, "*");
	} else {
		sprintf(buf, "%02X%02X%02X%02X%02X", addr->rose_addr[0] & 0xFF,
						addr->rose_addr[1] & 0xFF,
						addr->rose_addr[2] & 0xFF,
						addr->rose_addr[3] & 0xFF,
						addr->rose_addr[4] & 0xFF);
	}

	return buf;
}

char *rose2asc(char *buf, const rose_address *addr)
{
	if (addr->rose_addr[0] == 0x00 && addr->rose_addr[1] == 0x00 &&
	    addr->rose_addr[2] == 0x00 && addr->rose_addr[3] == 0x00 &&
	    addr->rose_addr[4] == 0x00) {
		strcpy(buf, "*");
	} else {
		sprintf(buf, "%02X%02X%02X%02X%02X", addr->rose_addr[0] & 0xFF,
						addr->rose_addr[1] & 0xFF,
						addr->rose_addr[2] & 0xFF,
						addr->rose_addr[3] & 0xFF,
						addr->rose_addr[4] & 0xFF);
	}

	return buf;
}
