libopenarc: Check length of header field name more tightly.

From the restriction of RFC5322 section 2.1.1 and section 2.2,
length of email header field name cannot be more than 997.

With this commit, we define a constant macro for it, and then
apply this restriction on parsing header field. Also, reduce
size of a buffer for copying header field name.

* libopenarc/arc.h (ARC_MAXLINELEN, ARC_MAXHDRNAMELEN): New macros.
* libopenarc/arc.c (arc_parse_header_field, ar_eoh):
  Use ARC_MAXHDRNAMELEN as maximum length of header field names.

trusteddomainproject/OpenARC#179

libopenarc/arc.c

@@ -2466,7 +2466,7 @@ arc_parse_header_field(ARC_MESSAGE *msg, u_char *hdr, size_t hlen,
 		end--;
 
 	/* don't allow incredibly large field names */
-	if (end - hdr > ARC_MAXHEADER)
+	if (end - hdr > ARC_MAXHDRNAMELEN)
 		return ARC_STAT_SYNTAX;
 
 	/* don't allow a field name containing a semicolon */
@@ -2816,8 +2816,8 @@ arc_eoh(ARC_MESSAGE *msg)
 
 	for (h = msg->arc_hhead; h != NULL; h = h->hdr_next)
 	{
-		char hnbuf[ARC_MAXHEADER + 1];
-		assert(h->hdr_namelen <= ARC_MAXHEADER);
+		char hnbuf[ARC_MAXHDRNAMELEN + 1];
+		assert(h->hdr_namelen <= ARC_MAXHDRNAMELEN);
 
 		memset(hnbuf, '\0', sizeof hnbuf);
 		strncpy(hnbuf, h->hdr_text, h->hdr_namelen);

libopenarc/arc.h

@@ -46,6 +46,8 @@ extern "C" {
 #define ARC_HDRMARGIN		75	/* "standard" header margin */
 #define ARC_MAXHEADER		4096	/* buffer for caching one header */
 #define	ARC_MAXHOSTNAMELEN	256	/* max. FQDN we support */
+#define ARC_MAXLINELEN		1000	/* physical line limit (RFC5321) */
+#define ARC_MAXHDRNAMELEN	(ARC_MAXLINELEN - 3) /* deduct ":" CRLF */
 
 #define	ARC_AR_HDRNAME		"ARC-Authentication-Results"
 #define	ARC_DEFAULT_MINKEYSIZE	1024