--- pptpd-1.3.4-orig/pptpgre.c	2007-04-16 02:21:02.000000000 +0200
+++ pptpd-1.3.4/pptpgre.c	2007-11-13 17:31:54.000000000 +0100
@@ -355,14 +355,49 @@
 	header = (struct pptp_gre_header *) (buffer + ip_len);
 
 	/* verify packet (else discard) */
-	if (((ntoh8(header->ver) & 0x7F) != PPTP_GRE_VER) ||	/* version should be 1   */
-	    (ntoh16(header->protocol) != PPTP_GRE_PROTO) ||	/* GRE protocol for PPTP */
-	    PPTP_GRE_IS_C(ntoh8(header->flags)) ||	/* flag C should be clear   */
-	    PPTP_GRE_IS_R(ntoh8(header->flags)) ||	/* flag R should be clear   */
-	    (!PPTP_GRE_IS_K(ntoh8(header->flags))) ||	/* flag K should be set     */
-	    ((ntoh8(header->flags) & 0xF) != 0)) {	/* routing and recursion ctrl = 0  */
+	if ( (ntoh8(header->ver) & 0x7F) != PPTP_GRE_VER )  {
+		/* version should be 1   */
 		/* if invalid, discard this packet */
-		syslog(LOG_ERR, "GRE: Discarding packet by header check");
+		syslog(LOG_ERR, "GRE: Discarding packet by header check. version should be 1. = %hhx ",(ntoh8(header->ver) & 0x7F));
+		stats.rx_invalid++;
+		return 0;
+	}
+	
+	if (ntoh16(header->protocol) != PPTP_GRE_PROTO)  {
+ 		/* GRE protocol for PPTP */
+		/* if invalid, discard this packet */
+		syslog(LOG_ERR, "GRE: Discarding packet by header check. not GRE protocol for PPTP ");
+		stats.rx_invalid++;
+		return 0;
+	}
+	if (    PPTP_GRE_IS_C(ntoh8(header->flags)) ) {  
+		/* flag C should be clear   */
+		/* if invalid, discard this packet */
+		syslog(LOG_ERR, "GRE: Discarding packet by header check.  flag C should be clear");
+		stats.rx_invalid++;
+		return 0;
+
+	}
+	if (PPTP_GRE_IS_R(ntoh8(header->flags))	) {
+		/* flag R should be clear   */
+		/* if invalid, discard this packet */
+		syslog(LOG_ERR, "GRE: Discarding packet by header check.  flag R should be clear");
+		stats.rx_invalid++;
+		return 0;
+	}
+	
+	if    (!PPTP_GRE_IS_K(ntoh8(header->flags))) {
+		/* flag K should be set     */
+		/* if invalid, discard this packet */
+		syslog(LOG_ERR, "GRE: Discarding packet by header check. flag K should be set");
+		stats.rx_invalid++;
+		return 0;		
+	}
+
+	if   ((ntoh8(header->flags) & 0xF) != 0) {
+		/* routing and recursion ctrl = 0  */
+		/* if invalid, discard this packet */
+		syslog(LOG_ERR, "GRE: Discarding packet by header check. routing and recursion ctrl = 0 ");
 		stats.rx_invalid++;
 		return 0;
 	}