From 38ba1ae58256dbc5619e8388824351b9d11047e8 Mon Sep 17 00:00:00 2001
From: Martin Mares <mj@ucw.cz>
Date: Mon, 17 Jun 2013 18:27:20 +0200
Subject: [PATCH] Added an option to accept broken checksums

This is needed for example when capturing on network interfaces
which make use of hardware checksum offloading.
---
 netgrind/ip.c       | 9 +++++++--
 netgrind/netgrind.c | 6 +++++-
 netgrind/netgrind.h | 1 +
 3 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/netgrind/ip.c b/netgrind/ip.c
index b021335..5280b9e 100644
--- a/netgrind/ip.c
+++ b/netgrind/ip.c
@@ -1,7 +1,7 @@
 /*
  *	Netgrind -- IP Layer Analyser
  *
- *	(c) 2003 Martin Mares <mj@ucw.cz>
+ *	(c) 2003--2013 Martin Mares <mj@ucw.cz>
  *
  *	This software may be freely distributed and used according to the terms
  *	of the GNU General Public License.
@@ -15,6 +15,8 @@
 #include <netinet/in.h>
 #include <netinet/ip.h>
 
+uns accept_broken_checksums;
+
 uns tcpip_calc_checksum(void *data, uns len, uns csum)
 {
   /* FIXME: This is awfully slow and it probably consumes most of our run time */
@@ -45,7 +47,10 @@ uns tcpip_calc_checksum(void *data, uns len, uns csum)
 
 uns tcpip_verify_checksum(uns csum)
 {
-  return (csum == 0xffff);
+  if (accept_broken_checksums)
+    return 1;
+  else
+    return (csum == 0xffff);
 }
 
 struct pkt_stats stat_ip_in, stat_ip_invalid, stat_ip_uninteresting, stat_ip_fragmented, stat_ip_badsum;
diff --git a/netgrind/netgrind.c b/netgrind/netgrind.c
index b3d1a3c..c20524d 100644
--- a/netgrind/netgrind.c
+++ b/netgrind/netgrind.c
@@ -117,6 +117,7 @@ static void usage(void)
   fprintf(stderr, "Usage: netgrind [<switches>] <capture-files>\n\
 \n\
 -a		TCP: Record arrival times instead of processing times\n\
+-b		Accept broken checksums\n\
 -c <count>	Stop after processing <count> packets\n\
 -d <dir>	Dump connections to a given directory\n\
 -D <dir>	Dump connections with more details\n\
@@ -142,12 +143,15 @@ int main(int argc, char **argv)
   byte *histogram = NULL;
 
   tcp_default_appl = &appl_mux;
-  while ((c = getopt(argc, argv, "ac:d:D:f:h:stwx:")) >= 0)
+  while ((c = getopt(argc, argv, "abc:d:D:f:h:stwx:")) >= 0)
     switch (c)
       {
       case 'a':
 	tcp_arrival_times = 1;
 	break;
+      case 'b':
+	accept_broken_checksums = 1;
+	break;
       case 'c':
 	max_packets = atol(optarg);
 	break;
diff --git a/netgrind/netgrind.h b/netgrind/netgrind.h
index a72fc3d..b32fe74 100644
--- a/netgrind/netgrind.h
+++ b/netgrind/netgrind.h
@@ -18,6 +18,7 @@ void link_eth_got_packet(struct pkt *p);
 /* ip.c */
 
 extern struct pkt_stats stat_ip_in, stat_ip_invalid, stat_ip_uninteresting, stat_ip_fragmented, stat_ip_badsum;
+extern uns accept_broken_checksums;
 
 uns tcpip_calc_checksum(void *data, uns len, uns csum);
 uns tcpip_verify_checksum(uns csum);
-- 
2.39.2