netfilter: add CHECKSUM target

This adds a `CHECKSUM' target, which can be used in the iptables mangle table.

You can use this target to compute and fill in the checksum in a packet that lacks a checksum. This is particularly useful, if you need to work around old applications such as dhcp clients, that do not work well with checksum offloads, but don't want to disable checksum offload in your device.

The problem happens in the field with virtualized applications. For reference, see Red Hat bz 605555, as well as
http://www.spinics.net/lists/kvm/msg37660.html

Typical expected use (helps old dhclient binary running in a VM):

iptables -A POSTROUTING -t mangle -p udp --dport bootpc \
	-j CHECKSUM --checksum-fill

Includes fixes by Jan Engelhardt <[email protected]>
---

Changes from v3: fix issues pointed out by Patrick McHardy:
fixed by Jan Engelhardt
use __u8 in public header files
remove in.h
fixed by me
kill change that does not belong into this patch add a dependency on the mangle table

 include/linux/netfilter/xt_CHECKSUM.h |   18 ++++++++
 net/netfilter/Kconfig                 |   16 +++++++
 net/netfilter/Makefile                |    1 +
 net/netfilter/xt_CHECKSUM.c           |   70 +++++++++++++++++++++++++++++++++
 4 files changed, 105 insertions(+), 0 deletions(-)
 create mode 100644 include/linux/netfilter/xt_CHECKSUM.h
 create mode 100644 net/netfilter/xt_CHECKSUM.c

new file mode 100644
index 0000000..3b4fb77
@@ -0,0 +1,18 @@
+/* Header file for iptables ipt_CHECKSUM target
+ *
+ * (C) 2002 by Harald Welte <[email protected]>
+ * (C) 2010 Red Hat Inc
+ * Author: Michael S. Tsirkin <[email protected]>
+ *
+ * This software is distributed under GNU GPL v2, 1991
+*/
+#ifndef _IPT_CHECKSUM_TARGET_H
+#define _IPT_CHECKSUM_TARGET_H
+
+#define XT_CHECKSUM_OP_FILL	0x01	/* fill in checksum in IP header */
+
+struct xt_CHECKSUM_info {
+	__u8 operation;	/* bitset of operations */
+};
+
+#endif /* _IPT_CHECKSUM_TARGET_H */

index 8593a77..16b2078 100644
@@ -347,6 +347,22 @@ config NETFILTER_XT_CONNMARK
 
 comment "Xtables targets"
 
+config NETFILTER_XT_TARGET_CHECKSUM
+	tristate "CHECKSUM target support"
+	depends on IP_NF_MANGLE || IP6_NF_MANGLE
+	depends on NETFILTER_ADVANCED
+	---help---
+	  This option adds a `CHECKSUM' target, which can be used in the iptables mangle
+	  table.  
+
+	  You can use this target to compute and fill in the checksum in
+	  a packet that lacks a checksum.  This is particularly useful,
+	  if you need to work around old applications such as dhcp clients,
+	  that do not work well with checksum offloads, but don't want to disable
+	  checksum offload in your device.
+
+	  To compile it as a module, choose M here.  If unsure, say N.
+
 config NETFILTER_XT_TARGET_CLASSIFY
 	tristate '"CLASSIFY" target support'
 	depends on NETFILTER_ADVANCED

index 14e3a8f..8eb541d 100644
@@ -45,6 +45,7 @@ obj-$(CONFIG_NETFILTER_XT_MARK) += xt_mark.o
 obj-$(CONFIG_NETFILTER_XT_CONNMARK) += xt_connmark.o
 
 # targets
+obj-$(CONFIG_NETFILTER_XT_TARGET_CHECKSUM) += xt_CHECKSUM.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_CLASSIFY) += xt_CLASSIFY.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_CONNSECMARK) += xt_CONNSECMARK.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_CT) += xt_CT.o

1.7.2.rc0.14.g41c1c

Am 15.07.2010 13:52, schrieb Michael S. Tsirkin:

Applied, thanks Michael.

I forgot to export the header. And once I added it, I got warning on header_check, so here's a fixup. Sorry about the noise.

netfilter: correct CHECKSUM header and export it

--

index 48767cd..0c3098f 100644
@@ -3,6 +3,7 @@ header-y += nf_conntrack_tuple_common.h
 header-y += nfnetlink_conntrack.h
 header-y += nfnetlink_log.h
 header-y += nfnetlink_queue.h
+header-y += xt_CHECKSUM.h
 header-y += xt_CLASSIFY.h
 header-y += xt_CONNMARK.h
 header-y += xt_CONNSECMARK.h

index 3b4fb77..9a2e466 100644
@@ -6,8 +6,10 @@
  *
  * This software is distributed under GNU GPL v2, 1991
 */
-#ifndef _IPT_CHECKSUM_TARGET_H
-#define _IPT_CHECKSUM_TARGET_H
+#ifndef _XT_CHECKSUM_TARGET_H
+#define _XT_CHECKSUM_TARGET_H
+
+#include <linux/types.h>
 
 #define XT_CHECKSUM_OP_FILL	0x01	/* fill in checksum in IP header */
 

@@ -15,4 +17,4 @@ struct xt_CHECKSUM_info {
 	__u8 operation;	/* bitset of operations */
 };
 
-#endif /* _IPT_CHECKSUM_TARGET_H */
+#endif /* _XT_CHECKSUM_TARGET_H */

Am 15.07.2010 19:42, schrieb Michael S. Tsirkin:

Applied, thanks.