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authorMichael S. Tsirkin <mst@redhat.com>2010-07-15 17:20:46 +0200
committerPatrick McHardy <kaber@trash.net>2010-07-15 17:20:46 +0200
commitedf0e1fb0d0910880881523cfaaabcec06a2c0d5 (patch)
tree9b113e0d86d8119a35b2af076a789b92fa341913 /net
parentfac42a9a922fe5eb87cac0b597010afb81e7ffe9 (diff)
downloadop-kernel-dev-edf0e1fb0d0910880881523cfaaabcec06a2c0d5.zip
op-kernel-dev-edf0e1fb0d0910880881523cfaaabcec06a2c0d5.tar.gz
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 <jengelh@medozas.de> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Patrick McHardy <kaber@trash.net>
Diffstat (limited to 'net')
-rw-r--r--net/netfilter/Kconfig16
-rw-r--r--net/netfilter/Makefile1
-rw-r--r--net/netfilter/xt_CHECKSUM.c70
3 files changed, 87 insertions, 0 deletions
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index aa2f106..5fb8efa 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -326,6 +326,22 @@ 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
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index e28420a..36ef8e6 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -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
diff --git a/net/netfilter/xt_CHECKSUM.c b/net/netfilter/xt_CHECKSUM.c
new file mode 100644
index 0000000..0f642ef
--- /dev/null
+++ b/net/netfilter/xt_CHECKSUM.c
@@ -0,0 +1,70 @@
+/* iptables module for the packet checksum mangling
+ *
+ * (C) 2002 by Harald Welte <laforge@netfilter.org>
+ * (C) 2010 Red Hat, Inc.
+ *
+ * Author: Michael S. Tsirkin <mst@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+*/
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+#include <linux/module.h>
+#include <linux/skbuff.h>
+
+#include <linux/netfilter/x_tables.h>
+#include <linux/netfilter/xt_CHECKSUM.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Michael S. Tsirkin <mst@redhat.com>");
+MODULE_DESCRIPTION("Xtables: checksum modification");
+MODULE_ALIAS("ipt_CHECKSUM");
+MODULE_ALIAS("ip6t_CHECKSUM");
+
+static unsigned int
+checksum_tg(struct sk_buff *skb, const struct xt_action_param *par)
+{
+ if (skb->ip_summed == CHECKSUM_PARTIAL)
+ skb_checksum_help(skb);
+
+ return XT_CONTINUE;
+}
+
+static int checksum_tg_check(const struct xt_tgchk_param *par)
+{
+ const struct xt_CHECKSUM_info *einfo = par->targinfo;
+
+ if (einfo->operation & ~XT_CHECKSUM_OP_FILL) {
+ pr_info("unsupported CHECKSUM operation %x\n", einfo->operation);
+ return -EINVAL;
+ }
+ if (!einfo->operation) {
+ pr_info("no CHECKSUM operation enabled\n");
+ return -EINVAL;
+ }
+ return 0;
+}
+
+static struct xt_target checksum_tg_reg __read_mostly = {
+ .name = "CHECKSUM",
+ .family = NFPROTO_UNSPEC,
+ .target = checksum_tg,
+ .targetsize = sizeof(struct xt_CHECKSUM_info),
+ .table = "mangle",
+ .checkentry = checksum_tg_check,
+ .me = THIS_MODULE,
+};
+
+static int __init checksum_tg_init(void)
+{
+ return xt_register_target(&checksum_tg_reg);
+}
+
+static void __exit checksum_tg_exit(void)
+{
+ xt_unregister_target(&checksum_tg_reg);
+}
+
+module_init(checksum_tg_init);
+module_exit(checksum_tg_exit);
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