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
Signed-off-by: Michael S. Tsirkin <[email protected]>
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
diff --git a/include/linux/netfilter/xt_CHECKSUM.h b/include/linux/netfilter/xt_CHECKSUM.h
new file mode 100644
index 0000000..3b4fb77
--- /dev/null
+++ b/include/linux/netfilter/xt_CHECKSUM.h
@@ -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 */
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index 8593a77..16b2078 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -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
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index 14e3a8f..8eb541d 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 <[email protected]>
+ * (C) 2010 Red Hat, Inc.
+ *
+ * Author: Michael S. Tsirkin <[email protected]>
+ *
+ * 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 <[email protected]>");
+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);
--
1.7.2.rc0.14.g41c1c
Am 15.07.2010 13:52, schrieb Michael S. Tsirkin:
> 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
>
> Signed-off-by: Michael S. Tsirkin <[email protected]>
> Includes fixes by Jan Engelhardt <[email protected]>
Applied, thanks Michael.
On Thu, Jul 15, 2010 at 05:22:10PM +0200, Patrick McHardy wrote:
> Am 15.07.2010 13:52, schrieb Michael S. Tsirkin:
> > 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
> >
> > Signed-off-by: Michael S. Tsirkin <[email protected]>
> > Includes fixes by Jan Engelhardt <[email protected]>
>
> 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
Signed-off-by: Michael S. Tsirkin <[email protected]>
--
diff --git a/include/linux/netfilter/Kbuild b/include/linux/netfilter/Kbuild
index 48767cd..0c3098f 100644
--- a/include/linux/netfilter/Kbuild
+++ b/include/linux/netfilter/Kbuild
@@ -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
diff --git a/include/linux/netfilter/xt_CHECKSUM.h b/include/linux/netfilter/xt_CHECKSUM.h
index 3b4fb77..9a2e466 100644
--- a/include/linux/netfilter/xt_CHECKSUM.h
+++ b/include/linux/netfilter/xt_CHECKSUM.h
@@ -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:
> netfilter: correct CHECKSUM header and export it
>
> Signed-off-by: Michael S. Tsirkin <[email protected]>
Applied, thanks.