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diff -ur linux-5.9/net/ipv4/netfilter.org/Kconfig linux-5.9/net/ipv4/netfilter/Kconfig
--- linux-5.9/net/ipv4/netfilter.org/Kconfig 2020-10-11 23:15:50.000000000 +0200
+++ linux-5.9/net/ipv4/netfilter/Kconfig 2020-11-03 13:07:22.874511004 +0100
@@ -356,5 +356,15 @@
endif # IP_NF_ARPTABLES
+config IP_NF_TARGET_IPV4OPTSSTRIP
+ tristate 'IPV4OPTSSTRIP target support'
+ depends on IP_NF_MANGLE
+ help
+ This option adds an IPV4OPTSSTRIP target.
+ This target allows you to strip all IP options in a packet.
+
+ If you want to compile it as a module, say M here and read
+ Documentation/modules.txt. If unsure, say `N'.
+
endmenu
diff -ur linux-5.9/net/ipv4/netfilter.org/Makefile linux-5.9/net/ipv4/netfilter/Makefile
--- linux-5.9/net/ipv4/netfilter.org/Makefile 2020-10-11 23:15:50.000000000 +0200
+++ linux-5.9/net/ipv4/netfilter/Makefile 2020-11-03 13:07:22.874511004 +0100
@@ -48,5 +48,6 @@
# targets
obj-$(CONFIG_IP_NF_TARGET_ECN) += ipt_ECN.o
+obj-$(CONFIG_IP_NF_TARGET_IPV4OPTSSTRIP) += ipt_IPV4OPTSSTRIP.o
obj-$(CONFIG_IP_NF_TARGET_REJECT) += ipt_REJECT.o
obj-$(CONFIG_IP_NF_TARGET_SYNPROXY) += ipt_SYNPROXY.o
diff -NurpP --minimal linux-2.6.21.b/net/ipv4/netfilter/ipt_IPV4OPTSSTRIP.c linux-2.6.21.a/net/ipv4/netfilter/ipt_IPV4OPTSSTRIP.c
--- linux-2.6.21.b/net/ipv4/netfilter/ipt_IPV4OPTSSTRIP.c 1970-01-01 01:00:00.000000000 +0100
+++ linux-2.6.21.a/net/ipv4/netfilter/ipt_IPV4OPTSSTRIP.c 2007-05-30 11:18:08.000000000 +0200
@@ -0,0 +1,75 @@
+/**
+ * Strip all IP options in the IP packet header.
+ *
+ * (C) 2001 by Fabrice MARIE <fabrice@netfilter.org>
+ * This software is distributed under GNU GPL v2, 1991
+ */
+
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <net/ip.h>
+#include <net/checksum.h>
+#include <linux/netfilter/x_tables.h>
+#include <linux/netfilter_ipv4/ip_tables.h>
+
+MODULE_AUTHOR("Fabrice MARIE <fabrice@netfilter.org>");
+MODULE_DESCRIPTION("Strip all options in IPv4 packets");
+MODULE_LICENSE("GPL");
+
+static unsigned int
+target(struct sk_buff *skb, const struct xt_action_param *par)
+{
+ struct iphdr *iph;
+ struct ip_options *opt;
+ unsigned char *optiph;
+ int l;
+
+ if (skb_ensure_writable(skb, skb->len))
+ return NF_DROP;
+
+ iph = ip_hdr(skb);
+
+ /* if no options in packet then nothing to clear. */
+ if (iph->ihl * 4 == sizeof(struct iphdr))
+ return XT_CONTINUE;
+
+ /* else clear all options */
+ optiph = skb_network_header(skb);
+ l = ((struct ip_options *)(&(IPCB(skb)->opt)))->optlen;
+ memset(&(IPCB(skb)->opt), 0, sizeof(struct ip_options));
+ memset(optiph+sizeof(struct iphdr), IPOPT_NOOP, l);
+ opt = &(IPCB(skb)->opt);
+ opt->optlen = l;
+
+ return XT_CONTINUE;
+}
+
+static int
+checkentry(const struct xt_tgchk_param *par)
+{
+ if (strcmp(par->table, "mangle")) {
+ printk(KERN_WARNING "IPV4OPTSSTRIP: can only be called from \"mangle\" table, not \"%s\"\n", par->table);
+ return 0;
+ }
+ /* nothing else to check because no parameters */
+ return 1;
+}
+
+static struct xt_target ipt_ipv4optsstrip_reg = {
+ .name = "IPV4OPTSSTRIP",
+ .target = target,
+ .checkentry = checkentry,
+ .me = THIS_MODULE };
+
+static int __init init(void)
+{
+ return xt_register_target(&ipt_ipv4optsstrip_reg);
+}
+
+static void __exit fini(void)
+{
+ xt_unregister_target(&ipt_ipv4optsstrip_reg);
+}
+
+module_init(init);
+module_exit(fini);
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