I just forward ported TTL.patch (attached) from patch-o-matic-20031103 to linux-2.6.0-test9 for fun and profit. It's rather mechanical port but it works at least build-in. I've veryfied this with tcpdump.
But I have two questions. First of course is: is this the proper way to port things like this, couse AFAIC 2.4 and 2.5 networking code is quite different, if not why. And second - where I can read about current implementation ot linux networking excetp kernel sources.
wwell Larry.
P.S please cc me, I'm not subscribet to the list.
diff -ruN linux-2.6.0-test9/include/linux/netfilter_ipv4/ipt_TTL.h linux-2.6.0-test9-my/include/linux/netfilter_ipv4/ipt_TTL.h
--- linux-2.6.0-test9/include/linux/netfilter_ipv4/ipt_TTL.h 1970-01-01 02:00:00.000000000 +0200
+++ linux-2.6.0-test9-my/include/linux/netfilter_ipv4/ipt_TTL.h 2003-11-04 11:31:22.000000000 +0200
@@ -0,0 +1,21 @@
+/* TTL modification module for IP tables
+ * (C) 2000 by Harald Welte <laforge@xxxxxxxxxxxx> */
+
+#ifndef _IPT_TTL_H
+#define _IPT_TTL_H
+
+enum {
+ IPT_TTL_SET = 0,
+ IPT_TTL_INC,
+ IPT_TTL_DEC
+};
+
+#define IPT_TTL_MAXMODE IPT_TTL_DEC
+
+struct ipt_TTL_info {
+ u_int8_t mode;
+ u_int8_t ttl;
+};
+
+
+#endif
diff -ruN linux-2.6.0-test9/net/ipv4/netfilter/Kconfig linux-2.6.0-test9-my/net/ipv4/netfilter/Kconfig
--- linux-2.6.0-test9/net/ipv4/netfilter/Kconfig 2003-10-25 21:44:33.000000000 +0300
+++ linux-2.6.0-test9-my/net/ipv4/netfilter/Kconfig 2003-11-04 14:32:09.000000000 +0200
@@ -478,6 +478,17 @@
To compile it as a module, choose M here. If unsure, say N.
+config IP_NF_TARGET_TTL
+ tristate "TTL target support"
+ depends on IP_NF_MANGLE
+ help
+ This option adds a `TTL' target, which enables the user to set
+ the TTL value or increment / decrement the TTL value by a given
+ amount.
+
+ If you want to compile it as a module, say M here and read
+ Documentation/modules.txt. If unsure, say `N'.
+
config IP_NF_TARGET_LOG
tristate "LOG target support"
depends on IP_NF_IPTABLES
diff -ruN linux-2.6.0-test9/net/ipv4/netfilter/Makefile linux-2.6.0-test9-my/net/ipv4/netfilter/Makefile
--- linux-2.6.0-test9/net/ipv4/netfilter/Makefile 2003-10-25 21:43:07.000000000 +0300
+++ linux-2.6.0-test9-my/net/ipv4/netfilter/Makefile 2003-11-04 11:29:22.000000000 +0200
@@ -78,6 +78,7 @@
obj-$(CONFIG_IP_NF_TARGET_SAME) += ipt_SAME.o
obj-$(CONFIG_IP_NF_TARGET_CLASSIFY) += ipt_CLASSIFY.o
obj-$(CONFIG_IP_NF_NAT_SNMP_BASIC) += ip_nat_snmp_basic.o
+obj-$(CONFIG_IP_NF_TARGET_TTL) += ipt_TTL.o
obj-$(CONFIG_IP_NF_TARGET_LOG) += ipt_LOG.o
obj-$(CONFIG_IP_NF_TARGET_ULOG) += ipt_ULOG.o
obj-$(CONFIG_IP_NF_TARGET_TCPMSS) += ipt_TCPMSS.o
diff -ruN linux-2.6.0-test9/net/ipv4/netfilter/ipt_TTL.c linux-2.6.0-test9-my/net/ipv4/netfilter/ipt_TTL.c
--- linux-2.6.0-test9/net/ipv4/netfilter/ipt_TTL.c 1970-01-01 02:00:00.000000000 +0200
+++ linux-2.6.0-test9-my/net/ipv4/netfilter/ipt_TTL.c 2003-11-04 13:00:00.000000000 +0200
@@ -0,0 +1,124 @@
+/* TTL modification target for IP tables
+ * (C) 2000 by Harald Welte <laforge@xxxxxxxxxxxx>
+ *
+ * Version: 1.8
+ *
+ * This software is distributed under the terms of GNU GPL
+ */
+
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/ip.h>
+#include <net/checksum.h>
+
+#include <linux/netfilter_ipv4/ip_tables.h>
+#include <linux/netfilter_ipv4/ipt_TTL.h>
+
+MODULE_AUTHOR("Harald Welte <laforge@xxxxxxxxxxxx>");
+MODULE_DESCRIPTION("IP tables TTL modification module");
+MODULE_LICENSE("GPL");
+
+static unsigned int
+ipt_ttl_target(struct sk_buff **pskb,
+ const struct net_device *in,
+ const struct net_device *out,
+ unsigned int hooknum,
+ const void *targinfo,
+ void *userinfo)
+{
+ struct iphdr *iph = (*pskb)->nh.iph;
+ const struct ipt_TTL_info *info = targinfo;
+ u_int16_t diffs[2];
+ int new_ttl;
+
+ switch (info->mode) {
+ case IPT_TTL_SET:
+ new_ttl = info->ttl;
+ break;
+ case IPT_TTL_INC:
+ new_ttl = iph->ttl + info->ttl;
+ if (new_ttl > 255)
+ new_ttl = 255;
+ break;
+ case IPT_TTL_DEC:
+ new_ttl = iph->ttl + info->ttl;
+ if (new_ttl < 0)
+ new_ttl = 0;
+ break;
+ default:
+ new_ttl = iph->ttl;
+ break;
+ }
+
+ if (new_ttl != iph->ttl) {
+ diffs[0] = htons(((unsigned)iph->ttl) << 8) ^ 0xFFFF;
+ iph->ttl = new_ttl;
+ diffs[1] = htons(((unsigned)iph->ttl) << 8);
+ iph->check = csum_fold(csum_partial((char *)diffs,
+ sizeof(diffs),
+ iph->check^0xFFFF));
+ (*pskb)->nfcache |= NFC_ALTERED;
+ }
+
+ return IPT_CONTINUE;
+}
+
+static int ipt_ttl_checkentry(const char *tablename,
+ const struct ipt_entry *e,
+ void *targinfo,
+ unsigned int targinfosize,
+ unsigned int hook_mask)
+{
+ struct ipt_TTL_info *info = targinfo;
+
+ if (targinfosize != IPT_ALIGN(sizeof(struct ipt_TTL_info))) {
+ printk(KERN_WARNING "TTL: targinfosize %u != %Zu\n",
+ targinfosize,
+ IPT_ALIGN(sizeof(struct ipt_TTL_info)));
+ return 0;
+ }
+
+ if (strcmp(tablename, "mangle")) {
+ printk(KERN_WARNING "TTL: can only be called from \"mangle\" table, not \"%s\"\n", tablename);
+ return 0;
+ }
+
+ if (info->mode > IPT_TTL_MAXMODE) {
+ printk(KERN_WARNING "TTL: invalid or unknown Mode %u\n",
+ info->mode);
+ return 0;
+ }
+
+ if ((info->mode != IPT_TTL_SET) && (info->ttl == 0)) {
+ printk(KERN_WARNING "TTL: increment/decrement doesn't make sense with value 0\n");
+ return 0;
+ }
+
+ return 1;
+}
+
+static struct ipt_target ipt_TTL_reg = {
+ .name = "TTL",
+ .target = ipt_ttl_target,
+ .checkentry = ipt_ttl_checkentry,
+ .me = THIS_MODULE,
+};
+
+static int __init init(void)
+{
+ if (ipt_register_target(&ipt_TTL_reg));
+ return -EINVAL;
+
+ return 0;
+}
+
+static void __exit fini(void)
+{
+ ipt_unregister_target(&ipt_TTL_reg);
+}
+
+module_init(init);
+module_exit(fini);
