netfilter: Combine ipt_TTL and ip6t_HL source

Suggested by: James King <t.james.king@gmail.com>

Similarly to commit c9fd49680954714473d6cbd2546d6ff120f96840, merge
TTL and HL. Since HL does not depend on any IPv6-specific function,
no new module dependencies would arise.

With slight adjustments to the Kconfig help text.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>

3 files changed, 187 insertions, 0 deletions

diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index c2bac9cd0ca..d99f29b7b98 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -357,6 +357,21 @@ config NETFILTER_XT_TARGET_DSCP
 
 	  To compile it as a module, choose M here.  If unsure, say N.
 
+config NETFILTER_XT_TARGET_HL
+	tristate '"HL" hoplimit target support'
+	depends on IP_NF_MANGLE || IP6_NF_MANGLE
+	depends on NETFILTER_ADVANCED
+	---help---
+	This option adds the "HL" (for IPv6) and "TTL" (for IPv4)
+	targets, which enable the user to change the
+	hoplimit/time-to-live value of the IP header.
+
+	While it is safe to decrement the hoplimit/TTL value, the
+	modules also allow to increment and set the hoplimit value of
+	the header to arbitrary values. This is EXTREMELY DANGEROUS
+	since you can easily create immortal packets that loop
+	forever on the network.
+
 config NETFILTER_XT_TARGET_MARK
 	tristate '"MARK" target support'
 	default m if NETFILTER_ADVANCED=n
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index da3d909e053..6ebe0482265 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -45,6 +45,7 @@ obj-$(CONFIG_NETFILTER_XT_TARGET_CLASSIFY) += xt_CLASSIFY.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_CONNMARK) += xt_CONNMARK.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_CONNSECMARK) += xt_CONNSECMARK.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_DSCP) += xt_DSCP.o
+obj-$(CONFIG_NETFILTER_XT_TARGET_HL) += xt_HL.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_MARK) += xt_MARK.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_NFLOG) += xt_NFLOG.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_NFQUEUE) += xt_NFQUEUE.o
diff --git a/net/netfilter/xt_HL.c b/net/netfilter/xt_HL.c
new file mode 100644
index 00000000000..10e789e2d12
--- /dev/null
+++ b/net/netfilter/xt_HL.c
@@ -0,0 +1,171 @@
+/*
+ * TTL modification target for IP tables
+ * (C) 2000,2005 by Harald Welte <laforge@netfilter.org>
+ *
+ * Hop Limit modification target for ip6tables
+ * Maciej Soltysiak <solt@dns.toxicfilms.tv>
+ *
+ * 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.
+ */
+
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/ip.h>
+#include <linux/ipv6.h>
+#include <net/checksum.h>
+
+#include <linux/netfilter/x_tables.h>
+#include <linux/netfilter_ipv4/ipt_TTL.h>
+#include <linux/netfilter_ipv6/ip6t_HL.h>
+
+MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
+MODULE_AUTHOR("Maciej Soltysiak <solt@dns.toxicfilms.tv>");
+MODULE_DESCRIPTION("Xtables: Hoplimit/TTL Limit field modification target");
+MODULE_LICENSE("GPL");
+
+static unsigned int
+ttl_tg(struct sk_buff *skb, const struct xt_target_param *par)
+{
+	struct iphdr *iph;
+	const struct ipt_TTL_info *info = par->targinfo;
+	int new_ttl;
+
+	if (!skb_make_writable(skb, skb->len))
+		return NF_DROP;
+
+	iph = ip_hdr(skb);
+
+	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) {
+		csum_replace2(&iph->check, htons(iph->ttl << 8),
+					   htons(new_ttl << 8));
+		iph->ttl = new_ttl;
+	}
+
+	return XT_CONTINUE;
+}
+
+static unsigned int
+hl_tg6(struct sk_buff *skb, const struct xt_target_param *par)
+{
+	struct ipv6hdr *ip6h;
+	const struct ip6t_HL_info *info = par->targinfo;
+	int new_hl;
+
+	if (!skb_make_writable(skb, skb->len))
+		return NF_DROP;
+
+	ip6h = ipv6_hdr(skb);
+
+	switch (info->mode) {
+		case IP6T_HL_SET:
+			new_hl = info->hop_limit;
+			break;
+		case IP6T_HL_INC:
+			new_hl = ip6h->hop_limit + info->hop_limit;
+			if (new_hl > 255)
+				new_hl = 255;
+			break;
+		case IP6T_HL_DEC:
+			new_hl = ip6h->hop_limit - info->hop_limit;
+			if (new_hl < 0)
+				new_hl = 0;
+			break;
+		default:
+			new_hl = ip6h->hop_limit;
+			break;
+	}
+
+	ip6h->hop_limit = new_hl;
+
+	return XT_CONTINUE;
+}
+
+static bool ttl_tg_check(const struct xt_tgchk_param *par)
+{
+	const struct ipt_TTL_info *info = par->targinfo;
+
+	if (info->mode > IPT_TTL_MAXMODE) {
+		printk(KERN_WARNING "ipt_TTL: invalid or unknown Mode %u\n",
+			info->mode);
+		return false;
+	}
+	if (info->mode != IPT_TTL_SET && info->ttl == 0)
+		return false;
+	return true;
+}
+
+static bool hl_tg6_check(const struct xt_tgchk_param *par)
+{
+	const struct ip6t_HL_info *info = par->targinfo;
+
+	if (info->mode > IP6T_HL_MAXMODE) {
+		printk(KERN_WARNING "ip6t_HL: invalid or unknown Mode %u\n",
+			info->mode);
+		return false;
+	}
+	if (info->mode != IP6T_HL_SET && info->hop_limit == 0) {
+		printk(KERN_WARNING "ip6t_HL: increment/decrement doesn't "
+			"make sense with value 0\n");
+		return false;
+	}
+	return true;
+}
+
+static struct xt_target hl_tg_reg[] __read_mostly = {
+	{
+		.name       = "TTL",
+		.revision   = 0,
+		.family     = NFPROTO_IPV4,
+		.target     = ttl_tg,
+		.targetsize = sizeof(struct ipt_TTL_info),
+		.table      = "mangle",
+		.checkentry = ttl_tg_check,
+		.me         = THIS_MODULE,
+	},
+	{
+		.name       = "HL",
+		.revision   = 0,
+		.family     = NFPROTO_IPV6,
+		.target     = hl_tg6,
+		.targetsize = sizeof(struct ip6t_HL_info),
+		.table      = "mangle",
+		.checkentry = hl_tg6_check,
+		.me         = THIS_MODULE,
+	},
+};
+
+static int __init hl_tg_init(void)
+{
+	return xt_register_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg));
+}
+
+static void __exit hl_tg_exit(void)
+{
+	xt_unregister_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg));
+}
+
+module_init(hl_tg_init);
+module_exit(hl_tg_exit);
+MODULE_ALIAS("ipt_TTL");
+MODULE_ALIAS("ip6t_HL");