[NETFILTER6]: Add new ip6tables HOPLIMIT target

This target allows users to modify the hoplimit header field of the
IPv6 header.

Signed-off-by: Harald Welte <laforge@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 118 insertions, 0 deletions

diff --git a/net/ipv6/netfilter/ip6t_HL.c b/net/ipv6/netfilter/ip6t_HL.c
new file mode 100644
index 000000000000..8f5549b72720
--- /dev/null
+++ b/net/ipv6/netfilter/ip6t_HL.c
@@ -0,0 +1,118 @@
+/* 
+ * Hop Limit modification target for ip6tables
+ * Maciej Soltysiak <solt@dns.toxicfilms.tv>
+ * Based on HW's TTL module
+ *
+ * This software is distributed under the terms of GNU GPL
+ */
+
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/ip.h>
+
+#include <linux/netfilter_ipv6/ip6_tables.h>
+#include <linux/netfilter_ipv6/ip6t_HL.h>
+
+MODULE_AUTHOR("Maciej Soltysiak <solt@dns.toxicfilms.tv>");
+MODULE_DESCRIPTION("IP tables Hop Limit modification module");
+MODULE_LICENSE("GPL");
+
+static unsigned int ip6t_hl_target(struct sk_buff **pskb, 
+				   const struct net_device *in,
+				   const struct net_device *out,
+				   unsigned int hooknum,
+				   const void *targinfo, void *userinfo)
+{
+	struct ipv6hdr *ip6h;
+	const struct ip6t_HL_info *info = targinfo;
+	u_int16_t diffs[2];
+	int new_hl;
+
+	if (!skb_make_writable(pskb, (*pskb)->len))
+		return NF_DROP;
+
+	ip6h = (*pskb)->nh.ipv6h;
+
+	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;
+	}
+
+	if (new_hl != ip6h->hop_limit) {
+		diffs[0] = htons(((unsigned)ip6h->hop_limit) << 8) ^ 0xFFFF;
+		ip6h->hop_limit = new_hl;
+		diffs[1] = htons(((unsigned)ip6h->hop_limit) << 8);
+	}
+
+	return IP6T_CONTINUE;
+}
+
+static int ip6t_hl_checkentry(const char *tablename,
+		const struct ip6t_entry *e,
+		void *targinfo,
+		unsigned int targinfosize,
+		unsigned int hook_mask)
+{
+	struct ip6t_HL_info *info = targinfo;
+
+	if (targinfosize != IP6T_ALIGN(sizeof(struct ip6t_HL_info))) {
+		printk(KERN_WARNING "ip6t_HL: targinfosize %u != %Zu\n",
+				targinfosize,
+				IP6T_ALIGN(sizeof(struct ip6t_HL_info)));
+		return 0;	
+	}	
+
+	if (strcmp(tablename, "mangle")) {
+		printk(KERN_WARNING "ip6t_HL: can only be called from "
+			"\"mangle\" table, not \"%s\"\n", tablename);
+		return 0;
+	}
+
+	if (info->mode > IP6T_HL_MAXMODE) {
+		printk(KERN_WARNING "ip6t_HL: invalid or unknown Mode %u\n", 
+			info->mode);
+		return 0;
+	}
+
+	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 0;
+	}
+	
+	return 1;
+}
+
+static struct ip6t_target ip6t_HL = { 
+	.name 		= "HL", 
+	.target		= ip6t_hl_target, 
+	.checkentry	= ip6t_hl_checkentry, 
+	.me		= THIS_MODULE
+};
+
+static int __init init(void)
+{
+	return ip6t_register_target(&ip6t_HL);
+}
+
+static void __exit fini(void)
+{
+	ip6t_unregister_target(&ip6t_HL);
+}
+
+module_init(init);
+module_exit(fini);