[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>

3 files changed, 135 insertions, 0 deletions

diff --git a/net/ipv6/netfilter/Kconfig b/net/ipv6/netfilter/Kconfig
index 8a10c2d0d154..216fbe1ac65c 100644
--- a/net/ipv6/netfilter/Kconfig
+++ b/net/ipv6/netfilter/Kconfig
@@ -239,6 +239,22 @@ config IP6_NF_TARGET_MARK
 
           To compile it as a module, choose M here.  If unsure, say N.
 
+config IP6_NF_TARGET_HL
+        tristate  'HL (hoplimit) target support'
+        depends on IP6_NF_MANGLE
+        help
+          This option adds a `HL' target, which enables the user to decrement
+          the hoplimit value of the IPv6 header or set it to a given (lower)
+          value.
+        
+          While it is safe to decrement the hoplimit value, this option also
+          enables functionality to increment and set the hoplimit value of the
+          IPv6 header to arbitrary values.  This is EXTREMELY DANGEROUS since
+          you can easily create immortal packets that loop forever on the
+          network.  
+
+          To compile it as a module, choose M here.  If unsure, say N.
+
 #dep_tristate '  LOG target support' CONFIG_IP6_NF_TARGET_LOG $CONFIG_IP6_NF_IPTABLES
 config IP6_NF_RAW
         tristate  'raw table support (required for TRACE)'
diff --git a/net/ipv6/netfilter/Makefile b/net/ipv6/netfilter/Makefile
index 70f6ba610102..bd9a16a5cbba 100644
--- a/net/ipv6/netfilter/Makefile
+++ b/net/ipv6/netfilter/Makefile
@@ -20,6 +20,7 @@ obj-$(CONFIG_IP6_NF_MATCH_PHYSDEV) += ip6t_physdev.o
 obj-$(CONFIG_IP6_NF_FILTER) += ip6table_filter.o
 obj-$(CONFIG_IP6_NF_MANGLE) += ip6table_mangle.o
 obj-$(CONFIG_IP6_NF_TARGET_MARK) += ip6t_MARK.o
+obj-$(CONFIG_IP6_NF_TARGET_HL) += ip6t_HL.o
 obj-$(CONFIG_IP6_NF_QUEUE) += ip6_queue.o
 obj-$(CONFIG_IP6_NF_TARGET_LOG) += ip6t_LOG.o
 obj-$(CONFIG_IP6_NF_RAW) += ip6table_raw.o
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);