xt_ECHO: IPv6 support

doc/changelog.txt

@@ -5,6 +5,8 @@ Fixes:
 - xt_ECHO: fix kernel warning about RTAX_HOPLIMIT being used
 Changes:
 - xt_ECHO: now calculates UDP checksum
+Enhancements:
+- xt_ECHO: IPv6 support
 
 
 v1.39 (2011-09-21)

extensions/xt_ECHO.c

@@ -1,7 +1,7 @@
 /*
  *	"ECHO" (RFC 862) target extension for Xtables
  *	Sample module for "Writing your own Netfilter Modules"
- *	Copyright © Jan Engelhardt <jengelh [at] medozas de>, 2008
+ *	Copyright © Jan Engelhardt <jengelh [at] medozas de>, 2008-2011
  *
  *	This program is free software; you can redistribute it and/or
  *	modify it under the terms of the GNU General Public License; either
@@ -18,9 +18,112 @@
 #	include <linux/netfilter_bridge.h>
 #endif
 #include <net/ip.h>
+#include <net/ip6_route.h>
 #include <net/route.h>
 #include "compat_xtables.h"
 
+static unsigned int
+echo_tg6(struct sk_buff **poldskb, const struct xt_action_param *par)
+{
+	const struct sk_buff *oldskb = *poldskb;
+	const struct udphdr *oldudp;
+	const struct ipv6hdr *oldip;
+	struct udphdr *newudp, oldudp_buf;
+	struct ipv6hdr *newip;
+	struct sk_buff *newskb;
+	unsigned int data_len;
+	void *payload;
+	struct flowi6 fl;
+	struct dst_entry *dst = NULL;
+	struct net *net = dev_net((par->in != NULL) ? par->in : par->out);
+
+	/* This allows us to do the copy operation in fewer lines of code. */
+	if (skb_linearize(*poldskb) < 0)
+		return NF_DROP;
+
+	oldip  = ipv6_hdr(oldskb);
+	oldudp = skb_header_pointer(oldskb, par->thoff,
+	         sizeof(*oldudp), &oldudp_buf);
+	if (oldudp == NULL)
+		return NF_DROP;
+	if (ntohs(oldudp->len) <= sizeof(*oldudp))
+		return NF_DROP;
+
+	newskb = alloc_skb(LL_MAX_HEADER + sizeof(*newip) +
+	         ntohs(oldudp->len), GFP_ATOMIC);
+	if (newskb == NULL)
+		return NF_DROP;
+
+	skb_reserve(newskb, LL_MAX_HEADER);
+	newskb->protocol = oldskb->protocol;
+
+	skb_reset_network_header(newskb);
+	newip = (void *)skb_put(newskb, sizeof(*newip));
+	newip->version  = oldip->version;
+	newip->priority = oldip->priority;
+	memcpy(newip->flow_lbl, oldip->flow_lbl, sizeof(newip->flow_lbl));
+	newip->nexthdr  = par->target->proto;
+	newip->saddr    = oldip->daddr;
+	newip->daddr    = oldip->saddr;
+
+	skb_reset_transport_header(newskb);
+	newudp = (void *)skb_put(newskb, sizeof(*newudp));
+	newudp->source = oldudp->dest;
+	newudp->dest   = oldudp->source;
+	newudp->len    = oldudp->len;
+
+	data_len = htons(oldudp->len) - sizeof(*oldudp);
+	payload  = skb_header_pointer(oldskb, par->thoff +
+	           sizeof(*oldudp), data_len, NULL);
+	memcpy(skb_put(newskb, data_len), payload, data_len);
+
+#if 0
+	/*
+	 * Since no fields are modified (we just swapped things around),
+	 * this works too in our specific echo case.
+	 */
+	newudp->check = oldudp->check;
+#else
+	newudp->check = 0;
+	newudp->check = csum_ipv6_magic(&newip->saddr, &newip->daddr,
+	                ntohs(newudp->len), IPPROTO_UDP,
+	                csum_partial(newudp, ntohs(newudp->len), 0));
+#endif
+
+	memset(&fl, 0, sizeof(fl));
+	fl.flowi6_proto = newip->nexthdr;
+	ipv6_addr_copy(&fl.saddr, &newip->saddr);
+	ipv6_addr_copy(&fl.daddr, &newip->daddr);
+	fl.fl6_sport = newudp->source;
+	fl.fl6_dport = newudp->dest;
+	security_skb_classify_flow((struct sk_buff *)oldskb, flowi6_to_flowi(&fl));
+	dst = ip6_route_output(net, NULL, &fl);
+	if (dst == NULL || dst->error != 0) {
+		dst_release(dst);
+		goto free_nskb;
+	}
+
+	skb_dst_set(newskb, dst);
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 38)
+	newip->hop_limit = ip6_dst_hoplimit(skb_dst(newskb));
+#else
+	newip->hop_limit = dst_metric(skb_dst(newskb), RTAX_HOPLIMIT);
+#endif
+	newskb->ip_summed = CHECKSUM_NONE;
+
+	/* "Never happens" (?) */
+	if (newskb->len > dst_mtu(skb_dst(newskb)))
+		goto free_nskb;
+
+	nf_ct_attach(newskb, *poldskb);
+	ip6_local_out(newskb);
+	return NF_DROP;
+
+ free_nskb:
+	kfree_skb(newskb);
+	return NF_DROP;
+}
+
 static unsigned int
 echo_tg4(struct sk_buff **poldskb, const struct xt_action_param *par)
 {
@@ -115,24 +218,35 @@ echo_tg4(struct sk_buff **poldskb, const struct xt_action_param *par)
 	return NF_DROP;
 }
 
-static struct xt_target echo_tg_reg __read_mostly = {
+static struct xt_target echo_tg_reg[] __read_mostly = {
-	.name       = "ECHO",
+	{
-	.revision   = 0,
+		.name       = "ECHO",
-	.family     = NFPROTO_IPV4,
+		.revision   = 0,
-	.proto      = IPPROTO_UDP,
+		.family     = NFPROTO_IPV6,
-	.table      = "filter",
+		.proto      = IPPROTO_UDP,
-	.target     = echo_tg4,
+		.table      = "filter",
-	.me         = THIS_MODULE,
+		.target     = echo_tg6,
+		.me         = THIS_MODULE,
+	},
+	{
+		.name       = "ECHO",
+		.revision   = 0,
+		.family     = NFPROTO_IPV4,
+		.proto      = IPPROTO_UDP,
+		.table      = "filter",
+		.target     = echo_tg4,
+		.me         = THIS_MODULE,
+	},
 };
 
 static int __init echo_tg_init(void)
 {
-	return xt_register_target(&echo_tg_reg);
+	return xt_register_targets(echo_tg_reg, ARRAY_SIZE(echo_tg_reg));
 }
 
 static void __exit echo_tg_exit(void)
 {
-	return xt_unregister_target(&echo_tg_reg);
+	return xt_unregister_targets(echo_tg_reg, ARRAY_SIZE(echo_tg_reg));
 }
 
 module_init(echo_tg_init);
@@ -140,4 +254,5 @@ module_exit(echo_tg_exit);
 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
 MODULE_DESCRIPTION("Xtables: ECHO diagnosis target");
 MODULE_LICENSE("GPL");
+MODULE_ALIAS("ip6t_ECHO");
 MODULE_ALIAS("ipt_ECHO");