ipv6: Kill ipv6 dependency of icmpv6_send().

Following patch adds icmp-registration module for ipv6. It allows
ipv6 protocol to register icmp_sender which is used for sending
ipv6 icmp msgs. This extra layer allows us to kill ipv6 dependency
for sending icmp packets.

This patch also fixes ip_tunnel compilation problem when ip_tunnel
is statically compiled in kernel but ipv6 is module

Signed-off-by: Pravin B Shelar <[e-mail]>
Acked-by: Eric Dumazet <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/icmpv6.h

···
 
 #include <linux/netdevice.h>
 
-extern void				icmpv6_send(struct sk_buff *skb,
-						    u8 type, u8 code,
-						    __u32 info);
+#if IS_ENABLED(CONFIG_IPV6)
+extern void icmpv6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info);
+
+typedef void ip6_icmp_send_t(struct sk_buff *skb, u8 type, u8 code, __u32 info);
+extern int inet6_register_icmp_sender(ip6_icmp_send_t *fn);
+extern int inet6_unregister_icmp_sender(ip6_icmp_send_t *fn);
+
+#else
+
+static inline void icmpv6_send(struct sk_buff *skb,
+			       u8 type, u8 code, __u32 info)
+{
+
+}
+#endif
 
 extern int				icmpv6_init(void);
 extern int				icmpv6_err_convert(u8 type, u8 code,

net/ipv6/Makefile

···
 obj-$(CONFIG_IPV6_TUNNEL) += ip6_tunnel.o
 obj-$(CONFIG_IPV6_GRE) += ip6_gre.o
 
-obj-y += addrconf_core.o exthdrs_core.o ip6_checksum.o
+obj-y += addrconf_core.o exthdrs_core.o ip6_checksum.o ip6_icmp.o
 obj-$(CONFIG_INET) += output_core.o protocol.o $(ipv6-offload)
 
 obj-$(subst m,y,$(CONFIG_IPV6)) += inet6_hashtables.o

net/ipv6/icmp.c

···
 }
 
 /*
- * Slightly more convenient version of icmpv6_send.
- */
-void icmpv6_param_prob(struct sk_buff *skb, u8 code, int pos)
-{
-	icmpv6_send(skb, ICMPV6_PARAMPROB, code, pos);
-	kfree_skb(skb);
-}
-
-/*
  * Figure out, may we reply to this packet with icmp error.
  *
  * We do not reply, if:
···
 	 * anycast.
 	 */
 	if (((struct rt6_info *)dst)->rt6i_flags & RTF_ANYCAST) {
-		LIMIT_NETDEBUG(KERN_DEBUG "icmpv6_send: acast source\n");
+		LIMIT_NETDEBUG(KERN_DEBUG "icmp6_send: acast source\n");
 		dst_release(dst);
 		return ERR_PTR(-EINVAL);
 	}
···
 /*
  *	Send an ICMP message in response to a packet in error
  */
-void icmpv6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info)
+static void icmp6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info)
 {
 	struct net *net = dev_net(skb->dev);
 	struct inet6_dev *idev = NULL;
···
 	/*
 	 *	Make sure we respect the rules
 	 *	i.e. RFC 1885 2.4(e)
-	 *	Rule (e.1) is enforced by not using icmpv6_send
+	 *	Rule (e.1) is enforced by not using icmp6_send
 	 *	in any code that processes icmp errors.
 	 */
 	addr_type = ipv6_addr_type(&hdr->daddr);
···
 	 *	and anycast addresses will be checked later.
 	 */
 	if ((addr_type == IPV6_ADDR_ANY) || (addr_type & IPV6_ADDR_MULTICAST)) {
-		LIMIT_NETDEBUG(KERN_DEBUG "icmpv6_send: addr_any/mcast source\n");
+		LIMIT_NETDEBUG(KERN_DEBUG "icmp6_send: addr_any/mcast source\n");
 		return;
 	}
 
···
 	 *	Never answer to a ICMP packet.
 	 */
 	if (is_ineligible(skb)) {
-		LIMIT_NETDEBUG(KERN_DEBUG "icmpv6_send: no reply to icmp error\n");
+		LIMIT_NETDEBUG(KERN_DEBUG "icmp6_send: no reply to icmp error\n");
 		return;
 	}
 
···
 out:
 	icmpv6_xmit_unlock(sk);
 }
-EXPORT_SYMBOL(icmpv6_send);
+
+/* Slightly more convenient version of icmp6_send.
+ */
+void icmpv6_param_prob(struct sk_buff *skb, u8 code, int pos)
+{
+	icmp6_send(skb, ICMPV6_PARAMPROB, code, pos);
+	kfree_skb(skb);
+}
 
 static void icmpv6_echo_reply(struct sk_buff *skb)
 {
···
 	err = -EAGAIN;
 	if (inet6_add_protocol(&icmpv6_protocol, IPPROTO_ICMPV6) < 0)
 		goto fail;
+
+	err = inet6_register_icmp_sender(icmp6_send);
+	if (err)
+		goto sender_reg_err;
 	return 0;
 
+sender_reg_err:
+	inet6_del_protocol(&icmpv6_protocol, IPPROTO_ICMPV6);
 fail:
 	pr_err("Failed to register ICMP6 protocol\n");
 	unregister_pernet_subsys(&icmpv6_sk_ops);
···
 
 void icmpv6_cleanup(void)
 {
+	inet6_unregister_icmp_sender(icmp6_send);
 	unregister_pernet_subsys(&icmpv6_sk_ops);
 	inet6_del_protocol(&icmpv6_protocol, IPPROTO_ICMPV6);
 }

net/ipv6/ip6_icmp.c

···
+#include <linux/export.h>
+#include <linux/icmpv6.h>
+#include <linux/mutex.h>
+#include <linux/netdevice.h>
+#include <linux/spinlock.h>
+
+#include <net/ipv6.h>
+
+#if IS_ENABLED(CONFIG_IPV6)
+
+static ip6_icmp_send_t __rcu *ip6_icmp_send;
+
+int inet6_register_icmp_sender(ip6_icmp_send_t *fn)
+{
+	return (cmpxchg((ip6_icmp_send_t **)&ip6_icmp_send, NULL, fn) == NULL) ?
+	        0 : -EBUSY;
+}
+EXPORT_SYMBOL(inet6_register_icmp_sender);
+
+int inet6_unregister_icmp_sender(ip6_icmp_send_t *fn)
+{
+	int ret;
+
+	ret = (cmpxchg((ip6_icmp_send_t **)&ip6_icmp_send, fn, NULL) == fn) ?
+	      0 : -EINVAL;
+
+	synchronize_net();
+
+	return ret;
+}
+EXPORT_SYMBOL(inet6_unregister_icmp_sender);
+
+void icmpv6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info)
+{
+	ip6_icmp_send_t *send;
+
+	rcu_read_lock();
+	send = rcu_dereference(ip6_icmp_send);
+
+	if (!send)
+		goto out;
+	send(skb, type, code, info);
+out:
+	rcu_read_unlock();
+}
+EXPORT_SYMBOL(icmpv6_send);
+#endif