ipv6: ICMPV6: add response to ICMPV6 RFC 8335 PROBE messages

This patch builds off of commit 2b246b2569cd2ac6ff700d0dce56b8bae29b1842
and adds functionality to respond to ICMPV6 PROBE requests.

Add icmp_build_probe function to construct PROBE requests for both
ICMPV4 and ICMPV6.

Modify icmpv6_rcv to detect ICMPV6 PROBE messages and call the
icmpv6_echo_reply handler.

Modify icmpv6_echo_reply to build a PROBE response message based on the
queried interface.

This patch has been tested using a branch of the iputils git repo which can
be found here: https://github.com/Juniper-Clinic-2020/iputils/tree/probe-request

Signed-off-by: Andreas Roeseler <[e-mail]>
Reviewed-by: Willem de Bruijn <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/icmp.h

···
 int icmp_err(struct sk_buff *skb, u32 info);
 int icmp_init(void);
 void icmp_out_count(struct net *net, unsigned char type);
+bool icmp_build_probe(struct sk_buff *skb, struct icmphdr *icmphdr);
 
 #endif	/* _ICMP_H */

net/ipv4/icmp.c

···
 
 static bool icmp_echo(struct sk_buff *skb)
 {
-	struct icmp_ext_hdr *ext_hdr, _ext_hdr;
-	struct icmp_ext_echo_iio *iio, _iio;
 	struct icmp_bxm icmp_param;
-	struct net_device *dev;
-	char buff[IFNAMSIZ];
 	struct net *net;
-	u16 ident_len;
-	u8 status;
 
 	net = dev_net(skb_dst(skb)->dev);
 	/* should there be an ICMP stat for ignored echos? */
···
 	icmp_param.data_len	   = skb->len;
 	icmp_param.head_len	   = sizeof(struct icmphdr);
 
-	if (icmp_param.data.icmph.type == ICMP_ECHO) {
+	if (icmp_param.data.icmph.type == ICMP_ECHO)
 		icmp_param.data.icmph.type = ICMP_ECHOREPLY;
-		goto send_reply;
-	}
-	if (!net->ipv4.sysctl_icmp_echo_enable_probe)
+	else if (!icmp_build_probe(skb, &icmp_param.data.icmph))
 		return true;
+
+	icmp_reply(&icmp_param, skb);
+	return true;
+}
+
+/*	Helper for icmp_echo and icmpv6_echo_reply.
+ *	Searches for net_device that matches PROBE interface identifier
+ *		and builds PROBE reply message in icmphdr.
+ *
+ *	Returns false if PROBE responses are disabled via sysctl
+ */
+
+bool icmp_build_probe(struct sk_buff *skb, struct icmphdr *icmphdr)
+{
+	struct icmp_ext_hdr *ext_hdr, _ext_hdr;
+	struct icmp_ext_echo_iio *iio, _iio;
+	struct net *net = dev_net(skb->dev);
+	struct net_device *dev;
+	char buff[IFNAMSIZ];
+	u16 ident_len;
+	u8 status;
+
+	if (!net->ipv4.sysctl_icmp_echo_enable_probe)
+		return false;
+
 	/* We currently only support probing interfaces on the proxy node
 	 * Check to ensure L-bit is set
 	 */
-	if (!(ntohs(icmp_param.data.icmph.un.echo.sequence) & 1))
-		return true;
+	if (!(ntohs(icmphdr->un.echo.sequence) & 1))
+		return false;
 	/* Clear status bits in reply message */
-	icmp_param.data.icmph.un.echo.sequence &= htons(0xFF00);
-	icmp_param.data.icmph.type = ICMP_EXT_ECHOREPLY;
+	icmphdr->un.echo.sequence &= htons(0xFF00);
+	if (icmphdr->type == ICMP_EXT_ECHO)
+		icmphdr->type = ICMP_EXT_ECHOREPLY;
+	else
+		icmphdr->type = ICMPV6_EXT_ECHO_REPLY;
 	ext_hdr = skb_header_pointer(skb, 0, sizeof(_ext_hdr), &_ext_hdr);
 	/* Size of iio is class_type dependent.
 	 * Only check header here and assign length based on ctype in the switch statement
···
 		goto send_mal_query;
 	}
 	if (!dev) {
-		icmp_param.data.icmph.code = ICMP_EXT_CODE_NO_IF;
-		goto send_reply;
+		icmphdr->code = ICMP_EXT_CODE_NO_IF;
+		return true;
 	}
 	/* Fill bits in reply message */
 	if (dev->flags & IFF_UP)
···
 	if (!list_empty(&rcu_dereference(dev->ip6_ptr)->addr_list))
 		status |= ICMP_EXT_ECHOREPLY_IPV6;
 	dev_put(dev);
-	icmp_param.data.icmph.un.echo.sequence |= htons(status);
-send_reply:
-	icmp_reply(&icmp_param, skb);
-		return true;
+	icmphdr->un.echo.sequence |= htons(status);
+	return true;
 send_mal_query:
-	icmp_param.data.icmph.code = ICMP_EXT_CODE_MAL_QUERY;
-	goto send_reply;
+	icmphdr->code = ICMP_EXT_CODE_MAL_QUERY;
+	return true;
 }
+EXPORT_SYMBOL_GPL(icmp_build_probe);
 
 /*
  *	Handle ICMP Timestamp requests.

net/ipv6/icmp.c

···
 	struct ipcm6_cookie ipc6;
 	u32 mark = IP6_REPLY_MARK(net, skb->mark);
 	bool acast;
+	u8 type;
 
 	if (ipv6_addr_is_multicast(&ipv6_hdr(skb)->daddr) &&
 	    net->ipv6.sysctl.icmpv6_echo_ignore_multicast)
···
 	    !(net->ipv6.sysctl.anycast_src_echo_reply && acast))
 		saddr = NULL;
 
+	if (icmph->icmp6_type == ICMPV6_EXT_ECHO_REQUEST)
+		type = ICMPV6_EXT_ECHO_REPLY;
+	else
+		type = ICMPV6_ECHO_REPLY;
+
 	memcpy(&tmp_hdr, icmph, sizeof(tmp_hdr));
-	tmp_hdr.icmp6_type = ICMPV6_ECHO_REPLY;
+	tmp_hdr.icmp6_type = type;
 
 	memset(&fl6, 0, sizeof(fl6));
 	if (net->ipv6.sysctl.flowlabel_reflect & FLOWLABEL_REFLECT_ICMPV6_ECHO_REPLIES)
···
 	if (saddr)
 		fl6.saddr = *saddr;
 	fl6.flowi6_oif = icmp6_iif(skb);
-	fl6.fl6_icmp_type = ICMPV6_ECHO_REPLY;
+	fl6.fl6_icmp_type = type;
 	fl6.flowi6_mark = mark;
 	fl6.flowi6_uid = sock_net_uid(net, NULL);
 	security_skb_classify_flow(skb, flowi6_to_flowi_common(&fl6));
···
 
 	msg.skb = skb;
 	msg.offset = 0;
-	msg.type = ICMPV6_ECHO_REPLY;
+	msg.type = type;
 
 	ipcm6_init_sk(&ipc6, np);
 	ipc6.hlimit = ip6_sk_dst_hoplimit(np, &fl6, dst);
 	ipc6.tclass = ipv6_get_dsfield(ipv6_hdr(skb));
 	ipc6.sockc.mark = mark;
+
+	if (icmph->icmp6_type == ICMPV6_EXT_ECHO_REQUEST)
+		if (!icmp_build_probe(skb, (struct icmphdr *)&tmp_hdr))
+			goto out_dst_release;
 
 	if (ip6_append_data(sk, icmpv6_getfrag, &msg,
 			    skb->len + sizeof(struct icmp6hdr),
···
 	switch (type) {
 	case ICMPV6_ECHO_REQUEST:
 		if (!net->ipv6.sysctl.icmpv6_echo_ignore_all)
+			icmpv6_echo_reply(skb);
+		break;
+	case ICMPV6_EXT_ECHO_REQUEST:
+		if (!net->ipv6.sysctl.icmpv6_echo_ignore_all &&
+		    net->ipv4.sysctl_icmp_echo_enable_probe)
 			icmpv6_echo_reply(skb);
 		break;