[PATCH V2 net-next 5/5] icmp: add response to RFC 8335 PROBE messages

[Andreas Roeseler <andreas.a.roeseler@gmail.com>]

Modify the icmp_rcv function to check for PROBE messages and call
icmp_echo if a PROBE request is detected.

Modify the existing icmp_echo function to respond to both ping and PROBE
requests.

This was tested using a custom modification of the iputils package and
wireshark. It supports IPV4 probing by name, ifindex, and probing by both IPV4 and IPV6
addresses. It currently does not support responding to probes off the proxy node
(See RFC 8335 Section 2). 


Signed-off-by: Andreas Roeseler <andreas.a.roeseler@gmail.com>
---
Changes since v1:
 - Reorder variable declarations to follow coding style
 - Switch to functions such as dev_get_by_name and ip_dev_find to lookup
   net devices
---
 net/ipv4/icmp.c | 98 ++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 88 insertions(+), 10 deletions(-)

diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 396b492c804f..18f9a2a3bf59 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -983,21 +983,85 @@ static bool icmp_redirect(struct sk_buff *skb)
 
 static bool icmp_echo(struct sk_buff *skb)
 {
+	struct icmp_bxm icmp_param;
 	struct net *net;
+	struct net_device *dev;
+	struct icmp_extobj_hdr *extobj_hdr;
+	struct icmp_ext_ctype3_hdr *ctype3_hdr;
+	__u8 status;
 
 	net = dev_net(skb_dst(skb)->dev);
-	if (!net->ipv4.sysctl_icmp_echo_ignore_all) {
-		struct icmp_bxm icmp_param;
+	/* should there be an ICMP stat for ignored echos? */
+	if (net->ipv4.sysctl_icmp_echo_ignore_all)
+		return true;
+
+	icmp_param.data.icmph		= *icmp_hdr(skb);
+	icmp_param.skb			= skb;
+	icmp_param.offset		= 0;
+	icmp_param.data_len		= skb->len;
+	icmp_param.head_len		= sizeof(struct icmphdr);
 
-		icmp_param.data.icmph	   = *icmp_hdr(skb);
+	if (icmp_param.data.icmph.type == ICMP_ECHO) {
 		icmp_param.data.icmph.type = ICMP_ECHOREPLY;
-		icmp_param.skb		   = skb;
-		icmp_param.offset	   = 0;
-		icmp_param.data_len	   = skb->len;
-		icmp_param.head_len	   = sizeof(struct icmphdr);
-		icmp_reply(&icmp_param, skb);
+		goto send_reply;
 	}
-	/* should there be an ICMP stat for ignored echos? */
+	if (!net->ipv4.sysctl_icmp_echo_enable_probe)
+		return true;
+	/* We currently do not support probing off the proxy node */
+	if (!(ntohs(icmp_param.data.icmph.un.echo.sequence) & 1))
+		return true;
+
+	icmp_param.data.icmph.type = ICMP_EXT_ECHOREPLY;
+	icmp_param.data.icmph.un.echo.sequence &= htons(0xFF00);
+	extobj_hdr = (struct icmp_extobj_hdr *)(skb->data + sizeof(struct icmp_ext_hdr));
+	ctype3_hdr = (struct icmp_ext_ctype3_hdr *)(extobj_hdr + 1);
+	status = 0;
+	switch (extobj_hdr->class_type) {
+	case CTYPE_NAME:
+		dev = dev_get_by_name(net, (char *)(extobj_hdr + 1));
+		break;
+	case CTYPE_INDEX:
+		dev = dev_get_by_index(net, ntohl(*((uint32_t *)(extobj_hdr + 1))));
+		break;
+	case CTYPE_ADDR:
+		switch (ntohs(ctype3_hdr->afi)) {
+		case AFI_IP:
+			dev = ip_dev_find(net, *(__be32 *)(ctype3_hdr + 1));
+			break;
+		case AFI_IP6:
+			dev = ipv6_dev_find(net, (struct in6_addr *)(ctype3_hdr + 1), dev);
+			if(dev) dev_hold(dev);
+			break;
+		default:
+			icmp_param.data.icmph.code = ICMP_EXT_MAL_QUERY;
+			goto send_reply;
+		}
+		break;
+	default:
+		icmp_param.data.icmph.code = ICMP_EXT_MAL_QUERY;
+		goto send_reply;
+	}
+	if(!dev) {
+		icmp_param.data.icmph.code = ICMP_EXT_NO_IF;
+		goto send_reply;
+	}
+	/* RFC 8335: 3 the last 8 bits of the Extended Echo Reply Message
+	 *  are laid out as follows:
+	 *	+-+-+-+-+-+-+-+-+
+	 *	|State|Res|A|4|6|
+	 *	+-+-+-+-+-+-+-+-+
+	 */
+	if (dev->flags & IFF_UP)
+		status |= EXT_ECHOREPLY_ACTIVE;
+	if (dev->ip_ptr->ifa_list)
+		status |= EXT_ECHOREPLY_IPV4;
+	if (!list_empty(&dev->ip6_ptr->addr_list))
+		status |= EXT_ECHOREPLY_IPV6;
+	dev_put(dev);
+	icmp_param.data.icmph.un.echo.sequence |= htons(status);
+
+send_reply:
+	icmp_reply(&icmp_param, skb);
 	return true;
 }
 
@@ -1087,6 +1151,13 @@ int icmp_rcv(struct sk_buff *skb)
 	icmph = icmp_hdr(skb);
 
 	ICMPMSGIN_INC_STATS(net, icmph->type);
+
+	/*
+	 *	Check for ICMP Extended Echo (PROBE) messages
+	 */
+	if (icmph->type == ICMP_EXT_ECHO || icmph->type == ICMPV6_EXT_ECHO_REQUEST)
+		goto probe;
+
 	/*
 	 *	18 is the highest 'known' ICMP type. Anything else is a mystery
 	 *
@@ -1096,7 +1167,6 @@ int icmp_rcv(struct sk_buff *skb)
 	if (icmph->type > NR_ICMP_TYPES)
 		goto error;
 
-
 	/*
 	 *	Parse the ICMP message
 	 */
@@ -1123,6 +1193,7 @@ int icmp_rcv(struct sk_buff *skb)
 
 	success = icmp_pointers[icmph->type].handler(skb);
 
+success_check:
 	if (success)  {
 		consume_skb(skb);
 		return NET_RX_SUCCESS;
@@ -1136,6 +1207,13 @@ int icmp_rcv(struct sk_buff *skb)
 error:
 	__ICMP_INC_STATS(net, ICMP_MIB_INERRORS);
 	goto drop;
+probe:
+	/*
+	 * We can't use icmp_pointers[].handler() because the codes for PROBE
+	 *   messages are 42 or 160
+	 */
+	success = icmp_echo(skb);
+	goto success_check;
 }
 
 static bool ip_icmp_error_rfc4884_validate(const struct sk_buff *skb, int off)
-- 
2.25.1