[PATCH V4 net-next 0/5] add support for RFC 8335 PROBE

The popular utility ping has several severe limitations, such as the
inability to query specific interfaces on a node and requiring
bidirectional connectivity between the probing and probed interfaces.
RFC 8335 attempts to solve these limitations by creating the new utility
PROBE which is a specialized ICMP message that makes use of the ICMP
Extension Structure outlined in RFC 4884.

This patchset adds definitions for the ICMP Extended Echo Request and
Reply (PROBE) types for both IPV4 and IPV6, adds a sysctl to enable
responses to PROBE messages, expands the list of supported ICMP messages
to accommodate PROBE types, and adds functionality to respond to PROBE
requests.

Changes:
v1 -> v2:
 - Add AFI definitions
 - Switch to functions such as dev_get_by_name and ip_dev_find to lookup
   net devices

v2 -> v3:
Suggested by Willem de Bruijn [off-list ref]
 - Add verification of incoming messages before looking up netdev
 - Add prefix for PROBE specific defined variables
 - Use proc_dointvec_minmax with zero and one for sysctl
 - Create struct icmp_ext_echo_iio for parsing incoming packets
Reported-by: kernel test robot <redacted>
Reported-by: Dan Carpenter <redacted>
 - Include net/addrconf.h library for ipv6_dev_find

v3 -> v4:
 - Use in_addr instead of __be32 for storing IPV4 addresses
 - Use IFNAMSIZ to statically allocate space for name in
   icmp_ext_echo_iio
Suggested by Willem de Bruijn [off-list ref]
 - Use skb_header_pointer to verify fields in incoming message
 - Add check to ensure that extobj_hdr.length is valid
 - Check to ensure object payload is padded with ASCII NULL characters
   when probing by name, as specified by RFC 8335
 - Statically allocate buff using IFNAMSIZ
 - Add rcu blocking around ipv6_dev_find
 - Use __in_dev_get_rcu to access IPV4 addresses of identified
   net_device
 - Remove check for ICMPV6 PROBE types

Andreas Roeseler (5):
  icmp: add support for RFC 8335 PROBE
  ICMPV6: add support for RFC 8335 PROBE
  net: add sysctl for enabling RFC 8335 PROBE messages
  net: add support for sending RFC 8335 PROBE messages
  icmp: add response to RFC 8335 PROBE messages

 include/net/netns/ipv4.h    |   1 +
 include/uapi/linux/icmp.h   |  42 +++++++++++
 include/uapi/linux/icmpv6.h |   3 +
 net/ipv4/icmp.c             | 145 ++++++++++++++++++++++++++++++++----
 net/ipv4/ping.c             |   4 +-
 net/ipv4/sysctl_net_ipv4.c  |   9 +++
 6 files changed, 188 insertions(+), 16 deletions(-)

-- 
2.17.1

Add definitions for PROBE ICMP types and codes.

Add AFI definitions for IP and IPV6 as specified by IANA

Add a struct to represent the additional header when probing by IP
address (ctype == 3) for use in parsing incoming PROBE messages

Add a struct to represent the entire Interface Identification Object
(IIO) section of an incoming PROBE packet

Signed-off-by: Andreas Roeseler <redacted>
---
Changes:
v1 -> v2:
 - Add AFI_IP and AFI_IP6 definitions

v2 -> v3:
Suggested by Willem de Bruijn [off-list ref]
 - Add prefix for PROBE specific defined variables
 - Create struct icmp_ext_echo_iio for parsing incoming packet

v3 -> v4:
 - Use in_addr instead of __be32 for storing IPV4 addresses
 - Use IFNAMSIZ to statically allocate space for name in
   icmp_ext_echo_iio 
---
 include/uapi/linux/icmp.h | 42 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/include/uapi/linux/icmp.h b/include/uapi/linux/icmp.h
index fb169a50895e..c074964aa4f3 100644
--- a/include/uapi/linux/icmp.h
+++ b/include/uapi/linux/icmp.h

@@ -20,6 +20,9 @@
 
 #include <linux/types.h>
 #include <asm/byteorder.h>
+#include <linux/in.h>
+#include <linux/if.h>
+#include <linux/in6.h>
 
 #define ICMP_ECHOREPLY		0	/* Echo Reply			*/
 #define ICMP_DEST_UNREACH	3	/* Destination Unreachable	*/

@@ -66,6 +69,23 @@
 #define ICMP_EXC_TTL		0	/* TTL count exceeded		*/
 #define ICMP_EXC_FRAGTIME	1	/* Fragment Reass time exceeded	*/
 
+/* Codes for EXT_ECHO (PROBE) */
+#define ICMP_EXT_ECHO		42
+#define ICMP_EXT_ECHOREPLY	43
+#define ICMP_EXT_MAL_QUERY	1	/* Malformed Query */
+#define ICMP_EXT_NO_IF		2	/* No such Interface */
+#define ICMP_EXT_NO_TABLE_ENT	3	/* No such Table Entry */
+#define ICMP_EXT_MULT_IFS	4	/* Multiple Interfaces Satisfy Query */
+
+/* Constants for EXT_ECHO (PROBE) */
+#define EXT_ECHOREPLY_ACTIVE	(1 << 2)/* active bit in reply message */
+#define EXT_ECHOREPLY_IPV4	(1 << 1)/* ipv4 bit in reply message */
+#define EXT_ECHOREPLY_IPV6	1	/* ipv6 bit in reply message */
+#define EXT_ECHO_CTYPE_NAME	1
+#define EXT_ECHO_CTYPE_INDEX	2
+#define EXT_ECHO_CTYPE_ADDR	3
+#define ICMP_AFI_IP		1	/* Address Family Identifier for ipv4 */
+#define ICMP_AFI_IP6		2	/* Address Family Identifier for ipv6 */
 
 struct icmphdr {
   __u8		type;

@@ -118,4 +138,26 @@ struct icmp_extobj_hdr {
 	__u8		class_type;
 };
 
+/* RFC 8335: 2.1 Header for c-type 3 payload */
+struct icmp_ext_echo_ctype3_hdr {
+	__u16		afi;
+	__u8		addrlen;
+	__u8		reserved;
+};
+
+/* RFC 8335: 2.1 Interface Identification Object */
+struct icmp_ext_echo_iio {
+	struct icmp_extobj_hdr extobj_hdr;
+	union {
+		char name[IFNAMSIZ];
+		__u32 ifindex;
+		struct {
+			struct icmp_ext_echo_ctype3_hdr ctype3_hdr;
+			union {
+				struct in_addr	ipv4_addr;
+				struct in6_addr	ipv6_addr;
+			} ip_addr;
+		} addr;
+	} ident;
+};
 #endif /* _UAPI_LINUX_ICMP_H */

-- 
2.17.1

Add definitions for the ICMPV6 type of Extended Echo Request and
Extended Echo Reply, as defined by sections 2 and 3 of RFC 8335.

Signed-off-by: Andreas Roeseler <redacted>
---
 include/uapi/linux/icmpv6.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/uapi/linux/icmpv6.h b/include/uapi/linux/icmpv6.h
index 0564fd7ccde4..ecaece3af38d 100644
--- a/include/uapi/linux/icmpv6.h
+++ b/include/uapi/linux/icmpv6.h

@@ -140,6 +140,9 @@ struct icmp6hdr {
 #define ICMPV6_UNK_OPTION		2
 #define ICMPV6_HDR_INCOMP		3
 
+/* Codes for EXT_ECHO (PROBE) */
+#define ICMPV6_EXT_ECHO_REQUEST		160
+#define ICMPV6_EXT_ECHO_REPLY		161
 /*
  *	constants for (set|get)sockopt
  */

-- 
2.17.1

Section 8 of RFC 8335 specifies potential security concerns of
responding to PROBE requests, and states that nodes that support PROBE
functionality MUST be able to enable/disable responses and that
responses MUST be disabled by default

Signed-off-by: Andreas Roeseler <redacted>
---
Changes:
v1 -> v2:
 - Combine patches related to sysctl

v2 -> v3:
Suggested by Willem de Bruijn [off-list ref]
 - Use proc_dointvec_minmax with zero and one
---
 include/net/netns/ipv4.h   | 1 +
 net/ipv4/sysctl_net_ipv4.c | 9 +++++++++
 2 files changed, 10 insertions(+)

diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index 70a2a085dd1a..362388ab40c8 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h

@@ -85,6 +85,7 @@ struct netns_ipv4 {
 #endif
 
 	int sysctl_icmp_echo_ignore_all;
+	int sysctl_icmp_echo_enable_probe;
 	int sysctl_icmp_echo_ignore_broadcasts;
 	int sysctl_icmp_ignore_bogus_error_responses;
 	int sysctl_icmp_ratelimit;

diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index f55095d3ed16..fec3f142d8c9 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c

@@ -599,6 +599,15 @@ static struct ctl_table ipv4_net_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec
 	},
+	{
+		.procname	= "icmp_echo_enable_probe",
+		.data		= &init_net.ipv4.sysctl_icmp_echo_enable_probe,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE
+	},
 	{
 		.procname	= "icmp_echo_ignore_broadcasts",
 		.data		= &init_net.ipv4.sysctl_icmp_echo_ignore_broadcasts,

-- 
2.17.1

Modify the ping_supported function to support PROBE message types. This
allows tools such as the ping command in the iputils package to be
modified to send PROBE requests through the existing framework for
sending ping requests.

Signed-off-by: Andreas Roeseler <redacted>
---
 net/ipv4/ping.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/ping.c b/net/ipv4/ping.c
index 8b943f85fff9..1c9f71a37258 100644
--- a/net/ipv4/ping.c
+++ b/net/ipv4/ping.c

@@ -453,7 +453,9 @@ EXPORT_SYMBOL_GPL(ping_bind);
 static inline int ping_supported(int family, int type, int code)
 {
 	return (family == AF_INET && type == ICMP_ECHO && code == 0) ||
-	       (family == AF_INET6 && type == ICMPV6_ECHO_REQUEST && code == 0);
+	       (family == AF_INET && type == ICMP_EXT_ECHO && code == 0) ||
+	       (family == AF_INET6 && type == ICMPV6_ECHO_REQUEST && code == 0) ||
+	       (family == AF_INET6 && type == ICMPV6_EXT_ECHO_REQUEST && code == 0);
 }
 
 /*

-- 
2.17.1

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

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

This was tested using a custom modification to 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 <redacted>
---
Changes:
v1 -> v2:
 - Reorder variable declarations to follow coding style
 - Switch to functions such as dev_get_by_name and ip_dev_find to lookup
   net devices

v2 -> v3:
Suggested by Willem de Bruijn [off-list ref]
 - Add verification of incoming messages before looking up netdev
Reported-by: kernel test robot <redacted>
Reported-by: Dan Carpenter <redacted>
 - Include net/addrconf.h library for ipv6_dev_find

v3 -> v4:
Suggested by Willem de Bruijn [off-list ref]
 - Use skb_header_pointer to verify fields in incoming message
 - Add check to ensure that extobj_hdr.length is valid
 - Check to ensure object payload is padded with ASCII NULL characters
   when probing by name, as specified by RFC 8335
 - Statically allocate buff using IFNAMSIZ
 - Add rcu blocking around ipv6_dev_find
 - Use __in_dev_get_rcu to access IPV4 addresses of identified
   net_device
 - Remove check for ICMPV6 PROBE types
---
 net/ipv4/icmp.c | 145 +++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 130 insertions(+), 15 deletions(-)

diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 616e2dc1c8fa..f1530011b7bc 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c

@@ -93,6 +93,10 @@
 #include <net/ip_fib.h>
 #include <net/l3mdev.h>
 
+#if IS_ENABLED(CONFIG_IPV6)
+#include <net/addrconf.h>
+#endif
+
 /*
  *	Build xmit assembly blocks
  */

@@ -971,7 +975,7 @@ static bool icmp_redirect(struct sk_buff *skb)
 }
 
 /*
- *	Handle ICMP_ECHO ("ping") requests.
+ *	Handle ICMP_ECHO ("ping") and ICMP_EXT_ECHO ("PROBE") requests.
  *
  *	RFC 1122: 3.2.2.6 MUST have an echo server that answers ICMP echo
  *		  requests.

@@ -979,27 +983,127 @@ static bool icmp_redirect(struct sk_buff *skb)
  *		  included in the reply.
  *	RFC 1812: 4.3.3.6 SHOULD have a config option for silently ignoring
  *		  echo requests, MUST have default=NOT.
+ *	RFC 8335: 8 MUST have a config option to enable/disable ICMP
+ *		  Extended Echo Functionality, MUST be disabled by default
  *	See also WRT handling of options once they are done and working.
  */
 
 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;
 	struct net *net;
+	u16 ident_len;
+	char *buff;
+	u8 status;
 
 	net = dev_net(skb_dst(skb)->dev);
-	if (!net->ipv4.sysctl_icmp_echo_ignore_all) {
-		struct icmp_bxm icmp_param;
-
-		icmp_param.data.icmph	   = *icmp_hdr(skb);
-		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);
-	}
 	/* should there be an ICMP stat for ignored echos? */
-	return true;
+	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);
+
+	if (icmp_param.data.icmph.type == ICMP_ECHO)
+		goto send_reply;
+	if (!net->ipv4.sysctl_icmp_echo_enable_probe)
+		return true;
+	/* 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;
+	/* Clear status bits in reply message */
+	icmp_param.data.icmph.un.echo.sequence &= htons(0xFF00);
+	icmp_param.data.icmph.type = ICMP_EXT_ECHOREPLY;
+	ext_hdr = skb_header_pointer(skb, 0, sizeof(_ext_hdr), &_ext_hdr);
+	iio = skb_header_pointer(skb, sizeof(_ext_hdr), sizeof(_iio), &_iio);
+	if (!ext_hdr || !iio)
+		goto send_mal_query;
+	if (ntohs(iio->extobj_hdr.length) <= sizeof(iio->extobj_hdr))
+		goto send_mal_query;
+	ident_len = ntohs(iio->extobj_hdr.length) - sizeof(iio->extobj_hdr);
+	status = 0;
+	dev = NULL;
+	switch (iio->extobj_hdr.class_type) {
+	case EXT_ECHO_CTYPE_NAME:
+		if (ident_len >= IFNAMSIZ)
+			goto send_mal_query;
+		buff = kcalloc(IFNAMSIZ, sizeof(char), GFP_KERNEL);
+		if (!buff)
+			return -ENOMEM;
+		memcpy(buff, &iio->ident.name, ident_len);
+		/* RFC 8335 2.1 If the Object Payload would not otherwise terminate
+		 * on a 32-bit boundary, it MUST be padded with ASCII NULL characters
+		 */
+		if (ident_len % sizeof(u32) != 0) {
+			u8 i;
+
+			for (i = ident_len; i % sizeof(u32) != 0; i++) {
+				if (buff[i] != '\0')
+					goto send_mal_query;
+			}
+		}
+		dev = dev_get_by_name(net, buff);
+		kfree(buff);
+		break;
+	case EXT_ECHO_CTYPE_INDEX:
+		if (ident_len != sizeof(iio->ident.ifindex))
+			goto send_mal_query;
+		dev = dev_get_by_index(net, ntohl(iio->ident.ifindex));
+		break;
+	case EXT_ECHO_CTYPE_ADDR:
+		if (ident_len != sizeof(iio->ident.addr.ctype3_hdr) + iio->ident.addr.ctype3_hdr.addrlen)
+			goto send_mal_query;
+		switch (ntohs(iio->ident.addr.ctype3_hdr.afi)) {
+		case ICMP_AFI_IP:
+			if (ident_len != sizeof(iio->ident.addr.ctype3_hdr) + sizeof(struct in_addr))
+				goto send_mal_query;
+			dev = ip_dev_find(net, iio->ident.addr.ip_addr.ipv4_addr.s_addr);
+			break;
+#if IS_ENABLED(CONFIG_IPV6)
+		case ICMP_AFI_IP6:
+			if (ident_len != sizeof(iio->ident.addr.ctype3_hdr) + sizeof(struct in6_addr))
+				goto send_mal_query;
+			rcu_read_lock();
+			dev = ipv6_dev_find(net, &iio->ident.addr.ip_addr.ipv6_addr, dev);
+			if (dev)
+				dev_hold(dev);
+			rcu_read_unlock();
+			break;
+#endif
+		default:
+			goto send_mal_query;
+		}
+		break;
+	default:
+		goto send_mal_query;
+	}
+	if (!dev) {
+		icmp_param.data.icmph.code = ICMP_EXT_NO_IF;
+		goto send_reply;
+	}
+	/* Fill bits in reply message */
+	if (dev->flags & IFF_UP)
+		status |= EXT_ECHOREPLY_ACTIVE;
+	if (__in_dev_get_rcu(dev) && __in_dev_get_rcu(dev)->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;
+send_mal_query:
+	icmp_param.data.icmph.code = ICMP_EXT_MAL_QUERY;
+	goto send_reply;
 }
 
 /*

@@ -1088,6 +1192,11 @@ 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)
+		goto probe;
+
 	/*
 	 *	18 is the highest 'known' ICMP type. Anything else is a mystery
 	 *

@@ -1097,7 +1206,6 @@ int icmp_rcv(struct sk_buff *skb)
 	if (icmph->type > NR_ICMP_TYPES)
 		goto error;
 
-
 	/*
 	 *	Parse the ICMP message
 	 */

@@ -1123,7 +1231,7 @@ 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;

@@ -1137,6 +1245,12 @@ 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 it is an array of
+	 * size NR_ICMP_TYPES + 1 (19 elements) and PROBE has code 42.
+	 */
+	success = icmp_echo(skb);
+	goto success_check;
 }
 
 static bool ip_icmp_error_rfc4884_validate(const struct sk_buff *skb, int off)

@@ -1340,6 +1454,7 @@ static int __net_init icmp_sk_init(struct net *net)
 
 	/* Control parameters for ECHO replies. */
 	net->ipv4.sysctl_icmp_echo_ignore_all = 0;
+	net->ipv4.sysctl_icmp_echo_enable_probe = 0;
 	net->ipv4.sysctl_icmp_echo_ignore_broadcasts = 1;
 
 	/* Control parameter - ignore bogus broadcast responses? */

-- 
2.17.1

On Sun, Mar 14, 2021 at 12:50 PM Andreas Roeseler
[off-list ref] wrote:

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

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

This was tested using a custom modification to 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).

If you happen to use github or something similar, if you don't mind
sharing the code, you could clone the iputils repo and publish the
changes. No pressure.

I don't think the conditional is needed (?)

 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;
        struct net *net;
+       u16 ident_len;
+       char *buff;
+       u8 status;

        net = dev_net(skb_dst(skb)->dev);
-       if (!net->ipv4.sysctl_icmp_echo_ignore_all) {
-               struct icmp_bxm icmp_param;
-
-               icmp_param.data.icmph      = *icmp_hdr(skb);
-               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);
-       }
        /* should there be an ICMP stat for ignored echos? */
-       return true;
+       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);
+
+       if (icmp_param.data.icmph.type == ICMP_ECHO)
+               goto send_reply;

Is this path now missing

               icmp_param.data.icmph.type = ICMP_ECHOREPLY;

+       if (!net->ipv4.sysctl_icmp_echo_enable_probe)
+               return true;
+       /* 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;
+       /* Clear status bits in reply message */
+       icmp_param.data.icmph.un.echo.sequence &= htons(0xFF00);
+       icmp_param.data.icmph.type = ICMP_EXT_ECHOREPLY;
+       ext_hdr = skb_header_pointer(skb, 0, sizeof(_ext_hdr), &_ext_hdr);
+       iio = skb_header_pointer(skb, sizeof(_ext_hdr), sizeof(_iio), &_iio);
+       if (!ext_hdr || !iio)
+               goto send_mal_query;
+       if (ntohs(iio->extobj_hdr.length) <= sizeof(iio->extobj_hdr))
+               goto send_mal_query;
+       ident_len = ntohs(iio->extobj_hdr.length) - sizeof(iio->extobj_hdr);
+       status = 0;
+       dev = NULL;
+       switch (iio->extobj_hdr.class_type) {
+       case EXT_ECHO_CTYPE_NAME:
+               if (ident_len >= IFNAMSIZ)
+                       goto send_mal_query;
+               buff = kcalloc(IFNAMSIZ, sizeof(char), GFP_KERNEL);
+               if (!buff)
+                       return -ENOMEM;
+               memcpy(buff, &iio->ident.name, ident_len);
+               /* RFC 8335 2.1 If the Object Payload would not otherwise terminate
+                * on a 32-bit boundary, it MUST be padded with ASCII NULL characters
+                */
+               if (ident_len % sizeof(u32) != 0) {
+                       u8 i;
+
+                       for (i = ident_len; i % sizeof(u32) != 0; i++) {
+                               if (buff[i] != '\0')
+                                       goto send_mal_query;

Memory leak. IFNAMSIZ is small enough that you can use on-stack allocation

Also, I think you can ignore if there are non-zero bytes beyond the
len. We need to safely parse to avoid integrity bugs in the kernel.
Beyond that, it's fine to be strict about what you send, liberal what
you accept.

just make this a branch instead of

On Mon, 2021-03-15 at 11:50 -0400, Willem de Bruijn wrote:

On Sun, Mar 14, 2021 at 12:50 PM Andreas Roeseler
[off-list ref] wrote:

quoted

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

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

This was tested using a custom modification to 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).

If you happen to use github or something similar, if you don't mind
sharing the code, you could clone the iputils repo and publish the
changes. No pressure.

Should I include the link to the github repo in the patch?

quoted

 net/ipv4/icmp.c | 145 +++++++++++++++++++++++++++++++++++++++++++-
----
 1 file changed, 130 insertions(+), 15 deletions(-)

diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 616e2dc1c8fa..f1530011b7bc 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c

@@ -93,6 +93,10 @@

 #include <net/ip_fib.h>
 #include <net/l3mdev.h>

+#if IS_ENABLED(CONFIG_IPV6)
+#include <net/addrconf.h>
+#endif

I don't think the conditional is needed (?)

quoted

 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;
        struct net *net;
+       u16 ident_len;
+       char *buff;
+       u8 status;

        net = dev_net(skb_dst(skb)->dev);
-       if (!net->ipv4.sysctl_icmp_echo_ignore_all) {
-               struct icmp_bxm icmp_param;
-
-               icmp_param.data.icmph      = *icmp_hdr(skb);
-               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);
-       }
        /* should there be an ICMP stat for ignored echos? */
-       return true;
+       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);
+
+       if (icmp_param.data.icmph.type == ICMP_ECHO)
+               goto send_reply;

Is this path now missing

               icmp_param.data.icmph.type = ICMP_ECHOREPLY;

quoted

+       if (!net->ipv4.sysctl_icmp_echo_enable_probe)
+               return true;
+       /* 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;
+       /* Clear status bits in reply message */
+       icmp_param.data.icmph.un.echo.sequence &= htons(0xFF00);
+       icmp_param.data.icmph.type = ICMP_EXT_ECHOREPLY;
+       ext_hdr = skb_header_pointer(skb, 0, sizeof(_ext_hdr),
&_ext_hdr);
+       iio = skb_header_pointer(skb, sizeof(_ext_hdr),
sizeof(_iio), &_iio);
+       if (!ext_hdr || !iio)
+               goto send_mal_query;
+       if (ntohs(iio->extobj_hdr.length) <= sizeof(iio-

quoted

extobj_hdr))

+               goto send_mal_query;
+       ident_len = ntohs(iio->extobj_hdr.length) - sizeof(iio-

quoted

extobj_hdr);

+       status = 0;
+       dev = NULL;
+       switch (iio->extobj_hdr.class_type) {
+       case EXT_ECHO_CTYPE_NAME:
+               if (ident_len >= IFNAMSIZ)
+                       goto send_mal_query;
+               buff = kcalloc(IFNAMSIZ, sizeof(char), GFP_KERNEL);
+               if (!buff)
+                       return -ENOMEM;
+               memcpy(buff, &iio->ident.name, ident_len);
+               /* RFC 8335 2.1 If the Object Payload would not
otherwise terminate
+                * on a 32-bit boundary, it MUST be padded with
ASCII NULL characters
+                */
+               if (ident_len % sizeof(u32) != 0) {
+                       u8 i;
+
+                       for (i = ident_len; i % sizeof(u32) != 0;
i++) {
+                               if (buff[i] != '\0')
+                                       goto send_mal_query;

Memory leak. IFNAMSIZ is small enough that you can use on-stack
allocation

Also, I think you can ignore if there are non-zero bytes beyond the
len. We need to safely parse to avoid integrity bugs in the kernel.
Beyond that, it's fine to be strict about what you send, liberal what
you accept.

This checks that the incoming request is padded to the nearest 32-bit
boundary by ASCII NULL characters, as specified by RFC 8335

quoted

+                       }
+               }
+               dev = dev_get_by_name(net, buff);
+               kfree(buff);
+               break;
+       case EXT_ECHO_CTYPE_INDEX:
+               if (ident_len != sizeof(iio->ident.ifindex))
+                       goto send_mal_query;
+               dev = dev_get_by_index(net, ntohl(iio-

quoted

ident.ifindex));

+               break;
+       case EXT_ECHO_CTYPE_ADDR:
+               if (ident_len != sizeof(iio->ident.addr.ctype3_hdr)
+ iio->ident.addr.ctype3_hdr.addrlen)
+                       goto send_mal_query;
+               switch (ntohs(iio->ident.addr.ctype3_hdr.afi)) {
+               case ICMP_AFI_IP:
+                       if (ident_len != sizeof(iio-

quoted

ident.addr.ctype3_hdr) + sizeof(struct in_addr))

+                               goto send_mal_query;
+                       dev = ip_dev_find(net, iio-

quoted

ident.addr.ip_addr.ipv4_addr.s_addr);

+                       break;
+#if IS_ENABLED(CONFIG_IPV6)
+               case ICMP_AFI_IP6:
+                       if (ident_len != sizeof(iio-

quoted

ident.addr.ctype3_hdr) + sizeof(struct in6_addr))

+                               goto send_mal_query;
+                       rcu_read_lock();
+                       dev = ipv6_dev_find(net, &iio-

quoted

ident.addr.ip_addr.ipv6_addr, dev);

+                       if (dev)
+                               dev_hold(dev);
+                       rcu_read_unlock();
+                       break;
+#endif
+               default:
+                       goto send_mal_query;
+               }
+               break;
+       default:
+               goto send_mal_query;
+       }
+       if (!dev) {
+               icmp_param.data.icmph.code = ICMP_EXT_NO_IF;
+               goto send_reply;
+       }
+       /* Fill bits in reply message */
+       if (dev->flags & IFF_UP)
+               status |= EXT_ECHOREPLY_ACTIVE;
+       if (__in_dev_get_rcu(dev) && __in_dev_get_rcu(dev)-

quoted

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;
+send_mal_query:
+       icmp_param.data.icmph.code = ICMP_EXT_MAL_QUERY;
+       goto send_reply;
 }

 /*

@@ -1088,6 +1192,11 @@ 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)
+               goto probe;
+
        /*
         *      18 is the highest 'known' ICMP type. Anything else
is a mystery
         *

@@ -1097,7 +1206,6 @@ int icmp_rcv(struct sk_buff *skb)

        if (icmph->type > NR_ICMP_TYPES)
                goto error;

-
        /*
         *      Parse the ICMP message
         */

@@ -1123,7 +1231,7 @@ 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;

@@ -1137,6 +1245,12 @@ 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 it is an
array of
+        * size NR_ICMP_TYPES + 1 (19 elements) and PROBE has code
42.
+        */
+       success = icmp_echo(skb);
+       goto success_check;

just make this a branch instead of

Could you clarify this comment? Do you mean move this code to the
section where we check for PROBE messages instead of jumping to probe
and then jumping to success_check?

On Mon, Mar 15, 2021 at 3:10 PM Andreas Roeseler
[off-list ref] wrote:

On Mon, 2021-03-15 at 11:50 -0400, Willem de Bruijn wrote:

quoted

On Sun, Mar 14, 2021 at 12:50 PM Andreas Roeseler
[off-list ref] wrote:

quoted

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

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

This was tested using a custom modification to 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).

If you happen to use github or something similar, if you don't mind
sharing the code, you could clone the iputils repo and publish the
changes. No pressure.

Should I include the link to the github repo in the patch?

If you don't mind, please do. It can serve as example for others to
use the feature, too.

quoted

quoted

 net/ipv4/icmp.c | 145 +++++++++++++++++++++++++++++++++++++++++++-
----
 1 file changed, 130 insertions(+), 15 deletions(-)

diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 616e2dc1c8fa..f1530011b7bc 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c

@@ -93,6 +93,10 @@
 #include <net/ip_fib.h>
 #include <net/l3mdev.h>

+#if IS_ENABLED(CONFIG_IPV6)
+#include <net/addrconf.h>
+#endif

I don't think the conditional is needed (?)

quoted

 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;
        struct net *net;
+       u16 ident_len;
+       char *buff;
+       u8 status;

        net = dev_net(skb_dst(skb)->dev);
-       if (!net->ipv4.sysctl_icmp_echo_ignore_all) {
-               struct icmp_bxm icmp_param;
-
-               icmp_param.data.icmph      = *icmp_hdr(skb);
-               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);
-       }
        /* should there be an ICMP stat for ignored echos? */
-       return true;
+       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);
+
+       if (icmp_param.data.icmph.type == ICMP_ECHO)
+               goto send_reply;

Is this path now missing

               icmp_param.data.icmph.type = ICMP_ECHOREPLY;

quoted

+       if (!net->ipv4.sysctl_icmp_echo_enable_probe)
+               return true;
+       /* 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;
+       /* Clear status bits in reply message */
+       icmp_param.data.icmph.un.echo.sequence &= htons(0xFF00);
+       icmp_param.data.icmph.type = ICMP_EXT_ECHOREPLY;
+       ext_hdr = skb_header_pointer(skb, 0, sizeof(_ext_hdr),
&_ext_hdr);
+       iio = skb_header_pointer(skb, sizeof(_ext_hdr),
sizeof(_iio), &_iio);
+       if (!ext_hdr || !iio)
+               goto send_mal_query;
+       if (ntohs(iio->extobj_hdr.length) <= sizeof(iio-

quoted

extobj_hdr))

+               goto send_mal_query;
+       ident_len = ntohs(iio->extobj_hdr.length) - sizeof(iio-

quoted

extobj_hdr);

+       status = 0;
+       dev = NULL;
+       switch (iio->extobj_hdr.class_type) {
+       case EXT_ECHO_CTYPE_NAME:
+               if (ident_len >= IFNAMSIZ)
+                       goto send_mal_query;
+               buff = kcalloc(IFNAMSIZ, sizeof(char), GFP_KERNEL);
+               if (!buff)
+                       return -ENOMEM;
+               memcpy(buff, &iio->ident.name, ident_len);
+               /* RFC 8335 2.1 If the Object Payload would not
otherwise terminate
+                * on a 32-bit boundary, it MUST be padded with
ASCII NULL characters
+                */
+               if (ident_len % sizeof(u32) != 0) {
+                       u8 i;
+
+                       for (i = ident_len; i % sizeof(u32) != 0;
i++) {
+                               if (buff[i] != '\0')
+                                       goto send_mal_query;

Memory leak. IFNAMSIZ is small enough that you can use on-stack
allocation

Also, I think you can ignore if there are non-zero bytes beyond the
len. We need to safely parse to avoid integrity bugs in the kernel.
Beyond that, it's fine to be strict about what you send, liberal what
you accept.

This checks that the incoming request is padded to the nearest 32-bit
boundary by ASCII NULL characters, as specified by RFC 8335

Right. The question is whether you need to be strict in enforcing
that. Perhaps the RFC states that explicitly. Else, it's up to your
interpretation. I suggested the robustness principle, which is
commonly employed in such instances.

quoted

quoted

+                       }
+               }
+               dev = dev_get_by_name(net, buff);
+               kfree(buff);
+               break;
+       case EXT_ECHO_CTYPE_INDEX:
+               if (ident_len != sizeof(iio->ident.ifindex))
+                       goto send_mal_query;
+               dev = dev_get_by_index(net, ntohl(iio-

quoted

ident.ifindex));

+               break;
+       case EXT_ECHO_CTYPE_ADDR:
+               if (ident_len != sizeof(iio->ident.addr.ctype3_hdr)
+ iio->ident.addr.ctype3_hdr.addrlen)
+                       goto send_mal_query;
+               switch (ntohs(iio->ident.addr.ctype3_hdr.afi)) {
+               case ICMP_AFI_IP:
+                       if (ident_len != sizeof(iio-

quoted

ident.addr.ctype3_hdr) + sizeof(struct in_addr))

+                               goto send_mal_query;
+                       dev = ip_dev_find(net, iio-

quoted

ident.addr.ip_addr.ipv4_addr.s_addr);

+                       break;
+#if IS_ENABLED(CONFIG_IPV6)
+               case ICMP_AFI_IP6:
+                       if (ident_len != sizeof(iio-

quoted

ident.addr.ctype3_hdr) + sizeof(struct in6_addr))

+                               goto send_mal_query;
+                       rcu_read_lock();
+                       dev = ipv6_dev_find(net, &iio-

quoted

ident.addr.ip_addr.ipv6_addr, dev);

+                       if (dev)
+                               dev_hold(dev);
+                       rcu_read_unlock();
+                       break;
+#endif
+               default:
+                       goto send_mal_query;
+               }
+               break;
+       default:
+               goto send_mal_query;
+       }
+       if (!dev) {
+               icmp_param.data.icmph.code = ICMP_EXT_NO_IF;
+               goto send_reply;
+       }
+       /* Fill bits in reply message */
+       if (dev->flags & IFF_UP)
+               status |= EXT_ECHOREPLY_ACTIVE;
+       if (__in_dev_get_rcu(dev) && __in_dev_get_rcu(dev)-

quoted

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;
+send_mal_query:
+       icmp_param.data.icmph.code = ICMP_EXT_MAL_QUERY;
+       goto send_reply;
 }

 /*

@@ -1088,6 +1192,11 @@ 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)
+               goto probe;
+
        /*
         *      18 is the highest 'known' ICMP type. Anything else

is a mystery
         *

@@ -1097,7 +1206,6 @@ int icmp_rcv(struct sk_buff *skb)
        if (icmph->type > NR_ICMP_TYPES)
                goto error;

-
        /*
         *      Parse the ICMP message
         */

@@ -1123,7 +1231,7 @@ 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;

@@ -1137,6 +1245,12 @@ 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 it is an

array of
+        * size NR_ICMP_TYPES + 1 (19 elements) and PROBE has code
42.
+        */
+       success = icmp_echo(skb);
+       goto success_check;

just make this a branch instead of

Could you clarify this comment? Do you mean move this code to the
section where we check for PROBE messages instead of jumping to probe
and then jumping to success_check?

Exactly