Message-Id: <20210317221959.4410-1-ishaangandhi@gmail.com>
Date:   Wed, 17 Mar 2021 15:19:59 -0700
From:   ishaangandhi <ishaangandhi@...il.com>
To:     davem@...emloft.net
Cc:     ishaangandhi@...il.com, netdev@...r.kernel.org, willemb@...gle.com,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Stephen Hemminger <stephen@...workplumber.org>
Subject: [PATCH v3] icmp: support rfc5837

From: ishaan <ishaangandhi@...il.com>

This patch identifies the interface a packet arrived on when sending
ICMP time exceeded, destination unreachable, and parameter problem
messages, in accordance with RFC 5837.

It was tested by pinging a machine with a ttl of 1, and observing the
response in Wireshark.

Changes since v1:
- Add sysctls, feature is disabled by default
- Device name is always less than 63, so don't check this
- MTU is always included in net_device, so don't check its presence
- Support IPv6 as first class citizen
- Increment lengths via sizeof operator as opposed to int literals
- Initialize more local variables with defaults

Changes since v2:
- Remove check for device name
- Get first entry instead of last in IPv6 addr list
- Use ALIGN macro for alignment
- Remove verification function only gets called with
  ip_version 4 or 6.
Reported-by: Willem de Bruijn <willemdebruijn.kernel@...il.com>
- Use /* */ style comments instead of // style
Reported-by: Stephen Hemminger <stephen@...workplumber.org>
- Use proc_dointvec_minmax to constrain sysctl values
- Release dev with dev_put once finished
- Simplify logic for padding the end of the original datagram
- Fix off by one error in where the length of the original datagram
  is written into the IP header (6th and 5th bytes for ICMPv4 and v6
  respectively are accessed at icmph[5] and icmph[4] respectively,
  not icmph[6] and icmph[5].)

Signed-off-by: Ishaan Gandhi <ishaangandhi@...il.com>

---
 Documentation/networking/ip-sysctl.rst |   9 ++
 include/linux/icmp.h                   |   3 +
 include/net/netns/ipv4.h               |   1 +
 include/net/netns/ipv6.h               |   1 +
 include/uapi/linux/icmp.h              |  26 ++++
 net/ipv4/icmp.c                        | 157 +++++++++++++++++++++++++
 net/ipv4/sysctl_net_ipv4.c             |   9 ++
 net/ipv6/af_inet6.c                    |   1 +
 net/ipv6/icmp.c                        |  17 +++
 9 files changed, 224 insertions(+)

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 837d51f9e1fa..55d38539a72a 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -1204,6 +1204,15 @@ icmp_errors_use_inbound_ifaddr - BOOLEAN
 
 	Default: 0
 
+icmp_errors_identify_if - BOOLEAN
+
+	If 1, then the kernel will append an extension object identifying
+	the interface on which the packet which caused the error. The
+	object will contain the ifIndex, interface name, interface IP
+	address, and/or MTU, in accordance with RFC5837.
+
+	Default: 0
+
 igmp_max_memberships - INTEGER
 	Change the maximum number of multicast groups we can subscribe to.
 	Default: 20
diff --git a/include/linux/icmp.h b/include/linux/icmp.h
index 8fc38a34cb20..db1a17dbc338 100644
--- a/include/linux/icmp.h
+++ b/include/linux/icmp.h
@@ -39,4 +39,7 @@ static inline bool icmp_is_err(int type)
 void ip_icmp_error_rfc4884(const struct sk_buff *skb,
 			   struct sock_ee_data_rfc4884 *out);
 
+void icmp_identify_arrival_interface(struct sk_buff *skb, struct net *net, int room,
+				     char *icmph, int ip_version);
+
 #endif	/* _LINUX_ICMP_H */
diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index 9e36738c1fe1..fd68a47f1130 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -90,6 +90,7 @@ struct netns_ipv4 {
 	int sysctl_icmp_ratelimit;
 	int sysctl_icmp_ratemask;
 	int sysctl_icmp_errors_use_inbound_ifaddr;
+	int sysctl_icmp_errors_identify_if;
 
 	struct local_ports ip_local_ports;
 
diff --git a/include/net/netns/ipv6.h b/include/net/netns/ipv6.h
index 5ec054473d81..9608e0a82401 100644
--- a/include/net/netns/ipv6.h
+++ b/include/net/netns/ipv6.h
@@ -36,6 +36,7 @@ struct netns_sysctl_ipv6 {
 	int icmpv6_echo_ignore_all;
 	int icmpv6_echo_ignore_multicast;
 	int icmpv6_echo_ignore_anycast;
+	int icmpv6_errors_identify_if;
 	DECLARE_BITMAP(icmpv6_ratemask, ICMPV6_MSG_MAX + 1);
 	unsigned long *icmpv6_ratemask_ptr;
 	int anycast_src_echo_reply;
diff --git a/include/uapi/linux/icmp.h b/include/uapi/linux/icmp.h
index fb169a50895e..f43ecd3c3677 100644
--- a/include/uapi/linux/icmp.h
+++ b/include/uapi/linux/icmp.h
@@ -118,4 +118,30 @@ struct icmp_extobj_hdr {
 	__u8		class_type;
 };
 
+/* RFC 5837 Bitmasks */
+#define ICMP_5837_MTU_CTYPE		(1 << 0)
+#define ICMP_5837_NAME_CTYPE		(1 << 1)
+#define ICMP_5837_IP_ADDR_CTYPE		(1 << 2)
+#define ICMP_5837_IF_INDEX_CTYPE	(1 << 3)
+
+#define ICMP_5837_ARRIVAL_ROLE_CTYPE	(0 << 6)
+#define ICMP_5837_SUB_IP_ROLE_CTYPE	(1 << 6)
+#define ICMP_5837_FORWARD_ROLE_CTYPE	(2 << 6)
+#define ICMP_5837_NEXT_HOP_ROLE_CTYPE	(3 << 6)
+
+#define ICMP_5837_MIN_ORIG_LEN 128
+
+/* RFC 5837 Interface IP Address sub-object */
+struct interface_ipv4_addr_sub_obj {
+	__be16 afi;
+	__be16 reserved;
+	__be32 addr;
+};
+
+struct interface_ipv6_addr_sub_obj {
+	__be16 afi;
+	__be16 reserved;
+	__be32 addr[4];
+};
+
 #endif /* _UAPI_LINUX_ICMP_H */
diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 793aebf07c2a..c203758471c7 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -87,6 +87,7 @@
 #include <linux/timer.h>
 #include <linux/init.h>
 #include <linux/uaccess.h>
+#include <net/addrconf.h>
 #include <net/checksum.h>
 #include <net/xfrm.h>
 #include <net/inet_common.h>
@@ -555,6 +556,156 @@ static struct rtable *icmp_route_lookup(struct net *net,
 	return ERR_PTR(err);
 }
 
+/*  Appends interface identification object to ICMP packet to identify
+ *  the interface on which the original datagram arrived, per RFC 5837.
+ *
+ *  Should only be called on the following messages
+ *  - ICMPv4 Time Exceeded
+ *  - ICMPv4 Destination Unreachable
+ *  - ICMPv4 Parameter Problem
+ *  - ICMPv6 Time Exceeded
+ *  - ICMPv6 Destination Unreachable
+ */
+
+void icmp_identify_arrival_interface(struct sk_buff *skb, struct net *net, int room,
+				     char *icmph, int ip_version)
+{
+	unsigned int ext_len, orig_len, word_aligned_orig_len, offset, extra_space_needed,
+		     if_index, mtu = 0, name_len = 0, name_subobj_len = 0;
+	struct interface_ipv4_addr_sub_obj ip4_addr_subobj = {.addr = 0};
+	struct interface_ipv6_addr_sub_obj ip6_addr_subobj;
+	struct icmp_extobj_hdr *iio_hdr;
+	struct inet6_ifaddr ip6_ifaddr;
+	struct inet6_dev *dev6 = NULL;
+	struct icmp_ext_hdr *ext_hdr;
+	char *name = NULL, ctype;
+	struct net_device *dev;
+	void *subobj_offset;
+
+	skb_linearize(skb);
+	if_index = inet_iif(skb);
+	orig_len = skb->len - skb_network_offset(skb);
+
+	/* IPv4 messages MUST be 32-bit aligned, IPv6 64-bit aligned.
+	 * Both must be padded to 128 bytes. */
+	if (ip_version == 4) {
+		word_aligned_orig_len = max_t(unsigned int, ALIGN(orig_len, 4), 128);
+		icmph[5] = word_aligned_orig_len / 4;
+	} else {
+		word_aligned_orig_len = max_t(unsigned int, ALIGN(orig_len, 8), 128);
+		icmph[4] = word_aligned_orig_len / 8;
+	}
+
+	ctype = ICMP_5837_ARRIVAL_ROLE_CTYPE;
+	ext_len = sizeof(struct icmp_ext_hdr) + sizeof(struct icmp_extobj_hdr);
+
+	/* Always add if_index to the IIO */
+	ext_len += sizeof(__be32);
+	ctype |= ICMP_5837_IF_INDEX_CTYPE;
+
+	dev = dev_get_by_index(net, if_index);
+	/* Try to append IP address, name, and MTU */
+	if (dev) {
+		if (ip_version == 4) {
+			ip4_addr_subobj.addr = inet_select_addr(dev, 0, RT_SCOPE_UNIVERSE);
+			if (ip4_addr_subobj.addr) {
+				ip4_addr_subobj.afi = htons(1);
+				ip4_addr_subobj.reserved = 0;
+				ctype |= ICMP_5837_IP_ADDR_CTYPE;
+				ext_len += sizeof(ip4_addr_subobj);
+			}
+		}
+		if (ip_version == 6) {
+			dev6 = in6_dev_get(dev);
+			if (dev6) {
+				ip6_ifaddr = *list_first_entry(&dev6->addr_list,
+							      struct inet6_ifaddr, if_list);
+				memcpy(ip6_addr_subobj.addr, ip6_ifaddr.addr.s6_addr32,
+				       sizeof(ip6_addr_subobj.addr));
+				ip6_addr_subobj.afi = htons(2);
+				ip6_addr_subobj.reserved = 0;
+				ctype |= ICMP_5837_IP_ADDR_CTYPE;
+				ext_len += sizeof(ip6_addr_subobj);
+			}
+		}
+
+		name = dev->name;
+		name_len = strlen(name);
+		/* Subobj has 1 extra byte for the length field, and is 32 bit-aligned */
+		name_subobj_len = ALIGN(name_len + 1, 4);
+		ctype |= ICMP_5837_NAME_CTYPE;
+		ext_len += name_subobj_len;
+
+		mtu = dev->mtu;
+		ctype |= ICMP_5837_MTU_CTYPE;
+		ext_len += sizeof(__be32);
+
+		dev_put(dev);
+	}
+
+	if (word_aligned_orig_len + ext_len > room) {
+		offset = room - ext_len;
+		extra_space_needed = room - orig_len;
+	} else {
+		/* There is enough room to just add to the end of the packet.
+		 * We need (word_aligned_orig_len - orig_len bytes) for padding
+		 * and ext_len bytes for the extension. */
+		offset = word_aligned_orig_len;
+		extra_space_needed = ext_len + (word_aligned_orig_len - orig_len);
+	}
+
+	if (skb_tailroom(skb) < extra_space_needed) {
+		if (pskb_expand_head(skb, 0, extra_space_needed - skb_tailroom(skb), GFP_ATOMIC))
+			return;
+	}
+	skb_put(skb, extra_space_needed);
+
+	/* Zero-pad from the end of the original message to the beginning of the header */
+	memset(skb_network_header(skb) + orig_len, 0, word_aligned_orig_len - orig_len);
+
+	ext_hdr = (struct icmp_ext_hdr *)(skb_network_header(skb) + offset);
+	iio_hdr = (struct icmp_extobj_hdr *)(ext_hdr + 1);
+	subobj_offset = (void *)(iio_hdr + 1);
+
+	ext_hdr->reserved1 = 0;
+	ext_hdr->reserved2 = 0;
+	ext_hdr->version = 2;
+	ext_hdr->checksum = 0;
+
+	iio_hdr->length = htons(ext_len - sizeof(struct icmp_ext_hdr));
+	iio_hdr->class_num = 2;
+	iio_hdr->class_type = ctype;
+
+	*(__be32 *)subobj_offset = htonl(if_index);
+	subobj_offset += sizeof(__be32);
+
+	if (ip4_addr_subobj.addr) {
+		*(struct interface_ipv4_addr_sub_obj *)subobj_offset = ip4_addr_subobj;
+		subobj_offset += sizeof(ip4_addr_subobj);
+	}
+
+	if (dev6) {
+		*(struct interface_ipv6_addr_sub_obj *)subobj_offset = ip6_addr_subobj;
+		subobj_offset += sizeof(ip6_addr_subobj);
+	}
+
+	if (name) {
+		*(__u8 *)subobj_offset = name_subobj_len;
+		subobj_offset += sizeof(__u8);
+		memcpy(subobj_offset, name, name_len);
+		memset(subobj_offset + name_len, 0, name_subobj_len - (name_len + sizeof(__u8)));
+		subobj_offset += name_subobj_len - sizeof(__u8);
+	}
+
+	if (mtu) {
+		*(__be32 *)subobj_offset = htonl(mtu);
+		subobj_offset += sizeof(__be32);
+	}
+
+	ext_hdr->checksum =
+		csum_fold(skb_checksum(skb, skb_network_offset(skb) + offset, ext_len, 0));
+}
+
 /*
  *	Send an ICMP message in response to a situation
  *
@@ -731,6 +882,11 @@ void __icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info,
 		room = 576;
 	room -= sizeof(struct iphdr) + icmp_param.replyopts.opt.opt.optlen;
 	room -= sizeof(struct icmphdr);
+	if (net->ipv4.sysctl_icmp_errors_identify_if && (type == ICMP_DEST_UNREACH ||
+	    type == ICMP_TIME_EXCEEDED || type == ICMP_PARAMETERPROB)) {
+		icmp_identify_arrival_interface(skb_in, net, room,
+						(char *)&icmp_param.data.icmph, 4);
+	}
 
 	icmp_param.data_len = skb_in->len - icmp_param.offset;
 	if (icmp_param.data_len > room)
@@ -1349,6 +1505,7 @@ static int __net_init icmp_sk_init(struct net *net)
 	net->ipv4.sysctl_icmp_ratelimit = 1 * HZ;
 	net->ipv4.sysctl_icmp_ratemask = 0x1818;
 	net->ipv4.sysctl_icmp_errors_use_inbound_ifaddr = 0;
+	net->ipv4.sysctl_icmp_errors_identify_if = 0;
 
 	return 0;
 
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 5653e3b011bf..c54881136497 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -628,6 +628,15 @@ static struct ctl_table ipv4_net_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec
 	},
+	{
+		.procname	= "icmp_errors_identify_if",
+		.data		= &init_net.ipv4.sysctl_icmp_errors_identify_if,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE,
+	},
 	{
 		.procname	= "icmp_ratelimit",
 		.data		= &init_net.ipv4.sysctl_icmp_ratelimit,
diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
index b304b882e031..3901c2a99be4 100644
--- a/net/ipv6/af_inet6.c
+++ b/net/ipv6/af_inet6.c
@@ -939,6 +939,7 @@ static int __net_init inet6_net_init(struct net *net)
 	net->ipv6.sysctl.icmpv6_echo_ignore_all = 0;
 	net->ipv6.sysctl.icmpv6_echo_ignore_multicast = 0;
 	net->ipv6.sysctl.icmpv6_echo_ignore_anycast = 0;
+	net->ipv6.sysctl.icmpv6_errors_identify_if = 0;
 
 	/* By default, rate limit error messages.
 	 * Except for pmtu discovery, it would break it.
diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
index 9df8737ae0d3..ad4c986b806b 100644
--- a/net/ipv6/icmp.c
+++ b/net/ipv6/icmp.c
@@ -595,6 +595,13 @@ static void icmp6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info,
 	msg.offset = skb_network_offset(skb);
 	msg.type = type;
 
+	if (net->ipv6.sysctl.icmpv6_errors_identify_if &&
+	    (type == ICMPV6_DEST_UNREACH || type == ICMPV6_TIME_EXCEED)) {
+		icmp_identify_arrival_interface(skb, net,
+			IPV6_MIN_MTU - sizeof(struct ipv6hdr) - sizeof(struct icmp6hdr),
+			(char *)&tmp_hdr, 6);
+	}
+
 	len = skb->len - msg.offset;
 	len = min_t(unsigned int, len, IPV6_MIN_MTU - sizeof(struct ipv6hdr) - sizeof(struct icmp6hdr));
 	if (len < 0) {
@@ -1184,6 +1191,15 @@ static struct ctl_table ipv6_icmp_table_template[] = {
 		.mode		= 0644,
 		.proc_handler = proc_do_large_bitmap,
 	},
+	{
+		.procname	= "errors_identify_if",
+		.data		= &init_net.ipv6.sysctl.icmpv6_errors_identify_if,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler = proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE,
+	},
 	{ },
 };
 
@@ -1201,6 +1217,7 @@ struct ctl_table * __net_init ipv6_icmp_sysctl_init(struct net *net)
 		table[2].data = &net->ipv6.sysctl.icmpv6_echo_ignore_multicast;
 		table[3].data = &net->ipv6.sysctl.icmpv6_echo_ignore_anycast;
 		table[4].data = &net->ipv6.sysctl.icmpv6_ratemask_ptr;
+		table[5].data = &net->ipv6.sysctl.icmpv6_errors_identify_if;
 	}
 	return table;
 }
-- 
2.25.1

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