[PATCH v2 2/4] net: ipv6: Add support for default gateway discovery.

emohandesi
2023-04-10T19:36:18Z

From: Ehsan Mohandesi <emohandesi@microsoft.com>

In IPv6, the default gateway and prefix length are determined by receiving
a router advertisement as defined in -
https://www.rfc-editor.org/rfc/rfc4861.

Add support for sending router solicitation (RS) and processing router
advertisements (RA).

If the RA has prefix info option and following conditions are met, then
gatewayip6 and net_prefix_length of ip6addr env variables are initialized.
These are later consumed by IPv6 code for non-local destination IP.

- "Router Lifetime" != 0
- Prefix is NOT link-local prefix (0xfe80::/10)
- L flag is 1
- "Valid Lifetime" != 0

Timing Parameters:
- MAX_RTR_SOLICITATION_DELAY (0-1s)
- RTR_SOLICITATION_INTERVAL (4s) (min retransmit delay)
- MAX_RTR_SOLICITATIONS (3 RS transmissions)

The functionality is enabled by CONFIG_IPV6_ROUTER_DISCOVERY and invoked
automatically from net_init_loop().

Signed-off-by: Ehsan Mohandesi <emohandesi@microsoft.com>

Conflicts:
cmd/Kconfig
net/net.c
---
Changes in v2:
- A few of cosmetic changes.
- Made some functions not static in order to be able to test them.

cmd/Kconfig | 6 ++
include/ndisc.h | 35 ++++++++
include/net.h | 3 +-
include/net6.h | 40 ++++++++++
net/ndisc.c | 243 +++++++++++++++++++++++++++++++++++++++++++++++++++++---
net/net.c | 23 +++++-
net/net6.c | 1 +
7 files changed, 339 insertions(+), 12 deletions(-)

diff --git a/cmd/Kconfig b/cmd/Kconfig
index e45b884..6919d31 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -1916,6 +1916,12 @@ config CMD_NCSI
Normally this happens automatically before other network
operations.

+config IPV6_ROUTER_DISCOVERY
+ bool "Do IPv6 router discovery"
+ depends on IPV6
+ help
+ Will automatically perform router solicitation on first IPv6
+ network operation
endif

config CMD_ETHSW
diff --git a/include/ndisc.h b/include/ndisc.h
index f6f8eb6..12fa9e7 100644
--- a/include/ndisc.h
+++ b/include/ndisc.h
@@ -19,6 +19,20 @@ struct nd_msg {
__u8 opt[0];
};

+/* struct rs_msg - ICMPv6 Router Solicitation message format */
+struct rs_msg {
+ struct icmp6hdr icmph;
+ __u8 opt[0];
+};
+
+/* struct ra_msg - ICMPv6 Router Advertisement message format */
+struct ra_msg {
+ struct icmp6hdr icmph;
+ __u32 reachable_time;
+ __u32 retransmission_timer;
+ __u8 opt[0];
+};
+
/* struct echo_msg - ICMPv6 echo request/reply message format */
struct echo_msg {
struct icmp6hdr icmph;
@@ -57,6 +71,11 @@ extern int net_nd_try;
*/
void ndisc_init(void);

+/*
+ * ip6_send_rs() - Send IPv6 Router Solicitation Message
+ */
+void ip6_send_rs(void);
+
/**
* ndisc_receive() - Handle ND packet
*
@@ -78,6 +97,8 @@ void ndisc_request(void);
* Return: 0 if no timeout, -1 otherwise
*/
int ndisc_timeout_check(void);
+bool validate_ra(struct ip6_hdr *ip6);
+int process_ra(struct ip6_hdr *ip6, int len);
#else
static inline void ndisc_init(void)
{
@@ -97,6 +118,20 @@ static inline int ndisc_timeout_check(void)
{
return 0;
}
+
+void ip6_send_rs(void)
+{
+}
+
+static inline bool validate_ra(struct ip6_hdr *ip6)
+{
+ return true;
+}
+
+static inline int process_ra(struct ip6_hdr *ip6, int len)
+{
+ return 0;
+}
#endif

#endif /* __NDISC_H__ */
diff --git a/include/net.h b/include/net.h
index 8ba50a0..58774f6 100644
--- a/include/net.h
+++ b/include/net.h
@@ -505,7 +505,8 @@ extern int net_restart_wrap; /* Tried all network devices */

enum proto_t {
BOOTP, RARP, ARP, TFTPGET, DHCP, DHCP6, PING, PING6, DNS, NFS, CDP,
- NETCONS, SNTP, TFTPSRV, TFTPPUT, LINKLOCAL, FASTBOOT, WOL, UDP, NCSI, WGET
+ NETCONS, SNTP, TFTPSRV, TFTPPUT, LINKLOCAL, FASTBOOT, WOL, UDP, NCSI,
+ WGET, RS
};

extern char net_boot_file_name[1024];/* Boot File name */
diff --git a/include/net6.h b/include/net6.h
index 2d7c5a0..beafc05 100644
--- a/include/net6.h
+++ b/include/net6.h
@@ -81,8 +81,17 @@ struct udp_hdr {
0x00, 0x00, 0x00, 0x00, \
0x00, 0x00, 0x00, 0x00, \
0x00, 0x00, 0x00, 0x00 } } }
+/*
+ * All-routers multicast address is the link-local scope address to reach all
+ * routers.
+ */
+#define ALL_ROUTERS_MULT_ADDR { { { 0xFF, 0x02, 0x00, 0x00, \
+ 0x00, 0x00, 0x00, 0x00, \
+ 0x00, 0x00, 0x00, 0x00, \
+ 0x00, 0x00, 0x00, 0x02 } } }

#define IPV6_LINK_LOCAL_PREFIX 0xfe80
+#define IPV6_LINK_LOCAL_MASK 0xffb0 /* The first 10-bit of address mask. */

/* hop limit for neighbour discovery packets */
#define IPV6_NDISC_HOPLIMIT 255
@@ -166,6 +175,37 @@ struct icmp6hdr {
#define icmp6_rt_lifetime icmp6_dataun.u_nd_ra.rt_lifetime
} __packed;

+/*
+ * struct icmp6_ra_prefix_info - Prefix Information option of the ICMPv6 message
+ * The Prefix Information option provides hosts with on-link prefixes and
+ * prefixes for Address Autoconfiguration. Refer to RFC 4861 for more info.
+ */
+struct icmp6_ra_prefix_info {
+ u8 type; /* Type is 3 for Prefix Information. */
+ u8 len; /* Len is 4 for Prefix Information. */
+ /* The number of leading bits in the Prefix that are valid. */
+ u8 prefix_len;
+ u8 reserved1:6, /* MUST be ignored by the receiver. */
+ aac:1, /* autonomous address-configuration flag */
+ /* Indicates that this prefix can be used for on-link determination. */
+ on_link:1;
+ /*
+ * The length of time in seconds that the prefix is valid for the
+ * purpose of on-link determination.
+ */
+ __be32 valid_lifetime;
+ /* The length of time addresses remain preferred. */
+ __be32 preferred_lifetime;
+ __be32 reserved2; /* MUST be ignored by the receiver. */
+ /*
+ * Prefix is an IP address or a prefix of an IP address. The Prefix
+ * Length field contains the number of valid leading bits in the prefix.
+ * The bits in the prefix after the prefix length are reserved and MUST
+ * be initialized to zero by the sender and ignored by the receiver.
+ */
+ struct in6_addr prefix;
+};
+
extern struct in6_addr const net_null_addr_ip6; /* NULL IPv6 address */
extern struct in6_addr net_gateway6; /* Our gateways IPv6 address */
extern struct in6_addr net_ip6; /* Our IPv6 addr (0 = unknown) */
diff --git a/net/ndisc.c b/net/ndisc.c
index 367dae7..0b27779 100644
--- a/net/ndisc.c
+++ b/net/ndisc.c
@@ -13,6 +13,8 @@
#include <net.h>
#include <net6.h>
#include <ndisc.h>
+#include <stdlib.h>
+#include <linux/delay.h>

/* IPv6 destination address of packet waiting for ND */
struct in6_addr net_nd_sol_packet_ip6 = ZERO_IPV6_ADDR;
@@ -29,31 +31,37 @@ int net_nd_tx_packet_size;
ulong net_nd_timer_start;
/* the number of requests we have sent so far */
int net_nd_try;
+struct in6_addr all_routers = ALL_ROUTERS_MULT_ADDR;
+
+#define MAX_RTR_SOLICITATIONS 3
+/* The maximum time to delay sending the first router solicitation message. */
+#define MAX_SOLICITATION_DELAY 1 // 1 second
+/* The time to wait before sending the next router solicitation message. */
+#define RTR_SOLICITATION_INTERVAL 4000 // 4 seconds

#define IP6_NDISC_OPT_SPACE(len) (((len) + 2 + 7) & ~7)

/**
* ndisc_insert_option() - Insert an option into a neighbor discovery packet
*
- * @ndisc: pointer to ND packet
+ * @opt: pointer to the option element of the neighbor discovery packet
* @type: option type to insert
* @data: option data to insert
* @len: data length
* Return: the number of bytes inserted (which may be >= len)
*/
-static int
-ndisc_insert_option(struct nd_msg *ndisc, int type, u8 *data, int len)
+static int ndisc_insert_option(__u8 *opt, int type, u8 *data, int len)
{
int space = IP6_NDISC_OPT_SPACE(len);

- ndisc->opt[0] = type;
- ndisc->opt[1] = space >> 3;
- memcpy(&ndisc->opt[2], data, len);
+ opt[0] = type;
+ opt[1] = space >> 3;
+ memcpy(&opt[2], data, len);
len += 2;

/* fill the remainder with 0 */
if (space - len > 0)
- memset(&ndisc->opt[len], '\0', space - len);
+ memset(&opt[len], '\0', space - len);

return space;
}
@@ -123,7 +131,7 @@ static void ip6_send_ns(struct in6_addr *neigh_addr)

/* Set the target address and llsaddr option */
net_copy_ip6(&msg->target, neigh_addr);
- ndisc_insert_option(msg, ND_OPT_SOURCE_LL_ADDR, net_ethaddr,
+ ndisc_insert_option(msg->opt, ND_OPT_SOURCE_LL_ADDR, net_ethaddr,
INETHADDRSZ);

/* checksum */
@@ -137,6 +145,76 @@ static void ip6_send_ns(struct in6_addr *neigh_addr)
net_send_packet(net_tx_packet, (pkt - net_tx_packet));
}

+/*
+ * ip6_send_rs() - Send IPv6 Router Solicitation Message.
+ *
+ * A router solicitation is sent to discover a router. RS message creation is
+ * based on RFC 4861 section 4.1. Router Solicitation Message Format.
+ */
+void ip6_send_rs(void)
+{
+ unsigned char enetaddr[6];
+ struct rs_msg *msg;
+ __u16 icmp_len;
+ uchar *pkt;
+ unsigned short csum;
+ unsigned int pcsum;
+ static unsigned int retry_count;
+
+ if (!ip6_is_unspecified_addr(&net_gateway6) &&
+ net_prefix_length != 0) {
+ net_set_state(NETLOOP_SUCCESS);
+ return;
+ } else if (retry_count >= MAX_RTR_SOLICITATIONS) {
+ net_set_state(NETLOOP_FAIL);
+ net_set_timeout_handler(0, NULL);
+ retry_count = 0;
+ return;
+ }
+
+ printf("ROUTER SOLICITATION %d\n", retry_count + 1);
+
+ ip6_make_mult_ethdstaddr(enetaddr, &all_routers);
+ /*
+ * ICMP length is the size of ICMP header (8) + one option (8) = 16.
+ * The option is 2 bytes of type and length + 6 bytes for MAC.
+ */
+ icmp_len = sizeof(struct icmp6hdr) + IP6_NDISC_OPT_SPACE(INETHADDRSZ);
+
+ pkt = (uchar *)net_tx_packet;
+ pkt += net_set_ether(pkt, enetaddr, PROT_IP6);
+ pkt += ip6_add_hdr(pkt, &net_link_local_ip6, &all_routers, PROT_ICMPV6,
+ IPV6_NDISC_HOPLIMIT, icmp_len);
+
+ /* ICMPv6 - RS */
+ msg = (struct rs_msg *)pkt;
+ msg->icmph.icmp6_type = IPV6_NDISC_ROUTER_SOLICITATION;
+ msg->icmph.icmp6_code = 0;
+ memset(&msg->icmph.icmp6_cksum, 0, sizeof(__be16));
+ memset(&msg->icmph.icmp6_unused, 0, sizeof(__be32));
+
+ /* Set the llsaddr option */
+ ndisc_insert_option(msg->opt, ND_OPT_SOURCE_LL_ADDR, net_ethaddr,
+ INETHADDRSZ);
+
+ /* checksum */
+ pcsum = csum_partial((__u8 *)msg, icmp_len, 0);
+ csum = csum_ipv6_magic(&net_link_local_ip6, &all_routers,
+ icmp_len, PROT_ICMPV6, pcsum);
+ msg->icmph.icmp6_cksum = csum;
+ pkt += icmp_len;
+
+ /* Wait up to 1 second if it is the first try to get the RA */
+ if (retry_count == 0)
+ udelay(((unsigned int)rand() % 1000000) * MAX_SOLICITATION_DELAY);
+
+ /* send it! */
+ net_send_packet(net_tx_packet, (pkt - net_tx_packet));
+
+ retry_count++;
+ net_set_timeout_handler(RTR_SOLICITATION_INTERVAL, ip6_send_rs);
+}
+
static void
ip6_send_na(uchar *eth_dst_addr, struct in6_addr *neigh_addr,
struct in6_addr *target)
@@ -167,7 +245,7 @@ ip6_send_na(uchar *eth_dst_addr, struct in6_addr *neigh_addr,
msg->icmph.icmp6_dataun.u_nd_advt.override = 1;
/* Set the target address and lltargetaddr option */
net_copy_ip6(&msg->target, target);
- ndisc_insert_option(msg, ND_OPT_TARGET_LL_ADDR, net_ethaddr,
+ ndisc_insert_option(msg->opt, ND_OPT_TARGET_LL_ADDR, net_ethaddr,
INETHADDRSZ);

/* checksum */
@@ -223,6 +301,10 @@ int ndisc_timeout_check(void)
return 1;
}

+/*
+ * ndisc_init() - Make initial steps for ND state machine.
+ * Usually move variables into initial state.
+ */
void ndisc_init(void)
{
net_nd_packet_mac = NULL;
@@ -234,12 +316,125 @@ void ndisc_init(void)
net_nd_tx_packet -= (ulong)net_nd_tx_packet % PKTALIGN;
}

+/*
+ * validate_ra() - Validate the router advertisement message.
+ *
+ * @ip6: Pointer to the router advertisement packet
+ *
+ * Check if the router advertisement message is valid. Conditions are
+ * according to RFC 4861 section 6.1.2. Validation of Router Advertisement
+ * Messages.
+ *
+ * Return: true if the message is valid and false if it is invalid.
+ */
+bool validate_ra(struct ip6_hdr *ip6)
+{
+ struct icmp6hdr *icmp = (struct icmp6hdr *)(ip6 + 1);
+
+ /* ICMP length (derived from the IP length) should be 16 or more octets. */
+ if (ip6->payload_len < 16)
+ return false;
+
+ /* Source IP Address should be a valid link-local address. */
+ if ((ntohs(ip6->saddr.s6_addr16[0]) & IPV6_LINK_LOCAL_MASK) !=
+ IPV6_LINK_LOCAL_PREFIX)
+ return false;
+
+ /*
+ * The IP Hop Limit field should have a value of 255, i.e., the packet
+ * could not possibly have been forwarded by a router.
+ */
+ if (ip6->hop_limit != 255)
+ return false;
+
+ /* ICMP checksum has already been checked in net_ip6_handler. */
+
+ if (icmp->icmp6_code != 0)
+ return false;
+
+ return true;
+}
+
+/*
+ * process_ra() - Process the router advertisement packet.
+ *
+ * @ip6: Pointer to the router advertisement packet
+ * @len: Length of the router advertisement packet
+ *
+ * Process the received router advertisement message.
+ * Although RFC 4861 requires retaining at least two router addresses, we only
+ * keep one because of the U-Boot limitations and its goal of lightweight code.
+ *
+ * Return: 0 - RA is a default router and contains valid prefix information.
+ * Non-zero - RA options are invalid or do not indicate it is a default router
+ * or do not contain valid prefix information.
+ */
+int process_ra(struct ip6_hdr *ip6, int len)
+{
+ /* Pointer to the ICMP section of the packet */
+ struct icmp6hdr *icmp = (struct icmp6hdr *)(ip6 + 1);
+ struct ra_msg *msg = (struct ra_msg *)icmp;
+ int remaining_option_len = len - IP6_HDR_SIZE - sizeof(struct ra_msg);
+ unsigned short int option_len; /* Length of each option */
+ /* Pointer to the ICMPv6 message options */
+ unsigned char *option = NULL;
+ /* 8-bit identifier of the type of ICMPv6 option */
+ unsigned char type = 0;
+ struct icmp6_ra_prefix_info *prefix = NULL;
+
+ /* Ignore the packet if router lifetime is 0. */
+ if (!icmp->icmp6_rt_lifetime)
+ return -EOPNOTSUPP;
+
+ /* Processing the options */
+ option = msg->opt;
+ while (remaining_option_len > 0) {
+ /* The 2nd byte of the option is its length. */
+ option_len = option[1];
+ /* All included options should have a positive length. */
+ if (option_len == 0)
+ return -EINVAL;
+
+ type = option[0];
+ /* All option types except Prefix Information are ignored. */
+ switch (type) {
+ case ND_OPT_SOURCE_LL_ADDR:
+ case ND_OPT_TARGET_LL_ADDR:
+ case ND_OPT_REDIRECT_HDR:
+ case ND_OPT_MTU:
+ break;
+ case ND_OPT_PREFIX_INFO:
+ prefix = (struct icmp6_ra_prefix_info *)option;
+ /* The link-local prefix 0xfe80::/10 is ignored. */
+ if ((ntohs(prefix->prefix.s6_addr16[0]) &
+ IPV6_LINK_LOCAL_MASK) == IPV6_LINK_LOCAL_PREFIX)
+ break;
+ if (prefix->on_link && ntohl(prefix->valid_lifetime)) {
+ net_prefix_length = prefix->prefix_len;
+ net_gateway6 = ip6->saddr;
+ return 0;
+ }
+ break;
+ default:
+ debug("Unknown IPv6 Neighbor Discovery Option 0x%x\n",
+ type);
+ }
+
+ option_len <<= 3; /* Option length is a multiple of 8. */
+ remaining_option_len -= option_len;
+ option += option_len;
+ }
+
+ return -EADDRNOTAVAIL;
+}
+
int ndisc_receive(struct ethernet_hdr *et, struct ip6_hdr *ip6, int len)
{
struct icmp6hdr *icmp =
(struct icmp6hdr *)(((uchar *)ip6) + IP6_HDR_SIZE);
struct nd_msg *ndisc = (struct nd_msg *)icmp;
uchar neigh_eth_addr[6];
+ int err = 0; // The error code returned calling functions.

switch (icmp->icmp6_type) {
case IPV6_NDISC_NEIGHBOUR_SOLICITATION:
@@ -280,6 +475,36 @@ int ndisc_receive(struct ethernet_hdr *et, struct ip6_hdr *ip6, int len)
net_nd_packet_mac = NULL;
}
break;
+ case IPV6_NDISC_ROUTER_SOLICITATION:
+ break;
+ case IPV6_NDISC_ROUTER_ADVERTISEMENT:
+ debug("Received router advertisement for %pI6c from %pI6c\n",
+ &ip6->daddr, &ip6->saddr);
+ /*
+ * If gateway and prefix are set, the RA packet is ignored. The
+ * reason is that the U-Boot code is supposed to be as compact
+ * as possible and does not need to take care of multiple
+ * routers. In addition to that, U-Boot does not want to handle
+ * scenarios like a router setting its lifetime to zero to
+ * indicate it is not routing anymore. U-Boot program has a
+ * short life when the system boots up and does not need such
+ * sophistication.
+ */
+ if (!ip6_is_unspecified_addr(&net_gateway6) &&
+ net_prefix_length != 0) {
+ break;
+ }
+ if (!validate_ra(ip6)) {
+ debug("Invalid router advertisement message.\n");
+ break;
+ }
+ err = process_ra(ip6, len);
+ if (err)
+ debug("Ignored router advertisement. Error: %d\n", err);
+ else
+ printf("Set gatewayip6: %pI6c, prefix_length: %d\n",
+ &net_gateway6, net_prefix_length);
+ break;
default:
debug("Unexpected ICMPv6 type 0x%x\n", icmp->icmp6_type);
return -1;
diff --git a/net/net.c b/net/net.c
index d69bfb0..abdb7e4 100644
--- a/net/net.c
+++ b/net/net.c
@@ -24,7 +24,7 @@
* - name of bootfile
* Next step: ARP
*
- * LINK_LOCAL:
+ * LINKLOCAL:
*
* Prerequisites: - own ethernet address
* We want: - own IP address
@@ -125,6 +125,7 @@
#if defined(CONFIG_CMD_DHCP6)
#include "dhcpv6.h"
#endif
+#include "net_rand.h"

/** BOOTP EXTENTIONS **/

@@ -349,6 +350,8 @@ void net_auto_load(void)

static int net_init_loop(void)
{
+ static bool first_call = true;
+
if (eth_get_dev()) {
memcpy(net_ethaddr, eth_get_ethaddr(), 6);

@@ -368,6 +371,12 @@ static int net_init_loop(void)
*/
return -ENONET;

+ if (IS_ENABLED(CONFIG_IPV6_ROUTER_DISCOVERY))
+ if (first_call && use_ip6) {
+ first_call = false;
+ srand_mac(); /* This is for rand used in ip6_send_rs. */
+ net_loop(RS);
+ }
return 0;
}

@@ -577,6 +586,10 @@ restart:
ncsi_probe_packages();
break;
#endif
+ case RS:
+ if (IS_ENABLED(CONFIG_IPV6_ROUTER_DISCOVERY))
+ ip6_send_rs();
+ break;
default:
break;
}
@@ -674,7 +687,13 @@ restart:
x = time_handler;
time_handler = (thand_f *)0;
(*x)();
- }
+ } else if (IS_ENABLED(CONFIG_IPV6_ROUTER_DISCOVERY))
+ if (time_handler && protocol == RS)
+ if (!ip6_is_unspecified_addr(&net_gateway6) &&
+ net_prefix_length != 0) {
+ net_set_state(NETLOOP_SUCCESS);
+ net_set_timeout_handler(0, NULL);
+ }

if (net_state == NETLOOP_FAIL)
ret = net_start_again();
diff --git a/net/net6.c b/net/net6.c
index 75577bc..2dd64c0 100644
--- a/net/net6.c
+++ b/net/net6.c
@@ -413,6 +413,7 @@ int net_ip6_handler(struct ethernet_hdr *et, struct ip6_hdr *ip6, int len)
break;
case IPV6_NDISC_NEIGHBOUR_SOLICITATION:
case IPV6_NDISC_NEIGHBOUR_ADVERTISEMENT:
+ case IPV6_NDISC_ROUTER_ADVERTISEMENT:
ndisc_receive(et, ip6, len);
break;
default:
--
1.8.3.1