subsys/net/lib/dns/resolve.c

/** @file
 * @brief DNS resolve API
 *
 * An API for applications to do DNS query.
 */

/*
 * Copyright (c) 2017 Intel Corporation
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <zephyr/logging/log.h>
LOG_MODULE_REGISTER(net_dns_resolve, CONFIG_DNS_RESOLVER_LOG_LEVEL);

#include <zephyr/types.h>
#include <zephyr/random/rand32.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>

#include <zephyr/sys/crc.h>
#include <zephyr/net/net_ip.h>
#include <zephyr/net/net_pkt.h>
#include <zephyr/net/net_mgmt.h>
#include <zephyr/net/dns_resolve.h>
#include "dns_pack.h"
#include "dns_internal.h"

#define DNS_SERVER_COUNT CONFIG_DNS_RESOLVER_MAX_SERVERS
#define SERVER_COUNT     (DNS_SERVER_COUNT + DNS_MAX_MCAST_SERVERS)

#define MDNS_IPV4_ADDR "224.0.0.251:5353"
#define MDNS_IPV6_ADDR "[ff02::fb]:5353"

#define LLMNR_IPV4_ADDR "224.0.0.252:5355"
#define LLMNR_IPV6_ADDR "[ff02::1:3]:5355"

#define DNS_BUF_TIMEOUT K_MSEC(500) /* ms */

/* RFC 1035, 3.1. Name space definitions
 * To simplify implementations, the total length of a domain name (i.e.,
 * label octets and label length octets) is restricted to 255 octets or
 * less.
 */
#define DNS_MAX_NAME_LEN	255

#define DNS_QUERY_MAX_SIZE	(DNS_MSG_HEADER_SIZE + DNS_MAX_NAME_LEN + \
				 DNS_QTYPE_LEN + DNS_QCLASS_LEN)

/* This value is recommended by RFC 1035 */
#define DNS_RESOLVER_MAX_BUF_SIZE	512
#define DNS_RESOLVER_MIN_BUF	1
#define DNS_RESOLVER_BUF_CTR	(DNS_RESOLVER_MIN_BUF + \
				 CONFIG_DNS_RESOLVER_ADDITIONAL_BUF_CTR)

/* Compressed RR uses a pointer to another RR. So, min size is 12 bytes without
 * considering RR payload.
 * See https://tools.ietf.org/html/rfc1035#section-4.1.4
 */
#define DNS_ANSWER_PTR_LEN	12

/* See dns_unpack_answer, and also see:
 * https://tools.ietf.org/html/rfc1035#section-4.1.2
 */
#define DNS_QUERY_POS		0x0c

#define DNS_IPV4_LEN		sizeof(struct in_addr)
#define DNS_IPV6_LEN		sizeof(struct in6_addr)

NET_BUF_POOL_DEFINE(dns_msg_pool, DNS_RESOLVER_BUF_CTR,
		    DNS_RESOLVER_MAX_BUF_SIZE, 0, NULL);

NET_BUF_POOL_DEFINE(dns_qname_pool, DNS_RESOLVER_BUF_CTR, DNS_MAX_NAME_LEN,
		    0, NULL);

static struct dns_resolve_context dns_default_ctx;

/* Must be invoked with context lock held */
static int dns_write(struct dns_resolve_context *ctx,
		     int server_idx,
		     int query_idx,
		     struct net_buf *dns_data,
		     struct net_buf *dns_qname,
		     int hop_limit);

static bool server_is_mdns(sa_family_t family, struct sockaddr *addr)
{
	if (family == AF_INET) {
		if (net_ipv4_is_addr_mcast(&net_sin(addr)->sin_addr) &&
		    net_sin(addr)->sin_addr.s4_addr[3] == 251U) {
			return true;
		}

		return false;
	}

	if (family == AF_INET6) {
		if (net_ipv6_is_addr_mcast(&net_sin6(addr)->sin6_addr) &&
		    net_sin6(addr)->sin6_addr.s6_addr[15] == 0xfb) {
			return true;
		}

		return false;
	}

	return false;
}

static bool server_is_llmnr(sa_family_t family, struct sockaddr *addr)
{
	if (family == AF_INET) {
		if (net_ipv4_is_addr_mcast(&net_sin(addr)->sin_addr) &&
		    net_sin(addr)->sin_addr.s4_addr[3] == 252U) {
			return true;
		}

		return false;
	}

	if (family == AF_INET6) {
		if (net_ipv6_is_addr_mcast(&net_sin6(addr)->sin6_addr) &&
		    net_sin6(addr)->sin6_addr.s6_addr[15] == 0x03) {
			return true;
		}

		return false;
	}

	return false;
}

static void dns_postprocess_server(struct dns_resolve_context *ctx, int idx)
{
	struct sockaddr *addr = &ctx->servers[idx].dns_server;

	if (addr->sa_family == AF_INET) {
		ctx->servers[idx].is_mdns = server_is_mdns(AF_INET, addr);
		if (!ctx->servers[idx].is_mdns) {
			ctx->servers[idx].is_llmnr =
				server_is_llmnr(AF_INET, addr);
		}

		if (net_sin(addr)->sin_port == 0U) {
			if (IS_ENABLED(CONFIG_MDNS_RESOLVER) &&
			    ctx->servers[idx].is_mdns) {
				/* We only use 5353 as a default port
				 * if mDNS support is enabled. User can
				 * override this by defining the port
				 * in config file.
				 */
				net_sin(addr)->sin_port = htons(5353);
			} else if (IS_ENABLED(CONFIG_LLMNR_RESOLVER) &&
				   ctx->servers[idx].is_llmnr) {
				/* We only use 5355 as a default port
				 * if LLMNR support is enabled. User can
				 * override this by defining the port
				 * in config file.
				 */
				net_sin(addr)->sin_port = htons(5355);
			} else {
				net_sin(addr)->sin_port = htons(53);
			}
		}
	} else {
		ctx->servers[idx].is_mdns = server_is_mdns(AF_INET6, addr);
		if (!ctx->servers[idx].is_mdns) {
			ctx->servers[idx].is_llmnr =
				server_is_llmnr(AF_INET6, addr);
		}

		if (net_sin6(addr)->sin6_port == 0U) {
			if (IS_ENABLED(CONFIG_MDNS_RESOLVER) &&
			    ctx->servers[idx].is_mdns) {
				net_sin6(addr)->sin6_port = htons(5353);
			} else if (IS_ENABLED(CONFIG_LLMNR_RESOLVER) &&
				   ctx->servers[idx].is_llmnr) {
				net_sin6(addr)->sin6_port = htons(5355);
			} else {
				net_sin6(addr)->sin6_port = htons(53);
			}
		}
	}
}

/* Must be invoked with context lock held */
static int dns_resolve_init_locked(struct dns_resolve_context *ctx,
				   const char *servers[],
				   const struct sockaddr *servers_sa[])
{
#if defined(CONFIG_NET_IPV6)
	struct sockaddr_in6 local_addr6 = {
		.sin6_family = AF_INET6,
		.sin6_port = 0,
	};
#endif
#if defined(CONFIG_NET_IPV4)
	struct sockaddr_in local_addr4 = {
		.sin_family = AF_INET,
		.sin_port = 0,
	};
#endif
	struct sockaddr *local_addr = NULL;
	socklen_t addr_len = 0;
	int i = 0, idx = 0;
	struct net_if *iface;
	int ret, count;

	if (!ctx) {
		return -ENOENT;
	}

	if (ctx->state != DNS_RESOLVE_CONTEXT_INACTIVE) {
		ret = -ENOTEMPTY;
		goto fail;
	}

	if (servers) {
		for (i = 0; idx < SERVER_COUNT && servers[i]; i++) {
			struct sockaddr *addr = &ctx->servers[idx].dns_server;

			(void)memset(addr, 0, sizeof(*addr));

			ret = net_ipaddr_parse(servers[i], strlen(servers[i]),
					       addr);
			if (!ret) {
				continue;
			}

			dns_postprocess_server(ctx, idx);

			NET_DBG("[%d] %s%s%s", i, servers[i],
				IS_ENABLED(CONFIG_MDNS_RESOLVER) ?
				(ctx->servers[i].is_mdns ? " mDNS" : "") : "",
				IS_ENABLED(CONFIG_LLMNR_RESOLVER) ?
				(ctx->servers[i].is_llmnr ?
							 " LLMNR" : "") : "");
			idx++;
		}
	}

	if (servers_sa) {
		for (i = 0; idx < SERVER_COUNT && servers_sa[i]; i++) {
			memcpy(&ctx->servers[idx].dns_server, servers_sa[i],
			       sizeof(ctx->servers[idx].dns_server));
			dns_postprocess_server(ctx, idx);
			idx++;
		}
	}

	for (i = 0, count = 0;
	     i < SERVER_COUNT && ctx->servers[i].dns_server.sa_family; i++) {

		if (ctx->servers[i].dns_server.sa_family == AF_INET6) {
#if defined(CONFIG_NET_IPV6)
			local_addr = (struct sockaddr *)&local_addr6;
			addr_len = sizeof(struct sockaddr_in6);

			if (IS_ENABLED(CONFIG_MDNS_RESOLVER) &&
			    ctx->servers[i].is_mdns) {
				local_addr6.sin6_port = htons(5353);
			}
#else
			continue;
#endif
		}

		if (ctx->servers[i].dns_server.sa_family == AF_INET) {
#if defined(CONFIG_NET_IPV4)
			local_addr = (struct sockaddr *)&local_addr4;
			addr_len = sizeof(struct sockaddr_in);

			if (IS_ENABLED(CONFIG_MDNS_RESOLVER) &&
			    ctx->servers[i].is_mdns) {
				local_addr4.sin_port = htons(5353);
			}
#else
			continue;
#endif
		}

		if (!local_addr) {
			NET_DBG("Local address not set");
			ret = -EAFNOSUPPORT;
			goto fail;
		}

		ret = net_context_get(ctx->servers[i].dns_server.sa_family,
				      SOCK_DGRAM, IPPROTO_UDP,
				      &ctx->servers[i].net_ctx);
		if (ret < 0) {
			NET_DBG("Cannot get net_context (%d)", ret);
			goto fail;
		}

		ret = net_context_bind(ctx->servers[i].net_ctx,
				       local_addr, addr_len);
		if (ret < 0) {
			NET_DBG("Cannot bind DNS context (%d)", ret);
			goto fail;
		}

		iface = net_context_get_iface(ctx->servers[i].net_ctx);

		if (IS_ENABLED(CONFIG_NET_MGMT_EVENT_INFO)) {
			net_mgmt_event_notify_with_info(
				NET_EVENT_DNS_SERVER_ADD,
				iface, (void *)&ctx->servers[i].dns_server,
				sizeof(struct sockaddr));
		} else {
			net_mgmt_event_notify(NET_EVENT_DNS_SERVER_ADD, iface);
		}

#if defined(CONFIG_NET_IPV6)
		local_addr6.sin6_port = 0;
#endif

#if defined(CONFIG_NET_IPV4)
		local_addr4.sin_port = 0;
#endif

		count++;
	}

	if (count == 0) {
		/* No servers defined */
		NET_DBG("No DNS servers defined.");
		ret = -EINVAL;
		goto fail;
	}

	ctx->state = DNS_RESOLVE_CONTEXT_ACTIVE;
	ctx->buf_timeout = DNS_BUF_TIMEOUT;
	ret = 0;

fail:
	return ret;
}

int dns_resolve_init(struct dns_resolve_context *ctx, const char *servers[],
		     const struct sockaddr *servers_sa[])
{
	if (!ctx) {
		return -ENOENT;
	}

	(void)memset(ctx, 0, sizeof(*ctx));

	(void)k_mutex_init(&ctx->lock);
	ctx->state = DNS_RESOLVE_CONTEXT_INACTIVE;

	/* As this function is called only once during system init, there is no
	 * reason to acquire lock.
	 */
	return dns_resolve_init_locked(ctx, servers, servers_sa);
}

/* Check whether a slot is available for use, or optionally whether it can be
 * reclaimed.
 *
 * @param pending_query the query slot in question
 *
 * @param reclaim_if_available if the slot is marked in use, but the query has
 * been completed and the work item is no longer pending, complete the release
 * of the slot.
 *
 * @return true if and only if the slot can be used for a new query.
 */
static inline bool check_query_active(struct dns_pending_query *pending_query,
				      bool reclaim_if_available)
{
	int ret = false;

	if (pending_query->cb != NULL) {
		ret = true;
		if (reclaim_if_available
		    && pending_query->query == NULL
		    && k_work_delayable_busy_get(&pending_query->timer) == 0) {
			pending_query->cb = NULL;
			ret = false;
		}
	}

	return ret;
}

/* Must be invoked with context lock held */
static inline int get_cb_slot(struct dns_resolve_context *ctx)
{
	int i;

	for (i = 0; i < CONFIG_DNS_NUM_CONCUR_QUERIES; i++) {
		if (!check_query_active(&ctx->queries[i], true)) {
			return i;
		}
	}

	return -ENOENT;
}

/* Invoke the callback associated with a query slot, if still relevant.
 *
 * Must be invoked with context lock held.
 *
 * @param status the query status value
 * @param info the query result structure
 * @param pending_query the query slot that will provide the callback
 **/
static inline void invoke_query_callback(int status,
					 struct dns_addrinfo *info,
					 struct dns_pending_query *pending_query)
{
	/* Only notify if the slot is neither released nor in the process of
	 * being released.
	 */
	if (pending_query->query != NULL)  {
		pending_query->cb(status, info, pending_query->user_data);
	}
}

/* Release a query slot reserved by get_cb_slot().
 *
 * Must be invoked with context lock held.
 *
 * @param pending_query the query slot to be released
 */
static void release_query(struct dns_pending_query *pending_query)
{
	int busy = k_work_cancel_delayable(&pending_query->timer);

	/* If the work item is no longer pending we're done. */
	if (busy == 0) {
		/* All done. */
		pending_query->cb = NULL;
	} else {
		/* Work item is still pending.  Set a secondary condition that
		 * can be checked by get_cb_slot() to complete release of the
		 * slot once the work item has been confirmed to be completed.
		 */
		pending_query->query = NULL;
	}
}

/* Must be invoked with context lock held */
static inline int get_slot_by_id(struct dns_resolve_context *ctx,
				 uint16_t dns_id,
				 uint16_t query_hash)
{
	int i;

	for (i = 0; i < CONFIG_DNS_NUM_CONCUR_QUERIES; i++) {
		if (check_query_active(&ctx->queries[i], false) &&
		    ctx->queries[i].id == dns_id &&
		    (query_hash == 0 ||
		     ctx->queries[i].query_hash == query_hash)) {
			return i;
		}
	}

	return -ENOENT;
}

/* Unit test needs to be able to call this function */
#if !defined(CONFIG_NET_TEST)
static
#endif
int dns_validate_msg(struct dns_resolve_context *ctx,
		     struct dns_msg_t *dns_msg,
		     uint16_t *dns_id,
		     int *query_idx,
		     struct net_buf *dns_cname,
		     uint16_t *query_hash)
{
	struct dns_addrinfo info = { 0 };
	uint32_t ttl; /* RR ttl, so far it is not passed to caller */
	uint8_t *src, *addr;
	const char *query_name;
	int address_size;
	/* index that points to the current answer being analyzed */
	int answer_ptr;
	int items;
	int server_idx;
	int ret = 0;

	/* Make sure that we can read DNS id, flags and rcode */
	if (dns_msg->msg_size < (sizeof(*dns_id) + sizeof(uint16_t))) {
		ret = DNS_EAI_FAIL;
		goto quit;
	}

	/* The dns_unpack_response_header() has design flaw as it expects
	 * dns id to be given instead of returning the id to the caller.
	 * In our case we would like to get it returned instead so that we
	 * can match the DNS query that we sent. When dns_read() is called,
	 * we do not know what the DNS id is yet.
	 */
	*dns_id = dns_unpack_header_id(dns_msg->msg);

	if (dns_header_rcode(dns_msg->msg) == DNS_HEADER_REFUSED) {
		ret = DNS_EAI_FAIL;
		goto quit;
	}

	/* We might receive a query while we are waiting for a response, in that
	 * case we just ignore the query instead of making the resolving fail.
	 */
	if (dns_header_qr(dns_msg->msg) == DNS_QUERY) {
		ret = 0;
		goto quit;
	}

	ret = dns_unpack_response_header(dns_msg, *dns_id);
	if (ret < 0) {
		ret = DNS_EAI_FAIL;
		goto quit;
	}

	if (dns_header_qdcount(dns_msg->msg) != 1) {
		/* For mDNS (when dns_id == 0) the query count is 0 */
		if (*dns_id > 0) {
			ret = DNS_EAI_FAIL;
			goto quit;
		}
	}

	ret = dns_unpack_response_query(dns_msg);
	if (ret < 0) {
		/* Check mDNS like above */
		if (*dns_id > 0) {
			ret = DNS_EAI_FAIL;
			goto quit;
		}

		/* mDNS responses to do not have the query part so the
		 * answer starts immediately after the header.
		 */
		dns_msg->answer_offset = dns_msg->query_offset;
	}

	/* Because in mDNS the DNS id is set to 0 and must be ignored
	 * on reply, we need to figure out the answer in order to find
	 * the proper query. To simplify things, the normal DNS responses
	 * are handled the same way.
	 */

	answer_ptr = DNS_QUERY_POS;
	items = 0;
	server_idx = 0;
	enum dns_rr_type answer_type = DNS_RR_TYPE_INVALID;

	while (server_idx < dns_header_ancount(dns_msg->msg)) {
		ret = dns_unpack_answer(dns_msg, answer_ptr, &ttl,
					&answer_type);
		if (ret < 0) {
			ret = DNS_EAI_FAIL;
			goto quit;
		}

		switch (dns_msg->response_type) {
		case DNS_RESPONSE_IP:
			if (*query_idx >= 0) {
				goto query_known;
			}

			query_name = dns_msg->msg + dns_msg->query_offset;

			/* Add \0 and query type (A or AAAA) to the hash */
			*query_hash = crc16_ansi(query_name,
						 strlen(query_name) + 1 + 2);

			*query_idx = get_slot_by_id(ctx, *dns_id, *query_hash);
			if (*query_idx < 0) {
				ret = DNS_EAI_SYSTEM;
				goto quit;
			}

query_known:
			if (ctx->queries[*query_idx].query_type ==
							DNS_QUERY_TYPE_A) {
				if (answer_type != DNS_RR_TYPE_A) {
					ret = DNS_EAI_ADDRFAMILY;
					goto quit;
				}

				address_size = DNS_IPV4_LEN;
				addr = (uint8_t *)&net_sin(&info.ai_addr)->
								sin_addr;
				info.ai_family = AF_INET;
				info.ai_addr.sa_family = AF_INET;
				info.ai_addrlen = sizeof(struct sockaddr_in);

			} else if (ctx->queries[*query_idx].query_type ==
							DNS_QUERY_TYPE_AAAA) {
				if (answer_type != DNS_RR_TYPE_AAAA) {
					ret = DNS_EAI_ADDRFAMILY;
					goto quit;
				}

				/* We cannot resolve IPv6 address if IPv6 is
				 * disabled. The reason being that
				 * "struct sockaddr" does not have enough space
				 * for IPv6 address in that case.
				 */
#if defined(CONFIG_NET_IPV6)
				address_size = DNS_IPV6_LEN;
				addr = (uint8_t *)&net_sin6(&info.ai_addr)->
								sin6_addr;
				info.ai_family = AF_INET6;
				info.ai_addr.sa_family = AF_INET6;
				info.ai_addrlen = sizeof(struct sockaddr_in6);
#else
				ret = DNS_EAI_FAMILY;
				goto quit;
#endif
			} else {
				ret = DNS_EAI_FAMILY;
				goto quit;
			}

			if (dns_msg->response_length < address_size) {
				/* it seems this is a malformed message */
				ret = DNS_EAI_FAIL;
				goto quit;
			}

			if ((dns_msg->response_position + address_size) >
			    dns_msg->msg_size) {
				/* Too short message */
				ret = DNS_EAI_FAIL;
				goto quit;
			}

			src = dns_msg->msg + dns_msg->response_position;
			memcpy(addr, src, address_size);

			invoke_query_callback(DNS_EAI_INPROGRESS, &info,
					      &ctx->queries[*query_idx]);
			items++;
			break;

		case DNS_RESPONSE_CNAME_NO_IP:
			/* Instead of using the QNAME at DNS_QUERY_POS,
			 * we will use this CNAME
			 */
			answer_ptr = dns_msg->response_position;
			break;

		default:
			ret = DNS_EAI_FAIL;
			goto quit;
		}

		/* Update the answer offset to point to the next RR (answer) */
		dns_msg->answer_offset += dns_msg->response_position -
							dns_msg->answer_offset;
		dns_msg->answer_offset += dns_msg->response_length;

		server_idx++;
	}

	if (*query_idx < 0) {
		/* If the query_idx is still unknown, try to get it here
		 * and hope it is found.
		 */
		query_name = dns_msg->msg + dns_msg->query_offset;
		*query_hash = crc16_ansi(query_name,
					 strlen(query_name) + 1 + 2);

		*query_idx = get_slot_by_id(ctx, *dns_id, *query_hash);
		if (*query_idx < 0) {
			ret = DNS_EAI_SYSTEM;
			goto quit;
		}
	}

	/* No IP addresses were found, so we take the last CNAME to generate
	 * another query. Number of additional queries is controlled via Kconfig
	 */
	if (items == 0) {
		if (dns_msg->response_type == DNS_RESPONSE_CNAME_NO_IP) {
			uint16_t pos = dns_msg->response_position;

			/* The dns_cname should always be set. As a special
			 * case, it might not be set for unit tests that call
			 * this function directly.
			 */
			if (dns_cname) {
				ret = dns_copy_qname(dns_cname->data,
						     &dns_cname->len,
						     dns_cname->size,
						     dns_msg, pos);
				if (ret < 0) {
					ret = DNS_EAI_SYSTEM;
					goto quit;
				}
			}

			ret = DNS_EAI_AGAIN;
			goto quit;
		}
	}

	if (items == 0) {
		ret = DNS_EAI_NODATA;
	} else {
		ret = DNS_EAI_ALLDONE;
	}

quit:
	return ret;
}

/* Must be invoked with context lock held */
static int dns_read(struct dns_resolve_context *ctx,
		    struct net_pkt *pkt,
		    struct net_buf *dns_data,
		    uint16_t *dns_id,
		    struct net_buf *dns_cname,
		    uint16_t *query_hash)
{
	/* Helper struct to track the dns msg received from the server */
	struct dns_msg_t dns_msg;
	int data_len;
	int ret;
	int query_idx = -1;

	data_len = MIN(net_pkt_remaining_data(pkt), DNS_RESOLVER_MAX_BUF_SIZE);

	/* TODO: Instead of this temporary copy, just use the net_pkt directly.
	 */
	ret = net_pkt_read(pkt, dns_data->data, data_len);
	if (ret < 0) {
		ret = DNS_EAI_MEMORY;
		goto quit;
	}

	dns_msg.msg = dns_data->data;
	dns_msg.msg_size = data_len;

	ret = dns_validate_msg(ctx, &dns_msg, dns_id, &query_idx,
			       dns_cname, query_hash);
	if (ret == DNS_EAI_AGAIN) {
		goto finished;
	}

	if (ret < 0 || query_idx < 0 ||
	    query_idx > CONFIG_DNS_NUM_CONCUR_QUERIES) {
		goto quit;
	}

	invoke_query_callback(ret, NULL, &ctx->queries[query_idx]);

	/* Marks the end of the results */
	release_query(&ctx->queries[query_idx]);

	net_pkt_unref(pkt);

	return 0;

finished:
	dns_resolve_cancel_with_name(ctx, *dns_id,
				     ctx->queries[query_idx].query,
				     ctx->queries[query_idx].query_type);
quit:
	net_pkt_unref(pkt);

	return ret;
}

static void cb_recv(struct net_context *net_ctx,
		    struct net_pkt *pkt,
		    union net_ip_header *ip_hdr,
		    union net_proto_header *proto_hdr,
		    int status,
		    void *user_data)
{
	struct dns_resolve_context *ctx = user_data;
	struct net_buf *dns_cname = NULL;
	struct net_buf *dns_data = NULL;
	uint16_t query_hash = 0U;
	uint16_t dns_id = 0U;
	int ret, i;

	ARG_UNUSED(net_ctx);

	k_mutex_lock(&ctx->lock, K_FOREVER);

	if (ctx->state != DNS_RESOLVE_CONTEXT_ACTIVE) {
		goto unlock;
	}

	if (status) {
		ret = DNS_EAI_SYSTEM;
		goto quit;
	}

	dns_data = net_buf_alloc(&dns_msg_pool, ctx->buf_timeout);
	if (!dns_data) {
		ret = DNS_EAI_MEMORY;
		goto quit;
	}

	dns_cname = net_buf_alloc(&dns_qname_pool, ctx->buf_timeout);
	if (!dns_cname) {
		ret = DNS_EAI_MEMORY;
		goto quit;
	}

	ret = dns_read(ctx, pkt, dns_data, &dns_id, dns_cname, &query_hash);
	if (!ret) {
		/* We called the callback already in dns_read() if there
		 * was no errors.
		 */
		goto free_buf;
	}

	/* Query again if we got CNAME */
	if (ret == DNS_EAI_AGAIN) {
		int failure = 0;
		int j;

		i = get_slot_by_id(ctx, dns_id, query_hash);
		if (i < 0) {
			goto free_buf;
		}

		for (j = 0; j < SERVER_COUNT; j++) {
			if (!ctx->servers[j].net_ctx) {
				continue;
			}

			ret = dns_write(ctx, j, i, dns_data, dns_cname, 0);
			if (ret < 0) {
				failure++;
			}
		}

		if (failure) {
			NET_DBG("DNS cname query failed %d times", failure);

			if (failure == j) {
				ret = DNS_EAI_SYSTEM;
				goto quit;
			}
		}

		goto free_buf;
	}

quit:
	i = get_slot_by_id(ctx, dns_id, query_hash);
	if (i < 0) {
		goto free_buf;
	}

	invoke_query_callback(ret, NULL, &ctx->queries[i]);

	/* Marks the end of the results */
	release_query(&ctx->queries[i]);

free_buf:
	if (dns_data) {
		net_buf_unref(dns_data);
	}

	if (dns_cname) {
		net_buf_unref(dns_cname);
	}

unlock:
	k_mutex_unlock(&ctx->lock);
}

/* Must be invoked with context lock held */
static int dns_write(struct dns_resolve_context *ctx,
		     int server_idx,
		     int query_idx,
		     struct net_buf *dns_data,
		     struct net_buf *dns_qname,
		     int hop_limit)
{
	enum dns_query_type query_type;
	struct net_context *net_ctx;
	struct sockaddr *server;
	int server_addr_len;
	uint16_t dns_id;
	int ret;

	net_ctx = ctx->servers[server_idx].net_ctx;
	server = &ctx->servers[server_idx].dns_server;
	dns_id = ctx->queries[query_idx].id;
	query_type = ctx->queries[query_idx].query_type;

	ret = dns_msg_pack_query(dns_data->data, &dns_data->len, dns_data->size,
				 dns_qname->data, dns_qname->len, dns_id,
				 (enum dns_rr_type)query_type);
	if (ret < 0) {
		return -EINVAL;
	}

	/* Add \0 and query type (A or AAAA) to the hash. Note that
	 * the dns_qname->len contains the length of \0
	 */
	ctx->queries[query_idx].query_hash =
		crc16_ansi(dns_data->data + DNS_MSG_HEADER_SIZE,
			   dns_qname->len + 2);

	if (IS_ENABLED(CONFIG_NET_IPV6) &&
	    net_context_get_family(net_ctx) == AF_INET6) {
		net_context_set_ipv6_hop_limit(net_ctx, hop_limit);
	} else if (IS_ENABLED(CONFIG_NET_IPV4) &&
		   net_context_get_family(net_ctx) == AF_INET) {
		net_context_set_ipv4_ttl(net_ctx, hop_limit);
	}

	ret = net_context_recv(net_ctx, cb_recv, K_NO_WAIT, ctx);
	if (ret < 0 && ret != -EALREADY) {
		NET_DBG("Could not receive from socket (%d)", ret);
		return ret;
	}

	if (server->sa_family == AF_INET) {
		server_addr_len = sizeof(struct sockaddr_in);
	} else {
		server_addr_len = sizeof(struct sockaddr_in6);
	}

	ret = k_work_reschedule(&ctx->queries[query_idx].timer,
				ctx->queries[query_idx].timeout);
	if (ret < 0) {
		NET_DBG("[%u] cannot submit work to server idx %d for id %u "
			"ret %d", query_idx, server_idx, dns_id, ret);
		return ret;
	}

	NET_DBG("[%u] submitting work to server idx %d for id %u "
		"hash %u", query_idx, server_idx, dns_id,
		ctx->queries[query_idx].query_hash);

	ret = net_context_sendto(net_ctx, dns_data->data, dns_data->len,
				 server, server_addr_len, NULL,
				 K_NO_WAIT, NULL);
	if (ret < 0) {
		NET_DBG("Cannot send query (%d)", ret);
		return ret;
	}

	return 0;
}

/* Must be invoked with context lock held */
static void dns_resolve_cancel_slot(struct dns_resolve_context *ctx, int slot)
{
	invoke_query_callback(DNS_EAI_CANCELED, NULL, &ctx->queries[slot]);

	release_query(&ctx->queries[slot]);
}

/* Must be invoked with context lock held */
static void dns_resolve_cancel_all(struct dns_resolve_context *ctx)
{
	int i;

	for (i = 0; i < CONFIG_DNS_NUM_CONCUR_QUERIES; i++) {
		if (ctx->queries[i].cb && ctx->queries[i].query) {
			dns_resolve_cancel_slot(ctx, i);
		}
	}
}

static int dns_resolve_cancel_with_hash(struct dns_resolve_context *ctx,
					uint16_t dns_id,
					uint16_t query_hash,
					const char *query_name)
{
	int ret = 0;
	int i;

	k_mutex_lock(&ctx->lock, K_FOREVER);

	if (ctx->state == DNS_RESOLVE_CONTEXT_DEACTIVATING) {
		/*
		 * Cancel is part of context "deactivating" process, so no need
		 * to do anything more.
		 */
		goto unlock;
	}

	i = get_slot_by_id(ctx, dns_id, query_hash);
	if (i < 0) {
		ret = -ENOENT;
		goto unlock;
	}

	NET_DBG("Cancelling DNS req %u (name %s type %d hash %u)", dns_id,
		query_name, ctx->queries[i].query_type,
		query_hash);

	dns_resolve_cancel_slot(ctx, i);

unlock:
	k_mutex_unlock(&ctx->lock);

	return ret;
}

int dns_resolve_cancel_with_name(struct dns_resolve_context *ctx,
				 uint16_t dns_id,
				 const char *query_name,
				 enum dns_query_type query_type)
{
	uint16_t query_hash = 0;

	if (query_name) {
		struct net_buf *buf;
		uint16_t len;
		int ret;

		/* Use net_buf as a temporary buffer to store the packed
		 * DNS name.
		 */
		buf = net_buf_alloc(&dns_msg_pool, ctx->buf_timeout);
		if (!buf) {
			return -ENOMEM;
		}

		ret = dns_msg_pack_qname(&len, buf->data, buf->size,
					 query_name);
		if (ret >= 0) {
			/* If the query string + \0 + query type (A or AAAA)
			 * does not fit the tmp buf, then bail out
			 */
			if ((len + 2) > buf->size) {
				net_buf_unref(buf);
				return -ENOMEM;
			}

			net_buf_add(buf, len);
			net_buf_add_be16(buf, query_type);

			query_hash = crc16_ansi(buf->data, len + 2);
		}

		net_buf_unref(buf);

		if (ret < 0) {
			return ret;
		}
	}

	return dns_resolve_cancel_with_hash(ctx, dns_id, query_hash,
					    query_name);
}

int dns_resolve_cancel(struct dns_resolve_context *ctx, uint16_t dns_id)
{
	return dns_resolve_cancel_with_name(ctx, dns_id, NULL, 0);
}

static void query_timeout(struct k_work *work)
{
	struct k_work_delayable *dwork = k_work_delayable_from_work(work);
	struct dns_pending_query *pending_query =
		CONTAINER_OF(dwork, struct dns_pending_query, timer);
	int ret;

	/* We have to take the lock as we're inspecting protected content
	 * associated with the query.  But don't block the system work queue:
	 * if the lock can't be taken immediately, reschedule the work item to
	 * be run again after everything else has had a chance.
	 *
	 * Note that it's OK to use the k_work API on the delayable work
	 * without holding the lock: it's only the associated state in the
	 * containing structure that must be protected.
	 */
	ret = k_mutex_lock(&pending_query->ctx->lock, K_NO_WAIT);
	if (ret != 0) {
		struct k_work_delayable *dwork = k_work_delayable_from_work(work);

		/*
		 * Reschedule query timeout handler with some delay, so that all
		 * threads (including those with lower priorities) have a chance
		 * to move forward and release DNS context lock.
		 *
		 * Timeout value was arbitrarily chosen and can be updated in
		 * future if needed.
		 */
		k_work_reschedule(dwork, K_MSEC(10));
		return;
	}

	NET_DBG("Query timeout DNS req %u type %d hash %u", pending_query->id,
		pending_query->query_type, pending_query->query_hash);

	/* The resolve cancel will invoke release_query(), but release will
	 * not be completed because the work item is still pending.  Instead
	 * the release will be completed when check_query_active() confirms
	 * the work item is no longer active.
	 */
	(void)dns_resolve_cancel_with_hash(pending_query->ctx,
					   pending_query->id,
					   pending_query->query_hash,
					   pending_query->query);

	k_mutex_unlock(&pending_query->ctx->lock);
}

int dns_resolve_name(struct dns_resolve_context *ctx,
		     const char *query,
		     enum dns_query_type type,
		     uint16_t *dns_id,
		     dns_resolve_cb_t cb,
		     void *user_data,
		     int32_t timeout)
{
	k_timeout_t tout;
	struct net_buf *dns_data = NULL;
	struct net_buf *dns_qname = NULL;
	struct sockaddr addr;
	int ret, i = -1, j = 0;
	int failure = 0;
	bool mdns_query = false;
	uint8_t hop_limit;

	if (!ctx || !query || !cb) {
		return -EINVAL;
	}

	tout = SYS_TIMEOUT_MS(timeout);

	/* Timeout cannot be 0 as we cannot resolve name that fast.
	 */
	if (K_TIMEOUT_EQ(tout, K_NO_WAIT)) {
		return -EINVAL;
	}

	ret = net_ipaddr_parse(query, strlen(query), &addr);
	if (ret) {
		/* The query name was already in numeric form, no
		 * need to continue further.
		 */
		struct dns_addrinfo info = { 0 };

		if (type == DNS_QUERY_TYPE_A) {
			if (net_sin(&addr)->sin_family == AF_INET6) {
				return -EPFNOSUPPORT;
			}

			memcpy(net_sin(&info.ai_addr), net_sin(&addr),
			       sizeof(struct sockaddr_in));
			info.ai_family = AF_INET;
			info.ai_addr.sa_family = AF_INET;
			info.ai_addrlen = sizeof(struct sockaddr_in);
		} else if (type == DNS_QUERY_TYPE_AAAA) {
			/* We do not support AI_V4MAPPED atm, so if the user
			 * asks an IPv6 address but it is an IPv4 one, then
			 * return an error. Note that getaddrinfo() will swap
			 * the error to EINVAL, the EPFNOSUPPORT is returned
			 * here so that we can find it easily.
			 */
			if (net_sin(&addr)->sin_family == AF_INET) {
				return -EPFNOSUPPORT;
			}

#if defined(CONFIG_NET_IPV6)
			memcpy(net_sin6(&info.ai_addr), net_sin6(&addr),
			       sizeof(struct sockaddr_in6));
			info.ai_family = AF_INET6;
			info.ai_addr.sa_family = AF_INET6;
			info.ai_addrlen = sizeof(struct sockaddr_in6);
#else
			return -EAFNOSUPPORT;
#endif
		} else {
			goto try_resolve;
		}

		cb(DNS_EAI_INPROGRESS, &info, user_data);
		cb(DNS_EAI_ALLDONE, NULL, user_data);

		return 0;
	}

try_resolve:
	k_mutex_lock(&ctx->lock, K_FOREVER);

	if (ctx->state != DNS_RESOLVE_CONTEXT_ACTIVE) {
		ret = -EINVAL;
		goto fail;
	}

	i = get_cb_slot(ctx);
	if (i < 0) {
		ret = -EAGAIN;
		goto fail;
	}

	ctx->queries[i].cb = cb;
	ctx->queries[i].timeout = tout;
	ctx->queries[i].query = query;
	ctx->queries[i].query_type = type;
	ctx->queries[i].user_data = user_data;
	ctx->queries[i].ctx = ctx;
	ctx->queries[i].query_hash = 0;

	k_work_init_delayable(&ctx->queries[i].timer, query_timeout);

	dns_data = net_buf_alloc(&dns_msg_pool, ctx->buf_timeout);
	if (!dns_data) {
		ret = -ENOMEM;
		goto quit;
	}

	dns_qname = net_buf_alloc(&dns_qname_pool, ctx->buf_timeout);
	if (!dns_qname) {
		ret = -ENOMEM;
		goto quit;
	}

	ret = dns_msg_pack_qname(&dns_qname->len, dns_qname->data,
				DNS_MAX_NAME_LEN, ctx->queries[i].query);
	if (ret < 0) {
		goto quit;
	}

	ctx->queries[i].id = sys_rand32_get();

	/* If mDNS is enabled, then send .local queries only to multicast
	 * address. For mDNS the id should be set to 0, see RFC 6762 ch. 18.1
	 * for details.
	 */
	if (IS_ENABLED(CONFIG_MDNS_RESOLVER)) {
		const char *ptr = strrchr(query, '.');

		/* Note that we memcmp() the \0 here too */
		if (ptr && !memcmp(ptr, (const void *){ ".local" }, 7)) {
			mdns_query = true;

			ctx->queries[i].id = 0;
		}
	}

	/* Do this immediately after calculating the Id so that the unit
	 * test will work properly.
	 */
	if (dns_id) {
		*dns_id = ctx->queries[i].id;

		NET_DBG("DNS id will be %u", *dns_id);
	}

	for (j = 0; j < SERVER_COUNT; j++) {
		hop_limit = 0U;

		if (!ctx->servers[j].net_ctx) {
			continue;
		}

		/* If mDNS is enabled, then send .local queries only to
		 * a well known multicast mDNS server address.
		 */
		if (IS_ENABLED(CONFIG_MDNS_RESOLVER) && mdns_query &&
		    !ctx->servers[j].is_mdns) {
			continue;
		}

		/* If llmnr is enabled, then all the queries are sent to
		 * LLMNR multicast address unless it is a mDNS query.
		 */
		if (!mdns_query && IS_ENABLED(CONFIG_LLMNR_RESOLVER)) {
			if (!ctx->servers[j].is_llmnr) {
				continue;
			}

			hop_limit = 1U;
		}

		ret = dns_write(ctx, j, i, dns_data, dns_qname, hop_limit);
		if (ret < 0) {
			failure++;
			continue;
		}

		/* Do one concurrent query only for each name resolve.
		 * TODO: Change the i (query index) to do multiple concurrent
		 *       to each server.
		 */
		break;
	}

	if (failure) {
		NET_DBG("DNS query failed %d times", failure);

		if (failure == j) {
			ret = -ENOENT;
			goto quit;
		}
	}

	ret = 0;

quit:
	if (ret < 0) {
		if (i >= 0) {
			release_query(&ctx->queries[i]);
		}

		if (dns_id) {
			*dns_id = 0U;
		}
	}

	if (dns_data) {
		net_buf_unref(dns_data);
	}

	if (dns_qname) {
		net_buf_unref(dns_qname);
	}

fail:
	k_mutex_unlock(&ctx->lock);

	return ret;
}

/* Must be invoked with context lock held */
static int dns_resolve_close_locked(struct dns_resolve_context *ctx)
{
	int i;

	if (ctx->state != DNS_RESOLVE_CONTEXT_ACTIVE) {
		return -ENOENT;
	}

	ctx->state = DNS_RESOLVE_CONTEXT_DEACTIVATING;

	/* ctx->net_ctx is never used in "deactivating" state. Additionally
	 * following code is guaranteed to be executed only by one thread at a
	 * time, due to required "active" -> "deactivating" state change. This
	 * means that it is safe to put net_ctx with mutex released.
	 *
	 * Released mutex will prevent lower networking layers from deadlock
	 * when calling cb_recv() (which acquires ctx->lock) just before closing
	 * network context.
	 */
	k_mutex_unlock(&ctx->lock);

	for (i = 0; i < SERVER_COUNT; i++) {
		if (ctx->servers[i].net_ctx) {
			struct net_if *iface;

			iface = net_context_get_iface(ctx->servers[i].net_ctx);

			if (IS_ENABLED(CONFIG_NET_MGMT_EVENT_INFO)) {
				net_mgmt_event_notify_with_info(
					NET_EVENT_DNS_SERVER_DEL,
					iface,
					(void *)&ctx->servers[i].dns_server,
					sizeof(struct sockaddr));
			} else {
				net_mgmt_event_notify(NET_EVENT_DNS_SERVER_DEL,
						      iface);
			}

			net_context_put(ctx->servers[i].net_ctx);
			ctx->servers[i].net_ctx = NULL;
		}
	}

	k_mutex_lock(&ctx->lock, K_FOREVER);

	ctx->state = DNS_RESOLVE_CONTEXT_INACTIVE;

	return 0;
}

int dns_resolve_close(struct dns_resolve_context *ctx)
{
	int ret;

	k_mutex_lock(&ctx->lock, K_FOREVER);
	ret = dns_resolve_close_locked(ctx);
	k_mutex_unlock(&ctx->lock);

	return ret;
}

int dns_resolve_reconfigure(struct dns_resolve_context *ctx,
			    const char *servers[],
			    const struct sockaddr *servers_sa[])
{
	int err;

	if (!ctx) {
		return -ENOENT;
	}

	k_mutex_lock(&ctx->lock, K_FOREVER);

	if (ctx->state == DNS_RESOLVE_CONTEXT_DEACTIVATING) {
		err = -EBUSY;
		goto unlock;
	}

	if (ctx->state == DNS_RESOLVE_CONTEXT_ACTIVE) {
		dns_resolve_cancel_all(ctx);

		err = dns_resolve_close_locked(ctx);
		if (err) {
			goto unlock;
		}
	}

	err = dns_resolve_init_locked(ctx, servers, servers_sa);

unlock:
	k_mutex_unlock(&ctx->lock);

	return err;
}

struct dns_resolve_context *dns_resolve_get_default(void)
{
	return &dns_default_ctx;
}

void dns_init_resolver(void)
{
#if defined(CONFIG_DNS_SERVER_IP_ADDRESSES)
	static const char *dns_servers[SERVER_COUNT + 1];
	int count = DNS_SERVER_COUNT;
	int ret;

	if (count > 5) {
		count = 5;
	}

	switch (count) {
#if DNS_SERVER_COUNT > 4
	case 5:
		dns_servers[4] = CONFIG_DNS_SERVER5;
		__fallthrough;
#endif
#if DNS_SERVER_COUNT > 3
	case 4:
		dns_servers[3] = CONFIG_DNS_SERVER4;
		__fallthrough;
#endif
#if DNS_SERVER_COUNT > 2
	case 3:
		dns_servers[2] = CONFIG_DNS_SERVER3;
		__fallthrough;
#endif
#if DNS_SERVER_COUNT > 1
	case 2:
		dns_servers[1] = CONFIG_DNS_SERVER2;
		__fallthrough;
#endif
#if DNS_SERVER_COUNT > 0
	case 1:
		dns_servers[0] = CONFIG_DNS_SERVER1;
		__fallthrough;
#endif
	case 0:
		break;
	}

#if defined(CONFIG_MDNS_RESOLVER) && (MDNS_SERVER_COUNT > 0)
#if defined(CONFIG_NET_IPV6) && defined(CONFIG_NET_IPV4)
	dns_servers[DNS_SERVER_COUNT + 1] = MDNS_IPV6_ADDR;
	dns_servers[DNS_SERVER_COUNT] = MDNS_IPV4_ADDR;
#else /* CONFIG_NET_IPV6 && CONFIG_NET_IPV4 */
#if defined(CONFIG_NET_IPV6)
	dns_servers[DNS_SERVER_COUNT] = MDNS_IPV6_ADDR;
#endif
#if defined(CONFIG_NET_IPV4)
	dns_servers[DNS_SERVER_COUNT] = MDNS_IPV4_ADDR;
#endif
#endif /* CONFIG_NET_IPV6 && CONFIG_NET_IPV4 */
#endif /* MDNS_RESOLVER && MDNS_SERVER_COUNT > 0 */

#if defined(CONFIG_LLMNR_RESOLVER) && (LLMNR_SERVER_COUNT > 0)
#if defined(CONFIG_NET_IPV6) && defined(CONFIG_NET_IPV4)
	dns_servers[DNS_SERVER_COUNT + MDNS_SERVER_COUNT + 1] =
							LLMNR_IPV6_ADDR;
	dns_servers[DNS_SERVER_COUNT + MDNS_SERVER_COUNT] = LLMNR_IPV4_ADDR;
#else /* CONFIG_NET_IPV6 && CONFIG_NET_IPV4 */
#if defined(CONFIG_NET_IPV6)
	dns_servers[DNS_SERVER_COUNT + MDNS_SERVER_COUNT] = LLMNR_IPV6_ADDR;
#endif
#if defined(CONFIG_NET_IPV4)
	dns_servers[DNS_SERVER_COUNT + MDNS_SERVER_COUNT] = LLMNR_IPV4_ADDR;
#endif
#endif /* CONFIG_NET_IPV6 && CONFIG_NET_IPV4 */
#endif /* LLMNR_RESOLVER && LLMNR_SERVER_COUNT > 0 */

	dns_servers[SERVER_COUNT] = NULL;

	ret = dns_resolve_init(dns_resolve_get_default(), dns_servers, NULL);
	if (ret < 0) {
		NET_WARN("Cannot initialize DNS resolver (%d)", ret);
	}
#endif
}