/** * @file * DNS - host name to IP address resolver. * */ /** * This file implements a DNS host name to IP address resolver. * Port to lwIP from uIP * by Jim Pettinato April 2007 * security fixes and more by Simon Goldschmidt * uIP version Copyright (c) 2002-2003, Adam Dunkels. * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. The name of the author may not be used to endorse or promote * products derived from this software without specific prior * written permission. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. * * * DNS.C * * The lwIP DNS resolver functions are used to lookup a host name and * map it to a numerical IP address. It maintains a list of resolved * hostnames that can be queried with the dns_lookup() function. * New hostnames can be resolved using the dns_query() function. * * The lwIP version of the resolver also adds a non-blocking version of * gethostbyname() that will work with a raw API application. This function * checks for an IP address string first and converts it if it is valid. * gethostbyname() then does a dns_lookup() to see if the name is * already in the table. If so, the IP is returned. If not, a query is * issued and the function returns with a ERR_INPROGRESS status. The app * using the dns client must then go into a waiting state. * * Once a hostname has been resolved (or found to be non-existent), * the resolver code calls a specified callback function (which * must be implemented by the module that uses the resolver). */ /*----------------------------------------------------------------------------- * RFC 1035 - Domain names - implementation and specification * RFC 2181 - Clarifications to the DNS Specification *----------------------------------------------------------------------------*/ /** @todo: define good default values (rfc compliance) */ /** @todo: improve answer parsing, more checkings... */ /** @todo: check RFC1035 - 7.3. Processing responses */ /*----------------------------------------------------------------------------- * Includes *----------------------------------------------------------------------------*/ #include "lwip/opt.h" #if LWIP_DNS /* don't build if not configured for use in lwipopts.h */ #include "lwip/udp.h" #include "lwip/mem.h" #include "lwip/memp.h" #include "lwip/dns.h" #include /* A list of DNS security features follows */ #define LWIP_DNS_SECURE_RAND_XID 1 #define LWIP_DNS_SECURE_NO_MULTIPLE_OUTSTANDING 2 #define LWIP_DNS_SECURE_RAND_SRC_PORT 4 /** Use all DNS security features by default. * This is overridable but should only be needed by very small targets * or when using against non standard DNS servers. */ #ifndef LWIP_DNS_SECURE #define LWIP_DNS_SECURE (LWIP_DNS_SECURE_RAND_XID | LWIP_DNS_SECURE_NO_MULTIPLE_OUTSTANDING | LWIP_DNS_SECURE_RAND_SRC_PORT) #endif /** Random generator function to create random TXIDs and source ports for queries */ #ifndef DNS_RAND_TXID #if ((LWIP_DNS_SECURE & LWIP_DNS_SECURE_RAND_XID) != 0) #define DNS_RAND_TXID LWIP_RAND #else static u16_t dns_txid; #define DNS_RAND_TXID() (++dns_txid) #endif #endif /** Limits the source port to be >= 1024 by default */ #ifndef DNS_PORT_ALLOWED #define DNS_PORT_ALLOWED(port) ((port) >= 1024) #endif /** DNS server IP address */ #ifndef DNS_SERVER_ADDRESS #if LWIP_IPV4 #define DNS_SERVER_ADDRESS(ipaddr) ip_addr_set_ip4_u32(ipaddr, ipaddr_addr("208.67.222.222")) /* resolver1.opendns.com */ #else #define DNS_SERVER_ADDRESS(ipaddr) ipaddr_aton("2001:4860:4860::8888", ipaddr) #endif #endif /** DNS server port address */ #ifndef DNS_SERVER_PORT #define DNS_SERVER_PORT 53 #endif /** DNS maximum number of retries when asking for a name, before "timeout". */ #ifndef DNS_MAX_RETRIES #define DNS_MAX_RETRIES 4 #endif /** DNS resource record max. TTL (one week as default) */ #ifndef DNS_MAX_TTL #define DNS_MAX_TTL 604800 #endif /* The number of parallel requests (i.e. calls to dns_gethostbyname * that cannot be answered from the DNS table. * This is set to the table size by default. */ #if ((LWIP_DNS_SECURE & LWIP_DNS_SECURE_NO_MULTIPLE_OUTSTANDING) != 0) #ifndef DNS_MAX_REQUESTS #define DNS_MAX_REQUESTS DNS_TABLE_SIZE #endif #else /* In this configuration, both arrays have to have the same size and are used * like one entry (used/free) */ #define DNS_MAX_REQUESTS DNS_TABLE_SIZE #endif /* The number of UDP source ports used in parallel */ #if ((LWIP_DNS_SECURE & LWIP_DNS_SECURE_RAND_SRC_PORT) != 0) #ifndef DNS_MAX_SOURCE_PORTS #define DNS_MAX_SOURCE_PORTS DNS_MAX_REQUESTS #endif #else #ifdef DNS_MAX_SOURCE_PORTS #undef DNS_MAX_SOURCE_PORTS #endif #define DNS_MAX_SOURCE_PORTS 1 #endif /* DNS protocol flags */ #define DNS_FLAG1_RESPONSE 0x80 #define DNS_FLAG1_OPCODE_STATUS 0x10 #define DNS_FLAG1_OPCODE_INVERSE 0x08 #define DNS_FLAG1_OPCODE_STANDARD 0x00 #define DNS_FLAG1_AUTHORATIVE 0x04 #define DNS_FLAG1_TRUNC 0x02 #define DNS_FLAG1_RD 0x01 #define DNS_FLAG2_RA 0x80 #define DNS_FLAG2_ERR_MASK 0x0f #define DNS_FLAG2_ERR_NONE 0x00 #define DNS_FLAG2_ERR_NAME 0x03 /* DNS protocol states */ #define DNS_STATE_UNUSED 0 #define DNS_STATE_NEW 1 #define DNS_STATE_ASKING 2 #define DNS_STATE_DONE 3 #ifdef PACK_STRUCT_USE_INCLUDES # include "arch/bpstruct.h" #endif PACK_STRUCT_BEGIN /** DNS message header */ struct dns_hdr { PACK_STRUCT_FIELD(u16_t id); PACK_STRUCT_FLD_8(u8_t flags1); PACK_STRUCT_FLD_8(u8_t flags2); PACK_STRUCT_FIELD(u16_t numquestions); PACK_STRUCT_FIELD(u16_t numanswers); PACK_STRUCT_FIELD(u16_t numauthrr); PACK_STRUCT_FIELD(u16_t numextrarr); } PACK_STRUCT_STRUCT; PACK_STRUCT_END #ifdef PACK_STRUCT_USE_INCLUDES # include "arch/epstruct.h" #endif #define SIZEOF_DNS_HDR 12 /** DNS query message structure. No packing needed: only used locally on the stack. */ struct dns_query { /* DNS query record starts with either a domain name or a pointer to a name already present somewhere in the packet. */ u16_t type; u16_t cls; }; #define SIZEOF_DNS_QUERY 4 /** DNS answer message structure. No packing needed: only used locally on the stack. */ struct dns_answer { /* DNS answer record starts with either a domain name or a pointer to a name already present somewhere in the packet. */ u16_t type; u16_t cls; u32_t ttl; u16_t len; }; #define SIZEOF_DNS_ANSWER 10 /* maximum allowed size for the struct due to non-packed */ #define SIZEOF_DNS_ANSWER_ASSERT 12 /** DNS table entry */ struct dns_table_entry { u32_t ttl; ip_addr_t ipaddr; u16_t txid; u8_t state; u8_t server_idx; u8_t tmr; u8_t retries; u8_t seqno; #if ((LWIP_DNS_SECURE & LWIP_DNS_SECURE_RAND_SRC_PORT) != 0) u8_t pcb_idx; #endif char name[DNS_MAX_NAME_LENGTH]; }; /** DNS request table entry: used when dns_gehostbyname cannot answer the * request from the DNS table */ struct dns_req_entry { /* pointer to callback on DNS query done */ dns_found_callback found; /* argument passed to the callback function */ void *arg; #if ((LWIP_DNS_SECURE & LWIP_DNS_SECURE_NO_MULTIPLE_OUTSTANDING) != 0) u8_t dns_table_idx; #endif }; #if DNS_LOCAL_HOSTLIST #if DNS_LOCAL_HOSTLIST_IS_DYNAMIC /** Local host-list. For hostnames in this list, no * external name resolution is performed */ static struct local_hostlist_entry *local_hostlist_dynamic; #else /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */ /** Defining this allows the local_hostlist_static to be placed in a different * linker section (e.g. FLASH) */ #ifndef DNS_LOCAL_HOSTLIST_STORAGE_PRE #define DNS_LOCAL_HOSTLIST_STORAGE_PRE static #endif /* DNS_LOCAL_HOSTLIST_STORAGE_PRE */ /** Defining this allows the local_hostlist_static to be placed in a different * linker section (e.g. FLASH) */ #ifndef DNS_LOCAL_HOSTLIST_STORAGE_POST #define DNS_LOCAL_HOSTLIST_STORAGE_POST #endif /* DNS_LOCAL_HOSTLIST_STORAGE_POST */ DNS_LOCAL_HOSTLIST_STORAGE_PRE struct local_hostlist_entry local_hostlist_static[] DNS_LOCAL_HOSTLIST_STORAGE_POST = DNS_LOCAL_HOSTLIST_INIT; #endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */ static void dns_init_local(); #endif /* DNS_LOCAL_HOSTLIST */ /* forward declarations */ static void dns_recv(void *s, struct udp_pcb *pcb, struct pbuf *p, const ip_addr_t *addr, u16_t port); static void dns_check_entries(void); /*----------------------------------------------------------------------------- * Globals *----------------------------------------------------------------------------*/ /* DNS variables */ static struct udp_pcb *dns_pcbs[DNS_MAX_SOURCE_PORTS]; #if ((LWIP_DNS_SECURE & LWIP_DNS_SECURE_RAND_SRC_PORT) != 0) static u8_t dns_last_pcb_idx; #endif static u8_t dns_seqno; static struct dns_table_entry dns_table[DNS_TABLE_SIZE]; static struct dns_req_entry dns_requests[DNS_MAX_REQUESTS]; static ip_addr_t dns_servers[DNS_MAX_SERVERS]; #ifndef LWIP_DNS_STRICMP #define LWIP_DNS_STRICMP(str1, str2) dns_stricmp(str1, str2) /** * A small but sufficient implementation for case insensitive strcmp. * This can be defined to e.g. stricmp for windows or strcasecmp for linux. */ static int dns_stricmp(const char* str1, const char* str2) { char c1, c2; do { c1 = *str1++; c2 = *str2++; if (c1 != c2) { char c1_upc = c1 | 0x20; if ((c1_upc >= 'a') && (c1_upc <= 'z')) { /* characters are not equal an one is in the alphabet range: downcase both chars and check again */ char c2_upc = c2 | 0x20; if (c1_upc != c2_upc) { /* still not equal */ /* don't care for < or > */ return 1; } } else { /* characters are not equal but none is in the alphabet range */ return 1; } } } while (c1 != 0); return 0; } #endif /* LWIP_DNS_STRICMP */ /** * Initialize the resolver: set up the UDP pcb and configure the default server * (DNS_SERVER_ADDRESS). */ void dns_init(void) { ip_addr_t dnsserver; LWIP_ASSERT("sanity check SIZEOF_DNS_QUERY", sizeof(struct dns_query) == SIZEOF_DNS_QUERY); LWIP_ASSERT("sanity check SIZEOF_DNS_ANSWER", sizeof(struct dns_answer) <= SIZEOF_DNS_ANSWER_ASSERT); /* initialize default DNS server address */ DNS_SERVER_ADDRESS(&dnsserver); LWIP_DEBUGF(DNS_DEBUG, ("dns_init: initializing\n")); /* if dns client not yet initialized... */ #if ((LWIP_DNS_SECURE & LWIP_DNS_SECURE_RAND_SRC_PORT) == 0) if (dns_pcbs[0] == NULL) { dns_pcbs[0] = udp_new(); LWIP_ASSERT("dns_pcbs[0] != NULL", dns_pcbs[0] != NULL); /* initialize DNS table not needed (initialized to zero since it is a * global variable) */ LWIP_ASSERT("For implicit initialization to work, DNS_STATE_UNUSED needs to be 0", DNS_STATE_UNUSED == 0); /* initialize DNS client */ udp_bind(dns_pcbs[0], IP_ADDR_ANY, 0); udp_recv(dns_pcbs[0], dns_recv, NULL); } #endif /* initialize default DNS primary server */ dns_setserver(0, &dnsserver); #if DNS_LOCAL_HOSTLIST dns_init_local(); #endif } /** * Initialize one of the DNS servers. * * @param numdns the index of the DNS server to set must be < DNS_MAX_SERVERS * @param dnsserver IP address of the DNS server to set */ void dns_setserver(u8_t numdns, ip_addr_t *dnsserver) { if (numdns < DNS_MAX_SERVERS) { if (dnsserver != NULL) { dns_servers[numdns] = (*dnsserver); } else { dns_servers[numdns] = *IP_ADDR_ANY; } } } /** * Obtain one of the currently configured DNS server. * * @param numdns the index of the DNS server * @return IP address of the indexed DNS server or "ip_addr_any" if the DNS * server has not been configured. */ ip_addr_t dns_getserver(u8_t numdns) { if (numdns < DNS_MAX_SERVERS) { return dns_servers[numdns]; } else { return *IP_ADDR_ANY; } } /** * The DNS resolver client timer - handle retries and timeouts and should * be called every DNS_TMR_INTERVAL milliseconds (every second by default). */ void dns_tmr(void) { LWIP_DEBUGF(DNS_DEBUG, ("dns_tmr: dns_check_entries\n")); dns_check_entries(); } #if DNS_LOCAL_HOSTLIST static void dns_init_local() { #if DNS_LOCAL_HOSTLIST_IS_DYNAMIC && defined(DNS_LOCAL_HOSTLIST_INIT) int i; struct local_hostlist_entry *entry; /* Dynamic: copy entries from DNS_LOCAL_HOSTLIST_INIT to list */ struct local_hostlist_entry local_hostlist_init[] = DNS_LOCAL_HOSTLIST_INIT; size_t namelen; for (i = 0; i < sizeof(local_hostlist_init) / sizeof(struct local_hostlist_entry); i++) { struct local_hostlist_entry *init_entry = &local_hostlist_init[i]; LWIP_ASSERT("invalid host name (NULL)", init_entry->name != NULL); namelen = strlen(init_entry->name); LWIP_ASSERT("namelen <= DNS_LOCAL_HOSTLIST_MAX_NAMELEN", namelen <= DNS_LOCAL_HOSTLIST_MAX_NAMELEN); entry = (struct local_hostlist_entry *)memp_malloc(MEMP_LOCALHOSTLIST); LWIP_ASSERT("mem-error in dns_init_local", entry != NULL); if (entry != NULL) { entry->name = (char*)entry + sizeof(struct local_hostlist_entry); MEMCPY((char*)entry->name, init_entry->name, namelen); ((char*)entry->name)[namelen] = 0; entry->addr = init_entry->addr; entry->next = local_hostlist_dynamic; local_hostlist_dynamic = entry; } } #endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC && defined(DNS_LOCAL_HOSTLIST_INIT) */ } /** * Scans the local host-list for a hostname. * * @param hostname Hostname to look for in the local host-list * @param addr the first IP address for the hostname in the local host-list or * IPADDR_NONE if not found. * @return ERR_OK if found, ERR_ARG if not found */ static err_t dns_lookup_local(const char *hostname, ip_addr_t *addr) { #if DNS_LOCAL_HOSTLIST_IS_DYNAMIC struct local_hostlist_entry *entry = local_hostlist_dynamic; while(entry != NULL) { if (LWIP_DNS_STRICMP(entry->name, hostname) == 0) { if (addr) { ip_addr_copy(*addr, entry->addr); } return ERR_OK; } entry = entry->next; } #else /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */ int i; for (i = 0; i < sizeof(local_hostlist_static) / sizeof(struct local_hostlist_entry); i++) { if (LWIP_DNS_STRICMP(local_hostlist_static[i].name, hostname) == 0) { if (addr) { ip_addr_copy(*addr, local_hostlist_static[i].addr); } return ERR_OK; } } #endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */ return ERR_ARG; } #if DNS_LOCAL_HOSTLIST_IS_DYNAMIC /** Remove all entries from the local host-list for a specific hostname * and/or IP address * * @param hostname hostname for which entries shall be removed from the local * host-list * @param addr address for which entries shall be removed from the local host-list * @return the number of removed entries */ int dns_local_removehost(const char *hostname, const ip_addr_t *addr) { int removed = 0; struct local_hostlist_entry *entry = local_hostlist_dynamic; struct local_hostlist_entry *last_entry = NULL; while (entry != NULL) { if (((hostname == NULL) || !LWIP_DNS_STRICMP(entry->name, hostname)) && ((addr == NULL) || ip_addr_cmp(&entry->addr, addr))) { struct local_hostlist_entry *free_entry; if (last_entry != NULL) { last_entry->next = entry->next; } else { local_hostlist_dynamic = entry->next; } free_entry = entry; entry = entry->next; memp_free(MEMP_LOCALHOSTLIST, free_entry); removed++; } else { last_entry = entry; entry = entry->next; } } return removed; } /** * Add a hostname/IP address pair to the local host-list. * Duplicates are not checked. * * @param hostname hostname of the new entry * @param addr IP address of the new entry * @return ERR_OK if succeeded or ERR_MEM on memory error */ err_t dns_local_addhost(const char *hostname, const ip_addr_t *addr) { struct local_hostlist_entry *entry; size_t namelen; LWIP_ASSERT("invalid host name (NULL)", hostname != NULL); namelen = strlen(hostname); LWIP_ASSERT("namelen <= DNS_LOCAL_HOSTLIST_MAX_NAMELEN", namelen <= DNS_LOCAL_HOSTLIST_MAX_NAMELEN); entry = (struct local_hostlist_entry *)memp_malloc(MEMP_LOCALHOSTLIST); if (entry == NULL) { return ERR_MEM; } entry->name = (char*)entry + sizeof(struct local_hostlist_entry); MEMCPY((char*)entry->name, hostname, namelen); ((char*)entry->name)[namelen] = 0; ip_addr_copy(entry->addr, *addr); entry->next = local_hostlist_dynamic; local_hostlist_dynamic = entry; return ERR_OK; } #endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC*/ #endif /* DNS_LOCAL_HOSTLIST */ /** * Look up a hostname in the array of known hostnames. * * @note This function only looks in the internal array of known * hostnames, it does not send out a query for the hostname if none * was found. The function dns_enqueue() can be used to send a query * for a hostname. * * @param name the hostname to look up * @param addr the hostname's IP address, as u32_t (instead of ip_addr_t to * better check for failure: != IPADDR_NONE) or IPADDR_NONE if the hostname * was not found in the cached dns_table. * @return ERR_OK if found, ERR_ARG if not found */ static err_t dns_lookup(const char *name, ip_addr_t *addr) { u8_t i; #if DNS_LOCAL_HOSTLIST || defined(DNS_LOOKUP_LOCAL_EXTERN) #endif /* DNS_LOCAL_HOSTLIST || defined(DNS_LOOKUP_LOCAL_EXTERN) */ #if DNS_LOCAL_HOSTLIST if (dns_lookup_local(name, addr) == ERR_OK) { return ERR_OK; } #endif /* DNS_LOCAL_HOSTLIST */ #ifdef DNS_LOOKUP_LOCAL_EXTERN if((addr = DNS_LOOKUP_LOCAL_EXTERN(name)) != IPADDR_NONE) { return addr; } #endif /* DNS_LOOKUP_LOCAL_EXTERN */ /* Walk through name list, return entry if found. If not, return NULL. */ for (i = 0; i < DNS_TABLE_SIZE; ++i) { if ((dns_table[i].state == DNS_STATE_DONE) && (LWIP_DNS_STRICMP(name, dns_table[i].name) == 0)) { LWIP_DEBUGF(DNS_DEBUG, ("dns_lookup: \"%s\": found = ", name)); ip_addr_debug_print(DNS_DEBUG, &(dns_table[i].ipaddr)); LWIP_DEBUGF(DNS_DEBUG, ("\n")); if (addr) { ip_addr_copy(*addr, dns_table[i].ipaddr); } return ERR_OK; } } return ERR_ARG; } /** * Compare the "dotted" name "query" with the encoded name "response" * to make sure an answer from the DNS server matches the current dns_table * entry (otherwise, answers might arrive late for hostname not on the list * any more). * * @param query hostname (not encoded) from the dns_table * @param p pbuf containing the encoded hostname in the DNS response * @param start_offset offset into p where the name starts * @return 0xFFFF: names differ, other: names equal -> offset behind name */ static u16_t dns_compare_name(char *query, struct pbuf* p, u16_t start_offset) { unsigned char n; u16_t response_offset = start_offset; do { n = pbuf_get_at(p, response_offset++); /** @see RFC 1035 - 4.1.4. Message compression */ if ((n & 0xc0) == 0xc0) { /* Compressed name: cannot be equal since we don't send them */ return 0xFFFF; } else { /* Not compressed name */ while (n > 0) { if ((*query) != pbuf_get_at(p, response_offset)) { return 0xFFFF; } ++response_offset; ++query; --n; }; ++query; } } while (pbuf_get_at(p, response_offset) != 0); return response_offset + 1; } /** * Walk through a compact encoded DNS name and return the end of the name. * * @param p pbuf containing the name * @param query_idx start index into p pointing to encoded DNS name in the DNS server response * @return index to end of the name */ static u16_t dns_parse_name(struct pbuf* p, u16_t query_idx) { unsigned char n; do { n = pbuf_get_at(p, query_idx++); /** @see RFC 1035 - 4.1.4. Message compression */ if ((n & 0xc0) == 0xc0) { /* Compressed name */ break; } else { /* Not compressed name */ while (n > 0) { ++query_idx; --n; }; } } while (pbuf_get_at(p, query_idx) != 0); return query_idx + 1; } /** * Send a DNS query packet. * * @param entry the DNS table entry for which to send a request * @return ERR_OK if packet is sent; an err_t indicating the problem otherwise */ static err_t dns_send(struct dns_table_entry* entry) { err_t err; struct dns_hdr hdr; struct dns_query qry; struct pbuf *p; u16_t query_idx, copy_len; const char *hostname, *hostname_part; u8_t n; u8_t pcb_idx; LWIP_DEBUGF(DNS_DEBUG, ("dns_send: dns_servers[%"U16_F"] \"%s\": request\n", (u16_t)(entry->server_idx), entry->name)); LWIP_ASSERT("dns server out of array", entry->server_idx < DNS_MAX_SERVERS); LWIP_ASSERT("dns server has no IP address set", !ip_addr_isany(&dns_servers[entry->server_idx])); /* if here, we have either a new query or a retry on a previous query to process */ p = pbuf_alloc(PBUF_TRANSPORT, SIZEOF_DNS_HDR + strlen(entry->name) + 2 + SIZEOF_DNS_QUERY, PBUF_RAM); if (p != NULL) { /* fill dns header */ memset(&hdr, 0, SIZEOF_DNS_HDR); hdr.id = htons(entry->txid); hdr.flags1 = DNS_FLAG1_RD; hdr.numquestions = PP_HTONS(1); pbuf_take(p, &hdr, SIZEOF_DNS_HDR); hostname = entry->name; --hostname; /* convert hostname into suitable query format. */ query_idx = SIZEOF_DNS_HDR; do { ++hostname; hostname_part = hostname; for(n = 0; *hostname != '.' && *hostname != 0; ++hostname) { ++n; } copy_len = hostname - hostname_part; pbuf_put_at(p, query_idx, n); pbuf_take_at(p, hostname_part, copy_len, query_idx + 1); query_idx += n + 1; } while(*hostname != 0); pbuf_put_at(p, query_idx, 0); query_idx++; /* fill dns query */ qry.type = PP_HTONS(DNS_RRTYPE_A); qry.cls = PP_HTONS(DNS_RRCLASS_IN); pbuf_take_at(p, &qry, SIZEOF_DNS_QUERY, query_idx); #if ((LWIP_DNS_SECURE & LWIP_DNS_SECURE_RAND_SRC_PORT) != 0) pcb_idx = entry->pcb_idx; #else pcb_idx = 0; #endif /* send dns packet */ LWIP_DEBUGF(DNS_DEBUG, ("sending DNS request ID %d for name \"%s\" to server %d\r\n", entry->txid, entry->name, entry->server_idx)); err = udp_sendto(dns_pcbs[pcb_idx], p, &dns_servers[entry->server_idx], DNS_SERVER_PORT); /* free pbuf */ pbuf_free(p); } else { err = ERR_MEM; } return err; } #if ((LWIP_DNS_SECURE & LWIP_DNS_SECURE_RAND_SRC_PORT) != 0) static struct udp_pcb* dns_alloc_random_port(void) { err_t err; struct udp_pcb* ret; ret = udp_new(); if (ret == NULL) { /* out of memory, have to reuse an existing pcb */ return NULL; } do { u16_t port = DNS_RAND_TXID(); if (!DNS_PORT_ALLOWED(port)) { /* this port is not allowed, try again */ err = ERR_USE; continue; } err = udp_bind(ret, IP_ADDR_ANY, port); } while(err == ERR_USE); if ((err != ERR_OK) && (err != ERR_USE)) { udp_remove(ret); return NULL; } udp_recv(ret, dns_recv, NULL); return ret; } /** * dns_alloc_pcb() - allocates a new pcb (or reuses an existing one) to be used * for sending a request * * @return an index into dns_pcbs */ static u8_t dns_alloc_pcb(void) { u8_t i; u8_t idx; for (i = 0; i < DNS_MAX_SOURCE_PORTS; i++) { if (dns_pcbs[i] == NULL) { break; } } if (i < DNS_MAX_SOURCE_PORTS) { dns_pcbs[i] = dns_alloc_random_port(); if (dns_pcbs[i] != NULL) { /* succeeded */ dns_last_pcb_idx = i; return i; } } /* if we come here, creating a new UDP pcb failed, so we have to use an already existing one */ idx = dns_last_pcb_idx + 1; for (i = 0; i < DNS_MAX_SOURCE_PORTS; i++) { if (idx >= DNS_MAX_SOURCE_PORTS) { idx = 0; } if (dns_pcbs[idx] != NULL) { dns_last_pcb_idx = idx; return idx; } } return DNS_MAX_SOURCE_PORTS; } #endif /* ((LWIP_DNS_SECURE & LWIP_DNS_SECURE_RAND_SRC_PORT) != 0) */ /** * dns_call_found() - call the found callback and check if there are duplicate * entries for the given hostname. If there are any, their found callback will * be called and they will be removed. * * @param idx dns table index of the entry that is resolved or removed * @param addr IP address for the hostname (or NULL on error or memory shortage) */ static void dns_call_found(u8_t idx, ip_addr_t* addr) { u8_t i; LWIP_UNUSED_ARG(i); #if ((LWIP_DNS_SECURE & LWIP_DNS_SECURE_NO_MULTIPLE_OUTSTANDING) != 0) for (i = 0; i < DNS_MAX_REQUESTS; i++) { if (dns_requests[i].found && (dns_requests[i].dns_table_idx == idx)) { (*dns_requests[i].found)(dns_table[idx].name, addr, dns_requests[i].arg); /* flush this entry */ dns_requests[i].found = NULL; } } #else if (dns_requests[idx].found) { (*dns_requests[idx].found)(dns_table[idx].name, addr, dns_requests[idx].arg); } dns_requests[idx].found = NULL; #endif #if ((LWIP_DNS_SECURE & LWIP_DNS_SECURE_RAND_SRC_PORT) != 0) /* close the pcb used unless other request are using it */ for (i = 0; i < DNS_MAX_REQUESTS; i++) { if (i == idx) { continue; /* only check other requests */ } if (dns_table[i].state == DNS_STATE_ASKING) { if (dns_table[i].pcb_idx == dns_table[idx].pcb_idx) { /* another request is still using the same pcb */ dns_table[idx].pcb_idx = DNS_MAX_SOURCE_PORTS; break; } } } if (dns_table[idx].pcb_idx < DNS_MAX_SOURCE_PORTS) { /* if we come here, the pcb is not used any more and can be removed */ udp_remove(dns_pcbs[dns_table[idx].pcb_idx]); dns_pcbs[dns_table[idx].pcb_idx] = NULL; dns_table[idx].pcb_idx = DNS_MAX_SOURCE_PORTS; } #endif } /* Create a query transmission ID that is unique for all outstanding queries */ static u16_t dns_create_txid(void) { u16_t txid; u8_t i; again: txid = DNS_RAND_TXID(); /* check whether the ID is unique */ for (i = 0; i < DNS_TABLE_SIZE; i++) { if ((dns_table[i].state == DNS_STATE_ASKING) && (dns_table[i].txid == txid)) { /* ID already used by another pending query */ goto again; } } return txid; } /** * dns_check_entry() - see if entry has not yet been queried and, if so, sends out a query. * Check an entry in the dns_table: * - send out query for new entries * - retry old pending entries on timeout (also with different servers) * - remove completed entries from the table if their TTL has expired * * @param i index of the dns_table entry to check */ static void dns_check_entry(u8_t i) { err_t err; struct dns_table_entry *entry = &dns_table[i]; LWIP_ASSERT("array index out of bounds", i < DNS_TABLE_SIZE); switch (entry->state) { case DNS_STATE_NEW: { u16_t txid; /* initialize new entry */ txid = dns_create_txid(); entry->txid = txid; entry->state = DNS_STATE_ASKING; entry->server_idx = 0; entry->tmr = 1; entry->retries = 0; /* send DNS packet for this entry */ err = dns_send(entry); if (err != ERR_OK) { LWIP_DEBUGF(DNS_DEBUG | LWIP_DBG_LEVEL_WARNING, ("dns_send returned error: %s\n", lwip_strerr(err))); } break; } case DNS_STATE_ASKING: if (--entry->tmr == 0) { if (++entry->retries == DNS_MAX_RETRIES) { if ((entry->server_idx + 1 < DNS_MAX_SERVERS) && !ip_addr_isany(&dns_servers[entry->server_idx + 1])) { /* change of server */ entry->server_idx++; entry->tmr = 1; entry->retries = 0; break; } else { LWIP_DEBUGF(DNS_DEBUG, ("dns_check_entry: \"%s\": timeout\n", entry->name)); /* call specified callback function if provided */ dns_call_found(i, NULL); /* flush this entry */ entry->state = DNS_STATE_UNUSED; break; } } /* wait longer for the next retry */ entry->tmr = entry->retries; /* send DNS packet for this entry */ err = dns_send(entry); if (err != ERR_OK) { LWIP_DEBUGF(DNS_DEBUG | LWIP_DBG_LEVEL_WARNING, ("dns_send returned error: %s\n", lwip_strerr(err))); } } break; case DNS_STATE_DONE: /* if the time to live is nul */ if ((entry->ttl == 0) || (--entry->ttl == 0)) { LWIP_DEBUGF(DNS_DEBUG, ("dns_check_entry: \"%s\": flush\n", entry->name)); /* flush this entry, there cannot be any related pending entries in this state */ entry->state = DNS_STATE_UNUSED; } break; case DNS_STATE_UNUSED: /* nothing to do */ break; default: LWIP_ASSERT("unknown dns_table entry state:", 0); break; } } /** * Call dns_check_entry for each entry in dns_table - check all entries. */ static void dns_check_entries(void) { u8_t i; for (i = 0; i < DNS_TABLE_SIZE; ++i) { dns_check_entry(i); } } /** * Receive input function for DNS response packets arriving for the dns UDP pcb. * * @params see udp.h */ static void dns_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p, const ip_addr_t *addr, u16_t port) { u8_t i, entry_idx = DNS_TABLE_SIZE; u16_t txid; u16_t res_idx; struct dns_hdr hdr; struct dns_answer ans; struct dns_query qry; u16_t nquestions, nanswers; LWIP_UNUSED_ARG(arg); LWIP_UNUSED_ARG(pcb); LWIP_UNUSED_ARG(port); /* is the dns message big enough ? */ if (p->tot_len < (SIZEOF_DNS_HDR + SIZEOF_DNS_QUERY + SIZEOF_DNS_ANSWER)) { LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: pbuf too small\n")); /* free pbuf and return */ goto memerr; } /* copy dns payload inside static buffer for processing */ if (pbuf_copy_partial(p, &hdr, SIZEOF_DNS_HDR, 0) == SIZEOF_DNS_HDR) { /* Match the ID in the DNS header with the name table. */ txid = htons(hdr.id); for (i = 0; i < DNS_TABLE_SIZE; i++) { struct dns_table_entry *entry = &dns_table[i]; entry_idx = i; if ((entry->state == DNS_STATE_ASKING) && (entry->txid == txid)) { u8_t dns_err; /* This entry is now completed. */ entry->state = DNS_STATE_DONE; dns_err = hdr.flags2 & DNS_FLAG2_ERR_MASK; /* We only care about the question(s) and the answers. The authrr and the extrarr are simply discarded. */ nquestions = htons(hdr.numquestions); nanswers = htons(hdr.numanswers); /* Check for error. If so, call callback to inform. */ if (((hdr.flags1 & DNS_FLAG1_RESPONSE) == 0) || (dns_err != 0) || (nquestions != 1)) { LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": error in flags\n", entry->name)); /* call callback to indicate error, clean up memory and return */ goto responseerr; } /* Check whether response comes from the same network address to which the question was sent. (RFC 5452) */ if (!ip_addr_cmp(addr, &dns_servers[entry->server_idx])) { /* call callback to indicate error, clean up memory and return */ goto responseerr; } /* Check if the name in the "question" part match with the name in the entry and skip it if equal. */ res_idx = dns_compare_name(entry->name, p, SIZEOF_DNS_HDR); if (res_idx == 0xFFFF) { LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": response not match to query\n", entry->name)); /* call callback to indicate error, clean up memory and return */ goto responseerr; } /* check if "question" part matches the request */ pbuf_copy_partial(p, &qry, SIZEOF_DNS_QUERY, res_idx); if((qry.type != PP_HTONS(DNS_RRTYPE_A)) || (qry.cls != PP_HTONS(DNS_RRCLASS_IN))) { LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": response not match to query\n", entry->name)); /* call callback to indicate error, clean up memory and return */ goto responseerr; } /* skip the rest of the "question" part */ res_idx += SIZEOF_DNS_QUERY; while (nanswers > 0) { /* skip answer resource record's host name */ res_idx = dns_parse_name(p, res_idx); /* Check for IP address type and Internet class. Others are discarded. */ pbuf_copy_partial(p, &ans, SIZEOF_DNS_ANSWER, res_idx); #if LWIP_IPV4 if((ans.type == PP_HTONS(DNS_RRTYPE_A)) && (ans.cls == PP_HTONS(DNS_RRCLASS_IN)) && (ans.len == PP_HTONS(sizeof(ip4_addr_t))) ) { res_idx += SIZEOF_DNS_ANSWER; /* read the answer resource record's TTL, and maximize it if needed */ entry->ttl = ntohl(ans.ttl); if (entry->ttl > DNS_MAX_TTL) { entry->ttl = DNS_MAX_TTL; } /* read the IP address after answer resource record's header */ pbuf_copy_partial(p, &(entry->ipaddr), sizeof(entry->ipaddr), res_idx); LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": response = ", entry->name)); ip4_addr_debug_print(DNS_DEBUG, (&(entry->ipaddr))); LWIP_DEBUGF(DNS_DEBUG, ("\n")); /* call specified callback function if provided */ dns_call_found(entry_idx, &entry->ipaddr); if (entry->ttl == 0) { /* RFC 883, page 29: "Zero values are interpreted to mean that the RR can only be used for the transaction in progress, and should not be cached." -> flush this entry now */ goto flushentry; } /* deallocate memory and return */ goto memerr; } else #endif /* LWIP_IPV4 */ { /* @todo: parse IPv6 answers */ res_idx += SIZEOF_DNS_ANSWER + htons(ans.len); } --nanswers; } LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": error in response\n", entry->name)); /* call callback to indicate error, clean up memory and return */ goto responseerr; } } } /* deallocate memory and return */ goto memerr; responseerr: /* ERROR: call specified callback function with NULL as name to indicate an error */ dns_call_found(entry_idx, NULL); #if LWIP_IPV4 flushentry: #endif /* LWIP_IPV4 */ /* flush this entry */ dns_table[entry_idx].state = DNS_STATE_UNUSED; memerr: /* free pbuf */ pbuf_free(p); return; } /** * Queues a new hostname to resolve and sends out a DNS query for that hostname * * @param name the hostname that is to be queried * @param hostnamelen length of the hostname * @param found a callback function to be called on success, failure or timeout * @param callback_arg argument to pass to the callback function * @return @return a err_t return code. */ static err_t dns_enqueue(const char *name, size_t hostnamelen, dns_found_callback found, void *callback_arg) { u8_t i; u8_t lseq, lseqi; struct dns_table_entry *entry = NULL; size_t namelen; struct dns_req_entry* req; #if ((LWIP_DNS_SECURE & LWIP_DNS_SECURE_NO_MULTIPLE_OUTSTANDING) != 0) u8_t r; /* check for duplicate entries */ for (i = 0; i < DNS_TABLE_SIZE; i++) { if ((dns_table[i].state == DNS_STATE_ASKING) && (LWIP_DNS_STRICMP(name, dns_table[i].name) == 0)) { /* this is a duplicate entry, find a free request entry */ for (r = 0; r < DNS_MAX_REQUESTS; r++) { if (dns_requests[r].found == 0) { dns_requests[r].found = found; dns_requests[r].arg = callback_arg; dns_requests[r].dns_table_idx = i; LWIP_DEBUGF(DNS_DEBUG, ("dns_enqueue: \"%s\": duplicate request\n", name)); return ERR_INPROGRESS; } } } } /* no duplicate entries found */ #endif /* search an unused entry, or the oldest one */ lseq = 0; lseqi = DNS_TABLE_SIZE; for (i = 0; i < DNS_TABLE_SIZE; ++i) { entry = &dns_table[i]; /* is it an unused entry ? */ if (entry->state == DNS_STATE_UNUSED) { break; } /* check if this is the oldest completed entry */ if (entry->state == DNS_STATE_DONE) { if ((u8_t)(dns_seqno - entry->seqno) > lseq) { lseq = dns_seqno - entry->seqno; lseqi = i; } } } /* if we don't have found an unused entry, use the oldest completed one */ if (i == DNS_TABLE_SIZE) { if ((lseqi >= DNS_TABLE_SIZE) || (dns_table[lseqi].state != DNS_STATE_DONE)) { /* no entry can be used now, table is full */ LWIP_DEBUGF(DNS_DEBUG, ("dns_enqueue: \"%s\": DNS entries table is full\n", name)); return ERR_MEM; } else { /* use the oldest completed one */ i = lseqi; entry = &dns_table[i]; } } #if ((LWIP_DNS_SECURE & LWIP_DNS_SECURE_NO_MULTIPLE_OUTSTANDING) != 0) /* find a free request entry */ req = NULL; for (r = 0; r < DNS_MAX_REQUESTS; r++) { if (dns_requests[r].found == NULL) { req = &dns_requests[r]; break; } } if (req == NULL) { /* no request entry can be used now, table is full */ LWIP_DEBUGF(DNS_DEBUG, ("dns_enqueue: \"%s\": DNS request entries table is full\n", name)); return ERR_MEM; } req->dns_table_idx = i; #else /* in this configuration, the entry index is the same as the request index */ req = &dns_requests[i]; #endif /* use this entry */ LWIP_DEBUGF(DNS_DEBUG, ("dns_enqueue: \"%s\": use DNS entry %"U16_F"\n", name, (u16_t)(i))); /* fill the entry */ entry->state = DNS_STATE_NEW; entry->seqno = dns_seqno; req->found = found; req->arg = callback_arg; namelen = LWIP_MIN(hostnamelen, DNS_MAX_NAME_LENGTH-1); MEMCPY(entry->name, name, namelen); entry->name[namelen] = 0; #if ((LWIP_DNS_SECURE & LWIP_DNS_SECURE_RAND_SRC_PORT) != 0) entry->pcb_idx = dns_alloc_pcb(); if (entry->pcb_idx >= DNS_MAX_SOURCE_PORTS) { /* failed to get a UDP pcb */ LWIP_DEBUGF(DNS_DEBUG, ("dns_enqueue: \"%s\": failed to allocate a pcb\n", name)); entry->state = DNS_STATE_UNUSED; req->found = NULL; return ERR_MEM; } LWIP_DEBUGF(DNS_DEBUG, ("dns_enqueue: \"%s\": use DNS pcb %"U16_F"\n", name, (u16_t)(entry->pcb_idx))); #endif dns_seqno++; /* force to send query without waiting timer */ dns_check_entry(i); /* dns query is enqueued */ return ERR_INPROGRESS; } /** * Resolve a hostname (string) into an IP address. * NON-BLOCKING callback version for use with raw API!!! * * Returns immediately with one of err_t return codes: * - ERR_OK if hostname is a valid IP address string or the host * name is already in the local names table. * - ERR_INPROGRESS enqueue a request to be sent to the DNS server * for resolution if no errors are present. * - ERR_ARG: dns client not initialized or invalid hostname * * @param hostname the hostname that is to be queried * @param addr pointer to a ip_addr_t where to store the address if it is already * cached in the dns_table (only valid if ERR_OK is returned!) * @param found a callback function to be called on success, failure or timeout (only if * ERR_INPROGRESS is returned!) * @param callback_arg argument to pass to the callback function * @return a err_t return code. */ err_t dns_gethostbyname(const char *hostname, ip_addr_t *addr, dns_found_callback found, void *callback_arg) { size_t hostnamelen; /* not initialized or no valid server yet, or invalid addr pointer * or invalid hostname or invalid hostname length */ if ((addr == NULL) || (!hostname) || (!hostname[0])) { return ERR_ARG; } #if ((LWIP_DNS_SECURE & LWIP_DNS_SECURE_RAND_SRC_PORT) == 0) if (dns_pcbs[0] == NULL) { return ERR_ARG; } #endif hostnamelen = strlen(hostname); if (hostnamelen >= DNS_MAX_NAME_LENGTH) { LWIP_DEBUGF(DNS_DEBUG, ("dns_gethostbyname: name too long to resolve")); return ERR_ARG; } #if LWIP_HAVE_LOOPIF if (strcmp(hostname, "localhost") == 0) { /* @todo: IPv6 support... */ ip_addr_set_loopback(0, addr); return ERR_OK; } #endif /* LWIP_HAVE_LOOPIF */ /* host name already in octet notation? set ip addr and return ERR_OK */ if (ipaddr_aton(hostname, addr)) { return ERR_OK; } /* already have this address cached? */ if(dns_lookup(hostname, addr) == ERR_OK) { return ERR_OK; } /* queue query with specified callback */ return dns_enqueue(hostname, hostnamelen, found, callback_arg); } #endif /* LWIP_DNS */