blob: 3439f7ee90e17415daf3812c90a94f8492bc7d4b [file] [log] [blame]
/*
* Name server resolution
*
* Copyright 2014 Baptiste Assmann <bedis9@gmail.com>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*
*/
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <common/time.h>
#include <common/ticks.h>
#include <types/global.h>
#include <types/dns.h>
#include <types/proto_udp.h>
#include <proto/checks.h>
#include <proto/dns.h>
#include <proto/fd.h>
#include <proto/log.h>
#include <proto/server.h>
#include <proto/task.h>
#include <proto/proto_udp.h>
struct list dns_resolvers = LIST_HEAD_INIT(dns_resolvers);
struct dns_resolution *resolution = NULL;
static int64_t dns_query_id_seed; /* random seed */
/* proto_udp callback functions for a DNS resolution */
struct dgram_data_cb resolve_dgram_cb = {
.recv = dns_resolve_recv,
.send = dns_resolve_send,
};
#if DEBUG
/*
* go through the resolutions associated to a resolvers section and print the ID and hostname in
* domain name format
* should be used for debug purpose only
*/
void dns_print_current_resolutions(struct dns_resolvers *resolvers)
{
list_for_each_entry(resolution, &resolvers->curr_resolution, list) {
printf(" resolution %d for %s\n", resolution->query_id, resolution->hostname_dn);
}
}
#endif
/*
* check if there is more than 1 resolution in the resolver's resolution list
* return value:
* 0: empty list
* 1: exactly one entry in the list
* 2: more than one entry in the list
*/
int dns_check_resolution_queue(struct dns_resolvers *resolvers)
{
if (LIST_ISEMPTY(&resolvers->curr_resolution))
return 0;
if ((resolvers->curr_resolution.n) && (resolvers->curr_resolution.n == resolvers->curr_resolution.p))
return 1;
if (! ((resolvers->curr_resolution.n == resolvers->curr_resolution.p)
&& (&resolvers->curr_resolution != resolvers->curr_resolution.n)))
return 2;
return 0;
}
/*
* reset all parameters of a DNS resolution to 0 (or equivalent)
* and clean it up from all associated lists (resolution->qid and resolution->list)
*/
void dns_reset_resolution(struct dns_resolution *resolution)
{
/* update resolution status */
resolution->step = RSLV_STEP_NONE;
resolution->try = 0;
resolution->try_cname = 0;
resolution->last_resolution = now_ms;
resolution->nb_responses = 0;
/* clean up query id */
eb32_delete(&resolution->qid);
resolution->query_id = 0;
resolution->qid.key = 0;
/* default values */
resolution->query_type = DNS_RTYPE_ANY;
/* the second resolution in the queue becomes the first one */
LIST_DEL(&resolution->list);
}
/*
* function called when a network IO is generated on a name server socket for an incoming packet
* It performs the following actions:
* - check if the packet requires processing (not outdated resolution)
* - ensure the DNS packet received is valid and call requester's callback
* - call requester's error callback if invalid response
*/
void dns_resolve_recv(struct dgram_conn *dgram)
{
struct dns_nameserver *nameserver;
struct dns_resolvers *resolvers;
struct dns_resolution *resolution;
unsigned char buf[DNS_MAX_UDP_MESSAGE + 1];
unsigned char *bufend;
int fd, buflen, ret;
unsigned short query_id;
struct eb32_node *eb;
fd = dgram->t.sock.fd;
/* check if ready for reading */
if (!fd_recv_ready(fd))
return;
/* no need to go further if we can't retrieve the nameserver */
if ((nameserver = (struct dns_nameserver *)dgram->owner) == NULL)
return;
resolvers = nameserver->resolvers;
/* process all pending input messages */
while (1) {
/* read message received */
memset(buf, '\0', DNS_MAX_UDP_MESSAGE + 1);
if ((buflen = recv(fd, (char*)buf , DNS_MAX_UDP_MESSAGE, 0)) < 0) {
/* FIXME : for now we consider EAGAIN only */
fd_cant_recv(fd);
break;
}
/* message too big */
if (buflen > DNS_MAX_UDP_MESSAGE) {
nameserver->counters.too_big += 1;
continue;
}
/* initializing variables */
bufend = buf + buflen; /* pointer to mark the end of the buffer */
/* read the query id from the packet (16 bits) */
if (buf + 2 > bufend) {
nameserver->counters.invalid += 1;
continue;
}
query_id = dns_response_get_query_id(buf);
/* search the query_id in the pending resolution tree */
eb = eb32_lookup(&resolvers->query_ids, query_id);
if (eb == NULL) {
/* unknown query id means an outdated response and can be safely ignored */
nameserver->counters.outdated += 1;
continue;
}
/* known query id means a resolution in prgress */
resolution = eb32_entry(eb, struct dns_resolution, qid);
if (!resolution) {
nameserver->counters.outdated += 1;
continue;
}
/* number of responses received */
resolution->nb_responses += 1;
ret = dns_validate_dns_response(buf, bufend, resolution->hostname_dn, resolution->hostname_dn_len);
/* treat only errors */
switch (ret) {
case DNS_RESP_INVALID:
case DNS_RESP_WRONG_NAME:
nameserver->counters.invalid += 1;
resolution->requester_error_cb(resolution, DNS_RESP_INVALID);
continue;
case DNS_RESP_ERROR:
nameserver->counters.other += 1;
resolution->requester_error_cb(resolution, DNS_RESP_ERROR);
continue;
case DNS_RESP_ANCOUNT_ZERO:
nameserver->counters.any_err += 1;
resolution->requester_error_cb(resolution, DNS_RESP_ANCOUNT_ZERO);
continue;
case DNS_RESP_NX_DOMAIN:
nameserver->counters.nx += 1;
resolution->requester_error_cb(resolution, DNS_RESP_NX_DOMAIN);
continue;
case DNS_RESP_REFUSED:
nameserver->counters.refused += 1;
resolution->requester_error_cb(resolution, DNS_RESP_REFUSED);
continue;
case DNS_RESP_CNAME_ERROR:
nameserver->counters.cname_error += 1;
resolution->requester_error_cb(resolution, DNS_RESP_CNAME_ERROR);
continue;
case DNS_RESP_TRUNCATED:
nameserver->counters.truncated += 1;
resolution->requester_error_cb(resolution, DNS_RESP_TRUNCATED);
continue;
case DNS_RESP_NO_EXPECTED_RECORD:
nameserver->counters.other += 1;
resolution->requester_error_cb(resolution, DNS_RESP_NO_EXPECTED_RECORD);
continue;
}
nameserver->counters.valid += 1;
resolution->requester_cb(resolution, nameserver, buf, buflen);
}
}
/*
* function called when a resolvers network socket is ready to send data
* It performs the following actions:
*/
void dns_resolve_send(struct dgram_conn *dgram)
{
int fd;
struct dns_nameserver *nameserver;
struct dns_resolvers *resolvers;
struct dns_resolution *resolution;
fd = dgram->t.sock.fd;
/* check if ready for sending */
if (!fd_send_ready(fd))
return;
/* we don't want/need to be waked up any more for sending */
fd_stop_send(fd);
/* no need to go further if we can't retrieve the nameserver */
if ((nameserver = (struct dns_nameserver *)dgram->owner) == NULL)
return;
resolvers = nameserver->resolvers;
resolution = LIST_NEXT(&resolvers->curr_resolution, struct dns_resolution *, list);
dns_send_query(resolution);
dns_update_resolvers_timeout(resolvers);
}
/*
* forge and send a DNS query to resolvers associated to a resolution
* It performs the following actions:
* returns:
* 0 in case of error or safe ignorance
* 1 if no error
*/
int dns_send_query(struct dns_resolution *resolution)
{
struct dns_resolvers *resolvers;
struct dns_nameserver *nameserver;
int ret, send_error, bufsize, fd;
resolvers = resolution->resolvers;
ret = send_error = 0;
bufsize = dns_build_query(resolution->query_id, resolution->query_type, resolution->hostname_dn,
resolution->hostname_dn_len, trash.str, trash.size);
if (bufsize == -1)
return 0;
list_for_each_entry(nameserver, &resolvers->nameserver_list, list) {
fd = nameserver->dgram->t.sock.fd;
errno = 0;
ret = send(fd, trash.str, bufsize, 0);
if (ret > 0)
nameserver->counters.sent += 1;
if (ret == 0 || errno == EAGAIN) {
/* nothing written, let's update the poller that we wanted to send
* but we were not able to */
fd_want_send(fd);
fd_cant_send(fd);
}
}
/* update resolution */
resolution->nb_responses = 0;
resolution->last_sent_packet = now_ms;
return 1;
}
/*
* update a resolvers' task timeout for next wake up
*/
void dns_update_resolvers_timeout(struct dns_resolvers *resolvers)
{
struct dns_resolution *resolution;
if (LIST_ISEMPTY(&resolvers->curr_resolution)) {
/* no more resolution pending, so no wakeup anymore */
resolvers->t->expire = TICK_ETERNITY;
}
else {
resolution = LIST_NEXT(&resolvers->curr_resolution, struct dns_resolution *, list);
resolvers->t->expire = tick_add(resolution->last_sent_packet, resolvers->timeout.retry);
}
}
/*
* Function to validate that the buffer DNS response provided in <resp> and
* finishing before <bufend> is valid from a DNS protocol point of view.
* The caller can also ask the function to check if the response contains data
* for a domain name <dn_name> whose length is <dn_name_len> returns one of the
* DNS_RESP_* code.
*/
int dns_validate_dns_response(unsigned char *resp, unsigned char *bufend, char *dn_name, int dn_name_len)
{
unsigned char *reader, *cname, *ptr;
int i, len, flags, type, ancount, cnamelen, expected_record;
reader = resp;
cname = NULL;
cnamelen = 0;
len = 0;
expected_record = 0; /* flag to report if at least one expected record type is found in the response.
* For now, only records containing an IP address (A and AAAA) are
* considered as expected.
* Later, this function may be updated to let the caller decide what type
* of record is expected to consider the response as valid. (SRV or TXT types)
*/
/* move forward 2 bytes for the query id */
reader += 2;
if (reader >= bufend)
return DNS_RESP_INVALID;
/*
* flags are stored over 2 bytes
* First byte contains:
* - response flag (1 bit)
* - opcode (4 bits)
* - authoritative (1 bit)
* - truncated (1 bit)
* - recursion desired (1 bit)
*/
if (reader + 2 >= bufend)
return DNS_RESP_INVALID;
flags = reader[0] * 256 + reader[1];
if (flags & DNS_FLAG_TRUNCATED)
return DNS_RESP_TRUNCATED;
if ((flags & DNS_FLAG_REPLYCODE) != DNS_RCODE_NO_ERROR) {
if ((flags & DNS_FLAG_REPLYCODE) == DNS_RCODE_NX_DOMAIN)
return DNS_RESP_NX_DOMAIN;
else if ((flags & DNS_FLAG_REPLYCODE) == DNS_RCODE_REFUSED)
return DNS_RESP_REFUSED;
return DNS_RESP_ERROR;
}
/* move forward 2 bytes for flags */
reader += 2;
if (reader >= bufend)
return DNS_RESP_INVALID;
/* move forward 2 bytes for question count */
reader += 2;
if (reader >= bufend)
return DNS_RESP_INVALID;
/* analyzing answer count */
if (reader + 2 > bufend)
return DNS_RESP_INVALID;
ancount = reader[0] * 256 + reader[1];
if (ancount == 0)
return DNS_RESP_ANCOUNT_ZERO;
/* move forward 2 bytes for answer count */
reader += 2;
if (reader >= bufend)
return DNS_RESP_INVALID;
/* move forward 4 bytes authority and additional count */
reader += 4;
if (reader >= bufend)
return DNS_RESP_INVALID;
/* check if the name can stand in response */
if (dn_name && ((reader + dn_name_len + 1) > bufend))
return DNS_RESP_INVALID;
/* check hostname */
if (dn_name && (memcmp(reader, dn_name, dn_name_len) != 0))
return DNS_RESP_WRONG_NAME;
/* move forward hostname len bytes + 1 for NULL byte */
if (dn_name) {
reader = reader + dn_name_len + 1;
}
else {
ptr = reader;
while (*ptr) {
ptr++;
if (ptr >= bufend)
return DNS_RESP_INVALID;
}
reader = ptr + 1;
}
/* move forward 4 bytes for question type and question class */
reader += 4;
if (reader >= bufend)
return DNS_RESP_INVALID;
/* now parsing response records */
for (i = 1; i <= ancount; i++) {
if (reader >= bufend)
return DNS_RESP_INVALID;
/*
* name can be a pointer, so move forward reader cursor accordingly
* if 1st byte is '11XXXXXX', it means name is a pointer
* and 2nd byte gives the offset from resp where the hostname can
* be found
*/
if ((*reader & 0xc0) == 0xc0) {
/*
* pointer, hostname can be found at resp + *(reader + 1)
*/
if (reader + 1 > bufend)
return DNS_RESP_INVALID;
ptr = resp + *(reader + 1);
/* check if the pointer points inside the buffer */
if (ptr >= bufend)
return DNS_RESP_INVALID;
}
else {
/*
* name is a string which starts at first byte
* checking against last cname when recursing through the response
*/
/* look for the end of the string and ensure it's in the buffer */
ptr = reader;
len = 0;
while (*ptr) {
++len;
++ptr;
if (ptr >= bufend)
return DNS_RESP_INVALID;
}
/* if cname is set, it means a CNAME recursion is in progress */
ptr = reader;
}
/* ptr now points to the name */
if ((*reader & 0xc0) != 0xc0) {
/* if cname is set, it means a CNAME recursion is in progress */
if (cname) {
/* check if the name can stand in response */
if ((reader + cnamelen) > bufend)
return DNS_RESP_INVALID;
/* compare cname and current name */
if (memcmp(ptr, cname, cnamelen) != 0)
return DNS_RESP_CNAME_ERROR;
cname = reader;
cnamelen = dns_str_to_dn_label_len((const char *)cname);
/* move forward cnamelen bytes + NULL byte */
reader += (cnamelen + 1);
}
/* compare server hostname to current name */
else if (dn_name) {
/* check if the name can stand in response */
if ((reader + dn_name_len) > bufend)
return DNS_RESP_INVALID;
if (memcmp(ptr, dn_name, dn_name_len) != 0)
return DNS_RESP_WRONG_NAME;
}
else {
reader += (len + 1);
}
}
else {
/* shortname in progress */
/* move forward 2 bytes for information pointer and address pointer */
reader += 2;
}
if (reader >= bufend)
return DNS_RESP_INVALID;
/*
* we know the record is either for our server hostname
* or a valid CNAME in a crecursion
*/
/* now reading record type (A, AAAA, CNAME, etc...) */
if (reader + 2 > bufend)
return DNS_RESP_INVALID;
type = reader[0] * 256 + reader[1];
/* move forward 2 bytes for type (2) */
reader += 2;
/* move forward 6 bytes for class (2) and ttl (4) */
reader += 6;
if (reader >= bufend)
return DNS_RESP_INVALID;
/* now reading data len */
if (reader + 2 > bufend)
return DNS_RESP_INVALID;
len = reader[0] * 256 + reader[1];
/* move forward 2 bytes for data len */
reader += 2;
/* analyzing record content */
switch (type) {
case DNS_RTYPE_A:
/* ipv4 is stored on 4 bytes */
if (len != 4)
return DNS_RESP_INVALID;
expected_record = 1;
break;
case DNS_RTYPE_CNAME:
cname = reader;
cnamelen = len;
break;
case DNS_RTYPE_AAAA:
/* ipv6 is stored on 16 bytes */
if (len != 16)
return DNS_RESP_INVALID;
expected_record = 1;
break;
} /* switch (record type) */
/* move forward len for analyzing next record in the response */
reader += len;
} /* for i 0 to ancount */
if (expected_record == 0)
return DNS_RESP_NO_EXPECTED_RECORD;
return DNS_RESP_VALID;
}
/*
* search dn_name resolution in resp.
* If existing IP not found, return the first IP matching family_priority,
* otherwise, first ip found
* The following tasks are the responsibility of the caller:
* - resp contains an error free DNS response
* - the response matches the dn_name
* For both cases above, dns_validate_dns_response is required
* returns one of the DNS_UPD_* code
*/
int dns_get_ip_from_response(unsigned char *resp, unsigned char *resp_end,
char *dn_name, int dn_name_len, void *currentip, short currentip_sin_family,
int family_priority, void **newip, short *newip_sin_family)
{
int i, ancount, cnamelen, type, data_len, currentip_found;
unsigned char *reader, *cname, *ptr, *newip4, *newip6;
cname = *newip = newip4 = newip6 = NULL;
cnamelen = currentip_found = 0;
*newip_sin_family = AF_UNSPEC;
ancount = (((struct dns_header *)resp)->ancount);
ancount = *(resp + 7);
/* bypass DNS response header */
reader = resp + sizeof(struct dns_header);
/* bypass DNS query section */
/* move forward hostname len bytes + 1 for NULL byte */
reader = reader + dn_name_len + 1;
/* move forward 4 bytes for question type and question class */
reader += 4;
/* now parsing response records */
for (i = 1; i <= ancount; i++) {
/*
* name can be a pointer, so move forward reader cursor accordingly
* if 1st byte is '11XXXXXX', it means name is a pointer
* and 2nd byte gives the offset from buf where the hostname can
* be found
*/
if ((*reader & 0xc0) == 0xc0)
ptr = resp + *(reader + 1);
else
ptr = reader;
if (cname && memcmp(ptr, cname, cnamelen))
return DNS_UPD_NAME_ERROR;
else if (memcmp(ptr, dn_name, dn_name_len))
return DNS_UPD_NAME_ERROR;
if ((*reader & 0xc0) == 0xc0) {
/* move forward 2 bytes for information pointer and address pointer */
reader += 2;
}
else {
if (cname) {
cname = reader;
cnamelen = dns_str_to_dn_label_len((char *)cname);
/* move forward cnamelen bytes + NULL byte */
reader += (cnamelen + 1);
}
else {
/* move forward dn_name_len bytes + NULL byte */
reader += (dn_name_len + 1);
}
}
/*
* we know the record is either for our server hostname
* or a valid CNAME in a crecursion
*/
/* now reading record type (A, AAAA, CNAME, etc...) */
type = reader[0] * 256 + reader[1];
/* move forward 2 bytes for type (2) */
reader += 2;
/* move forward 6 bytes for class (2) and ttl (4) */
reader += 6;
/* now reading data len */
data_len = reader[0] * 256 + reader[1];
/* move forward 2 bytes for data len */
reader += 2;
/* analyzing record content */
switch (type) {
case DNS_RTYPE_A:
/* check if current reccord's IP is the same as server one's */
if ((currentip_sin_family == AF_INET)
&& (*(uint32_t *)reader == *(uint32_t *)currentip)) {
currentip_found = 1;
newip4 = reader;
/* we can stop now if server's family preference is IPv4
* and its current IP is found in the response list */
if (family_priority == AF_INET)
return DNS_UPD_NO; /* DNS_UPD matrix #1 */
}
else if (!newip4) {
newip4 = reader;
}
/* move forward data_len for analyzing next record in the response */
reader += data_len;
break;
case DNS_RTYPE_CNAME:
cname = reader;
cnamelen = data_len;
reader += data_len;
break;
case DNS_RTYPE_AAAA:
/* check if current record's IP is the same as server's one */
if ((currentip_sin_family == AF_INET6) && (memcmp(reader, currentip, 16) == 0)) {
currentip_found = 1;
newip6 = reader;
/* we can stop now if server's preference is IPv6 or is not
* set (which implies we prioritize IPv6 over IPv4 */
if (family_priority == AF_INET6)
return DNS_UPD_NO;
}
else if (!newip6) {
newip6 = reader;
}
/* move forward data_len for analyzing next record in the response */
reader += data_len;
break;
default:
/* not supported record type */
/* move forward data_len for analyzing next record in the response */
reader += data_len;
} /* switch (record type) */
} /* for i 0 to ancount */
/* only CNAMEs in the response, no IP found */
if (cname && !newip4 && !newip6) {
return DNS_UPD_CNAME;
}
/* no IP found in the response */
if (!newip4 && !newip6) {
return DNS_UPD_NO_IP_FOUND;
}
/* case when the caller looks first for an IPv4 address */
if (family_priority == AF_INET) {
if (newip4) {
*newip = newip4;
*newip_sin_family = AF_INET;
if (currentip_found == 1)
return DNS_UPD_NO;
return DNS_UPD_SRVIP_NOT_FOUND;
}
else if (newip6) {
*newip = newip6;
*newip_sin_family = AF_INET6;
if (currentip_found == 1)
return DNS_UPD_NO;
return DNS_UPD_SRVIP_NOT_FOUND;
}
}
/* case when the caller looks first for an IPv6 address */
else if (family_priority == AF_INET6) {
if (newip6) {
*newip = newip6;
*newip_sin_family = AF_INET6;
if (currentip_found == 1)
return DNS_UPD_NO;
return DNS_UPD_SRVIP_NOT_FOUND;
}
else if (newip4) {
*newip = newip4;
*newip_sin_family = AF_INET;
if (currentip_found == 1)
return DNS_UPD_NO;
return DNS_UPD_SRVIP_NOT_FOUND;
}
}
/* case when the caller have no preference (we prefer IPv6) */
else if (family_priority == AF_UNSPEC) {
if (newip6) {
*newip = newip6;
*newip_sin_family = AF_INET6;
if (currentip_found == 1)
return DNS_UPD_NO;
return DNS_UPD_SRVIP_NOT_FOUND;
}
else if (newip4) {
*newip = newip4;
*newip_sin_family = AF_INET;
if (currentip_found == 1)
return DNS_UPD_NO;
return DNS_UPD_SRVIP_NOT_FOUND;
}
}
/* no reason why we should change the server's IP address */
return DNS_UPD_NO;
}
/*
* returns the query id contained in a DNS response
*/
int dns_response_get_query_id(unsigned char *resp)
{
/* read the query id from the response */
return resp[0] * 256 + resp[1];
}
/*
* used during haproxy's init phase
* parses resolvers sections and initializes:
* - task (time events) for each resolvers section
* - the datagram layer (network IO events) for each nameserver
* returns:
* 0 in case of error
* 1 when no error
*/
int dns_init_resolvers(void)
{
struct dns_resolvers *curr_resolvers;
struct dns_nameserver *curnameserver;
struct dgram_conn *dgram;
struct task *t;
int fd;
/* give a first random value to our dns query_id seed */
dns_query_id_seed = random();
/* run through the resolvers section list */
list_for_each_entry(curr_resolvers, &dns_resolvers, list) {
/* create the task associated to the resolvers section */
if ((t = task_new()) == NULL) {
Alert("Starting [%s] resolvers: out of memory.\n", curr_resolvers->id);
return 0;
}
/* update task's parameters */
t->process = dns_process_resolve;
t->context = curr_resolvers;
t->expire = TICK_ETERNITY;
curr_resolvers->t = t;
list_for_each_entry(curnameserver, &curr_resolvers->nameserver_list, list) {
if ((dgram = calloc(1, sizeof(struct dgram_conn))) == NULL) {
Alert("Starting [%s/%s] nameserver: out of memory.\n", curr_resolvers->id,
curnameserver->id);
return 0;
}
/* update datagram's parameters */
dgram->owner = (void *)curnameserver;
dgram->data = &resolve_dgram_cb;
/* create network UDP socket for this nameserver */
if ((fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1) {
Alert("Starting [%s/%s] nameserver: can't create socket.\n", curr_resolvers->id,
curnameserver->id);
free(dgram);
dgram = NULL;
return 0;
}
/* "connect" the UDP socket to the name server IP */
if (connect(fd, (struct sockaddr*)&curnameserver->addr, sizeof(curnameserver->addr)) == -1) {
Alert("Starting [%s/%s] nameserver: can't connect socket.\n", curr_resolvers->id,
curnameserver->id);
close(fd);
free(dgram);
dgram = NULL;
return 0;
}
/* make the socket non blocking */
fcntl(fd, F_SETFL, O_NONBLOCK);
/* add the fd in the fd list and update its parameters */
fd_insert(fd);
fdtab[fd].owner = dgram;
fdtab[fd].iocb = dgram_fd_handler;
fd_want_recv(fd);
dgram->t.sock.fd = fd;
/* update nameserver's datagram property */
curnameserver->dgram = dgram;
continue;
}
/* task can be queued */
task_queue(t);
}
return 1;
}
/*
* Forge a DNS query. It needs the following information from the caller:
* - <query_id>: the DNS query id corresponding to this query
* - <query_type>: DNS_RTYPE_* request DNS record type (A, AAAA, ANY, etc...)
* - <hostname_dn>: hostname in domain name format
* - <hostname_dn_len>: length of <hostname_dn>
* To store the query, the caller must pass a buffer <buf> and its size <bufsize>
*
* the DNS query is stored in <buf>
* returns:
* -1 if <buf> is too short
*/
int dns_build_query(int query_id, int query_type, char *hostname_dn, int hostname_dn_len, char *buf, int bufsize)
{
struct dns_header *dns;
struct dns_question *qinfo;
char *ptr, *bufend;
memset(buf, '\0', bufsize);
ptr = buf;
bufend = buf + bufsize;
/* check if there is enough room for DNS headers */
if (ptr + sizeof(struct dns_header) >= bufend)
return -1;
/* set dns query headers */
dns = (struct dns_header *)ptr;
dns->id = (unsigned short) htons(query_id);
dns->qr = 0; /* query */
dns->opcode = 0;
dns->aa = 0;
dns->tc = 0;
dns->rd = 1; /* recursion desired */
dns->ra = 0;
dns->z = 0;
dns->rcode = 0;
dns->qdcount = htons(1); /* 1 question */
dns->ancount = 0;
dns->nscount = 0;
dns->arcount = 0;
/* move forward ptr */
ptr += sizeof(struct dns_header);
/* check if there is enough room for query hostname */
if ((ptr + hostname_dn_len) >= bufend)
return -1;
/* set up query hostname */
memcpy(ptr, hostname_dn, hostname_dn_len);
ptr[hostname_dn_len + 1] = '\0';
/* move forward ptr */
ptr += (hostname_dn_len + 1);
/* check if there is enough room for query hostname*/
if (ptr + sizeof(struct dns_question) >= bufend)
return -1;
/* set up query info (type and class) */
qinfo = (struct dns_question *)ptr;
qinfo->qtype = htons(query_type);
qinfo->qclass = htons(DNS_RCLASS_IN);
ptr += sizeof(struct dns_question);
return ptr - buf;
}
/*
* turn a string into domain name label:
* www.haproxy.org into 3www7haproxy3org
* if dn memory is pre-allocated, you must provide its size in dn_len
* if dn memory isn't allocated, dn_len must be set to 0.
* In the second case, memory will be allocated.
* in case of error, -1 is returned, otherwise, number of bytes copied in dn
*/
char *dns_str_to_dn_label(const char *string, char *dn, int dn_len)
{
char *c, *d;
int i, offset;
/* offset between string size and theorical dn size */
offset = 1;
/*
* first, get the size of the string turned into its domain name version
* This function also validates the string respect the RFC
*/
if ((i = dns_str_to_dn_label_len(string)) == -1)
return NULL;
/* yes, so let's check there is enough memory */
if (dn_len < i + offset)
return NULL;
i = strlen(string);
memcpy(dn + offset, string, i);
dn[i + offset] = '\0';
/* avoid a '\0' at the beginning of dn string which may prevent the for loop
* below from working.
* Actually, this is the reason of the offset. */
dn[0] = '0';
for (c = dn; *c ; ++c) {
/* c points to the first '0' char or a dot, which we don't want to read */
d = c + offset;
i = 0;
while (*d != '.' && *d) {
i++;
d++;
}
*c = i;
c = d - 1; /* because of c++ of the for loop */
}
return dn;
}
/*
* compute and return the length of <string> it it were translated into domain name
* label:
* www.haproxy.org into 3www7haproxy3org would return 16
* NOTE: add +1 for '\0' when allocating memory ;)
*/
int dns_str_to_dn_label_len(const char *string)
{
return strlen(string) + 1;
}
/*
* validates host name:
* - total size
* - each label size individually
* returns:
* 0 in case of error. If <err> is not NULL, an error message is stored there.
* 1 when no error. <err> is left unaffected.
*/
int dns_hostname_validation(const char *string, char **err)
{
const char *c, *d;
int i;
if (strlen(string) > DNS_MAX_NAME_SIZE) {
if (err)
*err = DNS_TOO_LONG_FQDN;
return 0;
}
c = string;
while (*c) {
d = c;
i = 0;
while (*d != '.' && *d && i <= DNS_MAX_LABEL_SIZE) {
i++;
if (!((*d == '-') || (*d == '_') ||
((*d >= 'a') && (*d <= 'z')) ||
((*d >= 'A') && (*d <= 'Z')) ||
((*d >= '0') && (*d <= '9')))) {
if (err)
*err = DNS_INVALID_CHARACTER;
return 0;
}
d++;
}
if ((i >= DNS_MAX_LABEL_SIZE) && (d[i] != '.')) {
if (err)
*err = DNS_LABEL_TOO_LONG;
return 0;
}
if (*d == '\0')
goto out;
c = ++d;
}
out:
return 1;
}
/*
* 2 bytes random generator to generate DNS query ID
*/
uint16_t dns_rnd16(void)
{
dns_query_id_seed ^= dns_query_id_seed << 13;
dns_query_id_seed ^= dns_query_id_seed >> 7;
dns_query_id_seed ^= dns_query_id_seed << 17;
return dns_query_id_seed;
}
/*
* function called when a timeout occurs during name resolution process
* if max number of tries is reached, then stop, otherwise, retry.
*/
struct task *dns_process_resolve(struct task *t)
{
struct dns_resolvers *resolvers = t->context;
struct dns_resolution *resolution, *res_back;
/* timeout occurs inevitably for the first element of the FIFO queue */
if (LIST_ISEMPTY(&resolvers->curr_resolution)) {
/* no first entry, so wake up was useless */
t->expire = TICK_ETERNITY;
return t;
}
/* look for the first resolution which is not expired */
list_for_each_entry_safe(resolution, res_back, &resolvers->curr_resolution, list) {
/* when we find the first resolution in the future, then we can stop here */
if (tick_is_le(now_ms, resolution->last_sent_packet))
goto out;
/*
* if current resolution has been tried too many times and finishes in timeout
* we update its status and remove it from the list
*/
if (resolution->try <= 0) {
/* clean up resolution information and remove from the list */
dns_reset_resolution(resolution);
/* notify the result to the requester */
resolution->requester_error_cb(resolution, DNS_RESP_TIMEOUT);
}
resolution->try -= 1;
/* check current resolution status */
if (resolution->step == RSLV_STEP_RUNNING) {
/* resend the DNS query */
dns_send_query(resolution);
/* check if we have more than one resolution in the list */
if (dns_check_resolution_queue(resolvers) > 1) {
/* move the rsolution to the end of the list */
LIST_DEL(&resolution->list);
LIST_ADDQ(&resolvers->curr_resolution, &resolution->list);
}
}
}
out:
dns_update_resolvers_timeout(resolvers);
return t;
}