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#define DNS_USE_GETTIMEOFDAY_FOR_ID 1
#define HAVE_STRUCT_IN6_ADDR 1
/* The original version of this module was written by Adam Langley; for
* a history of modifications, check out the subversion logs.
*
* When editing this module, try to keep it re-mergeable by Adam. Don't
* reformat the whitespace, add Tor dependencies, or so on.
*
* TODO:
* - Support IPv6 and PTR records.
* - Replace all externally visible magic numbers with #defined constants.
* - Write doccumentation for APIs of all external functions.
*/
/* Async DNS Library
* Adam Langley <agl@imperialviolet.org>
* http://www.imperialviolet.org/eventdns.html
* Public Domain code
*
* This software is Public Domain. To view a copy of the public domain dedication,
* visit http://creativecommons.org/licenses/publicdomain/ or send a letter to
* Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.
*
* I ask and expect, but do not require, that all derivative works contain an
* attribution similar to:
* Parts developed by Adam Langley <agl@imperialviolet.org>
*
* You may wish to replace the word "Parts" with something else depending on
* the amount of original code.
*
* (Derivative works does not include programs which link against, run or include
* the source verbatim in their source distributions)
*
* Version: 0.1b
*/
#include <sys/types.h>
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#ifdef WIN32
#include "misc.h"
#endif
/* #define NDEBUG */
#ifndef DNS_USE_CPU_CLOCK_FOR_ID
#ifndef DNS_USE_GETTIMEOFDAY_FOR_ID
#ifndef DNS_USE_OPENSSL_FOR_ID
#error Must configure at least one id generation method.
#error Please see the documentation.
#endif
#endif
#endif
/* #define _POSIX_C_SOURCE 200507 */
#define _GNU_SOURCE
#ifdef DNS_USE_CPU_CLOCK_FOR_ID
#ifdef DNS_USE_OPENSSL_FOR_ID
#error Multiple id options selected
#endif
#ifdef DNS_USE_GETTIMEOFDAY_FOR_ID
#error Multiple id options selected
#endif
#include <time.h>
#endif
#ifdef DNS_USE_OPENSSL_FOR_ID
#ifdef DNS_USE_GETTIMEOFDAY_FOR_ID
#error Multiple id options selected
#endif
#include <openssl/rand.h>
#endif
#define _FORTIFY_SOURCE 3
#include <string.h>
#include <fcntl.h>
#include <sys/time.h>
#ifdef HAVE_STDINT_H
#include <stdint.h>
#endif
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <assert.h>
#include <unistd.h>
#include <limits.h>
#include <sys/stat.h>
#include <ctype.h>
#include <stdio.h>
#include <stdarg.h>
#include "evdns.h"
#ifdef WIN32
#include <windows.h>
#include <winsock2.h>
#include <iphlpapi.h>
#else
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#endif
#ifdef HAVE_NETINET_IN6_H
#include <netinet/in6.h>
#endif
#ifdef WIN32
typedef int socklen_t;
#endif
#define EVDNS_LOG_DEBUG 0
#define EVDNS_LOG_WARN 1
#ifndef HOST_NAME_MAX
#define HOST_NAME_MAX 255
#endif
#ifndef NDEBUG
#include <stdio.h>
#endif
#undef MIN
#define MIN(a,b) ((a)<(b)?(a):(b))
#ifdef __USE_ISOC99B
/* libevent doesn't work without this */
typedef uint8_t u_char;
typedef unsigned int uint;
#endif
#include <event.h>
#define u64 uint64_t
#define u32 uint32_t
#define u16 uint16_t
#define u8 uint8_t
#define MAX_ADDRS 4 /* maximum number of addresses from a single packet */
/* which we bother recording */
#define TYPE_A EVDNS_TYPE_A
#define TYPE_CNAME 5
#define TYPE_PTR EVDNS_TYPE_PTR
#define TYPE_AAAA EVDNS_TYPE_AAAA
#define CLASS_INET EVDNS_CLASS_INET
struct request {
u8 *request; /* the dns packet data */
unsigned int request_len;
int reissue_count;
int tx_count; /* the number of times that this packet has been sent */
unsigned int request_type; /* TYPE_PTR or TYPE_A */
void *user_pointer; /* the pointer given to us for this request */
evdns_callback_type user_callback;
struct nameserver *ns; /* the server which we last sent it */
/* elements used by the searching code */
int search_index;
struct search_state *search_state;
char *search_origname; /* needs to be free()ed */
int search_flags;
/* these objects are kept in a circular list */
struct request *next, *prev;
struct event timeout_event;
u16 trans_id; /* the transaction id */
char request_appended; /* true if the request pointer is data which follows this struct */
char transmit_me; /* needs to be transmitted */
};
#ifndef HAVE_STRUCT_IN6_ADDR
struct in6_addr {
u8 s6_addr[16];
};
#endif
struct reply {
unsigned int type;
unsigned int have_answer;
union {
struct {
u32 addrcount;
u32 addresses[MAX_ADDRS];
} a;
struct {
u32 addrcount;
struct in6_addr addresses[MAX_ADDRS];
} aaaa;
struct {
char name[HOST_NAME_MAX];
} ptr;
} data;
};
struct nameserver {
int socket; /* a connected UDP socket */
u32 address;
int failed_times; /* number of times which we have given this server a chance */
int timedout; /* number of times in a row a request has timed out */
struct event event;
/* these objects are kept in a circular list */
struct nameserver *next, *prev;
struct event timeout_event; /* used to keep the timeout for */
/* when we next probe this server. */
/* Valid if state == 0 */
char state; /* zero if we think that this server is down */
char choked; /* true if we have an EAGAIN from this server's socket */
char write_waiting; /* true if we are waiting for EV_WRITE events */
};
static struct request *req_head = NULL, *req_waiting_head = NULL;
static struct nameserver *server_head = NULL;
/* Represents a local port where we're listening for DNS requests. Right now, */
/* only UDP is supported. */
struct evdns_server_port {
int socket; /* socket we use to read queries and write replies. */
int refcnt; /* reference count. */
char choked; /* Are we currently blocked from writing? */
char closing; /* Are we trying to close this port, pending writes? */
evdns_request_callback_fn_type user_callback; /* Fn to handle requests */
void *user_data; /* Opaque pointer passed to user_callback */
struct event event; /* Read/write event */
/* circular list of replies that we want to write. */
struct server_request *pending_replies;
};
/* Represents part of a reply being built. (That is, a single RR.) */
struct server_reply_item {
struct server_reply_item *next; /* next item in sequence. */
char *name; /* name part of the RR */
u16 type : 16; /* The RR type */
u16 class : 16; /* The RR class (usually CLASS_INET) */
u32 ttl; /* The RR TTL */
char is_name; /* True iff data is a label */
u16 datalen; /* Length of data; -1 if data is a label */
void *data; /* The contents of the RR */
};
/* Represents a request that we've received as a DNS server, and holds */
/* the components of the reply as we're constructing it. */
struct server_request {
/* Pointers to the next and previous entries on the list of replies */
/* that we're waiting to write. Only set if we have tried to respond */
/* and gotten EAGAIN. */
struct server_request *next_pending;
struct server_request *prev_pending;
u16 trans_id; /* Transaction id. */
struct evdns_server_port *port; /* Which port received this request on? */
struct sockaddr_storage addr; /* Where to send the response */
socklen_t addrlen; /* length of addr */
int n_answer; /* how many answer RRs have been set? */
int n_authority; /* how many authority RRs have been set? */
int n_additional; /* how many additional RRs have been set? */
struct server_reply_item *answer; /* linked list of answer RRs */
struct server_reply_item *authority; /* linked list of authority RRs */
struct server_reply_item *additional; /* linked list of additional RRs */
/* Constructed response. Only set once we're ready to send a reply. */
/* Once this is set, the RR fields are cleared, and no more should be set. */
char *response;
size_t response_len;
/* Caller-visible fields: flags, questions. */
struct evdns_server_request base;
};
/* helper macro */
#define OFFSET_OF(st, member) ((off_t) (((char*)&((st*)0)->member)-(char*)0))
/* Given a pointer to an evdns_server_request, get the corresponding */
/* server_request. */
#define TO_SERVER_REQUEST(base_ptr) \
((struct server_request*) \
(((char*)(base_ptr) - OFFSET_OF(struct server_request, base))))
/* The number of good nameservers that we have */
static int global_good_nameservers = 0;
/* inflight requests are contained in the req_head list */
/* and are actually going out across the network */
static int global_requests_inflight = 0;
/* requests which aren't inflight are in the waiting list */
/* and are counted here */
static int global_requests_waiting = 0;
static int global_max_requests_inflight = 64;
static struct timeval global_timeout = {5, 0}; /* 5 seconds */
static int global_max_reissues = 1; /* a reissue occurs when we get some errors from the server */
static int global_max_retransmits = 3; /* number of times we'll retransmit a request which timed out */
/* number of timeouts in a row before we consider this server to be down */
static int global_max_nameserver_timeout = 3;
/* These are the timeout values for nameservers. If we find a nameserver is down */
/* we try to probe it at intervals as given below. Values are in seconds. */
static const struct timeval global_nameserver_timeouts[] = {{10, 0}, {60, 0}, {300, 0}, {900, 0}, {3600, 0}};
static const int global_nameserver_timeouts_length = sizeof(global_nameserver_timeouts)/sizeof(struct timeval);
static struct nameserver *nameserver_pick(void);
static void evdns_request_insert(struct request *req, struct request **head);
static void nameserver_ready_callback(int fd, short events, void *arg);
static int evdns_transmit(void);
static int evdns_request_transmit(struct request *req);
static void nameserver_send_probe(struct nameserver *const ns);
static void search_request_finished(struct request *const);
static int search_try_next(struct request *const req);
static int search_request_new(int type, const char *const name, int flags, evdns_callback_type user_callback, void *user_arg);
static void evdns_requests_pump_waiting_queue(void);
static u16 transaction_id_pick(void);
static struct request *request_new(int type, const char *name, int flags, evdns_callback_type callback, void *ptr);
static void request_submit(struct request *req);
static int server_request_free(struct server_request *req);
static void server_request_free_answers(struct server_request *req);
static void server_port_free(struct evdns_server_port *port);
static void server_port_ready_callback(int fd, short events, void *arg);
static int strtoint(const char *const str);
#ifdef WIN32
static int
last_error(int sock)
{
int optval, optvallen=sizeof(optval);
int err = WSAGetLastError();
if (err == WSAEWOULDBLOCK && sock >= 0) {
if (getsockopt(sock, SOL_SOCKET, SO_ERROR, (void*)&optval,
&optvallen))
return err;
if (optval)
return optval;
}
return err;
}
static int
error_is_eagain(int err)
{
return err == EAGAIN || err == WSAEWOULDBLOCK;
}
static int
inet_aton(const char *c, struct in_addr *addr)
{
uint32_t r;
if (strcmp(c, "255.255.255.255") == 0) {
addr->s_addr = 0xffffffffu;
} else {
r = inet_addr(c);
if (r == INADDR_NONE)
return 0;
addr->s_addr = r;
}
return 1;
}
#define CLOSE_SOCKET(x) closesocket(x)
#else
#define last_error(sock) (errno)
#define error_is_eagain(err) ((err) == EAGAIN)
#define CLOSE_SOCKET(x) close(x)
#endif
#define ISSPACE(c) isspace((int)(unsigned char)(c))
#define ISDIGIT(c) isdigit((int)(unsigned char)(c))
#ifndef NDEBUG
static const char *
debug_ntoa(u32 address)
{
static char buf[32];
u32 a = ntohl(address);
snprintf(buf, sizeof(buf), "%d.%d.%d.%d",
(int)(u8)((a>>24)&0xff),
(int)(u8)((a>>16)&0xff),
(int)(u8)((a>>8 )&0xff),
(int)(u8)((a )&0xff));
return buf;
}
#endif
static evdns_debug_log_fn_type evdns_log_fn = NULL;
void
evdns_set_log_fn(evdns_debug_log_fn_type fn)
{
evdns_log_fn = fn;
}
#ifdef __GNUC__
#define EVDNS_LOG_CHECK __attribute__ ((format(printf, 2, 3)))
#else
#define EVDNS_LOG_CHECK
#endif
static void _evdns_log(int warn, const char *fmt, ...) EVDNS_LOG_CHECK;
static void
_evdns_log(int warn, const char *fmt, ...)
{
va_list args;
static char buf[512];
if (!evdns_log_fn)
return;
va_start(args,fmt);
#ifdef WIN32
_vsnprintf(buf, sizeof(buf), fmt, args);
#else
vsnprintf(buf, sizeof(buf), fmt, args);
#endif
buf[sizeof(buf)-1] = '\0';
evdns_log_fn(warn, buf);
va_end(args);
}
#define log _evdns_log
/* This walks the list of inflight requests to find the */
/* one with a matching transaction id. Returns NULL on */
/* failure */
static struct request *
request_find_from_trans_id(u16 trans_id) {
struct request *req = req_head, *const started_at = req_head;
if (req) {
do {
if (req->trans_id == trans_id) return req;
req = req->next;
} while (req != started_at);
}
return NULL;
}
/* a libevent callback function which is called when a nameserver */
/* has gone down and we want to test if it has came back to life yet */
static void
nameserver_prod_callback(int fd, short events, void *arg) {
struct nameserver *const ns = (struct nameserver *) arg;
(void)fd;
(void)events;
nameserver_send_probe(ns);
}
/* a libevent callback which is called when a nameserver probe (to see if */
/* it has come back to life) times out. We increment the count of failed_times */
/* and wait longer to send the next probe packet. */
static void
nameserver_probe_failed(struct nameserver *const ns) {
const struct timeval * timeout;
(void) evtimer_del(&ns->timeout_event);
if (ns->state == 1) {
/* This can happen if the nameserver acts in a way which makes us mark */
/* it as bad and then starts sending good replies. */
return;
}
timeout =
&global_nameserver_timeouts[MIN(ns->failed_times,
global_nameserver_timeouts_length - 1)];
ns->failed_times++;
evtimer_set(&ns->timeout_event, nameserver_prod_callback, ns);
if (evtimer_add(&ns->timeout_event, (struct timeval *) timeout) < 0) {
log(EVDNS_LOG_WARN,
"Error from libevent when adding timer event for %s",
debug_ntoa(ns->address));
/* ???? Do more? */
}
}
/* called when a nameserver has been deemed to have failed. For example, too */
/* many packets have timed out etc */
static void
nameserver_failed(struct nameserver *const ns, const char *msg) {
struct request *req, *started_at;
/* if this nameserver has already been marked as failed */
/* then don't do anything */
if (!ns->state) return;
log(EVDNS_LOG_WARN, "Nameserver %s has failed: %s",
debug_ntoa(ns->address), msg);
global_good_nameservers--;
assert(global_good_nameservers >= 0);
if (global_good_nameservers == 0) {
log(EVDNS_LOG_WARN, "All nameservers have failed");
}
ns->state = 0;
ns->failed_times = 1;
evtimer_set(&ns->timeout_event, nameserver_prod_callback, ns);
if (evtimer_add(&ns->timeout_event, (struct timeval *) &global_nameserver_timeouts[0]) < 0) {
log(EVDNS_LOG_WARN,
"Error from libevent when adding timer event for %s",
debug_ntoa(ns->address));
/* ???? Do more? */
}
/* walk the list of inflight requests to see if any can be reassigned to */
/* a different server. Requests in the waiting queue don't have a */
/* nameserver assigned yet */
/* if we don't have *any* good nameservers then there's no point */
/* trying to reassign requests to one */
if (!global_good_nameservers) return;
req = req_head;
started_at = req_head;
if (req) {
do {
if (req->tx_count == 0 && req->ns == ns) {
/* still waiting to go out, can be moved */
/* to another server */
req->ns = nameserver_pick();
}
req = req->next;
} while (req != started_at);
}
}
static void
nameserver_up(struct nameserver *const ns) {
if (ns->state) return;
log(EVDNS_LOG_WARN, "Nameserver %s is back up",
debug_ntoa(ns->address));
evtimer_del(&ns->timeout_event);
ns->state = 1;
ns->failed_times = 0;
ns->timedout = 0;
global_good_nameservers++;
}
static void
request_trans_id_set(struct request *const req, const u16 trans_id) {
req->trans_id = trans_id;
*((u16 *) req->request) = htons(trans_id);
}
/* Called to remove a request from a list and dealloc it. */
/* head is a pointer to the head of the list it should be */
/* removed from or NULL if the request isn't in a list. */
static void
request_finished(struct request *const req, struct request **head) {
if (head) {
if (req->next == req) {
/* only item in the list */
*head = NULL;
} else {
req->next->prev = req->prev;
req->prev->next = req->next;
if (*head == req) *head = req->next;
}
}
log(EVDNS_LOG_DEBUG, "Removing timeout for request %lx",
(unsigned long) req);
evtimer_del(&req->timeout_event);
search_request_finished(req);
global_requests_inflight--;
if (!req->request_appended) {
/* need to free the request data on it's own */
free(req->request);
} else {
/* the request data is appended onto the header */
/* so everything gets free()ed when we: */
}
free(req);
evdns_requests_pump_waiting_queue();
}
/* This is called when a server returns a funny error code. */
/* We try the request again with another server. */
/* */
/* return: */
/* 0 ok */
/* 1 failed/reissue is pointless */
static int
request_reissue(struct request *req) {
const struct nameserver *const last_ns = req->ns;
/* the last nameserver should have been marked as failing */
/* by the caller of this function, therefore pick will try */
/* not to return it */
req->ns = nameserver_pick();
if (req->ns == last_ns) {
/* ... but pick did return it */
/* not a lot of point in trying again with the */
/* same server */
return 1;
}
req->reissue_count++;
req->tx_count = 0;
req->transmit_me = 1;
return 0;
}
/* this function looks for space on the inflight queue and promotes */
/* requests from the waiting queue if it can. */
static void
evdns_requests_pump_waiting_queue(void) {
while (global_requests_inflight < global_max_requests_inflight &&
global_requests_waiting) {
struct request *req;
/* move a request from the waiting queue to the inflight queue */
assert(req_waiting_head);
if (req_waiting_head->next == req_waiting_head) {
/* only one item in the queue */
req = req_waiting_head;
req_waiting_head = NULL;
} else {
req = req_waiting_head;
req->next->prev = req->prev;
req->prev->next = req->next;
req_waiting_head = req->next;
}
global_requests_waiting--;
global_requests_inflight++;
req->ns = nameserver_pick();
request_trans_id_set(req, transaction_id_pick());
evdns_request_insert(req, &req_head);
evdns_request_transmit(req);
evdns_transmit();
}
}
static void
reply_callback(struct request *const req, u32 ttl, u32 err, struct reply *reply) {
switch (req->request_type) {
case TYPE_A:
if (reply)
req->user_callback(DNS_ERR_NONE, DNS_IPv4_A,
reply->data.a.addrcount, ttl,
reply->data.a.addresses,
req->user_pointer);
else
req->user_callback(err, 0, 0, 0, NULL, req->user_pointer);
return;
case TYPE_PTR:
if (reply) {
char *name = reply->data.ptr.name;
req->user_callback(DNS_ERR_NONE, DNS_PTR, 1, ttl,
&name, req->user_pointer);
} else {
req->user_callback(err, 0, 0, 0, NULL,
req->user_pointer);
}
return;
case TYPE_AAAA:
if (reply)
req->user_callback(DNS_ERR_NONE, DNS_IPv6_AAAA,
reply->data.aaaa.addrcount, ttl,
reply->data.aaaa.addresses,
req->user_pointer);
else
req->user_callback(err, 0, 0, 0, NULL, req->user_pointer);
return;
}
assert(0);
}
/* this processes a parsed reply packet */
static void
reply_handle(struct request *const req, u16 flags, u32 ttl, struct reply *reply) {
int error;
static const int error_codes[] = {DNS_ERR_FORMAT, DNS_ERR_SERVERFAILED, DNS_ERR_NOTEXIST, DNS_ERR_NOTIMPL, DNS_ERR_REFUSED};
if (flags & 0x020f || !reply || !reply->have_answer) {
/* there was an error */
if (flags & 0x0200) {
error = DNS_ERR_TRUNCATED;
} else {
u16 error_code = (flags & 0x000f) - 1;
if (error_code > 4) {
error = DNS_ERR_UNKNOWN;
} else {
error = error_codes[error_code];
}
}
switch(error) {
case DNS_ERR_NOTIMPL:
case DNS_ERR_REFUSED:
/* we regard these errors as marking a bad nameserver */
if (req->reissue_count < global_max_reissues) {
char msg[64];
snprintf(msg, sizeof(msg), "Bad response %d (%s)",
error, evdns_err_to_string(error));
nameserver_failed(req->ns, msg);
if (!request_reissue(req)) return;
}
break;
case DNS_ERR_SERVERFAILED:
/* rcode 2 (servfailed) sometimes means "we are broken" and
* sometimes (with some binds) means "that request was very
* confusing." Treat this as a timeout, not a failure.
*/
log(EVDNS_LOG_DEBUG, "Got a SERVERFAILED from nameserver %s; "
"will allow the request to time out.",
debug_ntoa(req->ns->address));
break;
default:
/* we got a good reply from the nameserver */
nameserver_up(req->ns);
}
if (req->search_state && req->request_type != TYPE_PTR) {
/* if we have a list of domains to search in, try the next one */
if (!search_try_next(req)) {
/* a new request was issued so this request is finished and */
/* the user callback will be made when that request (or a */
/* child of it) finishes. */
request_finished(req, &req_head);
return;
}
}
/* all else failed. Pass the failure up */
reply_callback(req, 0, error, NULL);
request_finished(req, &req_head);
} else {
/* all ok, tell the user */
reply_callback(req, ttl, 0, reply);
nameserver_up(req->ns);
request_finished(req, &req_head);
}
}
static int
name_parse(u8 *packet, int length, int *idx, char *name_out, int name_out_len) {
int name_end = -1;
int j = *idx;
int ptr_count = 0;
#define GET32(x) do { if (j + 4 > length) goto err; memcpy(&_t32, packet + j, 4); j += 4; x = ntohl(_t32); } while(0)
#define GET16(x) do { if (j + 2 > length) goto err; memcpy(&_t, packet + j, 2); j += 2; x = ntohs(_t); } while(0)
#define GET8(x) do { if (j >= length) goto err; x = packet[j++]; } while(0)
char *cp = name_out;
const char *const end = name_out + name_out_len;
/* Normally, names are a series of length prefixed strings terminated */
/* with a length of 0 (the lengths are u8's < 63). */
/* However, the length can start with a pair of 1 bits and that */
/* means that the next 14 bits are a pointer within the current */
/* packet. */
for(;;) {
u8 label_len;
if (j >= length) return -1;
GET8(label_len);
if (!label_len) break;
if (label_len & 0xc0) {
u8 ptr_low;
GET8(ptr_low);
if (name_end < 0) name_end = j;
j = (((int)label_len & 0x3f) << 8) + ptr_low;
/* Make sure that the target offset is in-bounds. */
if (j < 0 || j >= length) return -1;
/* If we've jumped more times than there are characters in the
* message, we must have a loop. */
if (++ptr_count > length) return -1;
continue;
}
if (label_len > 63) return -1;
if (cp != name_out) {
if (cp + 1 >= end) return -1;
*cp++ = '.';
}
if (cp + label_len >= end) return -1;
memcpy(cp, packet + j, label_len);
cp += label_len;
j += label_len;
}
if (cp >= end) return -1;
*cp = '\0';
if (name_end < 0)
*idx = j;
else
*idx = name_end;
return 0;
err:
return -1;
}
/* parses a raw request from a nameserver */
static int
reply_parse(u8 *packet, int length) {
int j = 0; /* index into packet */
u16 _t; /* used by the macros */
u32 _t32; /* used by the macros */
char tmp_name[256]; /* used by the macros */
u16 trans_id, questions, answers, authority, additional, datalength;
u16 flags = 0;
u32 ttl, ttl_r = 0xffffffff;
struct reply reply;
struct request *req = NULL;
unsigned int i;
GET16(trans_id);
GET16(flags);
GET16(questions);
GET16(answers);
GET16(authority);
GET16(additional);
(void) authority; /* suppress "unused variable" warnings. */
(void) additional; /* suppress "unused variable" warnings. */
req = request_find_from_trans_id(trans_id);
if (!req) return -1;
memset(&reply, 0, sizeof(reply));
/* If it's not an answer, it doesn't correspond to any request. */
if (!(flags & 0x8000)) return -1; /* must be an answer */
if (flags & 0x020f) {
/* there was an error */
goto err;
}
/* if (!answers) return; */ /* must have an answer of some form */
/* This macro skips a name in the DNS reply. */
#define SKIP_NAME \
do { tmp_name[0] = '\0'; \
if (name_parse(packet, length, &j, tmp_name, sizeof(tmp_name))<0) \
goto err; \
} while(0);
reply.type = req->request_type;
/* skip over each question in the reply */
for (i = 0; i < questions; ++i) {
/* the question looks like
* <label:name><u16:type><u16:class>
*/
SKIP_NAME;
j += 4;
if (j >= length) goto err;
}
/* now we have the answer section which looks like
* <label:name><u16:type><u16:class><u32:ttl><u16:len><data...>
*/
for (i = 0; i < answers; ++i) {
u16 type, class;
SKIP_NAME;
GET16(type);
GET16(class);
GET32(ttl);
GET16(datalength);
if (type == TYPE_A && class == CLASS_INET) {
int addrcount, addrtocopy;
if (req->request_type != TYPE_A) {
j += datalength; continue;
}
if ((datalength & 3) != 0) /* not an even number of As. */
goto err;
addrcount = datalength >> 2;
addrtocopy = MIN(MAX_ADDRS - reply.data.a.addrcount, (unsigned)addrcount);
ttl_r = MIN(ttl_r, ttl);
/* we only bother with the first four addresses. */
if (j + 4*addrtocopy > length) goto err;
memcpy(&reply.data.a.addresses[reply.data.a.addrcount],
packet + j, 4*addrtocopy);
j += 4*addrtocopy;
reply.data.a.addrcount += addrtocopy;
reply.have_answer = 1;
if (reply.data.a.addrcount == MAX_ADDRS) break;
} else if (type == TYPE_PTR && class == CLASS_INET) {
if (req->request_type != TYPE_PTR) {
j += datalength; continue;
}
if (name_parse(packet, length, &j, reply.data.ptr.name,
sizeof(reply.data.ptr.name))<0)
goto err;
ttl_r = MIN(ttl_r, ttl);
reply.have_answer = 1;
break;
} else if (type == TYPE_AAAA && class == CLASS_INET) {
int addrcount, addrtocopy;
if (req->request_type != TYPE_AAAA) {
j += datalength; continue;
}
if ((datalength & 15) != 0) /* not an even number of AAAAs. */
goto err;
addrcount = datalength >> 4; /* each address is 16 bytes long */
addrtocopy = MIN(MAX_ADDRS - reply.data.aaaa.addrcount, (unsigned)addrcount);
ttl_r = MIN(ttl_r, ttl);
/* we only bother with the first four addresses. */
if (j + 16*addrtocopy > length) goto err;
memcpy(&reply.data.aaaa.addresses[reply.data.aaaa.addrcount],
packet + j, 16*addrtocopy);
reply.data.aaaa.addrcount += addrtocopy;
j += 16*addrtocopy;
reply.have_answer = 1;
if (reply.data.aaaa.addrcount == MAX_ADDRS) break;
} else {
/* skip over any other type of resource */
j += datalength;
}
}
reply_handle(req, flags, ttl_r, &reply);
return 0;
err:
if (req)
reply_handle(req, flags, 0, NULL);
return -1;
}
/* Parse a raw request (packet,length) sent to a nameserver port (port) from */
/* a DNS client (addr,addrlen), and if it's well-formed, call the corresponding */
/* callback. */
static int
request_parse(u8 *packet, int length, struct evdns_server_port *port, struct sockaddr *addr, socklen_t addrlen)
{
int j = 0; /* index into packet */
u16 _t; /* used by the macros */
char tmp_name[256]; /* used by the macros */
int i;
u16 trans_id, flags, questions, answers, authority, additional;
struct server_request *server_req = NULL;
/* Get the header fields */
GET16(trans_id);
GET16(flags);
GET16(questions);
GET16(answers);
GET16(authority);
GET16(additional);
if (flags & 0x8000) return -1; /* Must not be an answer. */
if (flags & 0x7800) return -1; /* only standard queries are supported */
flags &= 0x0300; /* Only TC and RD get preserved. */
server_req = malloc(sizeof(struct server_request));
if (server_req == NULL) return -1;
memset(server_req, 0, sizeof(struct server_request));
server_req->trans_id = trans_id;
memcpy(&server_req->addr, addr, addrlen);
server_req->addrlen = addrlen;
server_req->base.flags = flags;
server_req->base.nquestions = 0;
server_req->base.questions = malloc(sizeof(struct evdns_server_question *) * questions);
if (server_req->base.questions == NULL)
goto err;
for (i = 0; i < questions; ++i) {
u16 type, class;
struct evdns_server_question *q;
int namelen;
if (name_parse(packet, length, &j, tmp_name, sizeof(tmp_name))<0)
goto err;
GET16(type);
GET16(class);
namelen = strlen(tmp_name);
q = malloc(sizeof(struct evdns_server_question) + namelen);
if (!q)
goto err;
q->type = type;
q->class = class;
memcpy(q->name, tmp_name, namelen+1);
server_req->base.questions[server_req->base.nquestions++] = q;
}
/* Ignore answers, authority, and additional. */
server_req->port = port;
port->refcnt++;
port->user_callback(&(server_req->base), port->user_data);
return 0;
err:
if (server_req) {
if (server_req->base.questions) {
for (i = 0; i < server_req->base.nquestions; ++i)
free(server_req->base.questions[i]);
free(server_req->base.questions);
}
free(server_req);
}
return -1;
#undef SKIP_NAME
#undef GET32
#undef GET16
#undef GET8
}
/* Try to choose a strong transaction id which isn't already in flight */
static u16
transaction_id_pick(void) {
for (;;) {
const struct request *req = req_head, *started_at;
#ifdef DNS_USE_CPU_CLOCK_FOR_ID
struct timespec ts;
u16 trans_id;
#ifdef CLOCK_MONOTONIC
if (clock_gettime(CLOCK_MONOTONIC, &ts) == -1)
#else
if (clock_gettime(CLOCK_REALTIME, &ts) == -1)
#endif
event_err(1, "clock_gettime");
trans_id = ts.tv_nsec & 0xffff;
#endif
#ifdef DNS_USE_GETTIMEOFDAY_FOR_ID
struct timeval tv;
u16 trans_id;
gettimeofday(&tv, NULL);
trans_id = tv.tv_usec & 0xffff;
#endif
#ifdef DNS_USE_OPENSSL_FOR_ID
u16 trans_id;
if (RAND_pseudo_bytes((u8 *) &trans_id, 2) == -1) {
/* in the case that the RAND call fails we back */
/* down to using gettimeofday. */
struct timeval tv;
gettimeofday(&tv, NULL);
trans_id = tv.tv_usec & 0xffff; */
abort();
}
#endif
if (trans_id == 0xffff) continue;
/* now check to see if that id is already inflight */
req = started_at = req_head;
if (req) {
do {
if (req->trans_id == trans_id) break;
req = req->next;
} while (req != started_at);
}
/* we didn't find it, so this is a good id */
if (req == started_at) return trans_id;
}
}
/* choose a namesever to use. This function will try to ignore */
/* nameservers which we think are down and load balance across the rest */
/* by updating the server_head global each time. */
static struct nameserver *
nameserver_pick(void) {
struct nameserver *started_at = server_head, *picked;
if (!server_head) return NULL;
/* if we don't have any good nameservers then there's no */
/* point in trying to find one. */
if (!global_good_nameservers) {
server_head = server_head->next;
return server_head;
}
/* remember that nameservers are in a circular list */
for (;;) {
if (server_head->state) {
/* we think this server is currently good */
picked = server_head;
server_head = server_head->next;
return picked;
}
server_head = server_head->next;
if (server_head == started_at) {
/* all the nameservers seem to be down */
/* so we just return this one and hope for the */
/* best */
assert(global_good_nameservers == 0);
picked = server_head;
server_head = server_head->next;
return picked;
}
}
}
/* this is called when a namesever socket is ready for reading */
static void
nameserver_read(struct nameserver *ns) {
u8 packet[1500];
for (;;) {
const int r = recv(ns->socket, packet, sizeof(packet), 0);
if (r < 0) {
int err = last_error(ns->socket);
if (error_is_eagain(err)) return;
nameserver_failed(ns, strerror(err));
return;
}
ns->timedout = 0;
reply_parse(packet, r);
}
}
/* Read a packet from a DNS client on a server port s, parse it, and */
/* act accordingly. */
static void
server_port_read(struct evdns_server_port *s) {
u8 packet[1500];
struct sockaddr_storage addr;
socklen_t addrlen;
int r;
for (;;) {
addrlen = sizeof(struct sockaddr_storage);
r = recvfrom(s->socket, packet, sizeof(packet), 0,
(struct sockaddr*) &addr, &addrlen);
if (r < 0) {
int err = last_error(s->socket);
if (error_is_eagain(err)) return;
log(EVDNS_LOG_WARN, "Error %s (%d) while reading request.",
strerror(err), err);
return;
}
request_parse(packet, r, s, (struct sockaddr*) &addr, addrlen);
}
}
/* Try to write all pending replies on a given DNS server port. */
static void
server_port_flush(struct evdns_server_port *port)
{
while (port->pending_replies) {
struct server_request *req = port->pending_replies;
int r = sendto(port->socket, req->response, req->response_len, 0,
(struct sockaddr*) &req->addr, req->addrlen);
if (r < 0) {
int err = last_error(port->socket);
if (error_is_eagain(err))
return;
log(EVDNS_LOG_WARN, "Error %s (%d) while writing response to port; dropping", strerror(err), err);
}
if (server_request_free(req)) {
/* we released the last reference to req->port. */
return;
}
}
/* We have no more pending requests; stop listening for 'writeable' events. */
(void) event_del(&port->event);
event_set(&port->event, port->socket, EV_READ | EV_PERSIST,
server_port_ready_callback, port);
if (event_add(&port->event, NULL) < 0) {
log(EVDNS_LOG_WARN, "Error from libevent when adding event for DNS server.");
/* ???? Do more? */
}
}
/* set if we are waiting for the ability to write to this server. */
/* if waiting is true then we ask libevent for EV_WRITE events, otherwise */
/* we stop these events. */
static void
nameserver_write_waiting(struct nameserver *ns, char waiting) {
if (ns->write_waiting == waiting) return;
ns->write_waiting = waiting;
(void) event_del(&ns->event);
event_set(&ns->event, ns->socket, EV_READ | (waiting ? EV_WRITE : 0) | EV_PERSIST,
nameserver_ready_callback, ns);
if (event_add(&ns->event, NULL) < 0) {
log(EVDNS_LOG_WARN, "Error from libevent when adding event for %s",
debug_ntoa(ns->address));
/* ???? Do more? */
}
}
/* a callback function. Called by libevent when the kernel says that */
/* a nameserver socket is ready for writing or reading */
static void
nameserver_ready_callback(int fd, short events, void *arg) {
struct nameserver *ns = (struct nameserver *) arg;
(void)fd;
if (events & EV_WRITE) {
ns->choked = 0;
if (!evdns_transmit()) {
nameserver_write_waiting(ns, 0);
}
}
if (events & EV_READ) {
nameserver_read(ns);
}
}
/* a callback function. Called by libevent when the kernel says that */
/* a server socket is ready for writing or reading. */
static void
server_port_ready_callback(int fd, short events, void *arg) {
struct evdns_server_port *port = (struct evdns_server_port *) arg;
(void) fd;
if (events & EV_WRITE) {
port->choked = 0;
server_port_flush(port);
}
if (events & EV_READ) {
server_port_read(port);
}
}
/* This is an inefficient representation; only use it via the dnslabel_table_*
* functions, so that is can be safely replaced with something smarter later. */
#define MAX_LABELS 128
/* Structures used to implement name compression */
struct dnslabel_entry { char *v; off_t pos; };
struct dnslabel_table {
int n_labels; /* number of current entries */
/* map from name to position in message */
struct dnslabel_entry labels[MAX_LABELS];
};
/* Initialize dnslabel_table. */
static void
dnslabel_table_init(struct dnslabel_table *table)
{
table->n_labels = 0;
}
/* Free all storage held by table, but not the table itself. */
static void
dnslabel_clear(struct dnslabel_table *table)
{
int i;
for (i = 0; i < table->n_labels; ++i)
free(table->labels[i].v);
table->n_labels = 0;
}
/* return the position of the label in the current message, or -1 if the label */
/* hasn't been used yet. */
static int
dnslabel_table_get_pos(const struct dnslabel_table *table, const char *label)
{
int i;
for (i = 0; i < table->n_labels; ++i) {
if (!strcmp(label, table->labels[i].v))
return table->labels[i].pos;
}
return -1;
}
/* remember that we've used the label at position pos */
static int
dnslabel_table_add(struct dnslabel_table *table, const char *label, off_t pos)
{
char *v;
int p;
if (table->n_labels == MAX_LABELS)
return (-1);
v = strdup(label);
if (v == NULL)
return (-1);
p = table->n_labels++;
table->labels[p].v = v;
table->labels[p].pos = pos;
return (0);
}
/* Converts a string to a length-prefixed set of DNS labels, starting */
/* at buf[j]. name and buf must not overlap. name_len should be the length */
/* of name. table is optional, and is used for compression. */
/* */
/* Input: abc.def */
/* Output: <3>abc<3>def<0> */
/* */
/* Returns the first index after the encoded name, or negative on error. */
/* -1 label was > 63 bytes */
/* -2 name too long to fit in buffer. */
/* */
static off_t
dnsname_to_labels(u8 *const buf, size_t buf_len, off_t j,
const char *name, const int name_len,
struct dnslabel_table *table) {
const char *end = name + name_len;
int ref = 0;
u16 _t;
#define APPEND16(x) do { \
if (j + 2 > (off_t)buf_len) \
goto overflow; \
_t = htons(x); \
memcpy(buf + j, &_t, 2); \
j += 2; \
} while (0)
#define APPEND32(x) do { \
if (j + 4 > (off_t)buf_len) \
goto overflow; \
_t32 = htonl(x); \
memcpy(buf + j, &_t32, 4); \
j += 4; \
} while (0)
if (name_len > 255) return -2;
for (;;) {
const char *const start = name;
if (table && (ref = dnslabel_table_get_pos(table, name)) >= 0) {
APPEND16(ref | 0xc000);
return j;
}
name = strchr(name, '.');
if (!name) {
const unsigned int label_len = end - start;
if (label_len > 63) return -1;
if ((size_t)(j+label_len+1) > buf_len) return -2;
if (table) dnslabel_table_add(table, start, j);
buf[j++] = label_len;
memcpy(buf + j, start, end - start);
j += end - start;
break;
} else {
/* append length of the label. */
const unsigned int label_len = name - start;
if (label_len > 63) return -1;
if ((size_t)(j+label_len+1) > buf_len) return -2;
if (table) dnslabel_table_add(table, start, j);
buf[j++] = label_len;
memcpy(buf + j, start, name - start);
j += name - start;
/* hop over the '.' */
name++;
}
}
/* the labels must be terminated by a 0. */
/* It's possible that the name ended in a . */
/* in which case the zero is already there */
if (!j || buf[j-1]) buf[j++] = 0;
return j;
overflow:
return (-2);
}
/* Finds the length of a dns request for a DNS name of the given */
/* length. The actual request may be smaller than the value returned */
/* here */
static int
evdns_request_len(const int name_len) {
return 96 + /* length of the DNS standard header */
name_len + 2 +
4; /* space for the resource type */
}
/* build a dns request packet into buf. buf should be at least as long */
/* as evdns_request_len told you it should be. */
/* */
/* Returns the amount of space used. Negative on error. */
static int
evdns_request_data_build(const char *const name, const int name_len,
const u16 trans_id, const u16 type, const u16 class,
u8 *const buf, size_t buf_len) {
off_t j = 0; /* current offset into buf */
u16 _t; /* used by the macros */
APPEND16(trans_id);
APPEND16(0x0100); /* standard query, recusion needed */
APPEND16(1); /* one question */
APPEND16(0); /* no answers */
APPEND16(0); /* no authority */
APPEND16(0); /* no additional */
j = dnsname_to_labels(buf, buf_len, j, name, name_len, NULL);
if (j < 0) {
return (int)j;
}
APPEND16(type);
APPEND16(class);
return (int)j;
overflow:
return (-1);
}
/* exported function */
struct evdns_server_port *
evdns_add_server_port(int socket, int is_tcp, evdns_request_callback_fn_type cb, void *user_data)
{
struct evdns_server_port *port;
if (!(port = malloc(sizeof(struct evdns_server_port))))
return NULL;
memset(port, 0, sizeof(struct evdns_server_port));
assert(!is_tcp); /* TCP sockets not yet implemented */
port->socket = socket;
port->refcnt = 1;
port->choked = 0;
port->closing = 0;
port->user_callback = cb;
port->user_data = user_data;
port->pending_replies = NULL;
event_set(&port->event, port->socket, EV_READ | EV_PERSIST,
server_port_ready_callback, port);
event_add(&port->event, NULL); /* check return. */
return port;
}
/* exported function */
void
evdns_close_server_port(struct evdns_server_port *port)
{
if (--port->refcnt == 0)
server_port_free(port);
port->closing = 1;
}
/* exported function */
int
evdns_server_request_add_reply(struct evdns_server_request *_req, int section, const char *name, int type, int class, int ttl, int datalen, int is_name, const char *data)
{
struct server_request *req = TO_SERVER_REQUEST(_req);
struct server_reply_item **itemp, *item;
int *countp;
if (req->response) /* have we already answered? */
return (-1);
switch (section) {
case EVDNS_ANSWER_SECTION:
itemp = &req->answer;
countp = &req->n_answer;
break;
case EVDNS_AUTHORITY_SECTION:
itemp = &req->authority;
countp = &req->n_authority;
break;
case EVDNS_ADDITIONAL_SECTION:
itemp = &req->additional;
countp = &req->n_additional;
break;
default:
return (-1);
}
while (*itemp) {
itemp = &((*itemp)->next);
}
item = malloc(sizeof(struct server_reply_item));
if (!item)
return -1;
item->next = NULL;
if (!(item->name = strdup(name))) {
free(item);
return -1;
}
item->type = type;
item->class = class;
item->ttl = ttl;
item->is_name = is_name != 0;
item->datalen = 0;
item->data = NULL;
if (data) {
if (item->is_name) {
if (!(item->data = strdup(data))) {
free(item->name);
free(item);
return -1;
}
item->datalen = (u16)-1;
} else {
if (!(item->data = malloc(datalen))) {
free(item->name);
free(item);
return -1;
}
item->datalen = datalen;
memcpy(item->data, data, datalen);
}
}
*itemp = item;
++(*countp);
return 0;
}
/* exported function */
int
evdns_server_request_add_a_reply(struct evdns_server_request *req, const char *name, int n, void *addrs, int ttl)
{
return evdns_server_request_add_reply(
req, EVDNS_ANSWER_SECTION, name, TYPE_A, CLASS_INET,
ttl, n*4, 0, addrs);
}
/* exported function */
int
evdns_server_request_add_aaaa_reply(struct evdns_server_request *req, const char *name, int n, void *addrs, int ttl)
{
return evdns_server_request_add_reply(
req, EVDNS_ANSWER_SECTION, name, TYPE_AAAA, CLASS_INET,
ttl, n*16, 0, addrs);
}
/* exported function */
int
evdns_server_request_add_ptr_reply(struct evdns_server_request *req, struct in_addr *in, const char *inaddr_name, const char *hostname, int ttl)
{
u32 a;
char buf[32];
assert(in || inaddr_name);
assert(!(in && inaddr_name));
if (in) {
a = ntohl(in->s_addr);
snprintf(buf, sizeof(buf), "%d.%d.%d.%d.in-addr.arpa",
(int)(u8)((a )&0xff),
(int)(u8)((a>>8 )&0xff),
(int)(u8)((a>>16)&0xff),
(int)(u8)((a>>24)&0xff));
inaddr_name = buf;
}
return evdns_server_request_add_reply(
req, EVDNS_ANSWER_SECTION, inaddr_name, TYPE_PTR, CLASS_INET,
ttl, -1, 1, hostname);
}
/* exported function */
int
evdns_server_request_add_cname_reply(struct evdns_server_request *req, const char *name, const char *cname, int ttl)
{
return evdns_server_request_add_reply(
req, EVDNS_ANSWER_SECTION, name, TYPE_A, CLASS_INET,
ttl, -1, 1, cname);
}
static int
evdns_server_request_format_response(struct server_request *req, int err)
{
unsigned char buf[1500];
size_t buf_len = sizeof(buf);
off_t j = 0, r;
u16 _t;
u32 _t32;
int i;
u16 flags;
struct dnslabel_table table;
if (err < 0 || err > 15) return -1;
/* Set response bit and error code; copy OPCODE and RD fields from
* question; copy RA and AA if set by caller. */
flags = req->base.flags;
flags |= (0x8000 | err);
dnslabel_table_init(&table);
APPEND16(req->trans_id);
APPEND16(flags);
APPEND16(req->base.nquestions);
APPEND16(req->n_answer);
APPEND16(req->n_authority);
APPEND16(req->n_additional);
/* Add questions. */
for (i=0; i < req->base.nquestions; ++i) {
const char *s = req->base.questions[i]->name;
j = dnsname_to_labels(buf, buf_len, j, s, strlen(s), &table);
if (j < 0) {
dnslabel_clear(&table);
return (int) j;
}
APPEND16(req->base.questions[i]->type);
APPEND16(req->base.questions[i]->class);
}
/* Add answer, authority, and additional sections. */
for (i=0; i<3; ++i) {
struct server_reply_item *item;
if (i==0)
item = req->answer;
else if (i==1)
item = req->authority;
else
item = req->additional;
while (item) {
r = dnsname_to_labels(buf, buf_len, j, item->name, strlen(item->name), &table);
if (r < 0)
goto overflow;
j = r;
APPEND16(item->type);
APPEND16(item->class);
APPEND32(item->ttl);
if (item->is_name) {
off_t len_idx = j, name_start;
j += 2;
name_start = j;
r = dnsname_to_labels(buf, buf_len, j, item->data, strlen(item->data), &table);
if (r < 0)
goto overflow;
j = r;
_t = htons( (j-name_start) );
memcpy(buf+len_idx, &_t, 2);
} else {
APPEND16(item->datalen);
if (j+item->datalen > (off_t)buf_len)
goto overflow;
memcpy(buf+j, item->data, item->datalen);
j += item->datalen;
}
item = item->next;
}
}
if (j > 512) {
overflow:
j = 512;
buf[3] |= 0x02; /* set the truncated bit. */
}
req->response_len = j;
if (!(req->response = malloc(req->response_len))) {
server_request_free_answers(req);
dnslabel_clear(&table);
return (-1);
}
memcpy(req->response, buf, req->response_len);
server_request_free_answers(req);
dnslabel_clear(&table);
return (0);
}
/* exported function */
int
evdns_server_request_respond(struct evdns_server_request *_req, int err)
{
struct server_request *req = TO_SERVER_REQUEST(_req);
struct evdns_server_port *port = req->port;
int r;
if (!req->response) {
if ((r = evdns_server_request_format_response(req, err))<0)
return r;
}
r = sendto(port->socket, req->response, req->response_len, 0,
(struct sockaddr*) &req->addr, req->addrlen);
if (r<0) {
int err = last_error(port->socket);
if (! error_is_eagain(err))
return -1;
if (port->pending_replies) {
req->prev_pending = port->pending_replies->prev_pending;
req->next_pending = port->pending_replies;
req->prev_pending->next_pending =
req->next_pending->prev_pending = req;
} else {
req->prev_pending = req->next_pending = req;
port->pending_replies = req;
port->choked = 1;
(void) event_del(&port->event);
event_set(&port->event, port->socket, (port->closing?0:EV_READ) | EV_WRITE | EV_PERSIST, server_port_ready_callback, port);
if (event_add(&port->event, NULL) < 0) {
log(EVDNS_LOG_WARN, "Error from libevent when adding event for DNS server");
}
}
return 1;
}
if (server_request_free(req))
return 0;
if (port->pending_replies)
server_port_flush(port);
return 0;
}
/* Free all storage held by RRs in req. */
static void
server_request_free_answers(struct server_request *req)
{
struct server_reply_item *victim, *next, **list;
int i;
for (i = 0; i < 3; ++i) {
if (i==0)
list = &req->answer;
else if (i==1)
list = &req->authority;
else
list = &req->additional;
victim = *list;
while (victim) {
next = victim->next;
free(victim->name);
if (victim->data)
free(victim->data);
free(victim);
victim = next;
}
*list = NULL;
}
}
/* Free all storage held by req, and remove links to it. */
/* return true iff we just wound up freeing the server_port. */
static int
server_request_free(struct server_request *req)
{
int i, rc=1;
if (req->base.questions) {
for (i = 0; i < req->base.nquestions; ++i)
free(req->base.questions[i]);
free(req->base.questions);
}
if (req->port) {
if (req->port->pending_replies == req) {
if (req->next_pending)
req->port->pending_replies = req->next_pending;
else
req->port->pending_replies = NULL;
}
rc = --req->port->refcnt;
}
if (req->response) {
free(req->response);
}
server_request_free_answers(req);
if (req->next_pending && req->next_pending != req) {
req->next_pending->prev_pending = req->prev_pending;
req->prev_pending->next_pending = req->next_pending;
}
if (rc == 0) {
server_port_free(req->port);
free(req);
return (1);
}
free(req);
return (0);
}
/* Free all storage held by an evdns_server_port. Only called when */
static void
server_port_free(struct evdns_server_port *port)
{
assert(port);
assert(!port->refcnt);
assert(!port->pending_replies);
if (port->socket > 0) {
CLOSE_SOCKET(port->socket);
port->socket = -1;
}
(void) event_del(&port->event);
/* XXXX actually free the port? -NM */
}
/* exported function */
int
evdns_server_request_drop(struct evdns_server_request *_req)
{
struct server_request *req = TO_SERVER_REQUEST(_req);
server_request_free(req);
return 0;
}
/* exported function */
int
evdns_server_request_get_requesting_addr(struct evdns_server_request *_req, struct sockaddr *sa, int addr_len)
{
struct server_request *req = TO_SERVER_REQUEST(_req);
if (addr_len < (int)req->addrlen)
return -1;
memcpy(sa, &(req->addr), req->addrlen);
return req->addrlen;
}
#undef APPEND16
#undef APPEND32
/* this is a libevent callback function which is called when a request */
/* has timed out. */
static void
evdns_request_timeout_callback(int fd, short events, void *arg) {
struct request *const req = (struct request *) arg;
(void) fd;
(void) events;
log(EVDNS_LOG_DEBUG, "Request %lx timed out", (unsigned long) arg);
req->ns->timedout++;
if (req->ns->timedout > global_max_nameserver_timeout) {
req->ns->timedout = 0;
nameserver_failed(req->ns, "request timed out.");
}
(void) evtimer_del(&req->timeout_event);
if (req->tx_count >= global_max_retransmits) {
/* this request has failed */
reply_callback(req, 0, DNS_ERR_TIMEOUT, NULL);
request_finished(req, &req_head);
} else {
/* retransmit it */
evdns_request_transmit(req);
}
}
/* try to send a request to a given server. */
/* */
/* return: */
/* 0 ok */
/* 1 temporary failure */
/* 2 other failure */
static int
evdns_request_transmit_to(struct request *req, struct nameserver *server) {
const int r = send(server->socket, req->request, req->request_len, 0);
if (r < 0) {
int err = last_error(server->socket);
if (error_is_eagain(err)) return 1;
nameserver_failed(req->ns, strerror(err));
return 2;
} else if (r != (int)req->request_len) {
return 1; /* short write */
} else {
return 0;
}
}
/* try to send a request, updating the fields of the request */
/* as needed */
/* */
/* return: */
/* 0 ok */
/* 1 failed */
static int
evdns_request_transmit(struct request *req) {
int retcode = 0, r;
/* if we fail to send this packet then this flag marks it */
/* for evdns_transmit */
req->transmit_me = 1;
if (req->trans_id == 0xffff) abort();
if (req->ns->choked) {
/* don't bother trying to write to a socket */
/* which we have had EAGAIN from */
return 1;
}
r = evdns_request_transmit_to(req, req->ns);
switch (r) {
case 1:
/* temp failure */
req->ns->choked = 1;
nameserver_write_waiting(req->ns, 1);
return 1;
case 2:
/* failed in some other way */
retcode = 1;
/* fall through */
default:
/* all ok */
log(EVDNS_LOG_DEBUG,
"Setting timeout for request %lx", (unsigned long) req);
evtimer_set(&req->timeout_event, evdns_request_timeout_callback, req);
if (evtimer_add(&req->timeout_event, &global_timeout) < 0) {
log(EVDNS_LOG_WARN,
"Error from libevent when adding timer for request %lx",
(unsigned long) req);
/* ???? Do more? */
}
req->tx_count++;
req->transmit_me = 0;
return retcode;
}
}
static void
nameserver_probe_callback(int result, char type, int count, int ttl, void *addresses, void *arg) {
struct nameserver *const ns = (struct nameserver *) arg;
(void) type;
(void) count;
(void) ttl;
(void) addresses;
if (result == DNS_ERR_NONE || result == DNS_ERR_NOTEXIST) {
/* this is a good reply */
nameserver_up(ns);
} else nameserver_probe_failed(ns);
}
static void
nameserver_send_probe(struct nameserver *const ns) {
struct request *req;
/* here we need to send a probe to a given nameserver */
/* in the hope that it is up now. */
log(EVDNS_LOG_DEBUG, "Sending probe to %s", debug_ntoa(ns->address));
req = request_new(TYPE_A, "www.google.com", DNS_QUERY_NO_SEARCH, nameserver_probe_callback, ns);
if (!req) return;
/* we force this into the inflight queue no matter what */
request_trans_id_set(req, transaction_id_pick());
req->ns = ns;
request_submit(req);
}
/* returns: */
/* 0 didn't try to transmit anything */
/* 1 tried to transmit something */
static int
evdns_transmit(void) {
char did_try_to_transmit = 0;
if (req_head) {
struct request *const started_at = req_head, *req = req_head;
/* first transmit all the requests which are currently waiting */
do {
if (req->transmit_me) {
did_try_to_transmit = 1;
evdns_request_transmit(req);
}
req = req->next;
} while (req != started_at);
}
return did_try_to_transmit;
}
/* exported function */
int
evdns_count_nameservers(void)
{
const struct nameserver *server = server_head;
int n = 0;
if (!server)
return 0;
do {
++n;
server = server->next;
} while (server != server_head);
return n;
}
/* exported function */
int
evdns_clear_nameservers_and_suspend(void)
{
struct nameserver *server = server_head, *started_at = server_head;
struct request *req = req_head, *req_started_at = req_head;
if (!server)
return 0;
while (1) {
struct nameserver *next = server->next;
(void) event_del(&server->event);
(void) evtimer_del(&server->timeout_event);
if (server->socket >= 0)
CLOSE_SOCKET(server->socket);
free(server);
if (next == started_at)
break;
server = next;
}
server_head = NULL;
global_good_nameservers = 0;
while (req) {
struct request *next = req->next;
req->tx_count = req->reissue_count = 0;
req->ns = NULL;
/* ???? What to do about searches? */
(void) evtimer_del(&req->timeout_event);
req->trans_id = 0;
req->transmit_me = 0;
global_requests_waiting++;
evdns_request_insert(req, &req_waiting_head);
/* We want to insert these suspended elements at the front of
* the waiting queue, since they were pending before any of
* the waiting entries were added. This is a circular list,
* so we can just shift the start back by one.*/
req_waiting_head = req_waiting_head->prev;
if (next == req_started_at)
break;
req = next;
}
req_head = NULL;
global_requests_inflight = 0;
return 0;
}
/* exported function */
int
evdns_resume(void)
{
evdns_requests_pump_waiting_queue();
return 0;
}
static int
_evdns_nameserver_add_impl(unsigned long int address, int port) {
/* first check to see if we already have this nameserver */
const struct nameserver *server = server_head, *const started_at = server_head;
struct nameserver *ns;
struct sockaddr_in sin;
int err = 0;
if (server) {
do {
if (server->address == address) return 3;
server = server->next;
} while (server != started_at);
}
ns = (struct nameserver *) malloc(sizeof(struct nameserver));
if (!ns) return -1;
memset(ns, 0, sizeof(struct nameserver));
ns->socket = socket(PF_INET, SOCK_DGRAM, 0);
if (ns->socket < 0) { err = 1; goto out1; }
#ifdef WIN32
{
u_long nonblocking = 1;
ioctlsocket(ns->socket, FIONBIO, &nonblocking);
}
#else
fcntl(ns->socket, F_SETFL, O_NONBLOCK);
#endif
sin.sin_addr.s_addr = address;
sin.sin_port = htons(port);
sin.sin_family = AF_INET;
if (connect(ns->socket, (struct sockaddr *) &sin, sizeof(sin)) != 0) {
err = 2;
goto out2;
}
ns->address = address;
ns->state = 1;
event_set(&ns->event, ns->socket, EV_READ | EV_PERSIST, nameserver_ready_callback, ns);
if (event_add(&ns->event, NULL) < 0) {
err = 2;
goto out2;
}
log(EVDNS_LOG_DEBUG, "Added nameserver %s", debug_ntoa(address));
/* insert this nameserver into the list of them */
if (!server_head) {
ns->next = ns->prev = ns;
server_head = ns;
} else {
ns->next = server_head->next;
ns->prev = server_head;
server_head->next = ns;
if (server_head->prev == server_head) {
server_head->prev = ns;
}
}
global_good_nameservers++;
return 0;
out2:
CLOSE_SOCKET(ns->socket);
out1:
free(ns);
log(EVDNS_LOG_WARN, "Unable to add nameserver %s: error %d", debug_ntoa(address), err);
return err;
}
/* exported function */
int
evdns_nameserver_add(unsigned long int address) {
return _evdns_nameserver_add_impl(address, 53);
}
/* exported function */
int
evdns_nameserver_ip_add(const char *ip_as_string) {
struct in_addr ina;
int port;
char buf[20];
const char *cp;
cp = strchr(ip_as_string, ':');
if (! cp) {
cp = ip_as_string;
port = 53;
} else {
port = strtoint(cp+1);
if (port < 0 || port > 65535) {
return 4;
}
if ((cp-ip_as_string) >= (int)sizeof(buf)) {
return 4;
}
memcpy(buf, ip_as_string, cp-ip_as_string);
buf[cp-ip_as_string] = '\0';
cp = buf;
}
if (!inet_aton(cp, &ina)) {
return 4;
}
return _evdns_nameserver_add_impl(ina.s_addr, port);
}
/* insert into the tail of the queue */
static void
evdns_request_insert(struct request *req, struct request **head) {
if (!*head) {
*head = req;
req->next = req->prev = req;
return;
}
req->prev = (*head)->prev;
req->prev->next = req;
req->next = *head;
(*head)->prev = req;
}
static int
string_num_dots(const char *s) {
int count = 0;
while ((s = strchr(s, '.'))) {
s++;
count++;
}
return count;
}
static struct request *
request_new(int type, const char *name, int flags,
evdns_callback_type callback, void *user_ptr) {
const char issuing_now =
(global_requests_inflight < global_max_requests_inflight) ? 1 : 0;
const int name_len = strlen(name);
const int request_max_len = evdns_request_len(name_len);
const u16 trans_id = issuing_now ? transaction_id_pick() : 0xffff;
/* the request data is alloced in a single block with the header */
struct request *const req =
(struct request *) malloc(sizeof(struct request) + request_max_len);
int rlen;
(void) flags;
if (!req) return NULL;
memset(req, 0, sizeof(struct request));
/* request data lives just after the header */
req->request = ((u8 *) req) + sizeof(struct request);
/* denotes that the request data shouldn't be free()ed */
req->request_appended = 1;
rlen = evdns_request_data_build(name, name_len, trans_id,
type, CLASS_INET, req->request, request_max_len);
if (rlen < 0)
goto err1;
req->request_len = rlen;
req->trans_id = trans_id;
req->tx_count = 0;
req->request_type = type;
req->user_pointer = user_ptr;
req->user_callback = callback;
req->ns = issuing_now ? nameserver_pick() : NULL;
req->next = req->prev = NULL;
return req;
err1:
free(req);
return NULL;
}
static void
request_submit(struct request *const req) {
if (req->ns) {
/* if it has a nameserver assigned then this is going */
/* straight into the inflight queue */
evdns_request_insert(req, &req_head);
global_requests_inflight++;
evdns_request_transmit(req);
} else {
evdns_request_insert(req, &req_waiting_head);
global_requests_waiting++;
}
}
/* exported function */
int evdns_resolve_ipv4(const char *name, int flags,
evdns_callback_type callback, void *ptr) {
log(EVDNS_LOG_DEBUG, "Resolve requested for %s", name);
if (flags & DNS_QUERY_NO_SEARCH) {
struct request *const req =
request_new(TYPE_A, name, flags, callback, ptr);
if (req == NULL)
return (1);
request_submit(req);
return (0);
} else {
return (search_request_new(TYPE_A, name, flags, callback, ptr));
}
}
/* exported function */
int evdns_resolve_ipv6(const char *name, int flags,
evdns_callback_type callback, void *ptr) {
log(EVDNS_LOG_DEBUG, "Resolve requested for %s", name);
if (flags & DNS_QUERY_NO_SEARCH) {
struct request *const req =
request_new(TYPE_AAAA, name, flags, callback, ptr);
if (req == NULL)
return (1);
request_submit(req);
return (0);
} else {
return (search_request_new(TYPE_AAAA, name, flags, callback, ptr));
}
}
int evdns_resolve_reverse(struct in_addr *in, int flags, evdns_callback_type callback, void *ptr) {
char buf[32];
struct request *req;
u32 a;
assert(in);
a = ntohl(in->s_addr);
snprintf(buf, sizeof(buf), "%d.%d.%d.%d.in-addr.arpa",
(int)(u8)((a )&0xff),
(int)(u8)((a>>8 )&0xff),
(int)(u8)((a>>16)&0xff),
(int)(u8)((a>>24)&0xff));
log(EVDNS_LOG_DEBUG, "Resolve requested for %s (reverse)", buf);
req = request_new(TYPE_PTR, buf, flags, callback, ptr);
if (!req) return 1;
request_submit(req);
return 0;
}
int evdns_resolve_reverse_ipv6(struct in6_addr *in, int flags, evdns_callback_type callback, void *ptr) {
char buf[96];
char *cp;
struct request *req;
int i;
assert(in);
cp = buf;
for (i=15; i >= 0; --i) {
u8 byte = in->s6_addr[i];
*cp++ = "0123456789abcdef"[byte & 0x0f];
*cp++ = '.';
*cp++ = "0123456789abcdef"[byte >> 4];
*cp++ = '.';
}
assert(cp + strlen(".ip6.arpa") < buf+sizeof(buf));
memcpy(cp, ".ip6.arpa", strlen(".ip6.arpa")+1);
log(EVDNS_LOG_DEBUG, "Resolve requested for %s (reverse)", buf);
req = request_new(TYPE_PTR, buf, flags, callback, ptr);
if (!req) return 1;
request_submit(req);
return 0;
}
/*/////////////////////////////////////////////////////////////////// */
/* Search support */
/* */
/* the libc resolver has support for searching a number of domains */
/* to find a name. If nothing else then it takes the single domain */
/* from the gethostname() call. */
/* */
/* It can also be configured via the domain and search options in a */
/* resolv.conf. */
/* */
/* The ndots option controls how many dots it takes for the resolver */
/* to decide that a name is non-local and so try a raw lookup first. */
struct search_domain {
int len;
struct search_domain *next;
/* the text string is appended to this structure */
};
struct search_state {
int refcount;
int ndots;
int num_domains;
struct search_domain *head;
};
static struct search_state *global_search_state = NULL;
static void
search_state_decref(struct search_state *const state) {
if (!state) return;
state->refcount--;
if (!state->refcount) {
struct search_domain *next, *dom;
for (dom = state->head; dom; dom = next) {
next = dom->next;
free(dom);
}
free(state);
}
}
static struct search_state *
search_state_new(void) {
struct search_state *state = (struct search_state *) malloc(sizeof(struct search_state));
if (!state) return NULL;
memset(state, 0, sizeof(struct search_state));
state->refcount = 1;
state->ndots = 1;
return state;
}
static void
search_postfix_clear(void) {
search_state_decref(global_search_state);
global_search_state = search_state_new();
}
/* exported function */
void
evdns_search_clear(void) {
search_postfix_clear();
}
static void
search_postfix_add(const char *domain) {
int domain_len;
struct search_domain *sdomain;
while (domain[0] == '.') domain++;
domain_len = strlen(domain);
if (!global_search_state) global_search_state = search_state_new();
if (!global_search_state) return;
global_search_state->num_domains++;
sdomain = (struct search_domain *) malloc(sizeof(struct search_domain) + domain_len);
if (!sdomain) return;
memcpy( ((u8 *) sdomain) + sizeof(struct search_domain), domain, domain_len);
sdomain->next = global_search_state->head;
sdomain->len = domain_len;
global_search_state->head = sdomain;
}
/* reverse the order of members in the postfix list. This is needed because, */
/* when parsing resolv.conf we push elements in the wrong order */
static void
search_reverse(void) {
struct search_domain *cur, *prev = NULL, *next;
cur = global_search_state->head;
while (cur) {
next = cur->next;
cur->next = prev;
prev = cur;
cur = next;
}
global_search_state->head = prev;
}
/* exported function */
void
evdns_search_add(const char *domain) {
search_postfix_add(domain);
}
/* exported function */
void
evdns_search_ndots_set(const int ndots) {
if (!global_search_state) global_search_state = search_state_new();
if (!global_search_state) return;
global_search_state->ndots = ndots;
}
static void
search_set_from_hostname(void) {
char hostname[HOST_NAME_MAX + 1], *domainname;
search_postfix_clear();
if (gethostname(hostname, sizeof(hostname))) return;
domainname = strchr(hostname, '.');
if (!domainname) return;
search_postfix_add(domainname);
}
/* warning: returns malloced string */
static char *
search_make_new(const struct search_state *const state, int n, const char *const base_name) {
const int base_len = strlen(base_name);
const char need_to_append_dot = base_name[base_len - 1] == '.' ? 0 : 1;
struct search_domain *dom;
for (dom = state->head; dom; dom = dom->next) {
if (!n--) {
/* this is the postfix we want */
/* the actual postfix string is kept at the end of the structure */
const u8 *const postfix = ((u8 *) dom) + sizeof(struct search_domain);
const int postfix_len = dom->len;
char *const newname = (char *) malloc(base_len + need_to_append_dot + postfix_len + 1);
if (!newname) return NULL;
memcpy(newname, base_name, base_len);
if (need_to_append_dot) newname[base_len] = '.';
memcpy(newname + base_len + need_to_append_dot, postfix, postfix_len);
newname[base_len + need_to_append_dot + postfix_len] = 0;
return newname;
}
}
/* we ran off the end of the list and still didn't find the requested string */
abort();
return NULL; /* unreachable; stops warnings in some compilers. */
}
static int
search_request_new(int type, const char *const name, int flags, evdns_callback_type user_callback, void *user_arg) {
assert(type == TYPE_A || type == TYPE_AAAA);
if ( ((flags & DNS_QUERY_NO_SEARCH) == 0) &&
global_search_state &&
global_search_state->num_domains) {
/* we have some domains to search */
struct request *req;
if (string_num_dots(name) >= global_search_state->ndots) {
req = request_new(type, name, flags, user_callback, user_arg);
if (!req) return 1;
req->search_index = -1;
} else {
char *const new_name = search_make_new(global_search_state, 0, name);
if (!new_name) return 1;
req = request_new(type, new_name, flags, user_callback, user_arg);
free(new_name);
if (!req) return 1;
req->search_index = 0;
}
req->search_origname = strdup(name);
req->search_state = global_search_state;
req->search_flags = flags;
global_search_state->refcount++;
request_submit(req);
return 0;
} else {
struct request *const req = request_new(type, name, flags, user_callback, user_arg);
if (!req) return 1;
request_submit(req);
return 0;
}
}
/* this is called when a request has failed to find a name. We need to check */
/* if it is part of a search and, if so, try the next name in the list */
/* returns: */
/* 0 another request has been submitted */
/* 1 no more requests needed */
static int
search_try_next(struct request *const req) {
if (req->search_state) {
/* it is part of a search */
char *new_name;
struct request *newreq;
req->search_index++;
if (req->search_index >= req->search_state->num_domains) {
/* no more postfixes to try, however we may need to try */
/* this name without a postfix */
if (string_num_dots(req->search_origname) < req->search_state->ndots) {
/* yep, we need to try it raw */
struct request *const newreq = request_new(req->request_type, req->search_origname, req->search_flags, req->user_callback, req->user_pointer);
log(EVDNS_LOG_DEBUG, "Search: trying raw query %s", req->search_origname);
if (newreq) {
request_submit(newreq);
return 0;
}
}
return 1;
}
new_name = search_make_new(req->search_state, req->search_index, req->search_origname);
if (!new_name) return 1;
log(EVDNS_LOG_DEBUG, "Search: now trying %s (%d)", new_name, req->search_index);
newreq = request_new(req->request_type, new_name, req->search_flags, req->user_callback, req->user_pointer);
free(new_name);
if (!newreq) return 1;
newreq->search_origname = req->search_origname;
req->search_origname = NULL;
newreq->search_state = req->search_state;
newreq->search_flags = req->search_flags;
newreq->search_index = req->search_index;
newreq->search_state->refcount++;
request_submit(newreq);
return 0;
}
return 1;
}
static void
search_request_finished(struct request *const req) {
if (req->search_state) {
search_state_decref(req->search_state);
req->search_state = NULL;
}
if (req->search_origname) {
free(req->search_origname);
req->search_origname = NULL;
}
}
/*/////////////////////////////////////////////////////////////////// */
/* Parsing resolv.conf files */
static void
evdns_resolv_set_defaults(int flags) {
/* if the file isn't found then we assume a local resolver */
if (flags & DNS_OPTION_SEARCH) search_set_from_hostname();
if (flags & DNS_OPTION_NAMESERVERS) evdns_nameserver_ip_add("127.0.0.1");
}
#ifndef HAVE_STRTOK_R
static char *
fake_strtok_r(char *s, const char *delim, char **state) {
return strtok(s, delim);
}
#endif
/* helper version of atoi which returns -1 on error */
static int
strtoint(const char *const str) {
char *endptr;
const int r = strtol(str, &endptr, 10);
if (*endptr) return -1;
return r;
}
/* helper version of atoi that returns -1 on error and clips to bounds. */
static int
strtoint_clipped(const char *const str, int min, int max)
{
int r = strtoint(str);
if (r == -1)
return r;
else if (r<min)
return min;
else if (r>max)
return max;
else
return r;
}
/* exported function */
int
evdns_set_option(const char *option, const char *val, int flags)
{
if (!strncmp(option, "ndots:", 6)) {
const int ndots = strtoint(val);
if (ndots == -1) return -1;
if (!(flags & DNS_OPTION_SEARCH)) return 0;
log(EVDNS_LOG_DEBUG, "Setting ndots to %d", ndots);
if (!global_search_state) global_search_state = search_state_new();
if (!global_search_state) return -1;
global_search_state->ndots = ndots;
} else if (!strncmp(option, "timeout:", 8)) {
const int timeout = strtoint(val);
if (timeout == -1) return -1;
if (!(flags & DNS_OPTION_MISC)) return 0;
log(EVDNS_LOG_DEBUG, "Setting timeout to %d", timeout);
global_timeout.tv_sec = timeout;
} else if (!strncmp(option, "max-timeouts:", 12)) {
const int maxtimeout = strtoint_clipped(val, 1, 255);
if (maxtimeout == -1) return -1;
if (!(flags & DNS_OPTION_MISC)) return 0;
log(EVDNS_LOG_DEBUG, "Setting maximum allowed timeouts to %d",