2 dns.cpp - based on the firedns library Copyright (C) 2002 Ian Gulliver
4 This program is free software; you can redistribute it and/or modify
5 it under the terms of version 2 of the GNU General Public License as
6 published by the Free Software Foundation.
8 This program is distributed in the hope that it will be useful,
9 but WITHOUT ANY WARRANTY; without even the implied warranty of
10 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
11 GNU General Public License for more details.
13 You should have received a copy of the GNU General Public License
14 along with this program; if not, write to the Free Software
15 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
25 #include <sys/types.h>
26 #include <sys/socket.h>
34 #include <sys/types.h>
35 #include <sys/socket.h>
36 #include <netinet/in.h>
37 #include <arpa/inet.h>
39 #include "helperfuncs.h"
40 #include "socketengine.h"
42 extern SocketEngine* SE;
44 extern int statsAccept,statsRefused,statsUnknown,statsCollisions,statsDns,statsDnsGood,statsDnsBad,statsConnects,statsSent,statsRecv;
46 #define max(a,b) (a > b ? a : b)
47 #define DNS_MAX 8 /* max number of nameservers used */
48 #define DNS_CONFIG_FBCK "/etc/resolv.conf" /* fallback config file */
49 #define DNS_PORT 53 /* DNS well known port */
50 #define DNS_QRY_A 1 /* name to IP address */
51 #define DNS_QRY_AAAA 28 /* name to IP6 address */
52 #define DNS_QRY_PTR 12 /* IP address to name */
53 #define DNS_QRY_MX 15 /* name to MX */
54 #define DNS_QRY_TXT 16 /* name to TXT */
55 #define DNS_QRY_CNAME 5
57 #define DNS_ALIGN (sizeof(void *) > sizeof(long) ? sizeof(void *) : sizeof(long))
59 #define RESULTSIZE 1024
60 #define min(a,b) (a < b ? a : b)
62 static struct in_addr servers4[DNS_MAX]; /* up to DNS_MAX nameservers; populated by dns_init() */
63 static int i4; /* actual count of nameservers; set by dns_init() */
65 static int initdone = 0; /* to ensure dns_init() only runs once (on the first call) */
66 static int wantclose = 0;
67 static int lastcreate = -1;
69 struct s_connection { /* open DNS query */
70 struct s_connection *next; /* next in list */
75 int fd; /* file descriptor returned from sockets */
82 unsigned int rdlength;
85 #define DNS_POINTER_VALUE 0xc000
87 static s_connection *connection_head = NULL; /* linked list of open DNS queries; populated by dns_add_query(), decimated by dns_getresult_s() */
89 struct s_header { /* DNS query header */
92 #define FLAGS1_MASK_QR 0x80
93 #define FLAGS1_MASK_OPCODE 0x78 /* bitshift right 3 */
94 #define FLAGS1_MASK_AA 0x04
95 #define FLAGS1_MASK_TC 0x02
96 #define FLAGS1_MASK_RD 0x01
98 #define FLAGS2_MASK_RA 0x80
99 #define FLAGS2_MASK_Z 0x70
100 #define FLAGS2_MASK_RCODE 0x0f
101 unsigned int qdcount;
102 unsigned int ancount;
103 unsigned int nscount;
104 unsigned int arcount;
105 unsigned char payload[512]; /* DNS question, populated by dns_build_query_payload() */
110 void *dns_align(void *inp) {
111 char *p = (char*)inp;
112 int offby = ((char *)p - (char *)0) % DNS_ALIGN;
114 return p + (DNS_ALIGN - offby);
120 * These little hacks are here to avoid alignment and type sizing issues completely by doing manual copies
122 void dns_fill_rr(s_rr_middle* rr, const unsigned char *input) {
123 rr->type = input[0] * 256 + input[1];
124 rr->_class = input[2] * 256 + input[3];
125 rr->ttl = input[4] * 16777216 + input[5] * 65536 + input[6] * 256 + input[7];
126 rr->rdlength = input[8] * 256 + input[9];
129 void dns_fill_header(s_header *header, const unsigned char *input, const int l) {
130 header->id[0] = input[0];
131 header->id[1] = input[1];
132 header->flags1 = input[2];
133 header->flags2 = input[3];
134 header->qdcount = input[4] * 256 + input[5];
135 header->ancount = input[6] * 256 + input[7];
136 header->nscount = input[8] * 256 + input[9];
137 header->arcount = input[10] * 256 + input[11];
138 memcpy(header->payload,&input[12],l);
141 void dns_empty_header(unsigned char *output, const s_header *header, const int l) {
142 output[0] = header->id[0];
143 output[1] = header->id[1];
144 output[2] = header->flags1;
145 output[3] = header->flags2;
146 output[4] = header->qdcount / 256;
147 output[5] = header->qdcount % 256;
148 output[6] = header->ancount / 256;
149 output[7] = header->ancount % 256;
150 output[8] = header->nscount / 256;
151 output[9] = header->nscount % 256;
152 output[10] = header->arcount / 256;
153 output[11] = header->arcount % 256;
154 memcpy(&output[12],header->payload,l);
157 void dns_close(int fd) { /* close query */
158 log(DEBUG,"DNS: dns_close on fd %d",fd);
159 if (fd == lastcreate) {
168 void DNS::dns_init() { /* on first call only: populates servers4 struct with up to DNS_MAX nameserver IP addresses from /etc/resolv.conf */
178 srand((unsigned int) TIME);
179 memset(servers4,'\0',sizeof(in_addr) * DNS_MAX);
180 f = fopen(DNS_CONFIG_FBCK,"r");
183 while (fgets(buf,1024,f) != NULL) {
184 if (strncmp(buf,"nameserver",10) == 0) {
186 while (buf[i] == ' ' || buf[i] == '\t')
189 if (dns_aton4_s(&buf[i],&addr4) != NULL)
190 memcpy(&servers4[i4++],&addr4,sizeof(in_addr));
197 void DNS::dns_init_2(const char* dnsserver)
201 srand((unsigned int) TIME);
202 memset(servers4,'\0',sizeof(in_addr) * DNS_MAX);
203 if (dns_aton4_s(dnsserver,&addr4) != NULL)
204 memcpy(&servers4[i4++],&addr4,sizeof(in_addr));
208 static int dns_send_requests(const s_header *h, const s_connection *s, const int l)
212 unsigned char payload[sizeof(s_header)];
214 dns_empty_header(payload,h,l);
219 /* otherwise send via standard ipv4 boringness */
220 memset(&addr4,0,sizeof(addr4));
221 memcpy(&addr4.sin_addr,&servers4[i],sizeof(addr4.sin_addr));
222 addr4.sin_family = AF_INET;
223 addr4.sin_port = htons(DNS_PORT);
224 if (sendto(s->fd, payload, l + 12, 0, (sockaddr *) &addr4, sizeof(addr4)) == -1)
232 static s_connection *dns_add_query(s_header *h) { /* build DNS query, add to list */
235 s = new s_connection;
237 /* set header flags */
238 h->id[0] = s->id[0] = rand() % 255; /* verified by dns_getresult_s() */
239 h->id[1] = s->id[1] = rand() % 255;
240 h->flags1 = 0 | FLAGS1_MASK_RD;
247 /* turn off want_list by default */
250 /* try to create ipv6 or ipv4 socket */
251 s->fd = socket(PF_INET, SOCK_DGRAM, 0);
253 if (fcntl(s->fd, F_SETFL, O_NONBLOCK) != 0) {
261 memset(&addr,0,sizeof(addr));
262 addr.sin_family = AF_INET;
264 addr.sin_addr.s_addr = INADDR_ANY;
265 if (bind(s->fd,(sockaddr *)&addr,sizeof(addr)) != 0) {
275 /* create new connection object, add to linked list */
276 s->next = connection_head;
279 if (wantclose == 1) {
280 shutdown(lastcreate,2);
288 static int dns_build_query_payload(const char * const name, const unsigned short rr, const unsigned short _class, unsigned char * const payload) {
290 const char * tempchr, * tempchr2;
296 /* split name up into labels, create query */
297 while ((tempchr = strchr(tempchr2,'.')) != NULL) {
298 l = tempchr - tempchr2;
299 if (payloadpos + l + 1 > 507)
301 payload[payloadpos++] = l;
302 memcpy(&payload[payloadpos],tempchr2,l);
304 tempchr2 = &tempchr[1];
306 l = strlen(tempchr2);
308 if (payloadpos + l + 2 > 507)
310 payload[payloadpos++] = l;
311 memcpy(&payload[payloadpos],tempchr2,l);
313 payload[payloadpos++] = '\0';
315 if (payloadpos > 508)
318 memcpy(&payload[payloadpos],&l,2);
320 memcpy(&payload[payloadpos + 2],&l,2);
321 return payloadpos + 4;
324 in_addr* DNS::dns_aton4(const char * const ipstring) { /* ascii to numeric: convert string to static 4part IP addr struct */
326 return dns_aton4_s(ipstring,&ip);
329 in_addr* DNS::dns_aton4_r(const char *ipstring) { /* ascii to numeric (reentrant): convert string to new 4part IP addr struct */
332 if(dns_aton4_s(ipstring,ip) == NULL) {
339 in_addr* DNS::dns_aton4_s(const char *ipstring, in_addr *ip) { /* ascii to numeric (buffered): convert string to given 4part IP addr struct */
340 inet_aton(ipstring,ip);
344 int DNS::dns_getip4(const char *name) { /* build, add and send A query; retrieve result with dns_getresult() */
352 l = dns_build_query_payload(name,DNS_QRY_A,1,(unsigned char *)&h.payload);
355 s = dns_add_query(&h);
360 if (dns_send_requests(&h,s,l) == -1)
366 int DNS::dns_getip4list(const char *name) { /* build, add and send A query; retrieve result with dns_getresult() */
374 l = dns_build_query_payload(name,DNS_QRY_A,1,(unsigned char *)&h.payload);
377 s = dns_add_query(&h);
383 if (dns_send_requests(&h,s,l) == -1)
389 int DNS::dns_getname4(const in_addr *ip) { /* build, add and send PTR query; retrieve result with dns_getresult() */
396 c = (unsigned char *)&ip->s_addr;
398 sprintf(query,"%d.%d.%d.%d.in-addr.arpa",c[3],c[2],c[1],c[0]);
400 l = dns_build_query_payload(query,DNS_QRY_PTR,1,(unsigned char *)&h.payload);
403 s = dns_add_query(&h);
407 s->type = DNS_QRY_PTR;
408 if (dns_send_requests(&h,s,l) == -1)
414 char* DNS::dns_ntoa4(const in_addr * const ip) { /* numeric to ascii: convert 4part IP addr struct to static string */
416 return dns_ntoa4_s(ip,r);
419 char* DNS::dns_ntoa4_s(const in_addr *ip, char *r) { /* numeric to ascii (buffered): convert 4part IP addr struct to given string */
421 m = (unsigned char *)&ip->s_addr;
422 sprintf(r,"%d.%d.%d.%d",m[0],m[1],m[2],m[3]);
426 char* DNS::dns_getresult(const int cfd) { /* retrieve result of DNS query */
427 log(DEBUG,"DNS: dns_getresult with cfd=%d",cfd);
428 return dns_getresult_s(cfd,this->localbuf);
431 char* DNS::dns_getresult_s(const int cfd, char *res) { /* retrieve result of DNS query (buffered) */
433 s_connection *c, *prev;
434 int l,i,q,curanswer,o;
436 unsigned char buffer[sizeof(s_header)];
446 while (c != NULL) { /* find query in list of open queries */
453 log(DEBUG,"DNS: got a response for a query we didnt send with fd=%d",cfd);
454 return NULL; /* query not found */
456 /* query found-- pull from list: */
458 prev->next = c->next;
460 connection_head = c->next;
462 l = recv(c->fd,buffer,sizeof(s_header),0);
468 dns_fill_header(&h,buffer,l - 12);
469 if (c->id[0] != h.id[0] || c->id[1] != h.id[1]) {
470 log(DEBUG,"DNS: id mismatch on query");
472 return NULL; /* ID mismatch */
474 if ((h.flags1 & FLAGS1_MASK_QR) == 0) {
475 log(DEBUG,"DNS: didnt get a query result");
479 if ((h.flags1 & FLAGS1_MASK_OPCODE) != 0) {
480 log(DEBUG,"DNS: got an OPCODE and didnt want one");
484 if ((h.flags2 & FLAGS2_MASK_RCODE) != 0) {
485 log(DEBUG,"DNS lookup failed due to SERVFAIL");
489 if (h.ancount < 1) { /* no sense going on if we don't have any answers */
490 log(DEBUG,"DNS: no answers!");
498 while ((unsigned)q < h.qdcount && i < l) {
499 if (h.payload[i] > 63) { /* pointer */
500 i += 6; /* skip pointer, _class and type */
503 if (h.payload[i] == 0) {
505 i += 5; /* skip nil, _class and type */
507 i += h.payload[i] + 1; /* skip length and label */
510 /* &h.payload[i] should now be the start of the first response */
512 while ((unsigned)curanswer < h.ancount) {
514 while (q == 0 && i < l) {
515 if (h.payload[i] > 63) { /* pointer */
516 i += 2; /* skip pointer */
519 if (h.payload[i] == 0) {
523 i += h.payload[i] + 1; /* skip length and label */
530 dns_fill_rr(&rr,&h.payload[i]);
532 if (rr.type != c->type) {
537 if (rr._class != c->_class) {
544 if ((unsigned)curanswer == h.ancount)
546 if ((unsigned)i + rr.rdlength > (unsigned)l)
548 if (rr.rdlength > 1023)
553 log(DEBUG,"DNS: got a result of type DNS_QRY_PTR");
556 while (q == 0 && i < l && o + 256 < 1023) {
557 if (h.payload[i] > 63) { /* pointer */
558 memcpy(&p,&h.payload[i],2);
559 i = ntohs(p) - DNS_POINTER_VALUE - 12;
561 if (h.payload[i] == 0)
567 memcpy(&res[o],&h.payload[i + 1],h.payload[i]);
569 i += h.payload[i] + 1;
576 log(DEBUG,"DNS: got a result of type DNS_QRY_A");
578 dns_ip4list *alist = (dns_ip4list *) res; /* we have to trust that this is aligned */
579 while ((char *)alist - (char *)res < 700) {
580 if (rr.type != DNS_QRY_A)
584 if (rr.rdlength != 4) {
588 memcpy(&alist->ip,&h.payload[i],4);
589 if ((unsigned)++curanswer >= h.ancount)
595 while (q == 0 && i < l) {
596 if (h.payload[i] > 63) { /* pointer */
597 i += 2; /* skip pointer */
600 if (h.payload[i] == 0) {
604 i += h.payload[i] + 1; /* skip length and label */
612 dns_fill_rr(&rr,&h.payload[i]);
614 alist->next = (dns_ip4list *) dns_align(((char *) alist) + sizeof(dns_ip4list));
625 log(DEBUG,"DNS: doing something with result 'default'");
626 memcpy(res,&h.payload[i],rr.rdlength);
627 res[rr.rdlength] = '\0';
637 log(DEBUG,"Create blank DNS");
640 DNS::DNS(std::string dnsserver)
642 dns_init_2(dnsserver.c_str());
643 log(DEBUG,"Create DNS");
646 void DNS::SetNS(std::string dnsserver)
648 dns_init_2(dnsserver.c_str());
656 bool DNS::ReverseLookup(std::string ip)
659 binip = dns_aton4(ip.c_str());
664 this->myfd = dns_getname4(binip);
665 if (this->myfd == -1)
669 log(DEBUG,"DNS: ReverseLookup, fd=%d",this->myfd);
671 SE->AddFd(this->myfd,true,X_ESTAB_DNS);
676 bool DNS::ForwardLookup(std::string host)
679 this->myfd = dns_getip4(host.c_str());
680 if (this->myfd == -1)
684 log(DEBUG,"DNS: ForwardLookup, fd=%d",this->myfd);
686 SE->AddFd(this->myfd,true,X_ESTAB_DNS);
691 bool DNS::HasResult()
693 log(DEBUG,"DNS: HasResult, fd=%d",this->myfd);
695 polls.fd = this->myfd;
696 polls.events = POLLIN;
697 int ret = poll(&polls,1,1);
698 log(DEBUG,"DNS: Hasresult returning %d",ret);
707 std::string DNS::GetResult()
709 log(DEBUG,"DNS: GetResult()");
710 result = dns_getresult(this->myfd);
712 SE->DelFd(this->myfd);
716 dns_close(this->myfd);
720 if (this->myfd != -1)
722 dns_close(this->myfd);
728 std::string DNS::GetResultIP()
731 log(DEBUG,"DNS: GetResultIP()");
732 result = dns_getresult(this->myfd);
733 if (this->myfd != -1)
736 SE->DelFd(this->myfd);
738 dns_close(this->myfd);
743 unsigned char a = (unsigned)result[0];
744 unsigned char b = (unsigned)result[1];
745 unsigned char c = (unsigned)result[2];
746 unsigned char d = (unsigned)result[3];
747 snprintf(r,1024,"%u.%u.%u.%u",a,b,c,d);
753 log(DEBUG,"DANGER WILL ROBINSON! NXDOMAIN for forward lookup, but we got a reverse lookup!");