source/nmbd/asyncdns.c

   1 /*
   2    Unix SMB/CIFS implementation.
   3    a async DNS handler
   4    Copyright (C) Andrew Tridgell 1997-1998
   5
   6    This program is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  18    */
  19
  20 #include "includes.h"
  21
  22 /***************************************************************************
  23   Add a DNS result to the name cache.
  24 ****************************************************************************/
  25
  26 static struct name_record *add_dns_result(struct nmb_name *question, struct in_addr addr)
  27 {
  28         int name_type = question->name_type;
  29         unstring qname;
  30
  31         pull_ascii_nstring(qname, sizeof(qname), question->name);
  32
  33         if (!addr.s_addr) {
  34                 /* add the fail to WINS cache of names. give it 1 hour in the cache */
  35                 DEBUG(3,("add_dns_result: Negative DNS answer for %s\n", qname));
  36                 add_name_to_subnet( wins_server_subnet, qname, name_type,
  37                                 NB_ACTIVE, 60*60, DNSFAIL_NAME, 1, &addr );
  38                 return NULL;
  39         }
  40
  41         /* add it to our WINS cache of names. give it 2 hours in the cache */
  42         DEBUG(3,("add_dns_result: DNS gave answer for %s of %s\n", qname, inet_ntoa(addr)));
  43
  44         add_name_to_subnet( wins_server_subnet, qname, name_type,
  45                               NB_ACTIVE, 2*60*60, DNS_NAME, 1, &addr);
  46
  47         return find_name_on_subnet(wins_server_subnet, question, FIND_ANY_NAME);
  48 }
  49
  50 #ifndef SYNC_DNS
  51
  52 static int fd_in = -1, fd_out = -1;
  53 static pid_t child_pid = -1;
  54 static int in_dns;
  55
  56 /* this is the structure that is passed between the parent and child */
  57 struct query_record {
  58         struct nmb_name name;
  59         struct in_addr result;
  60 };
  61
  62 /* a queue of pending requests waiting to be sent to the DNS child */
  63 static struct packet_struct *dns_queue;
  64
  65 /* the packet currently being processed by the dns child */
  66 static struct packet_struct *dns_current;
  67
  68
  69 /***************************************************************************
  70   return the fd used to gather async dns replies. This is added to the select
  71   loop
  72   ****************************************************************************/
  73
  74 int asyncdns_fd(void)
  75 {
  76         return fd_in;
  77 }
  78
  79 /***************************************************************************
  80   handle DNS queries arriving from the parent
  81   ****************************************************************************/
  82 static void asyncdns_process(void)
  83 {
  84         struct query_record r;
  85         unstring qname;
  86
  87         DEBUGLEVEL = -1;
  88
  89         while (1) {
  90                 NTSTATUS status;
  91
  92                 status = read_data(fd_in, (char *)&r, sizeof(r));
  93
  94                 if (!NT_STATUS_IS_OK(status)) {
  95                         break;
  96                 }
  97
  98                 pull_ascii_nstring( qname, sizeof(qname), r.name.name);
  99                 r.result.s_addr = interpret_addr(qname);
 100
 101                 if (write_data(fd_out, (char *)&r, sizeof(r)) != sizeof(r))
 102                         break;
 103         }
 104
 105         _exit(0);
 106 }
 107
 108 /**************************************************************************** **
 109   catch a sigterm (in the child process - the parent has a different handler
 110   see nmbd.c for details).
 111   We need a separate term handler here so we don't release any
 112   names that our parent is going to release, or overwrite a
 113   WINS db that our parent is going to write.
 114  **************************************************************************** */
 115
 116 static void sig_term(int sig)
 117 {
 118         _exit(0);
 119 }
 120
 121 /***************************************************************************
 122  Called by the parent process when it receives a SIGTERM - also kills the
 123  child so we don't get child async dns processes lying around, causing trouble.
 124   ****************************************************************************/
 125
 126 void kill_async_dns_child(void)
 127 {
 128         if (child_pid > 0) {
 129                 kill(child_pid, SIGTERM);
 130                 child_pid = -1;
 131         }
 132 }
 133
 134 /***************************************************************************
 135   create a child process to handle DNS lookups
 136   ****************************************************************************/
 137 void start_async_dns(void)
 138 {
 139         int fd1[2], fd2[2];
 140
 141         CatchChild();
 142
 143         if (pipe(fd1) || pipe(fd2)) {
 144                 DEBUG(0,("can't create asyncdns pipes\n"));
 145                 return;
 146         }
 147
 148         child_pid = sys_fork();
 149
 150         if (child_pid) {
 151                 fd_in = fd1[0];
 152                 fd_out = fd2[1];
 153                 close(fd1[1]);
 154                 close(fd2[0]);
 155                 DEBUG(0,("started asyncdns process %d\n", (int)child_pid));
 156                 return;
 157         }
 158
 159         fd_in = fd2[0];
 160         fd_out = fd1[1];
 161
 162         CatchSignal(SIGUSR2, SIG_IGN);
 163         CatchSignal(SIGUSR1, SIG_IGN);
 164         CatchSignal(SIGHUP, SIG_IGN);
 165         CatchSignal(SIGTERM, SIGNAL_CAST sig_term );
 166
 167         if (!reinit_after_fork(nmbd_messaging_context(), true)) {
 168                 DEBUG(0,("reinit_after_fork() failed\n"));
 169                 smb_panic("reinit_after_fork() failed");
 170         }
 171
 172         asyncdns_process();
 173 }
 174
 175
 176 /***************************************************************************
 177 check if a particular name is already being queried
 178   ****************************************************************************/
 179 static bool query_current(struct query_record *r)
 180 {
 181         return dns_current &&
 182                 nmb_name_equal(&r->name,
 183                            &dns_current->packet.nmb.question.question_name);
 184 }
 185
 186
 187 /***************************************************************************
 188   write a query to the child process
 189   ****************************************************************************/
 190 static bool write_child(struct packet_struct *p)
 191 {
 192         struct query_record r;
 193
 194         r.name = p->packet.nmb.question.question_name;
 195
 196         return write_data(fd_out, (char *)&r, sizeof(r)) == sizeof(r);
 197 }
 198
 199 /***************************************************************************
 200   check the DNS queue
 201   ****************************************************************************/
 202 void run_dns_queue(void)
 203 {
 204         struct query_record r;
 205         struct packet_struct *p, *p2;
 206         struct name_record *namerec;
 207         NTSTATUS status;
 208
 209         if (fd_in == -1)
 210                 return;
 211
 212         /* Allow SIGTERM to kill us. */
 213         BlockSignals(False, SIGTERM);
 214
 215         if (!process_exists_by_pid(child_pid)) {
 216                 close(fd_in);
 217                 close(fd_out);
 218                 start_async_dns();
 219         }
 220
 221         status = read_data(fd_in, (char *)&r, sizeof(r));
 222
 223         if (!NT_STATUS_IS_OK(status)) {
 224                 DEBUG(0, ("read from child failed: %s\n", nt_errstr(status)));
 225                 fd_in = -1;
 226                 BlockSignals(True, SIGTERM);
 227                 return;
 228         }
 229
 230         BlockSignals(True, SIGTERM);
 231
 232         namerec = add_dns_result(&r.name, r.result);
 233
 234         if (dns_current) {
 235                 if (query_current(&r)) {
 236                         DEBUG(3,("DNS calling send_wins_name_query_response\n"));
 237                         in_dns = 1;
 238                         if(namerec == NULL)
 239                                 send_wins_name_query_response(NAM_ERR, dns_current, NULL);
 240                         else
 241                                 send_wins_name_query_response(0,dns_current,namerec);
 242                         in_dns = 0;
 243                 }
 244
 245                 dns_current->locked = False;
 246                 free_packet(dns_current);
 247                 dns_current = NULL;
 248         }
 249
 250         /* loop over the whole dns queue looking for entries that
 251            match the result we just got */
 252         for (p = dns_queue; p;) {
 253                 struct nmb_packet *nmb = &p->packet.nmb;
 254                 struct nmb_name *question = &nmb->question.question_name;
 255
 256                 if (nmb_name_equal(question, &r.name)) {
 257                         DEBUG(3,("DNS calling send_wins_name_query_response\n"));
 258                         in_dns = 1;
 259                         if(namerec == NULL)
 260                                 send_wins_name_query_response(NAM_ERR, p, NULL);
 261                         else
 262                                 send_wins_name_query_response(0,p,namerec);
 263                         in_dns = 0;
 264                         p->locked = False;
 265
 266                         if (p->prev)
 267                                 p->prev->next = p->next;
 268                         else
 269                                 dns_queue = p->next;
 270                         if (p->next)
 271                                 p->next->prev = p->prev;
 272                         p2 = p->next;
 273                         free_packet(p);
 274                         p = p2;
 275                 } else {
 276                         p = p->next;
 277                 }
 278         }
 279
 280         if (dns_queue) {
 281                 dns_current = dns_queue;
 282                 dns_queue = dns_queue->next;
 283                 if (dns_queue)
 284                         dns_queue->prev = NULL;
 285                 dns_current->next = NULL;
 286
 287                 if (!write_child(dns_current)) {
 288                         DEBUG(3,("failed to send DNS query to child!\n"));
 289                         return;
 290                 }
 291         }
 292 }
 293
 294 /***************************************************************************
 295 queue a DNS query
 296   ****************************************************************************/
 297
 298 bool queue_dns_query(struct packet_struct *p,struct nmb_name *question)
 299 {
 300         if (in_dns || fd_in == -1)
 301                 return False;
 302
 303         if (!dns_current) {
 304                 if (!write_child(p)) {
 305                         DEBUG(3,("failed to send DNS query to child!\n"));
 306                         return False;
 307                 }
 308                 dns_current = p;
 309                 p->locked = True;
 310         } else {
 311                 p->locked = True;
 312                 p->next = dns_queue;
 313                 p->prev = NULL;
 314                 if (p->next)
 315                         p->next->prev = p;
 316                 dns_queue = p;
 317         }
 318
 319         DEBUG(3,("added DNS query for %s\n", nmb_namestr(question)));
 320         return True;
 321 }
 322
 323 #else
 324
 325
 326 /***************************************************************************
 327   we use this when we can't do async DNS lookups
 328   ****************************************************************************/
 329
 330 bool queue_dns_query(struct packet_struct *p,struct nmb_name *question)
 331 {
 332         struct name_record *namerec = NULL;
 333         struct in_addr dns_ip;
 334         unstring qname;
 335
 336         pull_ascii_nstring(qname, sizeof(qname), question->name);
 337
 338         DEBUG(3,("DNS search for %s - ", nmb_namestr(question)));
 339
 340         /* Unblock TERM signal so we can be killed in DNS lookup. */
 341         BlockSignals(False, SIGTERM);
 342
 343         dns_ip.s_addr = interpret_addr(qname);
 344
 345         /* Re-block TERM signal. */
 346         BlockSignals(True, SIGTERM);
 347
 348         namerec = add_dns_result(question, dns_ip);
 349         if(namerec == NULL) {
 350                 send_wins_name_query_response(NAM_ERR, p, NULL);
 351         } else {
 352                 send_wins_name_query_response(0, p, namerec);
 353         }
 354         return False;
 355 }
 356
 357 /***************************************************************************
 358  With sync dns there is no child to kill on SIGTERM.
 359   ****************************************************************************/
 360
 361 void kill_async_dns_child(void)
 362 {
 363         return;
 364 }
 365 #endif