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 2 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, write to the Free Software
  18    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  19    */
  20
  21 #include "includes.h"
  22
  23 /***************************************************************************
  24   Add a DNS result to the name cache.
  25 ****************************************************************************/
  26
  27 static struct name_record *add_dns_result(struct nmb_name *question, struct in_addr addr)
  28 {
  29   int name_type = question->name_type;
  30   char *qname = question->name;
  31
  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     (void)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   return( add_name_to_subnet( wins_server_subnet, qname, name_type,
  45                               NB_ACTIVE, 2*60*60, DNS_NAME, 1, &addr ) );
  46 }
  47
  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 int asyncdns_fd(void)
  74 {
  75         return fd_in;
  76 }
  77
  78 /***************************************************************************
  79   handle DNS queries arriving from the parent
  80   ****************************************************************************/
  81 static void asyncdns_process(void)
  82 {
  83         struct query_record r;
  84         fstring qname;
  85
  86         DEBUGLEVEL = -1;
  87
  88         while (1) {
  89                 if (read_data(fd_in, (char *)&r, sizeof(r)) != sizeof(r))
  90                         break;
  91
  92                 fstrcpy(qname, r.name.name);
  93
  94                 r.result.s_addr = interpret_addr(qname);
  95
  96                 if (write_data(fd_out, (char *)&r, sizeof(r)) != sizeof(r))
  97                         break;
  98         }
  99
 100         _exit(0);
 101 }
 102
 103 /**************************************************************************** **
 104   catch a sigterm (in the child process - the parent has a different handler
 105   see nmbd.c for details).
 106   We need a separate term handler here so we don't release any
 107   names that our parent is going to release, or overwrite a
 108   WINS db that our parent is going to write.
 109  **************************************************************************** */
 110
 111 static void sig_term(int sig)
 112 {
 113   _exit(0);
 114 }
 115
 116 /***************************************************************************
 117  Called by the parent process when it receives a SIGTERM - also kills the
 118  child so we don't get child async dns processes lying around, causing trouble.
 119   ****************************************************************************/
 120
 121 void kill_async_dns_child(void)
 122 {
 123         if (child_pid > 0) {
 124                 kill(child_pid, SIGTERM);
 125                 child_pid = -1;
 126         }
 127 }
 128
 129 /***************************************************************************
 130   create a child process to handle DNS lookups
 131   ****************************************************************************/
 132 void start_async_dns(void)
 133 {
 134         int fd1[2], fd2[2];
 135
 136         CatchChild();
 137
 138         if (pipe(fd1) || pipe(fd2)) {
 139                 DEBUG(0,("can't create asyncdns pipes\n"));
 140                 return;
 141         }
 142
 143         child_pid = sys_fork();
 144
 145         if (child_pid) {
 146                 fd_in = fd1[0];
 147                 fd_out = fd2[1];
 148                 close(fd1[1]);
 149                 close(fd2[0]);
 150                 DEBUG(0,("started asyncdns process %d\n", (int)child_pid));
 151                 return;
 152         }
 153
 154         fd_in = fd2[0];
 155         fd_out = fd1[1];
 156
 157         CatchSignal(SIGUSR2, SIG_IGN);
 158         CatchSignal(SIGUSR1, SIG_IGN);
 159         CatchSignal(SIGHUP, SIG_IGN);
 160         CatchSignal(SIGTERM, SIGNAL_CAST sig_term );
 161
 162         asyncdns_process();
 163 }
 164
 165
 166 /***************************************************************************
 167 check if a particular name is already being queried
 168   ****************************************************************************/
 169 static BOOL query_current(struct query_record *r)
 170 {
 171         return dns_current &&
 172                 nmb_name_equal(&r->name,
 173                            &dns_current->packet.nmb.question.question_name);
 174 }
 175
 176
 177 /***************************************************************************
 178   write a query to the child process
 179   ****************************************************************************/
 180 static BOOL write_child(struct packet_struct *p)
 181 {
 182         struct query_record r;
 183
 184         r.name = p->packet.nmb.question.question_name;
 185
 186         return write_data(fd_out, (char *)&r, sizeof(r)) == sizeof(r);
 187 }
 188
 189 /***************************************************************************
 190   check the DNS queue
 191   ****************************************************************************/
 192 void run_dns_queue(void)
 193 {
 194         struct query_record r;
 195         struct packet_struct *p, *p2;
 196         struct name_record *namerec;
 197         int size;
 198
 199         if (fd_in == -1)
 200                 return;
 201
 202         /* Allow SIGTERM to kill us. */
 203         BlockSignals(False, SIGTERM);
 204
 205         if (!process_exists(child_pid)) {
 206                 close(fd_in);
 207                 start_async_dns();
 208         }
 209
 210         if ((size=read_data(fd_in, (char *)&r, sizeof(r))) != sizeof(r)) {
 211                 if (size) {
 212                         DEBUG(0,("Incomplete DNS answer from child!\n"));
 213                         fd_in = -1;
 214                 }
 215                 BlockSignals(True, SIGTERM);
 216                 return;
 217         }
 218
 219         BlockSignals(True, SIGTERM);
 220
 221         namerec = add_dns_result(&r.name, r.result);
 222
 223         if (dns_current) {
 224                 if (query_current(&r)) {
 225                         DEBUG(3,("DNS calling send_wins_name_query_response\n"));
 226                         in_dns = 1;
 227                         if(namerec == NULL)
 228                           send_wins_name_query_response(NAM_ERR, dns_current, NULL);
 229                         else
 230                           send_wins_name_query_response(0,dns_current,namerec);
 231                         in_dns = 0;
 232                 }
 233
 234                 dns_current->locked = False;
 235                 free_packet(dns_current);
 236                 dns_current = NULL;
 237         }
 238
 239         /* loop over the whole dns queue looking for entries that
 240            match the result we just got */
 241         for (p = dns_queue; p;) {
 242                 struct nmb_packet *nmb = &p->packet.nmb;
 243                 struct nmb_name *question = &nmb->question.question_name;
 244
 245                 if (nmb_name_equal(question, &r.name)) {
 246                         DEBUG(3,("DNS calling send_wins_name_query_response\n"));
 247                         in_dns = 1;
 248                         if(namerec == NULL)
 249                           send_wins_name_query_response(NAM_ERR, p, NULL);
 250                         else
 251                           send_wins_name_query_response(0,p,namerec);
 252                         in_dns = 0;
 253                         p->locked = False;
 254
 255                         if (p->prev)
 256                                 p->prev->next = p->next;
 257                         else
 258                                 dns_queue = p->next;
 259                         if (p->next)
 260                                 p->next->prev = p->prev;
 261                         p2 = p->next;
 262                         free_packet(p);
 263                         p = p2;
 264                 } else {
 265                         p = p->next;
 266                 }
 267         }
 268
 269         if (dns_queue) {
 270                 dns_current = dns_queue;
 271                 dns_queue = dns_queue->next;
 272                 if (dns_queue) dns_queue->prev = NULL;
 273                 dns_current->next = NULL;
 274
 275                 if (!write_child(dns_current)) {
 276                         DEBUG(3,("failed to send DNS query to child!\n"));
 277                         return;
 278                 }
 279         }
 280
 281 }
 282
 283 /***************************************************************************
 284 queue a DNS query
 285   ****************************************************************************/
 286 BOOL queue_dns_query(struct packet_struct *p,struct nmb_name *question,
 287                      struct name_record **n)
 288 {
 289         if (in_dns || fd_in == -1)
 290                 return False;
 291
 292         if (!dns_current) {
 293                 if (!write_child(p)) {
 294                         DEBUG(3,("failed to send DNS query to child!\n"));
 295                         return False;
 296                 }
 297                 dns_current = p;
 298                 p->locked = True;
 299         } else {
 300                 p->locked = True;
 301                 p->next = dns_queue;
 302                 p->prev = NULL;
 303                 if (p->next)
 304                         p->next->prev = p;
 305                 dns_queue = p;
 306         }
 307
 308         DEBUG(3,("added DNS query for %s\n", nmb_namestr(question)));
 309         return True;
 310 }
 311
 312 #else
 313
 314
 315 /***************************************************************************
 316   we use this when we can't do async DNS lookups
 317   ****************************************************************************/
 318 BOOL queue_dns_query(struct packet_struct *p,struct nmb_name *question,
 319                      struct name_record **n)
 320 {
 321         char *qname = question->name;
 322         struct in_addr dns_ip;
 323
 324         DEBUG(3,("DNS search for %s - ", nmb_namestr(question)));
 325
 326         /* Unblock TERM signal so we can be killed in DNS lookup. */
 327         BlockSignals(False, SIGTERM);
 328
 329         dns_ip.s_addr = interpret_addr(qname);
 330
 331         /* Re-block TERM signal. */
 332         BlockSignals(True, SIGTERM);
 333
 334         *n = add_dns_result(question, dns_ip);
 335         if(*n == NULL)
 336           send_wins_name_query_response(NAM_ERR, p, NULL);
 337         else
 338           send_wins_name_query_response(0, p, *n);
 339         return False;
 340 }
 341
 342 /***************************************************************************
 343  With sync dns there is no child to kill on SIGTERM.
 344   ****************************************************************************/
 345 void kill_async_dns_child(void)
 346 {
 347   return;
 348 }
 349 #endif