source4/libcli/resolve/host.c

   1 /*
   2    Unix SMB/CIFS implementation.
   3
   4    async gethostbyname() name resolution module
   5
   6    Copyright (C) Andrew Tridgell 2005
   7
   8    This program is free software; you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 2 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program; if not, write to the Free Software
  20    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  21 */
  22
  23 /*
  24   this module uses a fork() per gethostbyname() call. At first that
  25   might seem crazy, but it is actually very fast, and solves many of
  26   the tricky problems of keeping a child hanging around in a library
  27   (like what happens when the parent forks). We use a talloc
  28   destructor to ensure that the child is cleaned up when we have
  29   finished with this name resolution.
  30 */
  31
  32 #include "includes.h"
  33 #include "lib/events/events.h"
  34 #include "system/network.h"
  35 #include "system/filesys.h"
  36 #include "libcli/composite/composite.h"
  37 #include "librpc/gen_ndr/ndr_nbt.h"
  38
  39 struct host_state {
  40         struct nbt_name name;
  41         const char *reply_addr;
  42         pid_t child;
  43         int child_fd;
  44         struct fd_event *fde;
  45         struct event_context *event_ctx;
  46 };
  47
  48
  49 /*
  50   kill off a wayward child if needed. This allows us to stop an async
  51   name resolution without leaving a potentially blocking call running
  52   in a child
  53 */
  54 static int host_destructor(struct host_state *state)
  55 {
  56         close(state->child_fd);
  57         if (state->child != (pid_t)-1) {
  58                 kill(state->child, SIGTERM);
  59         }
  60         return 0;
  61 }
  62
  63 /*
  64   the blocking child
  65 */
  66 static void run_child(struct composite_context *c, int fd)
  67 {
  68         struct host_state *state = talloc_get_type(c->private_data, struct host_state);
  69         struct ipv4_addr ip;
  70         const char *address;
  71
  72         /* this is the blocking call we are going to lots of trouble
  73            to avoid in the parent */
  74         ip = interpret_addr2(state->name.name);
  75
  76         address = sys_inet_ntoa(ip);
  77         if (address != NULL) {
  78                 write(fd, address, strlen(address)+1);
  79         }
  80         close(fd);
  81 }
  82
  83 /*
  84   handle a read event on the pipe
  85 */
  86 static void pipe_handler(struct event_context *ev, struct fd_event *fde,
  87                          uint16_t flags, void *private_data)
  88 {
  89         struct composite_context *c = talloc_get_type(private_data, struct composite_context);
  90         struct host_state *state = talloc_get_type(c->private_data, struct host_state);
  91         char address[128];
  92         int ret;
  93
  94         /* if we get any event from the child then we know that we
  95            won't need to kill it off */
  96         state->child = (pid_t)-1;
  97
  98         /* yes, we don't care about EAGAIN or other niceities
  99            here. They just can't happen with this parent/child
 100            relationship, and even if they did then giving an error is
 101            the right thing to do */
 102         ret = read(state->child_fd, address, sizeof(address)-1);
 103         if (ret <= 0) {
 104                 composite_error(c, NT_STATUS_OBJECT_NAME_NOT_FOUND);
 105                 return;
 106         }
 107
 108         /* enusre the address looks good */
 109         address[ret] = 0;
 110         if (strcmp(address, "0.0.0.0") == 0 ||
 111             inet_addr(address) == INADDR_NONE) {
 112                 composite_error(c, NT_STATUS_OBJECT_NAME_NOT_FOUND);
 113                 return;
 114         }
 115
 116         state->reply_addr = talloc_strdup(state, address);
 117         if (composite_nomem(state->reply_addr, c)) return;
 118
 119         composite_done(c);
 120 }
 121
 122 /*
 123   gethostbyname name resolution method - async send
 124  */
 125 struct composite_context *resolve_name_host_send(TALLOC_CTX *mem_ctx,
 126                                                  struct event_context *event_ctx,
 127                                                  struct nbt_name *name)
 128 {
 129         struct composite_context *c;
 130         struct host_state *state;
 131         int fd[2] = { -1, -1 };
 132         int ret;
 133
 134         c = composite_create(mem_ctx, event_ctx);
 135         if (c == NULL) return NULL;
 136
 137         c->event_ctx = talloc_reference(c, event_ctx);
 138         if (composite_nomem(c->event_ctx, c)) return c;
 139
 140         state = talloc(c, struct host_state);
 141         if (composite_nomem(state, c)) return c;
 142         c->private_data = state;
 143
 144         c->status = nbt_name_dup(state, name, &state->name);
 145         if (!composite_is_ok(c)) return c;
 146
 147         /* setup a pipe to chat to our child */
 148         ret = pipe(fd);
 149         if (ret == -1) {
 150                 composite_error(c, map_nt_error_from_unix(errno));
 151                 return c;
 152         }
 153
 154         state->child_fd = fd[0];
 155         state->event_ctx = c->event_ctx;
 156
 157         /* we need to put the child in our event context so
 158            we know when the gethostbyname() has finished */
 159         state->fde = event_add_fd(c->event_ctx, c, state->child_fd, EVENT_FD_READ,
 160                                   pipe_handler, c);
 161         if (composite_nomem(state->fde, c)) {
 162                 close(fd[0]);
 163                 close(fd[1]);
 164                 return c;
 165         }
 166
 167         /* signal handling in posix really sucks - doing this in a library
 168            affects the whole app, but what else to do?? */
 169         signal(SIGCHLD, SIG_IGN);
 170
 171         state->child = fork();
 172         if (state->child == (pid_t)-1) {
 173                 composite_error(c, map_nt_error_from_unix(errno));
 174                 return c;
 175         }
 176
 177
 178         if (state->child == 0) {
 179                 close(fd[0]);
 180                 run_child(c, fd[1]);
 181                 _exit(0);
 182         }
 183         close(fd[1]);
 184
 185         /* cleanup wayward children */
 186         talloc_set_destructor(state, host_destructor);
 187
 188         return c;
 189 }
 190
 191 /*
 192   gethostbyname name resolution method - recv side
 193 */
 194 NTSTATUS resolve_name_host_recv(struct composite_context *c,
 195                                 TALLOC_CTX *mem_ctx, const char **reply_addr)
 196 {
 197         NTSTATUS status;
 198
 199         status = composite_wait(c);
 200
 201         if (NT_STATUS_IS_OK(status)) {
 202                 struct host_state *state = talloc_get_type(c->private_data, struct host_state);
 203                 *reply_addr = talloc_steal(mem_ctx, state->reply_addr);
 204         }
 205
 206         talloc_free(c);
 207         return status;
 208 }
 209
 210 /*
 211   gethostbyname name resolution method - sync call
 212  */
 213 NTSTATUS resolve_name_host(struct nbt_name *name,
 214                             TALLOC_CTX *mem_ctx,
 215                             const char **reply_addr)
 216 {
 217         struct composite_context *c = resolve_name_host_send(mem_ctx, NULL, name);
 218         return resolve_name_host_recv(c, mem_ctx, reply_addr);
 219 }
 220