source: trunk/server/source4/libcli/resolve/dns_ex.c

/*
   Unix SMB/CIFS implementation.

   async getaddrinfo()/dns_lookup() name resolution module

   Copyright (C) Andrew Tridgell 2005
   Copyright (C) Stefan Metzmacher 2008

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

/*
  this module uses a fork() per getaddrinfo() or dns_looup() call.
  At first that might seem crazy, but it is actually very fast,
  and solves many of the tricky problems of keeping a child
  hanging around in a librar (like what happens when the parent forks).
  We use a talloc destructor to ensure that the child is cleaned up
  when we have finished with this name resolution.
*/

#include "includes.h"
#include "lib/events/events.h"
#include "system/network.h"
#include "system/filesys.h"
#include "lib/socket/socket.h"
#include "libcli/composite/composite.h"
#include "librpc/gen_ndr/ndr_nbt.h"
#include "libcli/resolve/resolve.h"

#ifdef class
#undef class
#endif

#include "heimdal/lib/roken/resolve.h"

struct dns_ex_state {
        bool do_fallback;
        uint32_t flags;
        uint16_t port;
        struct nbt_name name;
        struct socket_address **addrs;
        char **names;
        pid_t child;
        int child_fd;
        struct tevent_fd *fde;
        struct tevent_context *event_ctx;
};

/*
  kill off a wayward child if needed. This allows us to stop an async
  name resolution without leaving a potentially blocking call running
  in a child
*/
static int dns_ex_destructor(struct dns_ex_state *state)
{
        int status;

        kill(state->child, SIGTERM);
        if (waitpid(state->child, &status, WNOHANG) == 0) {
                kill(state->child, SIGKILL);
                waitpid(state->child, &status, 0);
        }

        return 0;
}

/*
  the blocking child
*/
static void run_child_dns_lookup(struct dns_ex_state *state, int fd)
{
        struct rk_dns_reply *reply;
        struct rk_resource_record *rr;
        uint32_t count = 0;
        uint32_t srv_valid = 0;
        struct rk_resource_record **srv_rr;
        uint32_t addrs_valid = 0;
        struct rk_resource_record **addrs_rr;
        char *addrs;
        bool first;
        uint32_t i;
        bool do_srv = (state->flags & RESOLVE_NAME_FLAG_DNS_SRV);

        if (strchr(state->name.name, '.') && state->name.name[strlen(state->name.name)-1] != '.') {
                /* we are asking for a fully qualified name, but the
                   name doesn't end in a '.'. We need to prevent the
                   DNS library trying the search domains configured in
                   resolv.conf */
                state->name.name = talloc_strdup_append(discard_const_p(char, state->name.name),
                                                        ".");
        }

        /* this is the blocking call we are going to lots of trouble
           to avoid in the parent */
        reply = rk_dns_lookup(state->name.name, do_srv?"SRV":"A");
        if (!reply) {
                goto done;
        }

        if (do_srv) {
                rk_dns_srv_order(reply);
        }

        /* Loop over all returned records and pick the "srv" records */
        for (rr=reply->head; rr; rr=rr->next) {
                /* we are only interested in the IN class */
                if (rr->class != rk_ns_c_in) {
                        continue;
                }

                if (do_srv) {
                        /* we are only interested in SRV records */
                        if (rr->type != rk_ns_t_srv) {
                                continue;
                        }

                        /* verify we actually have a SRV record here */
                        if (!rr->u.srv) {
                                continue;
                        }

                        /* Verify we got a port */
                        if (rr->u.srv->port == 0) {
                                continue;
                        }
                } else {
                        /* we are only interested in A records */
                        /* TODO: add AAAA support */
                        if (rr->type != rk_ns_t_a) {
                                continue;
                        }

                        /* verify we actually have a A record here */
                        if (!rr->u.a) {
                                continue;
                        }
                }
                count++;
        }

        if (count == 0) {
                goto done;
        }

        srv_rr = talloc_zero_array(state,
                                   struct rk_resource_record *,
                                   count);
        if (!srv_rr) {
                goto done;
        }

        addrs_rr = talloc_zero_array(state,
                                     struct rk_resource_record *,
                                     count);
        if (!addrs_rr) {
                goto done;
        }

        /* Loop over all returned records and pick the records */
        for (rr=reply->head;rr;rr=rr->next) {
                /* we are only interested in the IN class */
                if (rr->class != rk_ns_c_in) {
                        continue;
                }

                if (do_srv) {
                        /* we are only interested in SRV records */
                        if (rr->type != rk_ns_t_srv) {
                                continue;
                        }

                        /* verify we actually have a srv record here */
                        if (!rr->u.srv) {
                                continue;
                        }

                        /* Verify we got a port */
                        if (rr->u.srv->port == 0) {
                                continue;
                        }

                        srv_rr[srv_valid] = rr;
                        srv_valid++;
                } else {
                        /* we are only interested in A records */
                        /* TODO: add AAAA support */
                        if (rr->type != rk_ns_t_a) {
                                continue;
                        }

                        /* verify we actually have a A record here */
                        if (!rr->u.a) {
                                continue;
                        }

                        addrs_rr[addrs_valid] = rr;
                        addrs_valid++;
                }
        }

        for (i=0; i < srv_valid; i++) {
                for (rr=reply->head;rr;rr=rr->next) {

                        if (rr->class != rk_ns_c_in) {
                                continue;
                        }

                        /* we are only interested in A records */
                        if (rr->type != rk_ns_t_a) {
                                continue;
                        }

                        /* verify we actually have a srv record here */
                        if (strcmp(&srv_rr[i]->u.srv->target[0], rr->domain) != 0) {
                                continue;
                        }

                        addrs_rr[i] = rr;
                        addrs_valid++;
                        break;
                }
        }

        if (addrs_valid == 0) {
                goto done;
        }

        addrs = talloc_strdup(state, "");
        if (!addrs) {
                goto done;
        }
        first = true;
        for (i=0; i < count; i++) {
                uint16_t port;
                if (!addrs_rr[i]) {
                        continue;
                }

                if (srv_rr[i] &&
                    (state->flags & RESOLVE_NAME_FLAG_OVERWRITE_PORT)) {
                        port = srv_rr[i]->u.srv->port;
                } else {
                        port = state->port;
                }

                addrs = talloc_asprintf_append_buffer(addrs, "%s%s:%u/%s",
                                                      first?"":",",
                                                      inet_ntoa(*addrs_rr[i]->u.a),
                                                      port,
                                                      addrs_rr[i]->domain);
                if (!addrs) {
                        goto done;
                }
                first = false;
        }

        if (addrs) {
                write(fd, addrs, talloc_get_size(addrs));
        }

done:
        close(fd);
}

/*
  the blocking child
*/
static void run_child_getaddrinfo(struct dns_ex_state *state, int fd)
{
        int ret;
        struct addrinfo hints;
        struct addrinfo *res;
        struct addrinfo *res_list = NULL;
        char *addrs;
        bool first;

        ZERO_STRUCT(hints);
        hints.ai_socktype = SOCK_STREAM;
        hints.ai_family = AF_INET;/* TODO: add AF_INET6 support */
        hints.ai_flags = AI_ADDRCONFIG | AI_NUMERICSERV;

        ret = getaddrinfo(state->name.name, "0", &hints, &res_list);
        /* try to fallback in case of error */
        if (state->do_fallback) {
                switch (ret) {
#ifdef EAI_NODATA
                case EAI_NODATA:
#endif
                case EAI_NONAME:
                        /* getaddrinfo() doesn't handle CNAME records */
                        run_child_dns_lookup(state, fd);
                        return;
                default:
                        break;
                }
        }
        if (ret != 0) {
                goto done;
        }

        addrs = talloc_strdup(state, "");
        if (!addrs) {
                goto done;
        }
        first = true;
        for (res = res_list; res; res = res->ai_next) {
                struct sockaddr_in *in;

                if (res->ai_family != AF_INET) {
                        continue;
                }
                in = (struct sockaddr_in *)res->ai_addr;

                addrs = talloc_asprintf_append_buffer(addrs, "%s%s:%u/%s",
                                                      first?"":",",
                                                      inet_ntoa(in->sin_addr),
                                                      state->port,
                                                      state->name.name);
                if (!addrs) {
                        goto done;
                }
                first = false;
        }

        if (addrs) {
                write(fd, addrs, talloc_get_size(addrs));
        }
done:
        if (res_list) {
                freeaddrinfo(res_list);
        }
        close(fd);
}

/*
  handle a read event on the pipe
*/
static void pipe_handler(struct tevent_context *ev, struct tevent_fd *fde, 
                         uint16_t flags, void *private_data)
{
        struct composite_context *c = talloc_get_type(private_data, struct composite_context);
        struct dns_ex_state *state = talloc_get_type(c->private_data,
                                     struct dns_ex_state);
        char *address;
        uint32_t num_addrs, i;
        char **addrs;
        int ret;
        int status;
        int value = 0;

        /* if we get any event from the child then we know that we
           won't need to kill it off */
        talloc_set_destructor(state, NULL);

        if (ioctl(state->child_fd, FIONREAD, &value) != 0) {
                value = 8192;
        }

        address = talloc_array(state, char, value+1);
        if (address) {
                /* yes, we don't care about EAGAIN or other niceities
                   here. They just can't happen with this parent/child
                   relationship, and even if they did then giving an error is
                   the right thing to do */
                ret = read(state->child_fd, address, value);
        } else {
                ret = -1;
        }
        if (waitpid(state->child, &status, WNOHANG) == 0) {
                kill(state->child, SIGKILL);
                waitpid(state->child, &status, 0);
        }

        if (ret <= 0) {
                DEBUG(3,("dns child failed to find name '%s' of type %s\n",
                         state->name.name, (state->flags & RESOLVE_NAME_FLAG_DNS_SRV)?"SRV":"A"));
                composite_error(c, NT_STATUS_OBJECT_NAME_NOT_FOUND);
                return;
        }

        /* enusre the address looks good */
        address[ret] = 0;

        addrs = str_list_make(state, address, ",");
        if (composite_nomem(addrs, c)) return;

        num_addrs = str_list_length((const char * const *)addrs);

        state->addrs = talloc_array(state, struct socket_address *,
                                    num_addrs+1);
        if (composite_nomem(state->addrs, c)) return;

        state->names = talloc_array(state, char *, num_addrs+1);
        if (composite_nomem(state->names, c)) return;

        for (i=0; i < num_addrs; i++) {
                uint32_t port = 0;
                char *p = strrchr(addrs[i], ':');
                char *n;

                if (!p) {
                        composite_error(c, NT_STATUS_OBJECT_NAME_NOT_FOUND);
                        return;
                }

                *p = '\0';
                p++;

                n = strrchr(p, '/');
                if (!n) {
                        composite_error(c, NT_STATUS_OBJECT_NAME_NOT_FOUND);
                        return;
                }

                *n = '\0';
                n++;

                if (strcmp(addrs[i], "0.0.0.0") == 0 ||
                    inet_addr(addrs[i]) == INADDR_NONE) {
                        composite_error(c, NT_STATUS_OBJECT_NAME_NOT_FOUND);
                        return;
                }
                port = strtoul(p, NULL, 10);
                if (port > UINT16_MAX) {
                        composite_error(c, NT_STATUS_OBJECT_NAME_NOT_FOUND);
                        return;
                }
                state->addrs[i] = socket_address_from_strings(state->addrs,
                                                              "ipv4",
                                                              addrs[i],
                                                              port);
                if (composite_nomem(state->addrs[i], c)) return;

                state->names[i] = talloc_strdup(state->names, n);
                if (composite_nomem(state->names[i], c)) return;
        }
        state->addrs[i] = NULL;
        state->names[i] = NULL;

        composite_done(c);
}

/*
  getaddrinfo() or dns_lookup() name resolution method - async send
 */
struct composite_context *resolve_name_dns_ex_send(TALLOC_CTX *mem_ctx,
                                                   struct tevent_context *event_ctx,
                                                   void *privdata,
                                                   uint32_t flags,
                                                   uint16_t port,
                                                   struct nbt_name *name,
                                                   bool do_fallback)
{
        struct composite_context *c;
        struct dns_ex_state *state;
        int fd[2] = { -1, -1 };
        int ret;

        c = composite_create(mem_ctx, event_ctx);
        if (c == NULL) return NULL;

        if (flags & RESOLVE_NAME_FLAG_FORCE_NBT) {
                composite_error(c, NT_STATUS_OBJECT_NAME_NOT_FOUND);
                return c;
        }

        state = talloc_zero(c, struct dns_ex_state);
        if (composite_nomem(state, c)) return c;
        c->private_data = state;

        c->status = nbt_name_dup(state, name, &state->name);
        if (!composite_is_ok(c)) return c;

        /* setup a pipe to chat to our child */
        ret = pipe(fd);
        if (ret == -1) {
                composite_error(c, map_nt_error_from_unix(errno));
                return c;
        }

        state->do_fallback = do_fallback;
        state->flags = flags;
        state->port = port;

        state->child_fd = fd[0];
        state->event_ctx = c->event_ctx;

        /* we need to put the child in our event context so
           we know when the dns_lookup() has finished */
        state->fde = event_add_fd(c->event_ctx, c, state->child_fd, EVENT_FD_READ, 
                                  pipe_handler, c);
        if (composite_nomem(state->fde, c)) {
                close(fd[0]);
                close(fd[1]);
                return c;
        }
        tevent_fd_set_auto_close(state->fde);

        state->child = fork();
        if (state->child == (pid_t)-1) {
                composite_error(c, map_nt_error_from_unix(errno));
                return c;
        }

        if (state->child == 0) {
                close(fd[0]);
                if (state->flags & RESOLVE_NAME_FLAG_FORCE_DNS) {
                        run_child_dns_lookup(state, fd[1]);
                } else {
                        run_child_getaddrinfo(state, fd[1]);
                }
                _exit(0);
        }
        close(fd[1]);

        /* cleanup wayward children */
        talloc_set_destructor(state, dns_ex_destructor);

        return c;
}

/*
  getaddrinfo() or dns_lookup() name resolution method - recv side
*/
NTSTATUS resolve_name_dns_ex_recv(struct composite_context *c, 
                                  TALLOC_CTX *mem_ctx,
                                  struct socket_address ***addrs,
                                  char ***names)
{
        NTSTATUS status;

        status = composite_wait(c);

        if (NT_STATUS_IS_OK(status)) {
                struct dns_ex_state *state = talloc_get_type(c->private_data,
                                             struct dns_ex_state);
                *addrs = talloc_steal(mem_ctx, state->addrs);
                if (names) {
                        *names = talloc_steal(mem_ctx, state->names);
                }
        }

        talloc_free(c);
        return status;
}