mdw@git.distorted.org.uk Git - fwd/blob - privconn.c

   1 /* -*-c-*-
   2  *
   3  * $Id: privconn.c,v 1.2 2003/11/29 20:43:01 mdw Exp $
   4  *
   5  * Making privileged connections
   6  *
   7  * (c) 2003 Straylight/Edgeware
   8  */
   9
  10 /*----- Licensing notice --------------------------------------------------*
  11  *
  12  * This file is part of the `fw' port forwarder.
  13  *
  14  * `fw' is free software; you can redistribute it and/or modify
  15  * it under the terms of the GNU General Public License as published by
  16  * the Free Software Foundation; either version 2 of the License, or
  17  * (at your option) any later version.
  18  *
  19  * `fw' is distributed in the hope that it will be useful,
  20  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  21  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  22  * GNU General Public License for more details.
  23  *
  24  * You should have received a copy of the GNU General Public License
  25  * along with `fw'; if not, write to the Free Software Foundation,
  26  * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  27  */
  28
  29 /*----- Revision history --------------------------------------------------*
  30  *
  31  * $Log: privconn.c,v $
  32  * Revision 1.2  2003/11/29 20:43:01  mdw
  33  * Don't do priv separation if no priv connections to make.
  34  *
  35  * Revision 1.1  2003/11/29 20:36:07  mdw
  36  * Privileged outgoing connections.
  37  *
  38  */
  39
  40 /*----- Header files ------------------------------------------------------*/
  41
  42 #include <assert.h>
  43 #include <errno.h>
  44 #include <signal.h>
  45 #include <string.h>
  46
  47 #include <sys/types.h>
  48 #include <unistd.h>
  49
  50 #include <sys/socket.h>
  51 #include <arpa/inet.h>
  52 #include <netinet/in.h>
  53
  54 #include <mLib/conn.h>
  55 #include <mLib/darray.h>
  56 #include <mLib/fdflags.h>
  57 #include <mLib/fdpass.h>
  58 #include <mLib/report.h>
  59 #include <mLib/sel.h>
  60
  61 #include "privconn.h"
  62
  63 /*----- Data structures ---------------------------------------------------*/
  64
  65 typedef struct connrec {
  66   struct in_addr peer;
  67   unsigned port;
  68 } connrec;
  69
  70 typedef struct connrq {
  71   int i;
  72   struct in_addr bind;
  73 } connrq;
  74
  75 DA_DECL(connrec_v, connrec);
  76
  77 /*----- Static variables --------------------------------------------------*/
  78
  79 static connrec_v cv = DA_INIT;
  80 static conn *qhead = 0, **qtail = &qhead;
  81 static int kidfd = -1;
  82 static sel_file sf;
  83
  84 /*----- Main code ---------------------------------------------------------*/
  85
  86 /* --- @doconn@ --- *
  87  *
  88  * Arguments:   @const connrq *rq@ = index of connection record
  89  *
  90  * Returns:     Connected file descriptor, or @-1@.
  91  *
  92  * Use:         Main privileged connection thing.
  93  */
  94
  95 static int doconn(const connrq *rq)
  96 {
  97   struct sockaddr_in sin_bind;
  98   struct sockaddr_in sin_peer;
  99   int fd;
 100   int i;
 101   connrec *c;
 102
 103   /* --- Check the argument --- */
 104
 105   if (rq->i < 0 || rq->i >= DA_LEN(&cv)) {
 106     errno = EINVAL;
 107     goto fail_0;
 108   }
 109   c = &DA(&cv)[rq->i];
 110
 111   /* --- Make a new socket --- */
 112
 113   if ((fd = socket(PF_INET, SOCK_STREAM, 0)) < 0)
 114     goto fail_0;
 115
 116   /* --- Bind it to a low-numbered port --- */
 117
 118   memset(&sin_bind, 0, sizeof(sin_bind));
 119   sin_bind.sin_family = AF_INET;
 120   sin_bind.sin_addr = rq->bind;
 121   for (i = 1023; i >= 512; i--) {
 122     sin_bind.sin_port = htons(i);
 123     if (!bind(fd, (struct sockaddr *)&sin_bind, sizeof(sin_bind)))
 124       goto bound;
 125     if (errno != EADDRINUSE)
 126       goto fail_1;
 127   }
 128   goto fail_1;
 129
 130   /* --- Connect to the peer --- *
 131    *
 132    * We can find out whether it's connected later, so there's no need to
 133    * distinguish these cases.
 134    */
 135
 136 bound:
 137   memset(&sin_peer, 0, sizeof(sin_peer));
 138   sin_peer.sin_family = AF_INET;
 139   sin_peer.sin_addr = c->peer;
 140   sin_peer.sin_port = c->port;
 141   fdflags(fd, O_NONBLOCK, O_NONBLOCK, 0, 0);
 142   if (connect(fd, (struct sockaddr *)&sin_peer, sizeof(sin_peer)) < 0 &&
 143       errno != EINPROGRESS)
 144     goto fail_1;
 145   return (fd);
 146
 147   /* --- Tidy up on errors --- */
 148
 149 fail_1:
 150   close(fd);
 151 fail_0:
 152   return (-1);
 153 }
 154
 155 /* --- @dochild@ --- *
 156  *
 157  * Arguments:   @int fd@ = my file descriptor
 158  *
 159  * Returns:     Never.
 160  *
 161  * Use:         Child process for making privileged connections, separated
 162  *              from main process after initialization.
 163  */
 164
 165 static void dochild(int fd)
 166 {
 167   int i;
 168   connrq rq;
 169   int nfd;
 170   ssize_t sz;
 171 #if defined(_SC_OPEN_MAX)
 172   int maxfd = sysconf(_SC_OPEN_MAX);
 173 #elif defined(OPEN_MAX)
 174   int maxfd = OPEN_MAX;
 175 #else
 176   int maxfd = -1;
 177 #endif
 178   struct sigaction sa;
 179   struct sigaction sa_dfl;
 180
 181   /* --- Clear out unnecessary file descriptors --- */
 182
 183   if (maxfd < 0)
 184     maxfd = 256;
 185   for (i = 3; i < maxfd; i++)
 186     if (i != fd) close(i);
 187
 188   /* --- Close off signal handlers --- */
 189
 190   sa_dfl.sa_handler = SIG_DFL;
 191   sigemptyset(&sa_dfl.sa_mask);
 192   sa_dfl.sa_flags = 0;
 193   for (i = 0; i < 256; i++) {
 194     if (sigaction(i, 0, &sa))
 195       break;
 196     if (sa.sa_handler != SIG_DFL && sa.sa_handler != SIG_IGN)
 197       sigaction(i, &sa_dfl, 0);
 198   }
 199
 200   /* --- Main loop --- */
 201
 202   for (;;) {
 203     sz = read(fd, &rq, sizeof(rq));
 204     if (!sz)
 205       break;
 206     if (sz < 0)
 207       die(1, "read error in privconn child: %s", strerror(errno));
 208     if ((nfd = doconn(&rq)) < 0)
 209       goto err;
 210     i = 0;
 211     sz = fdpass_send(fd, nfd, &i, sizeof(i));
 212     if (sz < 0)
 213       goto err;
 214     if (sz < sizeof(i))
 215       die(1, "short write in privconn child");
 216     continue;
 217
 218   err:
 219     if (write(fd, &errno, sizeof(errno)) < 0)
 220       die(1, "write error in privconn child: %s", strerror(errno));
 221   }
 222   _exit(0);
 223 }
 224
 225 /* --- @dorecvfd@ --- *
 226  *
 227  * Arguments:   @int fd@ = file descriptor (@== kidfd@)
 228  *              @unsigned mode@ = what's happening (@== SEL_READ@)
 229  *              @void *p@ = uninteresting (@== 0@)
 230  *
 231  * Returns:     ---
 232  *
 233  * Use:         Receives a file descriptor from the privileged part.
 234  */
 235
 236 void dorecvfd(int fd, unsigned mode, void *p)
 237 {
 238   conn *c, *cc;
 239   ssize_t n;
 240   int e;
 241
 242   n = fdpass_recv(kidfd, &fd, &e, sizeof(e));
 243   if (!n)
 244     goto close;
 245   assert(qhead);
 246   c = qhead;
 247   qhead = (conn *)c->writer.next;
 248   if (!qhead) qtail = &qhead;
 249   if (n < 0 || (errno = e) != 0)
 250     goto fail;
 251   if (fd == -1) {
 252     errno = EIO;
 253     goto fail;
 254   }
 255   conn_fd(c, c->writer.s, fd, c->func, c->p);
 256   return;
 257
 258 fail:
 259   c->func(-1, c->p);
 260   return;
 261
 262 close:
 263   close(kidfd);
 264   kidfd = 0;
 265   errno = EIO;
 266   sel_rmfile(&sf);
 267   for (c = qhead; c; c = cc) {
 268     cc = (conn *)c->writer.next;
 269     c->func(-1, c->p);
 270   }
 271   qhead = 0;
 272   qtail = &qhead;
 273   return;
 274 }
 275
 276 /* --- @privconn_split@ --- *
 277  *
 278  * Arguments:   @sel_state *s@ = select state
 279  *
 280  * Returns:     ---
 281  *
 282  * Use:         Splits off the privileged binding code into a separate
 283  *              process.
 284  */
 285
 286 void privconn_split(sel_state *s)
 287 {
 288   pid_t kid;
 289   int fd[2];
 290
 291   if (kidfd != -1 || DA_LEN(&cv) == 0)
 292     return;
 293   if (socketpair(PF_UNIX, SOCK_STREAM, 0, fd) < 0)
 294     die(1, "couldn't create privconn socketpair: %s", strerror(errno));
 295   kidfd = fd[0];
 296   if ((kid = fork()) < 0)
 297     die(1, "couldn't fork privconn child: %s", strerror(errno));
 298   if (!kid) {
 299     close(kidfd);
 300     dochild(fd[1]);
 301     _exit(127);
 302   }
 303   close(fd[1]);
 304   fdflags(kidfd, 0, 0, FD_CLOEXEC, FD_CLOEXEC);
 305   sel_initfile(s, &sf, kidfd, SEL_READ, dorecvfd, 0);
 306   sel_addfile(&sf);
 307 }
 308
 309 /* --- @privconn_adddest@ --- *
 310  *
 311  * Arguments:   @struct in_addr peer@ = address to connect to
 312  *              @unsigned port@ = port to connect to
 313  *
 314  * Returns:     Index for this destination address, or @-1@ if not
 315  *              available.
 316  *
 317  * Use:         Adds a valid destination for a privileged connection.
 318  */
 319
 320 int privconn_adddest(struct in_addr peer, unsigned port)
 321 {
 322   int i;
 323   struct connrec *c;
 324
 325   if (kidfd != -1)
 326     return (-1);
 327   for (i = 0; i < DA_LEN(&cv); i++) {
 328     c = &DA(&cv)[i];
 329     if (peer.s_addr == c->peer.s_addr && port == c->port)
 330       return (i);
 331   }
 332   DA_ENSURE(&cv, 1);
 333   DA_EXTEND(&cv, 1);
 334   c = &DA(&cv)[i];
 335   c->peer = peer;
 336   c->port = port;
 337   return (i);
 338 }
 339
 340 /* --- @privconn_connect@ --- *
 341  *
 342  * Arguments:   @conn *c@ = connection structure to fill in
 343  *              @sel_state *s@ = pointer to select state to attach to
 344  *              @int i@ = address index to connect to
 345  *              @struct in_addr bind@ = address to bind to
 346  *              @void (*func)(int, void *)@ = function to call on connect
 347  *              @void *p@ = argument for the function
 348  *
 349  * Returns:     Zero on success, @-1@ on failure.
 350  *
 351  * Use:         Sets up a privileged connection job.
 352  */
 353
 354 int privconn_connect(conn *c, sel_state *s, int i, struct in_addr bind,
 355                      void (*func)(int, void *), void *p)
 356 {
 357   int fd;
 358   connrq rq;
 359   ssize_t n;
 360
 361   rq.i = i;
 362   rq.bind = bind;
 363   if (kidfd == -1) {
 364     if ((fd = doconn(&rq)) < 0)
 365       return (-1);
 366     conn_fd(c, s, fd, func, p);
 367     return (0);
 368   }
 369
 370   n = write(kidfd, &rq, sizeof(rq));
 371   if (n < 0)
 372     return (-1);
 373   c->writer.fd = -1;
 374   c->writer.s = s;
 375   c->writer.next = 0;
 376   c->func = func;
 377   c->p = p;
 378   *qtail = c;
 379   qtail = (conn **)&c->writer.next;
 380   return (0);
 381 }
 382
 383 /*----- That's all, folks -------------------------------------------------*/