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

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