enable_passive.c

   1 /*
   2  * User FTP Server,  Share folders over FTP without being root.
   3  * Copyright (C) 2008  Isaac Jurado
   4  *
   5  * This program is free software; you can redistribute it and/or modify it under
   6  * the terms of the GNU General Public License as published by the Free Software
   7  * Foundation; either version 2 of the License, or (at your option) any later
   8  * version.
   9  *
  10  * This program is distributed in the hope that it will be useful, but WITHOUT
  11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
  12  * FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
  13  * details.
  14  *
  15  * You should have received a copy of the GNU General Public License along with
  16  * this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
  18  */
  19
  20 #include "uftps.h"
  21 #ifdef __MINGW32__
  22 #  include "hase.h"
  23 #else
  24 #  include <sys/socket.h>
  25 #  include <arpa/inet.h>
  26 #  include <unistd.h>
  27 #endif
  28 #include <string.h>
  29 #include <stdio.h>
  30
  31
  32 /*
  33  * PASV command implementation.  Nothing else to mention here, read the FTP RFC
  34  * if you don't know about data transmission in passive mode.
  35  */
  36 void enable_passive (void)
  37 {
  38         int                 bsk, l, e;
  39         struct sockaddr_in  sai;
  40         socklen_t           sai_len = sizeof(struct sockaddr_in);
  41         unsigned char       addr[6];
  42         char                pasv_reply[32];
  43
  44         /* Safety check in case there was some error before */
  45         if (SS.passive_sk != -1)
  46         {
  47                 closesocket(SS.passive_sk);
  48                 SS.passive_sk = -1;
  49                 SS.mode       = DEFAULT_MODE;
  50         }
  51
  52         bsk = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
  53         if (bsk == -1)
  54         {
  55                 error("Creating passive socket");
  56                 goto out_error;
  57         }
  58         e = 1;
  59         setsockopt(bsk, SOL_SOCKET, SO_REUSEADDR, CCP_CAST &e, sizeof(int));
  60
  61         /* In case there are various network interfaces, bind only to the one
  62          * the client is connected to; and use port 0 to let the system choose
  63          * one for us */
  64         sai_len = sizeof(struct sockaddr_in);
  65         memcpy(&sai, &SS.local_address, sai_len);
  66         sai.sin_port = 0;
  67         e = bind(bsk, (struct sockaddr *) &sai, sai_len);
  68         if (e == -1)
  69         {
  70                 error("Binding to a random port");
  71                 goto out_error;
  72         }
  73         e = listen(bsk, 1);
  74         if (e == -1)
  75         {
  76                 error("Listening on passive socket");
  77                 goto out_error;
  78         }
  79
  80         /* Check what port number we were assigned */
  81         e = getsockname(bsk, (struct sockaddr *) &sai, &sai_len);
  82         if (e == -1)
  83         {
  84                 error("Retrieving passive socket information");
  85                 goto out_error;
  86         }
  87         debug("Passive mode listening on port %d", ntohs(sai.sin_port));
  88
  89         /* String conversion is straightforward in IPv4, provided that all
  90          * fields in sockaddr_in structures are in network byte order */
  91         memcpy(&addr[0], &sai.sin_addr, 4);
  92         memcpy(&addr[4], &sai.sin_port, 2);
  93         l = snprintf(pasv_reply, 32, "227 =%u,%u,%u,%u,%u,%u\r\n", addr[0],
  94                      addr[1], addr[2], addr[3], addr[4], addr[5]);
  95
  96         SS.passive_sk = bsk;
  97         SS.mode       = PASSIVE_MODE;
  98         reply(pasv_reply, l);
  99         return;
 100
 101 out_error:
 102         closesocket(bsk); /* bsk could be -1; never mind, only produces EBADF */
 103         reply_c("425 No way to open a port.\r\n");
 104 }
 105