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 #include <arpa/inet.h>
  22 #include <unistd.h>
  23 #include <string.h>
  24 #include <stdio.h>
  25
  26
  27 /*
  28  * PASV command implementation.  Nothing else to mention here, read the FTP RFC
  29  * if you don't know about data transmission in passive mode.
  30  */
  31 void enable_passive (void)
  32 {
  33         int                 bsk, l, e;
  34         struct sockaddr_in  sai;
  35         socklen_t           sai_len = sizeof(struct sockaddr_in);
  36         unsigned char       addr[6];
  37         char                pasv_reply[32];
  38
  39         /* Safety check in case there was some error before */
  40         if (SS.passive_sk != -1)
  41         {
  42                 close(SS.passive_sk);
  43                 SS.passive_sk = -1;
  44                 SS.mode       = DEFAULT_MODE;
  45         }
  46
  47         bsk = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
  48         if (bsk == -1)
  49         {
  50                 error("Creating passive socket");
  51                 goto out_error;
  52         }
  53         e = 1;
  54         setsockopt(bsk, SOL_SOCKET, SO_REUSEADDR, &e, sizeof(int));
  55
  56         /* In case there are various network interfaces, bind only to the one
  57          * the client is connected to; and use port 0 to let the system choose
  58          * one for us */
  59         sai_len = sizeof(struct sockaddr_in);
  60         memcpy(&sai, &SS.local_address, sizeof(struct sockaddr_in));
  61         sai.sin_port = 0;
  62         e = bind(bsk, (struct sockaddr *) &sai, sai_len);
  63         if (e == -1)
  64         {
  65                 error("Binding to a random port");
  66                 goto out_error;
  67         }
  68         e = listen(bsk, 1);
  69         if (e == -1)
  70         {
  71                 error("Listening on passive socket");
  72                 goto out_error;
  73         }
  74
  75         /* Check what port number we were assigned */
  76         e = getsockname(bsk, (struct sockaddr *) &sai, &sai_len);
  77         if (e == -1)
  78         {
  79                 error("Retrieving passive socket information");
  80                 goto out_error;
  81         }
  82         debug("Passive mode listening on port %d", ntohs(sai.sin_port));
  83
  84         /* String conversion is straightforward in IPv4, provided that all
  85          * fields in sockaddr_in structures are in network byte order */
  86         memcpy(&addr[0], &sai.sin_addr, 4);
  87         memcpy(&addr[4], &sai.sin_port, 2);
  88         l = snprintf(pasv_reply, 32, "227 =%u,%u,%u,%u,%u,%u\r\n", addr[0],
  89                      addr[1], addr[2], addr[3], addr[4], addr[5]);
  90
  91         SS.passive_sk = bsk;
  92         SS.mode       = PASSIVE_MODE;
  93         reply(pasv_reply, l);
  94         return;
  95
  96 out_error:
  97         close(bsk);  /* bsk could be -1; never mind, only produces EBADF */
  98         reply_c("425 No way to open a port.\r\n");
  99 }
 100