open_data_channel.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 #ifndef __MINGW32__
  22 #  include <sys/socket.h>
  23 #  include <arpa/inet.h>
  24 #  include <unistd.h>
  25 #endif
  26
  27
  28 /*
  29  * Open a data channel in passive mode.  Return the socket of the data channel
  30  * if successful, -1 on any failure.
  31  */
  32 static int passive_connection (void)
  33 {
  34         int                 sk, e;
  35         struct sockaddr_in  sai;
  36         socklen_t           sai_len = sizeof(struct sockaddr_in);
  37
  38         sk = accept(SS.passive_sk, NULL, NULL);
  39
  40         /* Passive socket not needed anymore */
  41         closesocket(SS.passive_sk);
  42         SS.passive_sk = -1;
  43
  44         if (sk == -1)
  45                 return -1;
  46
  47         /* Check if this new connection comes from the same IP as the client */
  48         e = getpeername(sk, (struct sockaddr *) &sai, &sai_len);
  49         if (e == -1 || sai.sin_addr.s_addr != SS.client_address.sin_addr.s_addr)
  50         {
  51                 if (e == -1)
  52                         error("Getting remote data socket address");
  53                 else
  54                         warning("A different client (%s) connected to a passive socket",
  55                                 inet_ntoa(sai.sin_addr));
  56                 closesocket(sk);
  57                 return -1;
  58         }
  59
  60         return sk;
  61 }
  62
  63
  64 /*
  65  * Open a data channel in active mode.  Return the socket of the data channel if
  66  * successful, -1 on any failure.
  67  *
  68  * Note that peer IP check is not needed here because it was performed directly
  69  * on the PORT request.
  70  */
  71 static int active_connection (void)
  72 {
  73         int  sk, e;
  74
  75         sk = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
  76         if (sk == -1)
  77                 return -1;
  78
  79         e = connect(sk, (struct sockaddr *) &SS.port_destination,
  80                     sizeof(struct sockaddr_in));
  81         if (e == -1)
  82         {
  83                 error("Initiating active data connection");
  84                 closesocket(sk);
  85                 return -1;
  86         }
  87
  88         return sk;
  89 }
  90
  91
  92 /*
  93  * Open the data channel.  When successful, the "data_sk" session field is set
  94  * to the data channel socket and zero is returned.  If the connection
  95  * establishment fails, -1 is returned and the client is notified.
  96  */
  97 int open_data_channel (void)
  98 {
  99         int  sk;
 100
 101         switch (SS.mode)
 102         {
 103         case ACTIVE_MODE:
 104                 sk = active_connection();
 105                 break;
 106         case PASSIVE_MODE:
 107                 sk = passive_connection();
 108                 break;
 109         case DEFAULT_MODE:
 110         default:
 111                 warning("No data transfer mode selected");
 112                 reply_c("425 Default data transfer mode unsupported.\r\n");
 113                 return -1;
 114         }
 115
 116         SS.mode = DEFAULT_MODE;
 117
 118         if (sk == -1)
 119         {
 120                 error("Opening data connection");
 121                 reply_c("425 Can't open data connection.\r\n");
 122                 return -1;
 123         }
 124
 125         SS.data_sk = sk;
 126         return 0;
 127 }
 128