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