uftps.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 <sys/wait.h>
  22 #include <signal.h>
  23 #include <unistd.h>
  24 #include <stdlib.h>
  25 #include <stdio.h>
  26
  27 struct _SessionScope  SS;  /* SS --> Session State*/
  28
  29
  30 /*
  31  * clid_finish
  32  *
  33  * Reaper function.  For "zombies".
  34  */
  35 static void child_finish (int sig)
  36 {
  37         while (waitpid(-1, NULL, WNOHANG) > 0)
  38                 debug("Collecting children");
  39 }
  40
  41
  42 /*
  43  * end
  44  *
  45  * End. What where you expecting?
  46  */
  47 static void end (int sig)
  48 {
  49         notice("Signal caught, exiting");
  50         exit(EXIT_SUCCESS);
  51 }
  52
  53
  54 /*
  55  * Main program.  Opens the command port until a client requests a connection.
  56  * Then the server is forked the child will manage all that client's requests.
  57  *
  58  * Attending multiple clients is necessary to allow some clients (like lftp(1))
  59  * perform multiple concurrent jops.  Like moving current transfer to de
  60  * background and then browse through directories.
  61  *
  62  * Also note that here the root directory is fixed.  As we can't protect with
  63  * chroot(), due to de lack of privilege, we must do a series of safety checks
  64  * to simulate that behaviour.  Because of this, some strong restrictions have
  65  * arised; which could reduce de number of FTP clients compatible with this
  66  * server.
  67  */
  68
  69 int main (int argc, char **argv)
  70 {
  71         int                 bind_sk, cmd_sk, e, yes;
  72         int                 port = DEFAULT_PORT;
  73         struct sigaction    my_sa;
  74         struct sockaddr_in  sai;
  75         socklen_t           sai_len = sizeof(struct sockaddr_in);
  76
  77         setlinebuf(stdout);
  78
  79         if (argc > 1)
  80         {
  81                 port = atoi(argv[1]) & 0x00FFFF;
  82                 if (port <= 1024)
  83                         fatal("This port number is restricted");
  84         }
  85
  86         /* Signal handling */
  87         sigfillset(&my_sa.sa_mask);
  88         my_sa.sa_flags   = SA_RESTART;
  89         my_sa.sa_handler = child_finish;
  90         sigaction(SIGCHLD, &my_sa, NULL);
  91
  92         my_sa.sa_flags   = SA_NOMASK;
  93         my_sa.sa_handler = end;
  94         sigaction(SIGINT, &my_sa, NULL);
  95
  96         /* Connection handling */
  97         sai.sin_family      = AF_INET;
  98         sai.sin_port        = htons(port);
  99         sai.sin_addr.s_addr = INADDR_ANY;
 100
 101         bind_sk = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
 102         if (bind_sk == -1)
 103                 fatal("Creating main server socket");
 104
 105         yes = 1;
 106         setsockopt(bind_sk, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes));
 107         e = bind(bind_sk, (struct sockaddr *) &sai, sai_len);
 108         if (e == -1)
 109                 fatal("Binding main server socket");
 110
 111         e = listen(bind_sk, 5);
 112         if (e == -1)
 113                 fatal("Listening at main server socket");
 114
 115         notice("UFTPS listening on port %d (TCP)", port);
 116         notice("Use CTRL + C to finish");
 117         notice("If you want to use a different port, specify it as the only argument in the command line");
 118
 119         /* Main server loop (accepting connections) */
 120         do {
 121                 sai_len = sizeof(struct sockaddr_in);
 122                 cmd_sk  = accept(bind_sk, (struct sockaddr *) &sai, &sai_len);
 123                 if (cmd_sk == -1)
 124                 {
 125                         error("Accepting incoming connection");
 126                         continue;
 127                 }
 128
 129                 e = fork();
 130                 if (e == 0)
 131                 {
 132                         /***  CHILD  ***/
 133                         e = close(bind_sk);
 134                         if (e == -1)
 135                                 error("Closing server socket from child");
 136
 137                         init_session(cmd_sk);
 138                         command_loop();
 139                 }
 140                 else
 141                 {
 142                         /***  PARENT  ***/
 143                         if (e == -1)
 144                                 error("Could not create a child process");
 145
 146                         e = close(cmd_sk);
 147                         if (e == -1)
 148                                 error("Closing control channel %d from parent",
 149                                       cmd_sk);
 150                 }
 151         } while (1);
 152
 153         return EXIT_SUCCESS;
 154 }
 155