uftps.c

   1 /*
   2  * User FTP Server
   3  * Author : C2H5OH
   4  * License: GPL v2
   5  *
   6  * uftps.c - main
   7  *
   8  * Main program. Opens the command port until a client requests a connection.
   9  * Then the server is forked the child will manage all that client's requests.
  10  *
  11  * Attending multiple clients is necessary to allow some clients (like lftp(1))
  12  * perform multiple concurrent jops. Like moving current transfer to de
  13  * background and then browse through directories.
  14  *
  15  * Also note that here the root directory is fixed. As we can't protect with
  16  * chroot(), due to de lack of privilege, we must do a series of safety checks
  17  * to simulate that behaviour. Because of this, some strong restrictions have
  18  * arised; which could reduce de number of FTP clients compatible with this
  19  * server.
  20  */
  21
  22 #include "uftps.h"
  23
  24 /*
  25  * clid_finish
  26  *
  27  * Reaper function. For "zombies".
  28  */
  29 static void child_finish (int sig)
  30 {
  31         while (waitpid(-1, NULL, WNOHANG) > 0)
  32                 debug_msg("- Collecting children.\n");
  33 }
  34
  35
  36 /*
  37  * end
  38  *
  39  * End. What where you expecting?
  40  */
  41 static void end (int sig)
  42 {
  43         printf("(%d) Signal caught, exiting...\n", getpid());
  44         exit(EXIT_SUCCESS);
  45 }
  46
  47
  48 /***   MAIN   ***/
  49 int main (int argc, char **argv)
  50 {
  51         int                bind_sk, cmd_sk, err, yes = 1;
  52         unsigned short     port = 0;
  53         struct sockaddr_in saddr;
  54         struct sigaction   my_sa;
  55
  56         setlinebuf(stderr);
  57         setlinebuf(stdout);
  58
  59         if (argc > 1)
  60                 port = (unsigned short) atoi(argv[1]);
  61
  62         /* Fixate root directory */
  63         Basedir = getcwd(NULL, 0);
  64         if (Basedir == NULL)
  65                 fatal("Could not retrieve working directory");
  66         Basedir_len = strlen(Basedir);
  67         debug_msg("Working directory is: %s (strlen = %d)\n", Basedir,
  68                   Basedir_len);
  69
  70         /* Signal handling */
  71         sigfillset(&my_sa.sa_mask);
  72         my_sa.sa_flags   = SA_RESTART;
  73         my_sa.sa_handler = child_finish;
  74         sigaction(SIGCHLD, &my_sa, NULL);
  75
  76         my_sa.sa_flags   = SA_NOMASK;
  77         my_sa.sa_handler = end;
  78         sigaction(SIGINT, &my_sa, NULL);
  79
  80         /* Connection handling */
  81         saddr.sin_family = AF_INET;
  82         saddr.sin_port   = htons(port > 1024 ? port : DEFAULT_PORT);
  83         saddr.sin_addr.s_addr = INADDR_ANY;
  84
  85         bind_sk = socket(PF_INET, SOCK_STREAM, 0);
  86         if (bind_sk == -1)
  87                 fatal("Could not create socket");
  88
  89         setsockopt(bind_sk, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes));
  90         err = bind(bind_sk, (struct sockaddr *) &saddr, sizeof(saddr));
  91         if (err == -1)
  92                 fatal("Could not bind socket");
  93
  94         err = listen(bind_sk, 5);
  95         if (err == -1)
  96                 fatal("Could not listen at socket");
  97
  98         printf("UFTPS listening on port %d (TCP). Use CTRL+C to finish.\n\n",
  99                (port > 1024 ? port : DEFAULT_PORT));
 100         printf("If you want to use a different port use:\n"
 101                "\t%s <port>\n\n"
 102                "Where port must be between 1025 and 65535.\n", argv[0]);
 103
 104 #if 0
 105         /* It's nearly impossible, to my knowledge, debug a program that forks.
 106          * First try to find the error using the debug_msg() facility. Then, if
 107          * you really need to use a debugger, then replace the 0 with a 1 to
 108          * compile this code. But remember you won't be able to serve multiple
 109          * connections */
 110
 111         cmd_sk = accept(bind_sk, (struct sockaddr *) &saddr,
 112                           (socklen_t *) &yes);
 113         if (cmd_sk == -1)
 114                 fatal("could not open command connection");
 115
 116         init_session(cmd_sk);
 117         command_loop();
 118         return EXIT_SUCCESS;
 119 #endif
 120
 121         /* Main loop (accepting connections) */
 122         while (1) {
 123                 cmd_sk = accept(bind_sk, (struct sockaddr *) &saddr,
 124                                   (socklen_t *) &yes);
 125                 if (cmd_sk == -1) {
 126                         if (errno == EINTR)
 127                                 continue;
 128                         else
 129                                 fatal("Could not open command connection");
 130                 }
 131                 if (fork() == 0) {
 132                         /* Child */
 133                         close(bind_sk);
 134                         init_session(cmd_sk);
 135                         command_loop();
 136                 } else {
 137                         /* Parent */
 138                         close(cmd_sk);
 139                 }
 140         }
 141         return EXIT_SUCCESS;
 142 }
 143