init_session.c

   1 /*
   2  * User FTP Server
   3  * Autor  : C2H5OH
   4  * License: GPL v2
   5  *
   6  * init_session.c - Preparing to serve one client.
   7  */
   8
   9 #include "uftps.h"
  10
  11 #define ERR_FINISH_MSG "421 Cannot attend you now, sorry.\r\n"
  12
  13 /*
  14  * get_random_port
  15  *
  16  * Returns a random non-privileged port, range 1025..65536
  17  */
  18 static inline unsigned short get_random_port (void)
  19 {
  20         unsigned char  byte;
  21         unsigned short port;
  22
  23         port   = 0x0000U;
  24         byte   = (unsigned char) rand();
  25         port  |= byte;
  26         port <<= 8;
  27         byte   = (unsigned char) rand();
  28         port  |= byte;
  29         if (port < 1024)
  30                 port += 1024;
  31         return port;
  32 }
  33
  34
  35 void init_session (int cmd_sk)
  36 {
  37         unsigned short     port;
  38         int                err, i, sk;
  39         struct sockaddr_in saddr;
  40         socklen_t          saddr_len;
  41         char               address[16];
  42
  43         /* Get my own IP. As the server is listening to all network interfaces,
  44          * we won't know the real IP until we are connected to someone */
  45         saddr_len = (socklen_t) sizeof(saddr);
  46         err = getsockname(cmd_sk, (struct sockaddr *) &saddr, &saddr_len);
  47         if (err == -1) {
  48                 send_reply(cmd_sk, ERR_FINISH_MSG);
  49                 fatal("trying to get my own address");
  50         }
  51
  52         debug_msg("* Local address: %s\n", inet_ntoa(saddr.sin_addr));
  53
  54         /* Create a data socket to use in passive mode. This socket is cached
  55          * and only one of these sockets is created per client. Thus, the
  56          * response to PASV is easier (and, maybe, quicker) */
  57         sk = socket(PF_INET, SOCK_STREAM, 0);
  58         if (sk == -1) {
  59                 send_reply(cmd_sk, ERR_FINISH_MSG);
  60                 fatal("Could not create data socket");
  61         }
  62
  63         /* 9 random tries to get an available port */
  64         i   = 1;
  65         err = -1;
  66         setsockopt(sk, SOL_SOCKET, SO_REUSEADDR, &i, sizeof (i));
  67         srand((unsigned int) times (NULL));
  68         for (i = 9; i > 0 && err == -1; i--) {
  69                 port = get_random_port();
  70                 saddr.sin_port = htons(port);
  71                 err = bind(sk, (struct sockaddr *) &saddr, saddr_len);
  72         }
  73         if (i <= 0) {
  74                 send_reply(cmd_sk, ERR_FINISH_MSG);
  75                 fatal("Could not find any bindable port");
  76         }
  77
  78         debug_msg("* Number of bind() tries for PASV port: %d\n", 9 - i);
  79
  80         err = listen(sk, 1);
  81         if (err == -1) {
  82                 send_reply(cmd_sk, ERR_FINISH_MSG);
  83                 fatal("cannot listen on port");
  84         }
  85
  86         /* As de passive socket is cached, we can do the same for the PASV
  87          * response string */
  88         strncpy(address, inet_ntoa(saddr.sin_addr), 16);
  89         for (i = 0; i < 16; i++) {
  90                 if (address[i] == '.')
  91                         address[i] = ',';
  92         }
  93         snprintf(S_passive_str, 64,
  94                  "227 Entering Passive Mode (%s,%d,%d).\r\n", address,
  95                  port >> 8, port & 0x00FF);
  96
  97         debug_msg("* Passive data port: %d\n",  port);
  98         debug_msg("* Passive string reply: %s", S_passive_str);
  99
 100         /* Set up the rest of the session state variables, except for Basedir
 101          * which is inherited from uftps.c */
 102         S_cmd_sk          = cmd_sk;
 103         S_data_sk         = -1;
 104         S_offset          = 0;
 105         S_passive_bind_sk = sk;
 106         S_passive_mode    = 0;
 107
 108         send_reply(cmd_sk, "220 User FTP Server ready.\r\n");
 109 }
 110