release/src-rt-6.x.4708/router/vsftpd/ftpdataio.c

   1 /*
   2  * Part of Very Secure FTPd
   3  * Licence: GPL v2
   4  * Author: Chris Evans
   5  * ftpdataio.c
   6  *
   7  * Code to handle FTP data connections. This includes both PORT (server
   8  * connects) and PASV (client connects) modes of data transfer. This
   9  * includes sends and receives, files and directories.
  10  */
  11
  12 #include "ftpdataio.h"
  13 #include "session.h"
  14 #include "ftpcmdio.h"
  15 #include "ftpcodes.h"
  16 #include "utility.h"
  17 #include "tunables.h"
  18 #include "defs.h"
  19 #include "str.h"
  20 #include "strlist.h"
  21 #include "sysutil.h"
  22 #include "logging.h"
  23 #include "secbuf.h"
  24 #include "sysstr.h"
  25 #include "sysdeputil.h"
  26 #include "ascii.h"
  27 #include "oneprocess.h"
  28 #include "twoprocess.h"
  29 #include "ls.h"
  30 #include "ssl.h"
  31 #include "readwrite.h"
  32 #include "privsock.h"
  33
  34 static void init_data_sock_params(struct vsf_session* p_sess, int sock_fd);
  35 static filesize_t calc_num_send(int file_fd, filesize_t init_offset);
  36 static struct vsf_transfer_ret do_file_send_sendfile(
  37   struct vsf_session* p_sess, int net_fd, int file_fd,
  38   filesize_t curr_file_offset, filesize_t bytes_to_send);
  39 static struct vsf_transfer_ret do_file_send_rwloop(
  40   struct vsf_session* p_sess, int file_fd, int is_ascii);
  41 static struct vsf_transfer_ret do_file_recv(
  42   struct vsf_session* p_sess, int file_fd, int is_ascii);
  43 static void handle_sigalrm(void* p_private);
  44 static void start_data_alarm(struct vsf_session* p_sess);
  45 static void handle_io(int retval, int fd, void* p_private);
  46 static int transfer_dir_internal(
  47   struct vsf_session* p_sess, int is_control, struct vsf_sysutil_dir* p_dir,
  48   const struct mystr* p_base_dir_str, const struct mystr* p_option_str,
  49   const struct mystr* p_filter_str, int is_verbose);
  50 static int write_dir_list(struct vsf_session* p_sess,
  51                           struct mystr_list* p_dir_list,
  52                           enum EVSFRWTarget target);
  53 static unsigned int get_chunk_size();
  54
  55 int
  56 vsf_ftpdataio_dispose_transfer_fd(struct vsf_session* p_sess)
  57 {
  58   int dispose_ret = 1;
  59   int retval;
  60   if (p_sess->data_fd == -1)
  61   {
  62     bug("no data descriptor in vsf_ftpdataio_dispose_transfer_fd");
  63   }
  64   vsf_sysutil_uninstall_io_handler();
  65   if (p_sess->data_use_ssl && p_sess->ssl_slave_active)
  66   {
  67     char result;
  68     start_data_alarm(p_sess);
  69     priv_sock_send_cmd(p_sess->ssl_consumer_fd, PRIV_SOCK_DO_SSL_CLOSE);
  70     result = priv_sock_get_result(p_sess->ssl_consumer_fd);
  71     if (result != PRIV_SOCK_RESULT_OK)
  72     {
  73       dispose_ret = 0;
  74     }
  75   }
  76   else if (p_sess->p_data_ssl)
  77   {
  78     start_data_alarm(p_sess);
  79     dispose_ret = ssl_data_close(p_sess);
  80   }
  81   if (!p_sess->abor_received && !p_sess->data_timeout && dispose_ret == 1)
  82   {
  83     /* If we didn't get a failure, linger on the close() in order to get more
  84      * accurate transfer times.
  85      */
  86     start_data_alarm(p_sess);
  87     vsf_sysutil_activate_linger(p_sess->data_fd);
  88   }
  89   /* This close() blocks because we set SO_LINGER */
  90   retval = vsf_sysutil_close_failok(p_sess->data_fd);
  91   if (vsf_sysutil_retval_is_error(retval))
  92   {
  93     /* Do it again without blocking. */
  94     vsf_sysutil_deactivate_linger_failok(p_sess->data_fd);
  95     (void) vsf_sysutil_close_failok(p_sess->data_fd);
  96   }
  97   p_sess->data_fd = -1;
  98   if (tunable_data_connection_timeout > 0)
  99   {
 100     vsf_sysutil_clear_alarm();
 101   }
 102   if (p_sess->abor_received || p_sess->data_timeout)
 103   {
 104     dispose_ret = 0;
 105   }
 106   return dispose_ret;
 107 }
 108
 109 int
 110 vsf_ftpdataio_get_pasv_fd(struct vsf_session* p_sess)
 111 {
 112   int remote_fd;
 113   if (tunable_one_process_model)
 114   {
 115     remote_fd = vsf_one_process_get_pasv_fd(p_sess);
 116   }
 117   else
 118   {
 119     remote_fd = vsf_two_process_get_pasv_fd(p_sess);
 120   }
 121   /* Yes, yes, hardcoded bad I know. */
 122   if (remote_fd == -1)
 123   {
 124     vsf_cmdio_write(p_sess, FTP_BADSENDCONN,
 125                     "Failed to establish connection.");
 126     return remote_fd;
 127   }
 128   else if (remote_fd == -2)
 129   {
 130     vsf_cmdio_write(p_sess, FTP_BADSENDCONN, "Security: Bad IP connecting.");
 131     return -1;
 132   }
 133   init_data_sock_params(p_sess, remote_fd);
 134   return remote_fd;
 135 }
 136
 137 int
 138 vsf_ftpdataio_get_port_fd(struct vsf_session* p_sess)
 139 {
 140   int remote_fd;
 141   if (tunable_one_process_model || tunable_port_promiscuous)
 142   {
 143     remote_fd = vsf_one_process_get_priv_data_sock(p_sess);
 144   }
 145   else
 146   {
 147     remote_fd = vsf_two_process_get_priv_data_sock(p_sess);
 148   }
 149   if (vsf_sysutil_retval_is_error(remote_fd))
 150   {
 151     vsf_cmdio_write(p_sess, FTP_BADSENDCONN,
 152                     "Failed to establish connection.");
 153     return -1;
 154   }
 155   init_data_sock_params(p_sess, remote_fd);
 156   return remote_fd;
 157 }
 158
 159 int
 160 vsf_ftpdataio_post_mark_connect(struct vsf_session* p_sess)
 161 {
 162   int ret = 0;
 163   if (!p_sess->data_use_ssl)
 164   {
 165     return 1;
 166   }
 167   if (!p_sess->ssl_slave_active)
 168   {
 169     ret = ssl_accept(p_sess, p_sess->data_fd);
 170   }
 171   else
 172   {
 173     int sock_ret;
 174     priv_sock_send_cmd(p_sess->ssl_consumer_fd, PRIV_SOCK_DO_SSL_HANDSHAKE);
 175     priv_sock_send_fd(p_sess->ssl_consumer_fd, p_sess->data_fd);
 176     sock_ret = priv_sock_get_result(p_sess->ssl_consumer_fd);
 177     if (sock_ret == PRIV_SOCK_RESULT_OK)
 178     {
 179       ret = 1;
 180     }
 181   }
 182   if (ret != 1)
 183   {
 184     if (tunable_require_ssl_reuse)
 185     {
 186       vsf_cmdio_write_exit(p_sess, FTP_DATATLSBAD,
 187                            "SSL connection failed: session reuse required", 1);
 188     } else {
 189       vsf_cmdio_write(p_sess, FTP_DATATLSBAD, "SSL connection failed");
 190     }
 191   }
 192   return ret;
 193 }
 194
 195 static void
 196 handle_sigalrm(void* p_private)
 197 {
 198   struct vsf_session* p_sess = (struct vsf_session*) p_private;
 199   if (!p_sess->data_progress)
 200   {
 201     p_sess->data_timeout = 1;
 202     vsf_sysutil_shutdown_failok(p_sess->data_fd);
 203     vsf_sysutil_shutdown_read_failok(VSFTP_COMMAND_FD);
 204     vsf_sysutil_activate_noblock(VSFTP_COMMAND_FD);
 205   }
 206   else
 207   {
 208     p_sess->data_progress = 0;
 209     start_data_alarm(p_sess);
 210   }
 211 }
 212
 213 void
 214 start_data_alarm(struct vsf_session* p_sess)
 215 {
 216   if (tunable_data_connection_timeout > 0)
 217   {
 218     vsf_sysutil_install_sighandler(kVSFSysUtilSigALRM,
 219                                    handle_sigalrm,
 220                                    p_sess,
 221                                    1);
 222     vsf_sysutil_set_alarm(tunable_data_connection_timeout);
 223   }
 224   else if (tunable_idle_session_timeout > 0)
 225   {
 226     vsf_sysutil_clear_alarm();
 227   }
 228 }
 229
 230 static void
 231 init_data_sock_params(struct vsf_session* p_sess, int sock_fd)
 232 {
 233   if (p_sess->data_fd != -1)
 234   {
 235     bug("data descriptor still present in init_data_sock_params");
 236   }
 237   p_sess->data_fd = sock_fd;
 238   p_sess->data_progress = 0;
 239   vsf_sysutil_activate_keepalive(sock_fd);
 240   /* And in the vague hope it might help... */
 241   vsf_sysutil_set_iptos_throughput(sock_fd);
 242   /* Start the timeout monitor */
 243   vsf_sysutil_install_io_handler(handle_io, p_sess);
 244   start_data_alarm(p_sess);
 245 }
 246
 247 static void
 248 handle_io(int retval, int fd, void* p_private)
 249 {
 250   long curr_sec;
 251   long curr_usec;
 252   unsigned int bw_rate;
 253   double elapsed;
 254   double pause_time;
 255   double rate_ratio;
 256   struct vsf_session* p_sess = (struct vsf_session*) p_private;
 257   if (p_sess->data_fd != fd || vsf_sysutil_retval_is_error(retval) ||
 258       retval == 0)
 259   {
 260     return;
 261   }
 262   /* Note that the session hasn't stalled, i.e. don't time it out */
 263   p_sess->data_progress = 1;
 264   /* Apply bandwidth quotas via a little pause, if necessary */
 265   if (p_sess->bw_rate_max == 0)
 266   {
 267     return;
 268   }
 269   /* Calculate bandwidth rate */
 270   curr_sec = vsf_sysutil_get_time_sec();
 271   curr_usec = vsf_sysutil_get_time_usec();
 272   elapsed = (double) (curr_sec - p_sess->bw_send_start_sec);
 273   elapsed += (double) (curr_usec - p_sess->bw_send_start_usec) /
 274              (double) 1000000;
 275   if (elapsed <= (double) 0)
 276   {
 277     elapsed = (double) 0.01;
 278   }
 279   bw_rate = (unsigned int) ((double) retval / elapsed);
 280   if (bw_rate <= p_sess->bw_rate_max)
 281   {
 282     p_sess->bw_send_start_sec = curr_sec;
 283     p_sess->bw_send_start_usec = curr_usec;
 284     return;
 285   }
 286   /* Tut! Rate exceeded, calculate a pause to bring things back into line */
 287   rate_ratio = (double) bw_rate / (double) p_sess->bw_rate_max;
 288   pause_time = (rate_ratio - (double) 1) * elapsed;
 289   vsf_sysutil_sleep(pause_time);
 290   p_sess->bw_send_start_sec = vsf_sysutil_get_time_sec();
 291   p_sess->bw_send_start_usec = vsf_sysutil_get_time_usec();
 292 }
 293
 294 int
 295 vsf_ftpdataio_transfer_dir(struct vsf_session* p_sess, int is_control,
 296                            struct vsf_sysutil_dir* p_dir,
 297                            const struct mystr* p_base_dir_str,
 298                            const struct mystr* p_option_str,
 299                            const struct mystr* p_filter_str,
 300                            int is_verbose)
 301 {
 302   return transfer_dir_internal(p_sess, is_control, p_dir, p_base_dir_str,
 303                                p_option_str, p_filter_str, is_verbose);
 304 }
 305
 306 static int
 307 transfer_dir_internal(struct vsf_session* p_sess, int is_control,
 308                       struct vsf_sysutil_dir* p_dir,
 309                       const struct mystr* p_base_dir_str,
 310                       const struct mystr* p_option_str,
 311                       const struct mystr* p_filter_str,
 312                       int is_verbose)
 313 {
 314   struct mystr_list dir_list = INIT_STRLIST;
 315   struct mystr_list subdir_list = INIT_STRLIST;
 316   struct mystr dir_prefix_str = INIT_MYSTR;
 317   struct mystr_list* p_subdir_list = 0;
 318   struct str_locate_result loc_result = str_locate_char(p_option_str, 'R');
 319   int failed = 0;
 320   enum EVSFRWTarget target = kVSFRWData;
 321   if (is_control)
 322   {
 323     target = kVSFRWControl;
 324   }
 325   if (loc_result.found && tunable_ls_recurse_enable)
 326   {
 327     p_subdir_list = &subdir_list;
 328   }
 329   vsf_ls_populate_dir_list(&dir_list, p_subdir_list, p_dir, p_base_dir_str,
 330                            p_option_str, p_filter_str, is_verbose);
 331   if (p_subdir_list)
 332   {
 333     int retval;
 334     str_copy(&dir_prefix_str, p_base_dir_str);
 335     str_append_text(&dir_prefix_str, ":\r\n");
 336     retval = ftp_write_str(p_sess, &dir_prefix_str, target);
 337     if (retval != 0)
 338     {
 339       failed = 1;
 340     }
 341   }
 342   if (!failed)
 343   {
 344     failed = write_dir_list(p_sess, &dir_list, target);
 345   }
 346   /* Recurse into the subdirectories if required... */
 347   if (!failed)
 348   {
 349     struct mystr sub_str = INIT_MYSTR;
 350     unsigned int num_subdirs = str_list_get_length(&subdir_list);
 351     unsigned int subdir_index;
 352     for (subdir_index = 0; subdir_index < num_subdirs; subdir_index++)
 353     {
 354       int retval;
 355       struct vsf_sysutil_dir* p_subdir;
 356       const struct mystr* p_subdir_str =
 357         str_list_get_pstr(&subdir_list, subdir_index);
 358       if (str_equal_text(p_subdir_str, ".") ||
 359           str_equal_text(p_subdir_str, ".."))
 360       {
 361         continue;
 362       }
 363       str_copy(&sub_str, p_base_dir_str);
 364       str_append_char(&sub_str, '/');
 365       str_append_str(&sub_str, p_subdir_str);
 366       p_subdir = str_opendir(&sub_str);
 367       if (p_subdir == 0)
 368       {
 369         /* Unreadable, gone missing, etc. - no matter */
 370         continue;
 371       }
 372       str_alloc_text(&dir_prefix_str, "\r\n");
 373       retval = ftp_write_str(p_sess, &dir_prefix_str, target);
 374       if (retval != 0)
 375       {
 376         failed = 1;
 377         vsf_sysutil_closedir(p_subdir);
 378         break;
 379       }
 380       retval = transfer_dir_internal(p_sess, is_control, p_subdir, &sub_str,
 381                                      p_option_str, p_filter_str, is_verbose);
 382       vsf_sysutil_closedir(p_subdir);
 383       if (retval != 0)
 384       {
 385         failed = 1;
 386         break;
 387       }
 388     }
 389     str_free(&sub_str);
 390   }
 391   str_list_free(&dir_list);
 392   str_list_free(&subdir_list);
 393   str_free(&dir_prefix_str);
 394   if (!failed)
 395   {
 396     return 0;
 397   }
 398   else
 399   {
 400     return -1;
 401   }
 402 }
 403
 404 /* XXX - really, this should be refactored into a "buffered writer" object */
 405 static int
 406 write_dir_list(struct vsf_session* p_sess, struct mystr_list* p_dir_list,
 407                enum EVSFRWTarget target)
 408 {
 409   /* This function writes out a list of strings to the client, over the
 410    * data socket. We now coalesce the strings into fewer write() syscalls,
 411    * which saved 33% CPU time writing a large directory.
 412    */
 413   int retval = 0;
 414   unsigned int dir_index_max = str_list_get_length(p_dir_list);
 415   unsigned int dir_index;
 416   struct mystr buf_str = INIT_MYSTR;
 417   str_reserve(&buf_str, VSFTP_DIR_BUFSIZE);
 418   for (dir_index = 0; dir_index < dir_index_max; dir_index++)
 419   {
 420     str_append_str(&buf_str, str_list_get_pstr(p_dir_list, dir_index));
 421     if (dir_index == dir_index_max - 1 ||
 422         str_getlen(&buf_str) +
 423           str_getlen(str_list_get_pstr(p_dir_list, dir_index + 1)) >
 424             VSFTP_DIR_BUFSIZE)
 425     {
 426       /* Writeout needed - we're either at the end, or we filled the buffer */
 427       int writeret = ftp_write_str(p_sess, &buf_str, target);
 428       if (writeret != 0)
 429       {
 430         retval = 1;
 431         break;
 432       }
 433       str_empty(&buf_str);
 434     }
 435   }
 436   str_free(&buf_str);
 437   return retval;
 438 }
 439
 440 struct vsf_transfer_ret
 441 vsf_ftpdataio_transfer_file(struct vsf_session* p_sess, int remote_fd,
 442                             int file_fd, int is_recv, int is_ascii)
 443 {
 444   if (!is_recv)
 445   {
 446     if (is_ascii || p_sess->data_use_ssl)
 447     {
 448       return do_file_send_rwloop(p_sess, file_fd, is_ascii);
 449     }
 450     else
 451     {
 452       filesize_t curr_offset = vsf_sysutil_get_file_offset(file_fd);
 453       filesize_t num_send = calc_num_send(file_fd, curr_offset);
 454       return do_file_send_sendfile(
 455         p_sess, remote_fd, file_fd, curr_offset, num_send);
 456     }
 457   }
 458   else
 459   {
 460     return do_file_recv(p_sess, file_fd, is_ascii);
 461   }
 462 }
 463
 464 static struct vsf_transfer_ret
 465 do_file_send_rwloop(struct vsf_session* p_sess, int file_fd, int is_ascii)
 466 {
 467   static char* p_readbuf;
 468   static char* p_asciibuf;
 469   struct vsf_transfer_ret ret_struct = { 0, 0 };
 470   unsigned int chunk_size = get_chunk_size();
 471   char* p_writefrom_buf;
 472   int prev_cr = 0;
 473   if (p_readbuf == 0)
 474   {
 475     vsf_secbuf_alloc(&p_readbuf, VSFTP_DATA_BUFSIZE);
 476   }
 477   if (is_ascii)
 478   {
 479     if (p_asciibuf == 0)
 480     {
 481       /* NOTE!! * 2 factor because we can double the data by doing our ASCII
 482        * linefeed mangling
 483        */
 484       vsf_secbuf_alloc(&p_asciibuf, VSFTP_DATA_BUFSIZE * 2);
 485     }
 486     p_writefrom_buf = p_asciibuf;
 487   }
 488   else
 489   {
 490     p_writefrom_buf = p_readbuf;
 491   }
 492   while (1)
 493   {
 494     unsigned int num_to_write;
 495     int retval = vsf_sysutil_read(file_fd, p_readbuf, chunk_size);
 496     if (vsf_sysutil_retval_is_error(retval))
 497     {
 498       ret_struct.retval = -1;
 499       return ret_struct;
 500     }
 501     else if (retval == 0)
 502     {
 503       /* Success - cool */
 504       return ret_struct;
 505     }
 506     if (is_ascii)
 507     {
 508       struct bin_to_ascii_ret ret =
 509           vsf_ascii_bin_to_ascii(p_readbuf,
 510                                  p_asciibuf,
 511                                  (unsigned int) retval,
 512                                  prev_cr);
 513       num_to_write = ret.stored;
 514       prev_cr = ret.last_was_cr;
 515     }
 516     else
 517     {
 518       num_to_write = (unsigned int) retval;
 519     }
 520     retval = ftp_write_data(p_sess, p_writefrom_buf, num_to_write);
 521     if (!vsf_sysutil_retval_is_error(retval))
 522     {
 523       ret_struct.transferred += (unsigned int) retval;
 524     }
 525     if (vsf_sysutil_retval_is_error(retval) ||
 526         (unsigned int) retval != num_to_write)
 527     {
 528       ret_struct.retval = -2;
 529       return ret_struct;
 530     }
 531   }
 532 }
 533
 534 static struct vsf_transfer_ret
 535 do_file_send_sendfile(struct vsf_session* p_sess, int net_fd, int file_fd,
 536                       filesize_t curr_file_offset, filesize_t bytes_to_send)
 537 {
 538   int retval;
 539   unsigned int chunk_size = 0;
 540   struct vsf_transfer_ret ret_struct = { 0, 0 };
 541   filesize_t init_file_offset = curr_file_offset;
 542   filesize_t bytes_sent;
 543   if (p_sess->bw_rate_max)
 544   {
 545     chunk_size = get_chunk_size();
 546   }
 547   /* Just because I can ;-) */
 548   retval = vsf_sysutil_sendfile(net_fd, file_fd, &curr_file_offset,
 549                                 bytes_to_send, chunk_size);
 550   bytes_sent = curr_file_offset - init_file_offset;
 551   ret_struct.transferred = bytes_sent;
 552   if (vsf_sysutil_retval_is_error(retval))
 553   {
 554     ret_struct.retval = -2;
 555     return ret_struct;
 556   }
 557   else if (bytes_sent != bytes_to_send)
 558   {
 559     ret_struct.retval = -2;
 560     return ret_struct;
 561   }
 562   return ret_struct;
 563 }
 564
 565 static filesize_t
 566 calc_num_send(int file_fd, filesize_t init_offset)
 567 {
 568   static struct vsf_sysutil_statbuf* s_p_statbuf;
 569   filesize_t bytes_to_send;
 570   /* Work out how many bytes to send based on file size minus current offset */
 571   vsf_sysutil_fstat(file_fd, &s_p_statbuf);
 572   bytes_to_send = vsf_sysutil_statbuf_get_size(s_p_statbuf);
 573   if (init_offset < 0 || bytes_to_send < 0)
 574   {
 575     die("calc_num_send: negative file offset or send count");
 576   }
 577   /* Don't underflow if some bonehead sets a REST greater than the file size */
 578   if (init_offset > bytes_to_send)
 579   {
 580     bytes_to_send = 0;
 581   }
 582   else
 583   {
 584     bytes_to_send -= init_offset;
 585   }
 586   return bytes_to_send;
 587 }
 588
 589 static struct vsf_transfer_ret
 590 do_file_recv(struct vsf_session* p_sess, int file_fd, int is_ascii)
 591 {
 592   static char* p_recvbuf;
 593   unsigned int num_to_write;
 594   struct vsf_transfer_ret ret_struct = { 0, 0 };
 595   unsigned int chunk_size = get_chunk_size();
 596   int prev_cr = 0;
 597   if (p_recvbuf == 0)
 598   {
 599     /* Now that we do ASCII conversion properly, the plus one is to cater for
 600      * the fact we may need to stick a '\r' at the front of the buffer if the
 601      * last buffer fragment eneded in a '\r' and the current buffer fragment
 602      * does not start with a '\n'.
 603      */
 604     vsf_secbuf_alloc(&p_recvbuf, VSFTP_DATA_BUFSIZE + 1);
 605   }
 606   while (1)
 607   {
 608     const char* p_writebuf = p_recvbuf + 1;
 609     int retval = ftp_read_data(p_sess, p_recvbuf + 1, chunk_size);
 610     if (vsf_sysutil_retval_is_error(retval))
 611     {
 612       ret_struct.retval = -2;
 613       return ret_struct;
 614     }
 615     else if (retval == 0 && !prev_cr)
 616     {
 617       /* Transfer done, nifty */
 618       return ret_struct;
 619     }
 620     num_to_write = (unsigned int) retval;
 621     ret_struct.transferred += num_to_write;
 622     if (is_ascii)
 623     {
 624       /* Handle ASCII conversion if we have to. Note that using the same
 625        * buffer for source and destination is safe, because the ASCII ->
 626        * binary transform only ever results in a smaller file.
 627        */
 628       struct ascii_to_bin_ret ret =
 629         vsf_ascii_ascii_to_bin(p_recvbuf, num_to_write, prev_cr);
 630       num_to_write = ret.stored;
 631       prev_cr = ret.last_was_cr;
 632       p_writebuf = ret.p_buf;
 633     }
 634     retval = vsf_sysutil_write_loop(file_fd, p_writebuf, num_to_write);
 635     if (vsf_sysutil_retval_is_error(retval) ||
 636         (unsigned int) retval != num_to_write)
 637     {
 638       ret_struct.retval = -1;
 639       return ret_struct;
 640     }
 641   }
 642 }
 643
 644 static unsigned int
 645 get_chunk_size()
 646 {
 647   unsigned int ret = VSFTP_DATA_BUFSIZE;
 648   if (tunable_trans_chunk_size < VSFTP_DATA_BUFSIZE &&
 649       tunable_trans_chunk_size > 0)
 650   {
 651     ret = tunable_trans_chunk_size;
 652     if (ret < 4096)
 653     {
 654       ret = 4096;
 655     }
 656   }
 657   return ret;
 658 }
 659