This patch was provided by Maciej Pyszka, mpyszka {at} rekord {dot}
com {dot} pl.  It has been placed in the public domain.

It adds another option to sftpd, -u<N>, which specifies which data
port to bind when initiating active (PORT command) transfers.

To apply this patch:
  % cd sftpd-1.46
  % patch < bind-specified-active-port.txt
  % make distclean
  % ./configure && make
  (then copy the new binaries over the old ones)


diff -c sftpd-1.46/sftpd.cpp mpsafetp/sftpd.cpp
*** sftpd-1.46/sftpd.cpp	Wed Nov 22 15:44:55 2000
--- mpsafetp/sftpd.cpp	Tue Nov  6 14:54:15 2001
***************
*** 159,164 ****
--- 159,166 ----
  // if that member doesn't actually need an initialization
  SFTPD::SFTPD() :
    // ------ socket state ------
+ // UOF
+   ourDataPort(8100),
    useStdinStream(false),
    client_control(INVALID_SOCKET),
    clientControlStream(NULL),
***************
*** 398,404 ****
              artificialDelay = atoi(argString);
              break;

!           case 's':          // stdin stream
              useStdinStream = true;
              break;

--- 400,411 ----
              artificialDelay = atoi(argString);
              break;

! 	  //UOF
!           case 'u':
!             ourDataPort = atoi(argString);
!             break;
!
! 	  case 's':          // stdin stream
              useStdinStream = true;
              break;

***************
*** 584,589 ****
--- 591,597 ----
          "    -f<ADDR>:<N>   contact ftpd at another host (ADDR) and port N;\n"
          "                     (this is potentially INSECURE -- see sftpd.html)\n"
          "  data channel:\n"
+         "    -u<N>          port number server tries to bind for data channel (default: 8100)\n"
          "    -c             require all data transfers to be encrypted\n"
          "    -r<low>-<high> restrict ports used for PASV to range [low,high]\n"
          "  logging:\n"
***************
*** 897,903 ****
          diagnostic("received connection from ftpd, trying to connect to client");
          relayDataConnection(
            server_listen, server_data,
!           relayClientAddress, relayClientPort, client_data);
        }

        // --- client connects to me ---
--- 905,911 ----
          diagnostic("received connection from ftpd, trying to connect to client");
          relayDataConnection(
            server_listen, server_data,
!           relayClientAddress, relayClientPort, client_data, ourDataPort);
        }

        // --- client connects to me ---
***************
*** 1100,1106 ****
  //   peerB_data     - socket to connect to other peer, "B"
  bool SFTPD::relayDataConnection(
    SOCKET &peerA_listen, SOCKET &peerA_data,
!   IPAddress addrB, int portB, SOCKET &peerB_data)
  {
    // for errors and diagnostics, we need to determine
    // who is client and who is server
--- 1109,1115 ----
  //   peerB_data     - socket to connect to other peer, "B"
  bool SFTPD::relayDataConnection(
    SOCKET &peerA_listen, SOCKET &peerA_data,
!   IPAddress addrB, int portB, SOCKET &peerB_data, int ourport)
  {
    // for errors and diagnostics, we need to determine
    // who is client and who is server
***************
*** 1125,1131 ****
      diagnostic("trying to connect to " << B <<
                 " at " << formatAddress(addrB) <<
                 ", port " << portB);
!     peerB_data = connect_socket(addrB, portB);
      addEntropy();
    }

--- 1134,1140 ----
      diagnostic("trying to connect to " << B <<
                 " at " << formatAddress(addrB) <<
                 ", port " << portB);
!     peerB_data = connect_socket(addrB, portB, ourport);
      addEntropy();
    }

Only in sftpd-1.46: sftpd.dsp
diff -c sftpd-1.46/sftpd.h mpsafetp/sftpd.h
*** sftpd-1.46/sftpd.h	Wed Nov 22 15:44:55 2000
--- mpsafetp/sftpd.h	Tue Nov  6 12:35:40 2001
***************
*** 54,59 ****
--- 54,61 ----

  private:      // data
    // ------ socket state ------
+   // UOF - our port for data
+   int ourDataPort;
    // control connection to the client
    bool useStdinStream;                     // true if client_control is stdin
    SOCKET client_control;                   // send, select
***************
*** 235,241 ****
    // and connect to the other
    bool relayDataConnection(
      SOCKET &peerA_listen, SOCKET &peerA_data,
!     IPAddress addrB, int portB, SOCKET &peerB_data);

    // copy data from one socket to another, until no more is waiting
    void relaySocketData(SOCKET &dest, SOCKET &src);
--- 237,243 ----
    // and connect to the other
    bool relayDataConnection(
      SOCKET &peerA_listen, SOCKET &peerA_data,
!     IPAddress addrB, int portB, SOCKET &peerB_data, int ourport=0);

    // copy data from one socket to another, until no more is waiting
    void relaySocketData(SOCKET &dest, SOCKET &src);
diff -c sftpd-1.46/sockutil.cpp mpsafetp/sockutil.cpp
*** sftpd-1.46/sockutil.cpp	Wed Nov 22 15:44:55 2000
--- mpsafetp/sockutil.cpp	Tue Nov  6 14:58:13 2001
***************
*** 502,508 ****
  
  
  // initiate a connection
! SOCKET connect_socket(IPAddress ipaddr, int port)
  {
    // create address structure
    sockaddr_in saddr;      // address of receiver
--- 502,508 ----
  
  
  // initiate a connection
! SOCKET connect_socket(IPAddress ipaddr, int port, int ourport)
  {
    // create address structure
    sockaddr_in saddr;      // address of receiver
***************
*** 518,523 ****
--- 518,545 ----
    }
    incOpenSockets();
  
+   //UOF
+   if( ourport && ( s != INVALID_SOCKET ) ) {
+     int buffer,i;
+     
+     buffer=1;
+     i=sizeof( int );
+     
+     setsockopt( s, SOL_SOCKET, SO_REUSEADDR, (char *)&buffer, i); 
+  	  
+     sockaddr_in ouraddr;
+     memset((char *)&ouraddr, 0, sizeof( ouraddr));
+     ouraddr.sin_family = AF_INET;
+     ouraddr.sin_port = htons((short)ourport);
+     ouraddr.sin_addr.s_addr = htonl(INADDR_ANY);
+     
+     int ourp = ourport;
+     while( bind( s, (sockaddr *)&ouraddr, sizeof(ouraddr))) {
+       ourp++;	    
+       ouraddr.sin_port = htons((short)ourp);
+     }  
+   }
+   
    // connect the socket to the resolved address and port (sockaddr)
    if (connect(s, (sockaddr *)&saddr, sizeof(saddr))
         == SOCKET_ERROR) {
diff -c sftpd-1.46/sockutil.h mpsafetp/sockutil.h
*** sftpd-1.46/sockutil.h	Wed Nov 22 15:44:55 2000
--- mpsafetp/sockutil.h	Tue Nov  6 12:22:10 2001
***************
*** 186,192 ****
  SOCKET accept_socket(SOCKET s);
    // accept a connection on the given listening socket

! SOCKET connect_socket(IPAddress ipaddr, int port);
    // create a socket and connect it to a remote host/port

  void close_socket(SOCKET s);
--- 186,192 ----
  SOCKET accept_socket(SOCKET s);
    // accept a connection on the given listening socket

! SOCKET connect_socket(IPAddress ipaddr, int port, int ourport=0);
    // create a socket and connect it to a remote host/port

  void close_socket(SOCKET s);