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portfwd.c

/*
 * SSH port forwarding.
 */

#include <stdio.h>
#include <stdlib.h>

#include "putty.h"
#include "ssh.h"

#ifndef FALSE
#define FALSE 0
#endif
#ifndef TRUE
#define TRUE 1
#endif

struct PFwdPrivate {
    const struct plug_function_table *fn;
    /* the above variable absolutely *must* be the first in this structure */
    void *c;                         /* (channel) data used by ssh.c */
    void *backhandle;                /* instance of SSH backend itself */
    /* Note that backhandle need not be filled in if c is non-NULL */
    Socket s;
    int throttled, throttle_override;
    int ready;
    /*
     * `dynamic' does double duty. It's set to 0 for an ordinary
     * forwarded port, and nonzero for SOCKS-style dynamic port
     * forwarding; but it also represents the state of the SOCKS
     * exchange.
     */
    int dynamic;
    /*
     * `hostname' and `port' are the real hostname and port, once
     * we know what we're connecting to; they're unused for this
     * purpose while conducting a local SOCKS exchange, which means
     * we can also use them as a buffer and pointer for reading
     * data from the SOCKS client.
     */
    char hostname[256+8];
    int port;
    /*
     * When doing dynamic port forwarding, we can receive
     * connection data before we are actually able to send it; so
     * we may have to temporarily hold some in a dynamically
     * allocated buffer here.
     */
    void *buffer;
    int buflen;
};

static void pfd_log(Plug plug, int type, SockAddr addr, int port,
                const char *error_msg, int error_code)
{
    /* we have to dump these since we have no interface to logging.c */
}

static int pfd_closing(Plug plug, const char *error_msg, int error_code,
                   int calling_back)
{
    struct PFwdPrivate *pr = (struct PFwdPrivate *) plug;

    /*
     * We have no way to communicate down the forwarded connection,
     * so if an error occurred on the socket, we just ignore it
     * and treat it like a proper close.
     */
    if (pr->c)
      sshfwd_close(pr->c);
    pfd_close(pr->s);
    return 1;
}

static int pfd_receive(Plug plug, int urgent, char *data, int len)
{
    struct PFwdPrivate *pr = (struct PFwdPrivate *) plug;
    if (pr->dynamic) {
      while (len--) {
          /*
           * Throughout SOCKS negotiation, "hostname" is re-used as a
           * random protocol buffer with "port" storing the length.
           */ 
          if (pr->port >= lenof(pr->hostname)) {
            /* Request too long. */
            if ((pr->dynamic >> 12) == 4) {
                /* Send back a SOCKS 4 error before closing. */
                char data[8];
                memset(data, 0, sizeof(data));
                data[1] = 91;      /* generic `request rejected' */
                sk_write(pr->s, data, 8);
            }
            pfd_close(pr->s);
            return 1;
          }
          pr->hostname[pr->port++] = *data++;

          /*
           * Now check what's in the buffer to see if it's a
           * valid and complete message in the SOCKS exchange.
           */
          if ((pr->dynamic == 1 || (pr->dynamic >> 12) == 4) &&
            pr->hostname[0] == 4) {
            /*
             * SOCKS 4.
             */
            if (pr->dynamic == 1)
                pr->dynamic = 0x4000;
            if (pr->port < 2) continue;/* don't have command code yet */
            if (pr->hostname[1] != 1) {
                /* Not CONNECT. */
                /* Send back a SOCKS 4 error before closing. */
                char data[8];
                memset(data, 0, sizeof(data));
                data[1] = 91;      /* generic `request rejected' */
                sk_write(pr->s, data, 8);
                pfd_close(pr->s);
                return 1;
            }
            if (pr->port <= 8) continue; /* haven't started user/hostname */
            if (pr->hostname[pr->port-1] != 0)
                continue;            /* haven't _finished_ user/hostname */
            /*
             * Now we have a full SOCKS 4 request. Check it to
             * see if it's a SOCKS 4A request.
             */
            if (pr->hostname[4] == 0 && pr->hostname[5] == 0 &&
                pr->hostname[6] == 0 && pr->hostname[7] != 0) {
                /*
                 * It's SOCKS 4A. So if we haven't yet
                 * collected the host name, we should continue
                 * waiting for data in order to do so; if we
                 * have, we can go ahead.
                 */
                int len;
                if (pr->dynamic == 0x4000) {
                  pr->dynamic = 0x4001;
                  pr->port = 8;      /* reset buffer to overwrite name */
                  continue;
                }
                pr->hostname[0] = 0;   /* reply version code */
                pr->hostname[1] = 90;   /* request granted */
                sk_write(pr->s, pr->hostname, 8);
                len= pr->port - 8;
                pr->port = GET_16BIT_MSB_FIRST(pr->hostname+2);
                memmove(pr->hostname, pr->hostname + 8, len);
                goto connect;
            } else {
                /*
                 * It's SOCKS 4, which means we should format
                 * the IP address into the hostname string and
                 * then just go.
                 */
                pr->hostname[0] = 0;   /* reply version code */
                pr->hostname[1] = 90;   /* request granted */
                sk_write(pr->s, pr->hostname, 8);
                pr->port = GET_16BIT_MSB_FIRST(pr->hostname+2);
                sprintf(pr->hostname, "%d.%d.%d.%d",
                      (unsigned char)pr->hostname[4],
                      (unsigned char)pr->hostname[5],
                      (unsigned char)pr->hostname[6],
                      (unsigned char)pr->hostname[7]);
                goto connect;
            }
          }

          if ((pr->dynamic == 1 || (pr->dynamic >> 12) == 5) &&
            pr->hostname[0] == 5) {
            /*
             * SOCKS 5.
             */
            if (pr->dynamic == 1)
                pr->dynamic = 0x5000;

            if (pr->dynamic == 0x5000) {
                int i, method;
                char data[2];
                /*
                 * We're receiving a set of method identifiers.
                 */
                if (pr->port < 2) continue;/* no method count yet */
                if (pr->port < 2 + (unsigned char)pr->hostname[1])
                  continue;      /* no methods yet */
                method = 0xFF;     /* invalid */
                for (i = 0; i < (unsigned char)pr->hostname[1]; i++)
                  if (pr->hostname[2+i] == 0) {
                      method = 0;/* no auth */
                      break;
                  }
                data[0] = 5;
                data[1] = method;
                sk_write(pr->s, data, 2);
                pr->dynamic = 0x5001;
                pr->port = 0;      /* re-empty the buffer */
                continue;
            }

            if (pr->dynamic == 0x5001) {
                /*
                 * We're receiving a SOCKS request.
                 */
                unsigned char reply[10]; /* SOCKS5 atyp=1 reply */
                int atype, alen = 0;

                /*
                 * Pre-fill reply packet.
                 * In all cases, we set BND.{HOST,ADDR} to 0.0.0.0:0
                 * (atyp=1) in the reply; if we succeed, we don't know
                 * the right answers, and if we fail, they should be
                 * ignored.
                 */
                memset(reply, 0, lenof(reply));
                reply[0] = 5; /* VER */
                reply[3] = 1; /* ATYP = 1 (IPv4, 0.0.0.0:0) */

                if (pr->port < 6) continue;
                atype = (unsigned char)pr->hostname[3];
                if (atype == 1)    /* IPv4 address */
                  alen = 4;
                if (atype == 4)    /* IPv6 address */
                  alen = 16;
                if (atype == 3)    /* domain name has leading length */
                  alen = 1 + (unsigned char)pr->hostname[4];
                if (pr->port < 6 + alen) continue;
                if (pr->hostname[1] != 1 || pr->hostname[2] != 0) {
                  /* Not CONNECT or reserved field nonzero - error */
                  reply[1] = 1;     /* generic failure */
                  sk_write(pr->s, (char *) reply, lenof(reply));
                  pfd_close(pr->s);
                  return 1;
                }
                /*
                 * Now we have a viable connect request. Switch
                 * on atype.
                 */
                pr->port = GET_16BIT_MSB_FIRST(pr->hostname+4+alen);
                if (atype == 1) {
                  /* REP=0 (success) already */
                  sk_write(pr->s, (char *) reply, lenof(reply));
                  sprintf(pr->hostname, "%d.%d.%d.%d",
                        (unsigned char)pr->hostname[4],
                        (unsigned char)pr->hostname[5],
                        (unsigned char)pr->hostname[6],
                        (unsigned char)pr->hostname[7]);
                  goto connect;
                } else if (atype == 3) {
                  /* REP=0 (success) already */
                  sk_write(pr->s, (char *) reply, lenof(reply));
                  memmove(pr->hostname, pr->hostname + 5, alen-1);
                  pr->hostname[alen-1] = '\0';
                  goto connect;
                } else {
                  /*
                   * Unknown address type. (FIXME: support IPv6!)
                   */
                  reply[1] = 8;     /* atype not supported */
                  sk_write(pr->s, (char *) reply, lenof(reply));
                  pfd_close(pr->s);
                  return 1;
                }
            }
          }

          /*
           * If we get here without either having done `continue'
           * or `goto connect', it must be because there is no
           * sensible interpretation of what's in our buffer. So
           * close the connection rudely.
           */
          pfd_close(pr->s);
          return 1;
      }
      return 1;

      /*
       * We come here when we're ready to make an actual
       * connection.
       */
      connect:

      pr->c = new_sock_channel(pr->backhandle, pr->s);
      if (pr->c == NULL) {
          pfd_close(pr->s);
          return 1;
      } else {
          /* asks to forward to the specified host/port for this */
          ssh_send_port_open(pr->c, pr->hostname, pr->port, "forwarding");
      }
      pr->dynamic = 0;

      /*
       * Now freeze the socket until the SSH server confirms the
       * connection.
       */
      sk_set_frozen(pr->s, 1);
      /*
       * If there's any data remaining in our current buffer,
       * save it to be sent on pfd_confirm().
       */
      if (len > 0) {
          pr->buffer = snewn(len, char);
          memcpy(pr->buffer, data, len);
          pr->buflen = len;
      }
    }
    if (pr->ready) {
      if (sshfwd_write(pr->c, data, len) > 0) {
          pr->throttled = 1;
          sk_set_frozen(pr->s, 1);
      }
    }
    return 1;
}

static void pfd_sent(Plug plug, int bufsize)
{
    struct PFwdPrivate *pr = (struct PFwdPrivate *) plug;

    if (pr->c)
      sshfwd_unthrottle(pr->c, bufsize);
}

/*
 * Called when receiving a PORT OPEN from the server
 */
const char *pfd_newconnect(Socket *s, char *hostname, int port,
                     void *c, const Config *cfg, int addressfamily)
{
    static const struct plug_function_table fn_table = {
      pfd_log,
      pfd_closing,
      pfd_receive,
      pfd_sent,
      NULL
    };

    SockAddr addr;
    const char *err;
    char *dummy_realhost;
    struct PFwdPrivate *pr;

    /*
     * Try to find host.
     */
    addr = name_lookup(hostname, port, &dummy_realhost, cfg, addressfamily);
    if ((err = sk_addr_error(addr)) != NULL) {
      sk_addr_free(addr);
      return err;
    }

    /*
     * Open socket.
     */
    pr = snew(struct PFwdPrivate);
    pr->buffer = NULL;
    pr->fn = &fn_table;
    pr->throttled = pr->throttle_override = 0;
    pr->ready = 1;
    pr->c = c;
    pr->backhandle = NULL;           /* we shouldn't need this */
    pr->dynamic = 0;

    pr->s = *s = new_connection(addr, dummy_realhost, port,
                        0, 1, 0, 0, (Plug) pr, cfg);
    if ((err = sk_socket_error(*s)) != NULL) {
      sfree(pr);
      return err;
    }

    sk_set_private_ptr(*s, pr);
    return NULL;
}

/*
 called when someone connects to the local port
 */

static int pfd_accepting(Plug p, OSSocket sock)
{
    static const struct plug_function_table fn_table = {
      pfd_log,
      pfd_closing,
      pfd_receive,
      pfd_sent,
      NULL
    };
    struct PFwdPrivate *pr, *org;
    Socket s;
    const char *err;

    org = (struct PFwdPrivate *)p;
    pr = snew(struct PFwdPrivate);
    pr->buffer = NULL;
    pr->fn = &fn_table;

    pr->c = NULL;
    pr->backhandle = org->backhandle;

    pr->s = s = sk_register(sock, (Plug) pr);
    if ((err = sk_socket_error(s)) != NULL) {
      sfree(pr);
      return err != NULL;
    }

    sk_set_private_ptr(s, pr);

    pr->throttled = pr->throttle_override = 0;
    pr->ready = 0;

    if (org->dynamic) {
      pr->dynamic = 1;
      pr->port = 0;                  /* "hostname" buffer is so far empty */
      sk_set_frozen(s, 0);           /* we want to receive SOCKS _now_! */
    } else {
      pr->dynamic = 0;
      strcpy(pr->hostname, org->hostname);
      pr->port = org->port;   
      pr->c = new_sock_channel(org->backhandle, s);

      if (pr->c == NULL) {
          sfree(pr);
          return 1;
      } else {
          /* asks to forward to the specified host/port for this */
          ssh_send_port_open(pr->c, pr->hostname, pr->port, "forwarding");
      }
    }

    return 0;
}


/* Add a new forwarding from port -> desthost:destport
 sets up a listener on the local machine on (srcaddr:)port
 */
const char *pfd_addforward(char *desthost, int destport, char *srcaddr,
                     int port, void *backhandle, const Config *cfg,
                     void **sockdata, int address_family)
{
    static const struct plug_function_table fn_table = {
      pfd_log,
      pfd_closing,
      pfd_receive,                   /* should not happen... */
      pfd_sent,                /* also should not happen */
      pfd_accepting
    };

    const char *err;
    struct PFwdPrivate *pr;
    Socket s;

    /*
     * Open socket.
     */
    pr = snew(struct PFwdPrivate);
    pr->buffer = NULL;
    pr->fn = &fn_table;
    pr->c = NULL;
    if (desthost) {
      strcpy(pr->hostname, desthost);
      pr->port = destport;
      pr->dynamic = 0;
    } else
      pr->dynamic = 1;
    pr->throttled = pr->throttle_override = 0;
    pr->ready = 0;
    pr->backhandle = backhandle;

    pr->s = s = new_listener(srcaddr, port, (Plug) pr,
                       !cfg->lport_acceptall, cfg, address_family);
    if ((err = sk_socket_error(s)) != NULL) {
      sfree(pr);
      return err;
    }

    sk_set_private_ptr(s, pr);

    *sockdata = (void *)s;

    return NULL;
}

void pfd_close(Socket s)
{
    struct PFwdPrivate *pr;

    if (!s)
      return;

    pr = (struct PFwdPrivate *) sk_get_private_ptr(s);

    sfree(pr->buffer);
    sfree(pr);

    sk_close(s);
}

/*
 * Terminate a listener.
 */
void pfd_terminate(void *sv)
{
    pfd_close((Socket)sv);
}

void pfd_unthrottle(Socket s)
{
    struct PFwdPrivate *pr;
    if (!s)
      return;
    pr = (struct PFwdPrivate *) sk_get_private_ptr(s);

    pr->throttled = 0;
    sk_set_frozen(s, pr->throttled || pr->throttle_override);
}

void pfd_override_throttle(Socket s, int enable)
{
    struct PFwdPrivate *pr;
    if (!s)
      return;
    pr = (struct PFwdPrivate *) sk_get_private_ptr(s);

    pr->throttle_override = enable;
    sk_set_frozen(s, pr->throttled || pr->throttle_override);
}

/*
 * Called to send data down the raw connection.
 */
int pfd_send(Socket s, char *data, int len)
{
    if (s == NULL)
      return 0;
    return sk_write(s, data, len);
}


void pfd_confirm(Socket s)
{
    struct PFwdPrivate *pr;

    if (s == NULL)
      return;

    pr = (struct PFwdPrivate *) sk_get_private_ptr(s);
    pr->ready = 1;
    sk_set_frozen(s, 0);
    sk_write(s, NULL, 0);
    if (pr->buffer) {
      sshfwd_write(pr->c, pr->buffer, pr->buflen);
      sfree(pr->buffer);
      pr->buffer = NULL;
    }
}

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