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ncat_posix.c

/***************************************************************************
 * ncat_posix.c -- POSIX-specific functions.                               *
 ***********************IMPORTANT NMAP LICENSE TERMS************************
 *                                                                         *
 * The Nmap Security Scanner is (C) 1996-2009 Insecure.Com LLC. Nmap is    *
 * also a registered trademark of Insecure.Com LLC.  This program is free  *
 * software; you may redistribute and/or modify it under the terms of the  *
 * GNU General Public License as published by the Free Software            *
 * Foundation; Version 2 with the clarifications and exceptions described  *
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 * technology into proprietary software, we sell alternative licenses      *
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 ***************************************************************************/

/* $Id$ */

#include <assert.h>

#include "ncat.h"

char **cmdline_split(const char *cmdexec);

/* fork and exec a child process with netexec. Close the given file descriptor
   in the parent process. Return the child's PID or -1 on error. */
int netrun(struct fdinfo *info, char *cmdexec)
{
    int pid;

    errno = 0;
    pid = fork();
    if (pid == 0) {
        /* In the child process. */
        netexec(info, cmdexec);
    }

    Close(info->fd);

    if (pid == -1 && o.verbose)
        logdebug("Error in fork: %s\n", strerror(errno));

    return pid;
}

/* Call write in a loop until all the data is written or an error occurs. The
   return value is the number of bytes written. If it is less than size, then
   there was an error. */
static int write_loop(int fd, char *buf, size_t size)
{
    char *p;
    int n;

    p = buf;
    while (p - buf < size) {
      n = write(fd, p, size - (p - buf));
      if (n == -1) {
          if (errno == EINTR)
            continue;
          else
            break;
      }
      p += n;
    }

    return p - buf;
}

/* Run the given command line as if with exec. What we actually do is fork the
   command line as a subprocess, then loop, relaying data between the socket and
   the subprocess. This allows Ncat to handle SSL from the socket and give plain
   text to the subprocess, and also allows things like logging and line delays.
   Never returns. */
void netexec(struct fdinfo *info, char *cmdexec)
{
    int child_stdin[2];
    int child_stdout[2];
    int pid;

    char buf[DEFAULT_TCP_BUF_LEN];
    int maxfd;

    if (o.debug) {
        if (o.shellexec)
            logdebug("Executing with shell: %s\n", cmdexec);
        else
            logdebug("Executing: %s\n", cmdexec);
    }

    if (pipe(child_stdin) == -1 || pipe(child_stdout) == -1)
      bye("Can't create child pipes: %s", strerror(errno));

    pid = fork();
    if (pid == -1)
      bye("Error in fork: %s", strerror(errno));
    if (pid == 0) {
      /* This is the child process. Exec the command. */
      close(child_stdin[1]);
      close(child_stdout[0]);

      /* rearrange stdin and stdout */
      Dup2(child_stdin[0], STDIN_FILENO);
      Dup2(child_stdout[1], STDOUT_FILENO);

      if (o.shellexec) {
          execl("/bin/sh", "sh", "-c", cmdexec, NULL);
      } else {
          char **cmdargs;

          cmdargs = cmdline_split(cmdexec);
          execv(cmdargs[0], cmdargs);
      }

      /* exec failed.*/
      die("exec");
    }

    close(child_stdin[0]);
    close(child_stdout[1]);

    maxfd = child_stdout[0];
    if (info->fd > maxfd)
      maxfd = info->fd;

    /* This is the parent process. Enter a "caretaker" loop that reads from the
       socket and writes to the suprocess, and reads from the subprocess and
       writes to the socket. */
    for (;;) {
      fd_set fds;
      int r, n_r, n_w;

      FD_ZERO(&fds);
      FD_SET(info->fd, &fds);
      FD_SET(child_stdout[0], &fds);

      r = fselect(maxfd + 1, &fds, NULL, NULL, NULL);
      if (r == -1) {
          if (errno == EINTR)
            continue;
          else
            break;
      }
      if (FD_ISSET(info->fd, &fds)) {
          int pending;

          do {
            n_r = ncat_recv(info, buf, sizeof(buf), &pending);
            if (n_r <= 0)
                goto loop_end;
            n_w = write_loop(child_stdin[1], buf, n_r);
            if (n_w < n_r)
                goto loop_end;
          } while (pending);
      }
      if (FD_ISSET(child_stdout[0], &fds)) {
          char *crlf = NULL, *wbuf;
          n_r = read(child_stdout[0], buf, sizeof(buf));
          if (n_r <= 0)
            break;
          wbuf = buf;
          if (o.crlf) {
            if (fix_line_endings((char *) buf, &n_r, &crlf))
                wbuf = crlf;
          }
          n_w = ncat_send(info, wbuf, n_r);
          if (crlf != NULL)
            free(crlf);
          if (n_w <= 0)
            break;
      }
    }
loop_end:

#ifdef HAVE_OPENSSL
    if (info->ssl != NULL) {
      SSL_shutdown(info->ssl);
      SSL_free(info->ssl);
    }
#endif
    close(info->fd);

    exit(0);
}

/*
 * Split a command line into an array suitable for handing to execv.
 *
 * A note on syntax: words are split on whitespace and '\' escapes characters.
 * '\\' will show up as '\' and '\ ' will leave a space, combining two
 * words.  Examples:
 * "ncat\ experiment -l -k" will be parsed as the following tokens:
 * "ncat experiment", "-l", "-k".
 * "ncat\\ -l -k" will be parsed as "ncat\", "-l", "-k"
 * See the test program, test/test-cmdline-split to see additional cases.
 */
char **cmdline_split(const char *cmdexec)
{
    const char *ptr;
    char *cur_arg, **cmd_args;
    int max_tokens = 0, arg_idx = 0, ptr_idx = 0;

    /* Figure out the maximum number of tokens needed */
    ptr = cmdexec;
    while (*ptr) {
        // Find the start of the token
        while (('\0' != *ptr) && isspace((int) (unsigned char) *ptr)) ptr++;
        if ('\0' == *ptr)     break;
        max_tokens++;
        // Find the start of the whitespace again
        while (('\0' != *ptr) && !isspace((int) (unsigned char) *ptr)) ptr++;
    }

    /* The line is not empty so we've got something to deal with */
    cmd_args = (char**)safe_malloc(sizeof(char*) * (max_tokens + 1));
    cur_arg = (char*)Calloc(sizeof(char), strlen(cmdexec));

    /* Get and copy the tokens */
    ptr = cmdexec;
    while (*ptr) {
        while (('\0' != *ptr) && isspace((int) (unsigned char) *ptr)) ptr++;
        if ('\0' == *ptr)     break;

        while (('\0' != *ptr) && !isspace((int) (unsigned char) *ptr)) {
            if ('\\' == *ptr) {
                ptr++;
                if ('\0' == *ptr)   break;

                cur_arg[ptr_idx] = *ptr;
                ptr_idx++;
                ptr++;

                if ('\\' != *(ptr - 1)) {
                    while (('\0' != *ptr) && isspace((int) (unsigned char) *ptr)) ptr++;
                }
            } else {
                cur_arg[ptr_idx] = *ptr;
                ptr_idx++;
                ptr++;
            }
        }
        cur_arg[ptr_idx] = '\0';

        cmd_args[arg_idx] = strdup(cur_arg);
        cur_arg[0] = '\0';
        ptr_idx = 0;
        arg_idx++;
    }

    cmd_args[arg_idx] = NULL;

    /* Clean up */
    free(cur_arg);

    return cmd_args;
}

void set_lf_mode(void)
{
    /* Nothing needed. */
}

#ifdef HAVE_OPENSSL

#define NCAT_CA_CERTS_PATH (NCAT_DATADIR "/" NCAT_CA_CERTS_FILE)

int ssl_load_default_ca_certs(SSL_CTX *ctx)
{
    int rc;

    if (o.debug)
        logdebug("Using system default trusted CA certificates and those in %s.\n", NCAT_CA_CERTS_PATH);

    /* Load distribution-provided defaults, if any. */
    assert(SSL_CTX_set_default_verify_paths(ctx) > 0);

    /* Also load the trusted certificates we ship. */
    rc = SSL_CTX_load_verify_locations(ctx, NCAT_CA_CERTS_PATH, NULL);
    if (rc != 1) {
        if (o.debug)
            logdebug("Unable to load trusted CA certificates from %s: %s\n",
                NCAT_CA_CERTS_PATH, ERR_error_string(ERR_get_error(), NULL));
        return -1;
    }

    return 0;
}
#endif

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