libc/bionic/__fgets_chk.cpp

/*
 * Copyright (C) 2012 The Android Open Source Project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *  * Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *  * Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#undef _FORTIFY_SOURCE

#include <stdio.h>
#include <stdlib.h>
#include "private/libc_logging.h"

/*
 * __fgets_chk. Called in place of fgets() when we know the
 * size of the buffer we're writing into.
 *
 * See
 *   http://gcc.gnu.org/onlinedocs/gcc/Object-Size-Checking.html
 * for details.
 *
 * This fgets check is called if _FORTIFY_SOURCE is defined and
 * greater than 0.
 */
char* __fgets_chk(char* dest, int supplied_size, FILE* stream,
                  size_t dest_len_from_compiler) {
  if (supplied_size < 0) {
    __fortify_chk_fail("fgets: buffer size < 0", 0);
  }

  if (((size_t) supplied_size) > dest_len_from_compiler) {
    __fortify_chk_fail("fgets: prevented write past end of buffer", 0);
  }

  return fgets(dest, supplied_size, stream);
}