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#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>

void open_some_file(const char *file) {
  int fd = open(file, O_CREAT | O_EXCL | O_WRONLY);
  if (-1 != fd) {
    FILE *f = fdopen(fd, "w");
    if (NULL != f) {
      /* Write to file */

      if (fclose(f) == EOF) {
        /* Handle error */
      }
    }
    else {
      if (close(fd) == -1) {
        /* Handle error */
      }
    }
  }
}

Exceptions

FIO45-C-EX1: TOCTOU race conditions require that the vulnerable process is more privileged than the attacker; otherwise there is nothing to be gained from a successful attack. An unprivileged process is not subject to this rule.

FIO45-C-EX2: Accessing a file name or path name multiple times is permitted if the file referenced resides in a secure directory (for more information, see FIO15-C. Ensure that file operations are performed in a secure directory).

FIO45-C-EX3: Accessing a file name or path name multiple times is permitted if the program can verify that every operation operates on the same file.

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