fedora 24
race weakness #12


Weakness Breakdown


A race condition exists when parallel code accesses shared data without proper coordination. An attack that uses a race-condition weakness takes advantage of the unsafe data access to manipulate how one of the parallel sections of code reacts. Even though each process runs as intended, the outcome is unexpected. For example, consider a bank service that depends on an encryption key that it reads from a known location. An independent cryptography service is responsible for generating the key and placing it where the bank is expected to read it in a timely manner. If the bank and cryptography services do not coordinate with each other, then the bank may read a blank encryption key before cryptography writes the key to the location. This can effectively turn off all encryption for the bank without either service, or the administrator, knowing that something has gone wrong.

Warning code(s):

This accepts filename arguments; if an attacker can move those files or change the link content, a race condition results. Also, it does not terminate with ASCII NUL..

File Name:



The highlighted line of code below is the trigger point of this particular Fedora 24 race weakness.

 # include <execinfo.h>

// See comment in autotest.py; This can trigger bug in 32-bit Linux
// because original app places vdso and libs in low memory when kernel uses
// legacy_va_layout (which is forced when stacksize is small), and the new
// vdso collides with the old libs in mtcp_restart.  So, it gets unmapped.

void myHandler(int i){
  int nptrs;
  void * buffer[BT_SIZE];

  printf("signal %d received.\n", i);
  nptrs = backtrace (buffer, BT_SIZE);
  backtrace_symbols_fd ( buffer, nptrs, STDOUT_FILENO );

int main(int argc, char* argv[]){
  char cmd_file[256];
  int cmd_len = readlink("/proc/self/exe", cmd_file, 255);
  if (cmd_len == -1)
    printf("WARNING:  Couldn't find /proc/self/exe."
	   "  Trying to continue anyway.\n");
  else {
    cmd_file[cmd_len] = '\0';
    signal(SIGUSR1, &myHandler);
    signal(SIGUSR2, &myHandler); // DMTCP should not enable this.
    if ( !getenv("IS_CHILD") && 0 != fork() ) { /* if child, do exec */
      setenv("IS_CHILD", "true", 1);
      execv(cmd_file, argv);

  while (1){

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