SEI CERT C Coding Standard

Space shortcuts

Page tree

Versions Compared

Old Version 9

changes.mady.by.user Justin Pincar

Saved on

compared with

New Version 10

changes.mady.by.user Justin Pincar

Saved on

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.

...

This non-compliant code example invokes the longjmp free function to transfer control from within the signal handler int_ handler() back into main(). Once control returns to main(), a potentially non-reentrant system call is made to strcpy(). Using the longjmp function inside a signal handler is particularly dangerous, as it could call any part of your code. If an interrupt signal is received during or after the free call in main, the heap will be corrupted.

Code Block
bgColor#FFcccc
#include <setjmp<signal.h> 
#include <signal.h> 
 
static jmp_buf env;char *foo;  
 
void int_handler() { 
  longjmp(env, 1free(foo); 
  return_exit(0); 
} 
  
int main(void) {  
  foo char *foo= malloc(15); 

  signal(SIGINT, int_handler); 
 
  if (setjmp(env) == 0) { 
    foo = malloc(15);
    strcpy(foo, "NothingHello yetWorld.");
  }
  else {
    strcpy(foo, "Signal caught.");
  }

  /* main loop which displays foo */
puts(foo); 
 
  free(foo); 
  return 0; 
}

Compliant Solution

Signal handlers should be as minimal as possible, only unconditionally setting a flag where appropriate, and returning. You may also call the _exit function to immediately terminate program execution.

Code Block
bgColor#ccccff
#include <signal.h> 

int interrupted = 0;
 
void int_handler() { 
  interrupted = 1;
  return_exit(0);
} 
 
int main(void) { 
  char *foo; 

  signal(SIGINT, int_handler); 
    
  foo = malloc(15);
  strcpy(foo, "Nothing yet.");
  
  /* main loop which displays foo */
  if (interrupted == 1) {
    strcpy(foo, "Signal caught.");
  }

  return 0;
}

...